Integrated Diagnosis of plugging in Western Sichuan Sour Gas Reservoirs: From Plugging Mechanisms to Mitigation Strategies

Integrated Diagnosis of plugging in Western Sichuan Sour Gas Reservoirs: From Plugging Mechanisms to Mitigation Strategies | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Integrated Diagnosis of plugging in Western Sichuan Sour Gas Reservoirs: From Plugging Mechanisms to Mitigation Strategies Zheng Kang, Yin-Tao Liu, Guo-Dong Zhang, Biao Su, Xiao-Feng Liu, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7224036/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 9 You are reading this latest preprint version Abstract Since their commissioning in 2023, eighteen sour gas wells in the West Sichuan Gas Field have experienced over forty significant plugging incidents, severely compromising field productivity. This study employed multidisciplinary experimental methods to analyze plugging mechanism. Spearman correlation analysis identified plugging influencing factors, enabling recognition of plugging characterization and optimal unplugging timing. An optimized plugging removal fluid system was developed alongside a novel Quantitative Plugging Degree (QPD) assessment methodology, forming the basis of a targeted well mitigation strategy. Key findings reveal: (1) Three distinct plugging types—organic (predominantly long-chain alkanes and benzene compounds), inorganic (iron sulfides/oxides, BaSO 4 , and clays), and composite plugging; (2) Acid demonstrates superior efficacy, with initial plugging diagnosis indicated at incremental pressure decline rates ≥ 0.02 MPa/d, necessitating intervention before rates exceed 0.2 MPa/d; (3) The QPD method enables precise plugging location identification, facilitating optimized mitigation strategy. Implemented in Wells P5 and X1, this classified mitigation strategies significantly extended unplugging validity periods with demonstrable field success. plugging West Sichuan gas field sour mitigation strategies plugging degree Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 1 Introduction The producing layer of the West Sichuan gas field is the Lei 4 member (T 2 l 4 ) of the Leikoupo Formation, located in the territory of Pengzhou and Deyang, including the three gas fields of Pengzhou, Majing and Xinchang (as shown in Figure. 1 ). Reservoir depth 5700 ~ 6300m, reservoir thickness 66.2 ~ 70.5m, porosity 5.09%, permeability 5.66mD, H 2 S content 3.88 ~ 5.45%, CO 2 content 4.31 ~ 5.51%, geopressure coefficient 1 ~ 1.2, geothermal gradient 2.27 ~ 2.33℃/100m (Li et al. 2016 . Wang et al. 2022 ). The gas wells are mainly put into production by the “screened pipe + sliding sleeve” method, and some of the wells are completed by open segmented completion and well-case perforating completion. Since 2023, after 18 wells were successively put into production, the annual production capacity of 1.5 billion cubic metres of sour natural gas. It has been supplying gas smoothly to the south-west of China and along the Sichuan-East gas transmission route. However, by the end of 2024, more than 40 wells had been significantly blocked, seriously affecting gas field production. A large number of scholars have done a lot of research on the plugging treatment of sour gas wells, mainly including the analysis of plugging causes and the development of removing fluid systems. As for the analysis of plugging causes, Luo and Wu. (2020) analyzed the plugging materials for Yuanba gas field and concluded that the inorganic components are mainly FeS 2 , CaCO 3 , BaSO 4 and SiO 2 , and the organic components are mainly the decomposition products of macromolecules and asphaltenes, and that some wells belong to organic plugging, and some wells belong to inorganic plugging. Chen et al. ( 2023 ) concluded that the plugging of gas reservoirs in the Dengying Formation in Gaoshi-Moxi Platform Margin Belt is dominated by inorganic materials (65.02–85.43%), and the main components are corrosion products such as FeS and FeS 2 . Haris et al. ( 2018 ) and Memon et al. ( 2017 ) concluded that the decrease in temperature and pressure leads to asphaltene precipitation. Hu et al. ( 2011 ) found that the presence of Fe ions exacerbates sulfur deposition damage. For removing fluids, Lv et al. ( 2023 ) used “chelating agent + hydrochloric acid” to remove sulfur and iron compounds. Abbasi et al. ( 2024 ) used “hydrochloric acid + methanol” to remove oily organic matter. Cao et al. ( 2024 ) used chelating agent to remove CaCO 3 and CaSO 4 . Although, there are removal fluid systems for different types of plugging, acid is mainly used for on-site construction because of its cheapness and extensiveness. West Sichuan gas field have disadvantages in plugging removal, because the surrounding area is densely populated and requires high environmental protection. The construction of the platform wells adopts the model of “integrated gas production and purification”. Subject to the complex human environment and station conditions in the region, conventional injection plugging remover can only be used to return to the gas transmission process, plugging remover size, liquid nitrogen discharge measures are limited, and can not realize rapid, large displacement blowout. These limitations place higher demands on plugging diagnosis and removal techniques. This paper presents the first comprehensive analysis of plugging in sour gas wells in western Sichuan. In addition, except for continuous tubing (CT) (Riyanto et al. 2015 ), pumping removal fluids directly from the tubing is a common practice for plug removal in sour gas wells. Unfortunately, there are few detailed reports on how to optimise the removal process. “Quantifying plugging degree, judging plugging location, and predicting plugging trend” are the keys to optimise the removal process and improve removal effects. The current methods for evaluating plugging degree mainly include sulphur deposition prediction(Hu et al. 2014 ), calcium carbonate etc. scaling prediction (Safari et al. 2014 ), and asphaltene production prediction (Zhang et al. 2019 ). However, these are prediction methods for a single plugging, which is difficult to predict due to the complex composition of the plugging. This paper innovates a simple and accurate method to quantify the plugging degree, which can accurately determine the plugging location and predict the plugging trend so as to optimise the removal process. This study systematically presents the following key contributions: (1) Characterization of plugging material composition and mechanisms through integrated experimental methodologies. (2) Comprehensive analysis of plugging characteristics and influencing factors. (3) Development of an optimized plugging removal fluid system coupled with establishment of a Quantitative Plugging Degree (QPD) assessment methodology, culminating in formulation of classified mitigation strategies for plugged wells. (4) Demonstration of field application outcomes validating the proposed solutions. 2 Research Methods 2.1 Plugging Detection methods Plugging materials were retrieved from six production wells via three collection methods: separators, sand filter during CT operations, and downhole tools. Representative samples exhibited black coloration with variable viscosity, ranging from semi-solid to consolidated states (Fig. 2 ). A multi-analytical approach was implemented: Scorch experiment: Quantification of organic/inorganic fractions was achieved through controlled pyrolysis. Pre-weighed samples (vacuum-dried at 60°C for 24 h) underwent muffle furnace combustion (600°C for 8 h), with mass loss determining organic content. SEM-EDS: Pristine plugging specimens were sputter-coated with Au/Pd to prevent charging. High-resolution imaging (10–20 kV, WD 8–12 mm) revealed surface morphologies, with EDS mapping performed on representative zones for localized elemental quantification. XPF: Ash residues from scorched samples were homogenized, and pellets into pellets for elemental profiling. Characteristic X-ray fluorescence spectra identified major/minor elements through wavelength-dispersive detection. FTIR: Cryogenically milled samples were blended with KBr (1:100) and pelletized. Spectral acquisition (4000–400 cm⁻¹, 4 cm⁻¹ resolution, 32 scans) detected functional groups via transmission mode. GC-MS: Organic extracts were prepared by toluene dissolution, centrifugation (12,000 rpm/10 min), and microfiltration (0.22 µm). Chromatographic separation (DB-5MS column) coupled with quadrupole MS enabled compound identification through NIST library matching (match factor > 85%) with retention index verification. 2.2 Spearman method The Spearman's rank correlation method was employed to assess the nonlinear dependencies between 16 variables (pre-production flowback rate, open-flow potential, initial tubing pressure, etc.) and two critical plugging indicators: (i) time to first plugging and (ii) plugging removal frequency. The parameter ranges are summarized in Table 1 . Notably, three completion methodologies were represented by open-hole section length, liner length, and number of perforation intervals. Categorical variables included: (i) Drilling mud type: Coded as 1 for oil-based mud and 0 for water-based mud (WBM) during target zone drilling. (ii)Downhole anomalies: Coded as 1 for mechanical failures (e.g., tubing misplacement or rupture) and 0 for normal operations. All other parameters were treated as continuous variables. Spearman's method was selected for its distribution-free nature and robustness to outliers, making it particularly suitable for the nonlinear and non-Gaussian data characteristics observed in this study (Wang and Feng. 1993). The mathematical formulation is expressed in Equations ( 1 ) and ( 2 ): $$\:{R}_{S1}=1-\frac{6\sum\:{d}_{i}^{2}}{n\left({n}^{2}-1\right)}$$ 1 $$\:{R}_{S2}=\frac{\left[\left({n}^{3}-n\right)/6\right]-\left(Tx+Ty\right)-\sum\:{d}_{i}^{2}}{\sqrt{\left(\frac{{n}^{3}-n}{6}-2Tx\right)}\sqrt{\left(\frac{{n}^{3}-n}{6}-2Ty\right)}}$$ 2 where \(\:n\) denotes the number of observed data points, \(\:{d}_{i}\) represents the rank difference between paired variables ( \(\:x,y\) ), and \(\:Tx\:\) (or \(\:Ty\) ) is calculated as \(\:\sum\:(t3-t)/12\) , where \(\:t\) corresponds to the number of tied ranks in \(\:x\) (or \(\:y\) ). Eq. ( 2 ) (denoted as \(\:{R}_{S2}\) ) is applied when \(\:x\) or \(\:y\) contains tied ranks, whereas Eq. ( 1 ) ( \(\:{R}_{S1}\) ) is used for datasets without ties. Notably, when \(\:Tx\) = \(\:Ty\) =0, Equations ( 1 ) and ( 2 ) become mathematically equivalent. Table 1 Range of parameters affecting plugging Influence factor Range Pre-production flowback rate, % 7.8−73.24 Open-flow potential (OFP), 10 4 m 3 /d 70–335 Initial tubing pressure, MPa 35.36–47.72 Pre-production shut-in duration, d 457–1245 Open-hole section length, m 0−1272.5 Liner length, m 0−2087.5 Number of sliding sleeves 0–9 Number of perforation intervals 0–3 Total stimulation fluid volume, m 3 1020–3272 Acid volume used in stimulation, m 3 720–2550 Diverting agent dosage, kg 0−4500 Fiber volume, kg 0−470 Drilling fluid loss volume, m 3 0−503 Completion fluid loss volume, m 3 0−427.64 Downhole anomalies 0 or 1 Drilling mud type 0 or 1 Time to first plugging, d 51.7–355 Plugging removal frequency, d 74–486 2.3 Preferred method of plugging removal fluid The removal efficacy of five distinct plugging removal fluids was systematically evaluated: Fluid A (toluene-dominated formulation), Fluid B (ethanol-based composition), Fluid C (acetone-primary solvent), Fluid D (15% HCl + 5.5% high-temperature corrosion inhibitor), and Fluid E (neutral viscosity-reducing fluid synthesized from surfactant-viscosity modifier complexes). Inorganic plugging samples from Well P6 were pulverized, dried in a vacuum oven at 60°C for 24 hours to achieve baseline mass ( \(\:{\text{m}}_{1}\) ), then subjected to 30-minute reactions with 50 mL of each fluid under 80°C water bath conditions. Post-treatment residues were redried at 60°C to constant mass ( \(\:{\text{m}}_{2}\) ), with dissolution efficiency ( \(\:{\eta\:}\) ) calculated as Eq. 3 . $$\:{\eta\:}=\frac{{\text{m}}_{1}-{\text{m}}_{2}}{{\text{m}}_{1}}\times\:100\text{%}$$ 3 Organic plugging samples from Well M1 were subjected to rheological characterization using a Brookfield DV2T rotational viscometerto determine baseline apparent viscosity ( \(\:{\mu\:}_{0}\) ) at room temperature. Each plugging removal fluid (A-E) was mixed with the organic plugging at a 1:1 mass ratio. The reaction was carried out for 30 min at 80°C in a water bath. At the end of the reaction, the apparent viscosity ( \(\:{\mu\:}_{1}\) ) of the mixture was determined. The rate of viscosity reduction ( \(\:\text{R}\) ) is shown in Eq. 4 . $$\:\text{R}=\frac{{\mu\:}_{0}-{\mu\:}_{1}}{{\mu\:}_{0}}\times\:100\text{%}$$ 4 2.4 Methodology for quantifying plugging degree(QPD) Gas well plugging is systematically classified into wellbore plugging (W wellbore ) and reservoir plugging (W reservoir ), with the latter comprising blockages in tubing sections, screen annuli, and productive intervals. The fundamental relationship governing plugging severity is defined as Total Plugging Degree ( \(\:\varDelta\:P\) ) = W wellbore +W reservoir , where spatial and temporal plugging patterns are discerned through comparative analysis of W wellbore and \(\:\varDelta\:P\) variations. W wellbore is quantified as the integral pressure differential between measured pump pressure during plugging removal operations and theoretical unplugged pump pressure (Fig. 3 ). Force equilibrium analysis of the wellbore liquid column identifies three dominant components: gravitational force, frictional resistance, and upward thrust from gas influx. In deviated well sections, gravitational potential energy in vertical intervals substantially exceeds frictional losses in inclined segments, justifying the simplified pump pressure model: the pumping pressure = wellbore flow pressure - liquid column pressure, where negative values are considered to zero. While established methods for calculating wellbore flow pressure (Beggs and Brill. 1973. Hagedorn. 1965. Mukherjee and Brill. 1985. Hasan and Kabir. 1983), this study adopts an empirical correlation for gas-dominated systems (Eq. 5 ). Based on the natural rate of pressure drop in the well, the wellhead oil pressure ( \(\:{P}_{2}\) ) under non-clogging conditions is deduced, and the difference between \(\:{P}_{2}\) and the current oil pressure ( \(\:{P}_{1}\) ) is \(\:\varDelta\:P\) as in Eq. ( 6 ). $$\:{P}_{\text{i}}={P}_{1}{e}^{\frac{0.03415\gamma\:ℎ}{{T}_{cp}{Z}_{cp}}}$$ 5 $$\:\varDelta\:P={P}_{2}-{P}_{1}$$ 6 \(\:{P}_{i}\) —Any well depth flow pressure. γ—relative density of natural gas. h—vertical depth, m. \(\:{\text{T}}_{\text{c}\text{p}}\) —Average wellbore temperature, K. \(\:{\text{Z}}_{\text{c}\text{p}}\) —Average wellbore compression factor. e—Natural logarithm. \(\:\varDelta\:P\) —gas well plugging pressure drop. \(\:{P}_{1}\) —actual oil pressure. \(\:{P}_{2}\) —wellhead oil pressure under non-clogging conditions. 3 Results and Discussion 3.1 Plugging Characterization Analysis of 40 well cases compared pressure decline rates during plugging and normal production (Fig. 4 ). Some wells exhibiting higher pressure decline rates during plugging suggest instantaneous wellbore blockage or rapid near-wellbore debris accumulation, while lower rates indicate gradual plugging. The average pressure decline rates before and after plugging show an order of magnitude difference (0.025 vs 0.434 MPa/d), with an increase of 17.36 times. A incremental pressure decline rate of ≥ 0.02 MPa/d, which is the difference between “the baseline pressure decline rate” and “the plugging-induced pressure decline rate”, can be used as the plugging warning threshold. 3.2 Plugging mechanism 3.2.1 Scorch experiment The results are shown in Table 2 , the plugging materials in the west Sichuan gas field can be divided into three categories. The first category is organic plugging, with organic matter accounting for more than 70%, and this plugging material presents solid state below 50℃ and molten state above 70℃, and P3 and M1 wells are organic plugging. The second category is compound plugging, with the ratio of organic and inorganic materials from 44.8 to 55.2%, and X1 and P4 wells are compound plugging. The third category is inorganic plugging, the proportion of inorganic matter is more than 80%, and P6 and P5 wells are inorganic plugging. Table 2 Sample scorching results Sample Well Channels Before scorching (g) After scorching (g) organic content (%) Inorganic content (%) Plugging type G1 P3 Splitter 7.6167 0.6677 91.2 8.8 Organic G2 P3 Downhole tools 34.3778 9.5364 72.3 27.7 Organic G3 X1 Sand filer 10.5772 5.6071 46.9 53.1 Compound G4 M1 Sand filer 12.5501 1.2427 90.1 9.9 Organic G5 P4 Splitter 1.2354 0.6819 44.8 55.2 Compound G6 P6 Splitter 2.3456 2.0243 13.7 86.3 Inorganic G7 P5 Splitter 1.6873 1.4224 15.7 84.3 Inorganic 3.2.2 SEM + EDS Microstructural characterization (Fig. 5 ) demonstrates granular-dominated architectures across all types. Organic plugs (G1) display surface encapsulation features, contrasting with the textural heterogeneity of composite (G5) and inorganic (G6) variants, potentially attributable to declining organic fractions. EDS quantification (Table 3 ) identifies C, O, S, Si, Fe, and Ba as primary constituents. Elevated carbon concentrations in G1, G2, and G4 confirm their organic-rich nature, aligning with scorch test mass-loss measurements. Table 3 EDS test results Element Atomic content/Weight content, % G1 G2 G3 G4 G5 G6 G7 C 68.8/54.3 92.4/85 28.3/50.6 49.1/73.4 41.8/20.2 29.8/14.9 35.2/16.3 O 26.1/27.5 3.4/4.2 20.3/27.2 11.6/13.1 6.7/4.3 40.5/27 3.9/2.4 N - - - - 6.2/3.5 0.5/0.3 - Mg - - 0.2/0.2 - - 0.9/0.9 - Na - - - - 10.4/9.6 3.2/3.1 25.0/22.2 Al - - 0.18/0.14 - - 2.0/2.3 - Si 0.01/0.02 0.1/0.3 0.47/0.36 0.6/0.4 0.3/0.3 4.5/5.3 - S 0.04/0.08 3.5/8.6 6.12/4.09 6.6/3.7 19.7/25.4 3.1/4.2 20.2/25 Ca 0.03/0.08 - 3.87/2.07 1.9/0.9 - 1.5/2.5 0.39/0.6 K - - - - - 7.9/13 - Mn - - 0.44/0.17 - - - - Fe 4.8/17.7 0.4/1.9 38.7/14.8 2.3/0.8 4.1/9.3 1.4/3.3 - Ba 0.02/0.14 - 0.66/0.1 - 0.8/4.6 3.2/18.1 - 3.2.3 XRF X-ray fluorescence (XRF) characterization of the calcined powders (Table 4) reveals inorganic constituents dominated by Fe, S, Ba, Si, and transition metals. Samples G1-G3 exhibit elevated iron content coupled with sulfur, suggesting predominant phases of iron oxides in G1/G3 and iron sulfide (FeS) in G2 through stoichiometric parity analysis. Notably, G7 demonstrates a superstoichiometric Ba/S mass ratio of 5.69 versus the theoretical 4.43 for pure BaSO₄, indicating free BaO phase coexistence. Conversely, G3 and G6 display substoichiometric Ba/S ratios (1.2–1.5) with respective Ba (11.3–11.7 wt%) and S (7.4–9.5 wt%) concentrations, consistent with intermediate barium sulfate phases formation. These mineralogical signatures collectively indicate complex assemblages of iron oxides (Fe 3 O 4 /Fe 2 O 3 ), sulfides (FeS/FeS 2 ), and barium sulfate (BaSO 4 ). 3.2.4 FTIR FTIR analysis of pre-sintered samples (Fig. 6 ) identified characteristic functional groups (Table 5 ). Broad absorption bands at 3313–3439 cm − 1 correspond to O-H/N-H stretching vibrations. Peaks between 2907–2952 cm − 1 indicate C-H stretching modes in aliphatic chains (-CH 3 , -CH 2 -), confirming alkane presence. The 1600 cm − 1 region suggests aromatic C = C, carbonyl (C = O), or amide groups. A distinct C-H bending vibration occurs at 1352 cm − 1 . Functional group analysis reveals organic constituents dominated by alkanes and aromatic hydrocarbons. Table 5 Functional group analysis of each sample Sample Functional Location (cm − 1 ) Sample Functional Location (cm − 1 ) G1 Hydroxyl (-OH) or amine (-NH) 3428 G2 Hydroxyl (-OH) or amine (-NH) 3435 Alkyl -CH 3 and -CH 2 - 2952 Alkyl -CH 3 and -CH 2 - 2907 Amide or benzene ring or carbonyl C = O 1620 Amide or benzene ring or carbonyl C = O 1600 -C-O-C or -COO 1206 C-H bond 1352 Aromatic or olefinic C-H 558 ether bond 1105 G3 Hydroxyl (-OH) or amine (-NH) 3439 Characteristic peaks of substitution on the benzene ring 620 The -C-H of the benzene ring 3058 G4 Hydroxyl (-OH) or amine (-NH) 3419 Alkyl -CH 3 and -CH 2 - 2918 Alkyl -CH 3 and -CH 2 - 2923 Amide or benzene ring or carbonyl C = O 1600 Amide or benzene ring or carbonyl C = O 1631 -C-O-C or -COO 1233 Naphthalene C-C 1459 Secondary or tertiary alcohols 1070 Secondary or tertiary alcohols 1064 Characteristic peaks of substitution on the benzene ring 702 G6 Hydroxyl (-OH) or amine (-NH) 3384 G5 Hydroxyl (-OH) or amine (-NH) 3313 Alkyl -CH 3 and -CH 2 - 2925 Alkyl -CH 3 and -CH 2 - 2919、2852 Amide or benzene ring or carbonyl C = O 1592 Amide or benzene ring or carbonyl C = O 1652 C-H bond 1382 hydroxyl alcohol 1513 ether 1008 Ester cyclic ether C-O-C- 1086 G7 -CH 2 - 1459 G7 Hydroxyl (-OH) or amine (-NH) 3313 -C-O-C or -COO 1251 Alkyl -CH 3 and -CH 2 - 2919 amide 948 Amide or benzene ring or carbonyl C = O 1608 3.2.5 GC-MS As shown in Table 6 , all samples exhibit at least one dominant component: either alkanes (C 14 -C 44 ) or aromatic hydrocarbons (e.g., G1/G5 with > 70% alkanes; G2/G4 with > 89% aromatics). Siloxanes (0.51–5.65%) are present in all samples except G4 and G5. The elevated aromatic hydrocarbon content suggests contamination from wellbore-introduced materials such as drilling fluid additives. Table 6 GC-MS analysis results Organic component Content (%) G1 G2 G3 G4 G5 Alkane (C 14 -C 44) 73.79 4.61 35.43 0.33 78.14 Silicone 0.51 4.73 5.65 0.02 - Ethers 8.1 - - - - Aldehydes 4.83 - - - - Benzene-containing compounds 10.06 89.29 38.02 99.62 12.6 Carboxylic acid-containing hydrocarbons 2.33 - 1.25 - 9.75 3.2.6 Mechanical analysis According to the results of plugging material analysis (Table 7 ), the plugging material types in the West Sichuan gas field are complex, with three types of plugging: organic, inorganic, and composite. The main components of organic materials are long-chain alkanes and benzene-containing compounds, and the main components of inorganic materials are iron sulphides and oxides, BaSO 4 and clay. Based on the whole-rock analysis, there is no pyrite in the area, and it is judged that the iron sulphides and oxides are mainly from the corrosion products of H 2 S with downhole metal tubing (Chen et al. 2020 . Ye et al. 2019 ). BaSO 4 originates from barite, a weighting material in drilling fluids, and is inert and insoluble in hydrochloric acid. For the long-chain alkanes of organic materials, most scholars now generally believe that there are two main reasons (Lou and Wu. 2020. Abbasi et al. 2024 . Lu et al. 2023 ): (1) The reservoir contains organic components such as asphalt. (2) Organic components of the working fluids such as amide, methanol and quaternary ammonium salt of corrosion inhibitors, oil-soluble substances of drilling fluids, fatty acids, fatty acid lipids sulphonated tannin (SMT), sulphonated quebracho ketene (SMK) and polymers such as sulphonated phenolic resins (SMP). We trace the materials of the working fluids and analyse that polyacrylamide mainly originates from polymers such as phenolic resins, sulphonated tannins, polymer blocking agents, temperature-resistant viscosity enhancers, and polyacrylamide of gelling acids in drilling fluids. Long-chain alkanes and phenyl compounds originate from the reservoirs and working fluids. Asphaltenes have been found in cast thin sections of the destination layer of the P-1 well, an exploratory well in the West Sichuan gas field (Wu et al. 2022 ). Asphaltenes, defoamers (silicone oils), emulsions, polymer additives, viscosity enhancers in drilling fluids, substances such as aldehydes and amines in completion fluids, and amides, methanol, and quaternary ammonium salts in corrosion inhibitors. These organics generate long-chain alkanes and benzene-containing compounds with a certain viscosity at high temperatures and pressures. Table 7 Results of plugging analysis Type Sample well Plugging components organic G1 P3 91.2% Organic (long-chain alkanes and benzene-containing compounds) 8.8% Inorganic (iron oxides and sulphides, BaSO 4 , clay) G2 P3 72.3% Organic (benzene-containing compounds and long-chain alkanes) 27.7% Inorganic (iron sulphides, clay) G4 M1 90.1%Organic (benzene-containing compounds) 9.9% Inorganic (CaSO 4 、FeS、clay) Compound G3 X1 46.9% Organic (long-chain alkanes and benzene-containing compounds) 53.1% Inorganic (iron oxides and sulphides, BaSO 4 , clay) G5 P4 44.8% Organic (long-chain alkanes and benzene-containing compounds) 55.2% Inorganic (S, FeS, BaSO 4 ) Inorganic G6 P6 86.4% Inorganic (BaSO 4 , FeS, metal oxide) 13.7% Organic (alkanes and benzene-containing compounds) G7 P5 84.3% Inorganic (BaSO 4 , FeS, metal oxide) 15.7% Organic (benzene-containing compounds and alkanes) 3.3 Plugging Correlation Analysis​ Spearman correlation analysis (Fig. 7 ) delineated the statistical dependencies between 16 parameters and two plugging metrics—time to first plugging (TFP) and plugging removal frequency (PRF). Following statistical conventions (Zhao et al. 2022 ), correlation strength was classified as: moderate ( \(\:\left|\rho\:\right|\) =0.4–0.59), weak ( \(\:\left|\rho\:\right|\) =0.2–0.39), and negligible ( \(\:\left|\rho\:\right|\) ≤0.19). Downhole anomalies exhibited moderate inverse correlations with both metrics (TFP: \(\:\rho\:\) =−0.47; PRF: \(\:\rho\:\) =−0.43), while drilling fluid loss volume showed moderate anti-correlation with PRF (ρ=−0.45), substantiating the hypothesis of composite plugging formation through physical retention of wellbore-introduced materials (e.g., drilling fluid solids, unbroken fracturing gel) coupled with sulfide coprecipitation. Notably, stimulation fluid volume and acid volume demonstrated weak negative correlations with PRF ( \(\:\rho\:\) =−0.24 and−0.26 respectively), suggesting potential wettability alteration reversal from high-intensity acidizing that enhances particle adhesion in pore throats. Divergent correlations between open-hole section length ( \(\:\rho\:\) =−0.24) and liner length ( \(\:\rho\:\) =0.077) expose open-hole completion risks: the packer-isolated annular spaces in open-hole segments create stagnant zones prone to particulate settling, contrasting with liner-sleeve completions during gas surges. 3.4 Preferred plugging removal fluid Experimental evaluations (Table 8 ) demonstrate that “Fluid D (15% HCl + 5.5% high-temperature corrosion inhibitor)” achieves superior efficacy, dissolving > 60% of inorganic plugging materials and reducing organic plugging viscosity by > 90%. While inorganic solubility remains partial, the solution effectively disrupts plugging matrix integrity by dissolving structural frameworks and destabilizing organic agglomerations, enabling wellbore evacuation through dissolution and mechanical loosening. Field applications in the western Sichuan gas field prioritize this acid-based remediation, though operational constraints, notably ground purification capacity, currently limit maximum treatment volumes to 25 m³per operation. Table 8 Dissolving Effectiveness of Five Removal Fluids for plugging Plugging Removal Fluid Inorganic plugging Organic plugging A dissolution efficiency<33% viscosity reduction rate<60% B dissolution efficiency<36% viscosity reduction rate<58% C dissolution efficiency<30% viscosity reduction rate60% viscosity reduction rate>90% E dissolution efficiency90% 3.5 Optimization of Unplugging Timing​ Statistical evaluation of 33 well interventions reveals a consistent trend: higher incremental pressure decline rates correlate with shorter unplugging cycle durations and greater post-treatment tubing pressure increase ratios. As empirically illustrated in Fig. 8 , the longest average unplugging interval occurs when interventions are initiated while the incremental pressure decline rate remains ≤ 0.2 MPa/d. This relationship between incremental pressure decline rate and unplugging interval, highlighting the criticality of timely unplugging for productivity preservation. 3.6 Classified Mitigation Strategies Based on the identification of plugging characterization, mechanism, analysis of influencing factors, optimization of plugging removal fluids, unplugging timing, and quantifying plugging degree, this study proposes classified mitigation strategies for plugged wells. As illustrated in Fig. 9 , an initial diagnosis of plugging is indicated when the incremental pressure decline rate reaches or exceeds 0.02 MPa/d. Intervention should be initiated as early as possible while the pressure decline rate remains below 0.2 MPa/d. For wells experiencing their first blockage, the adopted approach involves “small dosage injection of removal fluid + flowback of gas transmission process”. Previous operational experience revealed that verifying wellbore clearance using water alone proved ineffective for blockage removal. Consequently, the method “15 m 3 acid followed by one tubing volume of water” is employed, followed by an appropriate shut-in period prior to flowback. Wells exhibiting pump injection overpressure (unable injection) undergo “deep plugging removal utilizing coiled tubing (CT) deployment, large-scale acid fluid (≥ 100 m 3 ), and controlled blowdown flowback”. For wells with two or more prior plugging, the remediation method is optimized based on a quantitative assessment of the current plugging degree. As shown in Fig. 9 , based on the QPD method, gas well plugging degree is classified into Types I through IV. Type I is characterized by a progressively increasing difference between \(\:\varDelta\:P\) and W wellbore , signifying a gradual increase in W reservoir . This represents the most challenging type to remediate. Category II is characterized by a progressively decreasing difference between \(\:\varDelta\:P\) and W wellbore , indicating a reduction in W reservoir . This signifies a progressive shift of the plugging from the reservoir towards the wellbore, reflecting an improving condition. Categories III and IV exhibit consistent trends between \(\:\varDelta\:P\) and W wellbore , demonstrating that the wellhead pressure decline is primarily governed by wellbore plugging. Consequently, the plugging location is confined to the wellbore, representing a more favorable scenario. For Type I: Displacement rate should be increased to enhance the impingement of the plugging removal fluid on downhole plugging. Acid volume should be increased and delivered via staged displacement, ensuring the acid remains in contact with the lower tubing and annulus for over 30 minutes. Finally, all acid is injected into the reservoir. This approach enhances dissolution efficiency at downhole plugging points but increases tubing corrosion hazards, it is therefore reserved exclusively for Type I scenarios. For Type II: Displacement rate and acid volume should be increased to accelerate the transition of plugging material from the reservoir toward the wellbore. For Type III: Both displacement fluid and acid should be injected at low displacement rates to maximize contact time with wellbore plugging material. Staged displacement reduces the concentration of the initial acid stage. During pump injection overpressure, this mitigates corrosion damage caused by excessively high acid concentration in the wellbore. For Type IV: As plugging conditions progressively improve, low displacement rates are primarily employed to maximize acid contact time with wellbore plugging deposits. 4 Typical well applications 4.1 P5 well This open-hole staged completion well (OFP: 110.6×10 4 m³/d, initial wellhead pressure: 42.5 MPa) commenced production in January 2024. Initial remediation attempts employed conventional treatment (15–20 m 3 acid + one tubing-volume water), proving ineffective with short plugging cycles (mean: 50 days) and rapid pressure decline (> 0.2 MPa/d). Diagnostic analysis of the 2nd and 3rd plugging events (Fig. 10 a) identified Type III. Consequently, the 4th treatment implemented an optimized protocol: Variable-rate pumping + staged fluid displacement + high-volume treatment. During execution, wellbore plugging caused pump overpressure after injecting 5 m 3 acid and 10 m 3 water. Flowback was initiated before completing treatment. Crucially, conventional method would have retained high-concentration acid in the wellbore, risking prolonged tubing corrosion. Through QPD-optimized procedures, the operation succeeded. Post-treatment results (Figs. 10 b-c) show significantly extended effectiveness (> 120 days) and reduced pressure decline (0.04 MPa/d). While plugging recurrence occurred, the 4th intervention demonstrated marked improvement over prior attempts. 4.2 X1 well This cased/perforated completion well (OFP: 70×10 4 m 3 /d; initial pressure: 40.34 MPa) began production in December 2023. By August 2024, six plugging removal operations had been performed, averaging just 23.6 days of effectiveness. Pumping diagnostics revealed multiple migrating obstruction points from the formation to ~ 346m inside tubing. The 6th treatment failed due to pump overpressure, confirming untreatable plugging within 1,200m of tubing - necessitating coiled tubing (CT) intervention. Initial CT operations (Φ44mm milling shoe, 150 L/min) encountered obstruction at 88.8m (subsurface safety valve), stalling at 6-ton resistance. Analysis indicated gas-mobilized plugging material ascending and encapsulating the valve assembly. The small-diameter tool's limited flow prevented circulation. Switching to a Φ54mm nozzle enabled 300 L/min displacement, circulating out safety-valve deposits and successfully penetrating to the formation. Post-treatment (100m³ HCl + blowdown flowback) recovered ~ 1m³ of solids. Wellhead pressure increased from 36.86 to 42.3 MPa with gas production rising from 7.19 to 12.8×10 4 m³/d. As of January 2025, production has stabilized > 170 days at 19×10 4 m 3 /d with minimal pressure decline (0.0125 MPa/d), demonstrating exceptional remediation efficacy (Fig. 11 ). 5 Conclusion Plugging mechanisms in the West Sichuan gas field are categorized into three primary types: organic (predominantly long-chain alkanes and phenyl compounds originating from reservoirs/work fluids), inorganic (chiefly iron sulfides/oxides, barite, and clay derived from corrosion products and drilling additives), and composite plugging. Diagnostic thresholds establish that an incremental pressure decline rate ≥0.02 MPa/d indicates initial plugging, mandating intervention initiation before the rate exceeds 0.2 MPa/d. Spearman correlation analysis reveals significant trends: wells exhibiting more Downhole anomalies and drilling fluid loss earlier plugging onset and demonstrate greater remediation complexity. Comparative evaluation of five removal fluid types confirms acid fluids as most effective, achieving >60% dissolution efficiency for inorganic deposits and >90% degradation rate for organic accumulations. Wellbore plugging degree can be characterized through differential analysis between actual removal fluid pump pressure and theoretical non-plugging pressure profiles. This approach provides a feasible methodology for locating plugging zones and optimizing mitigation strategies. Field applications of the CT-QPD integrated mitigation strategy in Wells P5 and X1 demonstrate substantially extended unplugging validity periods and significantly reduced pressure decline rates, validating the methodology's efficacy. Declarations Disclosure statement The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Funding This paper was supported by Sinopec Southwest Oil and Gas Branch Project (Grant NO. CYQ-104-2403) Author Contribution Z.K.​​ (Zheng Kang): Conceptualization, Methodology, Funding acquisition, Supervision, Writing – original draft. ​​Y.-T.L.​​ (Yin-Tao Liu): Investigation, Formal analysis, Data curation, Writing – review & editing. ​​G.-D.Z.​​ (Guo-Dong Zhang): Validation, Visualization. ​​B.S.​​ (Biao Su): Resources, Project administration. ​​X.-F.L.​​ (Xiao-Feng Liu): Investigation, Writing – review & editing. ​​B.X.​​ (Biao Xia): Formal analysis, Visualization. ​​W.-Z.W.​​ (Wei-zhi Wang): Supervision, Funding acquisition, Writing – review & editing. All authors critically reviewed and approved the final manuscript. References Abbasi A, Khamehchi E, Khaleghi M R, et al. A new formulation for removing condensate blockage for low permeable gas reservoir. Journal of Petroleum Exploration and Production Technology, 2024, 14(8): 2491-2507. Beggs D H, Brill J P. A study of two-phase flow in inclined pipes. Journal of Petroleum technology, 1973, 25(05): 607-617. Cao, L., Jiang T., Pan Z., Sun, T., Zhang, B., Wu, H., Yi, J. Formation mechanism and targeted descaling technology of sand-scale composites in ultra-deep gas wells in the Kuqa piedmont of the Tarim Basin. Natural Gas Industry, 2024, 44(8): 85-94. Chen T, Wang Q, Chang F, et al. Recent development and remaining challenges of iron sulfide scale mitigation in sour-gas wells. SPE Production & Operations, 2020, 35(04): 0979-0986. Chen, L., Lu, Y., Ou J., Zhang, K., Li, J. Plugging Mechanism and Treatment Measures of Dengying Formation Gas Reservoir in Gaoshi-Moxi Platform Margin Belt. Journal of Southwest Petroleum University (Science & Technology Edition), 2023, 45(06): 113-124. Hagedorn A R, Brown K E. Experimental study of pressure gradients occurring during continuous two-phase flow in small-diameter vertical conduits. Journal of Petroleum technology, 1965, 17(04): 475-484. Haris A, Kamadibrata A T, Riyanto A. Condensate gas blockage simulation in a gas reservoir: a case study of a gas field in the Mahakam Delta, East Kalimantan, Indonesia. Arabian Journal of Geosciences, 2018, 11: 1-10. Hasan A R, Kabir C S. Pressure Buildup Analysis: A Simplified Approach (includes associated papers 11862 and 11867 and 11925 and 11926 and 13676). Journal of Petroleum Technology, 1983, 35(01): 178-188. Hu J H, He S L, Yang X F, et al. A Sulfur Plugging Experiment in the Presence of Ferric Ion. Petroleum Science and Technology, 2011, 29(1): 13-18. Hu J H, Zhao J Z, Wang L, et al. Prediction model of elemental sulfur solubility in sour gas mixtures. Journal of Natural Gas Science and Engineering, 2014, 18: 31-38. Li, S.B., Xu, G.M., Song, X.B. Forming conditions of Pengzhou large gas field of Leikoupo Formation in Longmenshan piedmont tectonic belt, western Sichuan Basin. China Petroleum Exploration, 2016, 21(3): 74. Lu Z, Chen Z, Xie W. A Study on the Material Composition and Traceability of the Wellhead Blockage in the Process of Oil and Gas Exploitation—A Case of the DH231 Well in the Tarim Basin, China. Applied Sciences, 2023, 13(3): 1504. Luo W, Wu Q. Development of wellbore compound blockage removal technology to reduce production loss in the ultra-deep and high-sulfur Yuanba gas field. Journal of Petroleum Exploration and Production Technology, 2020, 10(8): 3711-3721. Lv Y, Ou J, Fu H, et al. Unblocking Process of Complex Sulfur–Iron Scale Blockage in Sulfur-Bearing Gas Wells and Its Mechanism. ACS omega, 2023, 8(43): 40242-40250. Memon A, Borman C, Mohammadzadeh O, et al. Systematic evaluation of asphaltene formation damage of black oil reservoir fluid from Lake Maracaibo, Venezuela. Fuel, 2017, 206: 258-275. Mukherjee H, Brill J P. Pressure drop correlations for inclined two-phase flow. 1985. Qing Y H, Li S, Liao Z Y, et al. Dolomitisation under an arid climate at low sea-level: a case study of the Lei 4 Member of the Middle Triassic Leikoupo Formation, Western Sichuan Depression, China. Australian Journal of Earth Sciences, 2023, 70(3): 423-441. Riyanto L, Musa M N, Deris N A, et al. Innovative Process for Formation Damage Removal in Sandstone Reservoir Based on Real-Time Downhole Monitoring: A Malaysia Case History//SPE Annual Technical Conference and Exhibition?. SPE, 2015: D021S024R002. Safari H, Shokrollahi A, Jamialahmadi M, et al. Prediction of the aqueous solubility of BaSO4 using pitzer ion interaction model and LSSVM algorithm. Fluid Phase Equilibria, 2014, 374: 48-62. Wang Q, Feng S. The demonstration and application about calculating formula of spearman coefficient. J. Shanxi Agric. Univ.(Soc. Sci. Ed.), 1993, 1: 30-33. Wang, G., Song, X., Liu, Y., Meng, X., Long, K. Natural gas accumulation characteristics and exploration prospects of the 4 th member of Leikoupo Formation in the western Sichuan Basin. Natural Gas Geoscience, 2022, 33(3): 333-343. Wu, X., Chen, Y., Zhai, C., Zhou, L., Zhou, X,. Yang, J., Wang, Y., Song, X. Geochemical characteristics of bitumen and tracing of gas source in the Middle Triassic Leikoupo Formation, Western Sichuan Depression. Oil & Gas Geology, 2022, 43(2): 407-418. Xiong L, Long K, Cao Q, et al. Multilayer accumulation conditions and key technologies for exploration and development of the West Sichuan gas field in Sichuan Basin. Acta Petrolei Sinica, 2024, 45(3): 595. Ye C, Gou S, Feng Y, et al. Analysis of the causes of tube blocking in Jingbian gas field[C]//IOP Conference Series: Materials Science and Engineering. IOP Publishing, 2019, 542(1): 012072. Zhang Y, Arya A, Kontogeorgis G, et al. Modeling the phase behaviour of bitumen/n-alkane systems with the cubic plus association (CPA) equation of state. Fluid Phase Equilibria, 2019, 486: 119-138. Zhao G, Ding W, Tian J, et al. Spearman rank correlations analysis of the elemental, mineral concentrations, and mechanical parameters of the Lower Cambrian Niutitang shale: A case study in the Fenggang block, Northeast Guizhou Province, South China. Journal of Petroleum Science and Engineering, 2022, 208: 109550. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 10 Oct, 2025 Reviews received at journal 06 Sep, 2025 Reviewers agreed at journal 27 Aug, 2025 Reviews received at journal 19 Aug, 2025 Reviewers agreed at journal 19 Aug, 2025 Reviewers invited by journal 03 Aug, 2025 Editor assigned by journal 28 Jul, 2025 Submission checks completed at journal 28 Jul, 2025 First submitted to journal 27 Jul, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7224036","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":495864233,"identity":"c143583b-e357-4afe-8951-cd2264fcd928","order_by":0,"name":"Zheng 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04:23:10","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7224036/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7224036/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":88625571,"identity":"6d551518-648b-4996-8401-6b7aa6f6ae15","added_by":"auto","created_at":"2025-08-08 12:49:46","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1247037,"visible":true,"origin":"","legend":"\u003cp\u003esimple structural map of T\u003csub\u003e2\u003c/sub\u003el\u003csup\u003e4\u003c/sup\u003e in the Western Sichuan gas field (adapt from Xiong et al. 2024, Qing et al. 2023)\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-7224036/v1/20645f90465bacc08f3a869a.png"},{"id":88625570,"identity":"1d62f5f5-df09-4dbd-aba0-8b1fd0acfe28","added_by":"auto","created_at":"2025-08-08 12:49:46","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":714468,"visible":true,"origin":"","legend":"\u003cp\u003ePlugging collection pathways and testing methods\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-7224036/v1/7da0280222ea9f67dea9a726.png"},{"id":88626459,"identity":"d3543be2-7f1d-423d-906b-04b200b5aaf5","added_by":"auto","created_at":"2025-08-08 12:57:46","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":674122,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagram to quantify W\u003csub\u003ewellbore\u003c/sub\u003e\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-7224036/v1/67099db8ef94468334e3f9f8.png"},{"id":88625569,"identity":"fdc57e32-607c-458f-834b-0df816c108e6","added_by":"auto","created_at":"2025-08-08 12:49:46","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":1348441,"visible":true,"origin":"","legend":"\u003cp\u003ePressure drop rate before and after 40 plugging\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-7224036/v1/3ac38fae478273802c778b07.png"},{"id":88626461,"identity":"11f50317-1714-4696-af8c-7ea81239304e","added_by":"auto","created_at":"2025-08-08 12:57:47","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":577256,"visible":true,"origin":"","legend":"\u003cp\u003eMicroscopic morphology of the sample\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-7224036/v1/11b5b812f11ffd3968b82a1c.png"},{"id":88625579,"identity":"fed129ba-0750-49cb-9eeb-6ac32827edc1","added_by":"auto","created_at":"2025-08-08 12:49:47","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":920934,"visible":true,"origin":"","legend":"\u003cp\u003eInfrared spectra of each sample\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-7224036/v1/213d85058654c850a0e64355.png"},{"id":88625586,"identity":"2ed59f27-afbc-4719-98ae-b44914e4ced6","added_by":"auto","created_at":"2025-08-08 12:49:47","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":1523836,"visible":true,"origin":"","legend":"\u003cp\u003eThe Spearman correlation coefficients of multiple influencing factors\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-7224036/v1/f3d94c86d3c38b9daea13338.png"},{"id":88626467,"identity":"1eab7571-1a4f-47ae-bb79-4bb74eee915b","added_by":"auto","created_at":"2025-08-08 12:57:47","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":703058,"visible":true,"origin":"","legend":"\u003cp\u003eRelationship between incremental pressure decline rate and average unplugging validity period\u003c/p\u003e","description":"","filename":"floatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-7224036/v1/ed50309cbbf3fdd580df8e17.png"},{"id":88626466,"identity":"116b8872-b35e-4f7d-ac81-6bc7759df4f3","added_by":"auto","created_at":"2025-08-08 12:57:47","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":1124650,"visible":true,"origin":"","legend":"\u003cp\u003eClassified mitigation strategies for plugged wells\u003c/p\u003e","description":"","filename":"floatimage9.png","url":"https://assets-eu.researchsquare.com/files/rs-7224036/v1/fa23770856e1e20bd09588ce.png"},{"id":88625594,"identity":"e295e6d3-9fef-43c0-8824-aa4141d8fb51","added_by":"auto","created_at":"2025-08-08 12:49:47","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":970738,"visible":true,"origin":"","legend":"\u003cp\u003eEffectiveness of P5 well removal operations. (a: Plugging diagnosis based on the QPD method. b: Oil pressure during the production phase. c: Gas production during the production phase)\u003c/p\u003e","description":"","filename":"floatimage10.png","url":"https://assets-eu.researchsquare.com/files/rs-7224036/v1/7838456f8b721819ce7d87e9.png"},{"id":88626464,"identity":"10922cd4-39e2-4b0c-ae75-f3f5e4cf99df","added_by":"auto","created_at":"2025-08-08 12:57:47","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":1064818,"visible":true,"origin":"","legend":"\u003cp\u003eX1 well production curve\u003c/p\u003e","description":"","filename":"floatimage11.png","url":"https://assets-eu.researchsquare.com/files/rs-7224036/v1/b3cd904249e60a536dcf80a0.png"},{"id":88627711,"identity":"d99ec82d-f99e-475d-af7f-ad2e22ecba59","added_by":"auto","created_at":"2025-08-08 13:13:52","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":12118304,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7224036/v1/fc11d714-ef90-401b-9795-6f138e5f677a.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Integrated Diagnosis of plugging in Western Sichuan Sour Gas Reservoirs: From Plugging Mechanisms to Mitigation Strategies","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eThe producing layer of the West Sichuan gas field is the Lei 4 member (T\u003csub\u003e2\u003c/sub\u003el\u003csup\u003e4\u003c/sup\u003e) of the Leikoupo Formation, located in the territory of Pengzhou and Deyang, including the three gas fields of Pengzhou, Majing and Xinchang (as shown in \u003cb\u003eFigure. 1\u003c/b\u003e). Reservoir depth 5700\u0026thinsp;~\u0026thinsp;6300m, reservoir thickness 66.2\u0026thinsp;~\u0026thinsp;70.5m, porosity 5.09%, permeability 5.66mD, H\u003csub\u003e2\u003c/sub\u003eS content 3.88\u0026thinsp;~\u0026thinsp;5.45%, CO\u003csub\u003e2\u003c/sub\u003e content 4.31\u0026thinsp;~\u0026thinsp;5.51%, geopressure coefficient 1\u0026thinsp;~\u0026thinsp;1.2, geothermal gradient 2.27\u0026thinsp;~\u0026thinsp;2.33℃/100m (Li et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2016\u003c/span\u003e. Wang et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). The gas wells are mainly put into production by the \u0026ldquo;screened pipe\u0026thinsp;+\u0026thinsp;sliding sleeve\u0026rdquo; method, and some of the wells are completed by open segmented completion and well-case perforating completion. Since 2023, after 18 wells were successively put into production, the annual production capacity of 1.5\u0026nbsp;billion cubic metres of sour natural gas. It has been supplying gas smoothly to the south-west of China and along the Sichuan-East gas transmission route. However, by the end of 2024, more than 40 wells had been significantly blocked, seriously affecting gas field production.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eA large number of scholars have done a lot of research on the plugging treatment of sour gas wells, mainly including the analysis of plugging causes and the development of removing fluid systems. As for the analysis of plugging causes, Luo and Wu. (2020) analyzed the plugging materials for Yuanba gas field and concluded that the inorganic components are mainly FeS\u003csub\u003e2\u003c/sub\u003e, CaCO\u003csub\u003e3\u003c/sub\u003e, BaSO\u003csub\u003e4\u003c/sub\u003e and SiO\u003csub\u003e2\u003c/sub\u003e, and the organic components are mainly the decomposition products of macromolecules and asphaltenes, and that some wells belong to organic plugging, and some wells belong to inorganic plugging. Chen et al. (\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2023\u003c/span\u003e) concluded that the plugging of gas reservoirs in the Dengying Formation in Gaoshi-Moxi Platform Margin Belt is dominated by inorganic materials (65.02\u0026ndash;85.43%), and the main components are corrosion products such as FeS and FeS\u003csub\u003e2\u003c/sub\u003e. Haris et al. (\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) and Memon et al. (\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2017\u003c/span\u003e) concluded that the decrease in temperature and pressure leads to asphaltene precipitation. Hu et al. (\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2011\u003c/span\u003e) found that the presence of Fe ions exacerbates sulfur deposition damage. For removing fluids, Lv et al. (\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2023\u003c/span\u003e) used \u0026ldquo;chelating agent\u0026thinsp;+\u0026thinsp;hydrochloric acid\u0026rdquo; to remove sulfur and iron compounds. Abbasi et al. (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2024\u003c/span\u003e) used \u0026ldquo;hydrochloric acid\u0026thinsp;+\u0026thinsp;methanol\u0026rdquo; to remove oily organic matter. Cao et al. (\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2024\u003c/span\u003e) used chelating agent to remove CaCO\u003csub\u003e3\u003c/sub\u003e and CaSO\u003csub\u003e4\u003c/sub\u003e. Although, there are removal fluid systems for different types of plugging, acid is mainly used for on-site construction because of its cheapness and extensiveness.\u003c/p\u003e\u003cp\u003eWest Sichuan gas field have disadvantages in plugging removal, because the surrounding area is densely populated and requires high environmental protection. The construction of the platform wells adopts the model of \u0026ldquo;integrated gas production and purification\u0026rdquo;. Subject to the complex human environment and station conditions in the region, conventional injection plugging remover can only be used to return to the gas transmission process, plugging remover size, liquid nitrogen discharge measures are limited, and can not realize rapid, large displacement blowout. These limitations place higher demands on plugging diagnosis and removal techniques. This paper presents the first comprehensive analysis of plugging in sour gas wells in western Sichuan. In addition, except for continuous tubing (CT) (Riyanto et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2015\u003c/span\u003e), pumping removal fluids directly from the tubing is a common practice for plug removal in sour gas wells. Unfortunately, there are few detailed reports on how to optimise the removal process. \u0026ldquo;Quantifying plugging degree, judging plugging location, and predicting plugging trend\u0026rdquo; are the keys to optimise the removal process and improve removal effects. The current methods for evaluating plugging degree mainly include sulphur deposition prediction(Hu et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2014\u003c/span\u003e), calcium carbonate etc. scaling prediction (Safari et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2014\u003c/span\u003e), and asphaltene production prediction (Zhang et al. \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). However, these are prediction methods for a single plugging, which is difficult to predict due to the complex composition of the plugging. This paper innovates a simple and accurate method to quantify the plugging degree, which can accurately determine the plugging location and predict the plugging trend so as to optimise the removal process.\u003c/p\u003e\u003cp\u003eThis study systematically presents the following key contributions: (1) Characterization of plugging material composition and mechanisms through integrated experimental methodologies. (2) Comprehensive analysis of plugging characteristics and influencing factors. (3) Development of an optimized plugging removal fluid system coupled with establishment of a Quantitative Plugging Degree (QPD) assessment methodology, culminating in formulation of classified mitigation strategies for plugged wells. (4) Demonstration of field application outcomes validating the proposed solutions.\u003c/p\u003e"},{"header":"2 Research Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1 Plugging Detection methods\u003c/h2\u003e\u003cp\u003ePlugging materials were retrieved from six production wells via three collection methods: separators, sand filter during CT operations, and downhole tools. Representative samples exhibited black coloration with variable viscosity, ranging from semi-solid to consolidated states (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). A multi-analytical approach was implemented:\u003c/p\u003e\u003cp\u003e\u003col\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eScorch experiment: Quantification of organic/inorganic fractions was achieved through controlled pyrolysis. Pre-weighed samples (vacuum-dried at 60\u0026deg;C for 24 h) underwent muffle furnace combustion (600\u0026deg;C for 8 h), with mass loss determining organic content.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eSEM-EDS: Pristine plugging specimens were sputter-coated with Au/Pd to prevent charging. High-resolution imaging (10\u0026ndash;20 kV, WD 8\u0026ndash;12 mm) revealed surface morphologies, with EDS mapping performed on representative zones for localized elemental quantification.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eXPF: Ash residues from scorched samples were homogenized, and pellets into pellets for elemental profiling. Characteristic X-ray fluorescence spectra identified major/minor elements through wavelength-dispersive detection.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eFTIR: Cryogenically milled samples were blended with KBr (1:100) and pelletized. Spectral acquisition (4000\u0026ndash;400 cm⁻\u0026sup1;, 4 cm⁻\u0026sup1; resolution, 32 scans) detected functional groups via transmission mode.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eGC-MS: Organic extracts were prepared by toluene dissolution, centrifugation (12,000 rpm/10 min), and microfiltration (0.22 \u0026micro;m). Chromatographic separation (DB-5MS column) coupled with quadrupole MS enabled compound identification through NIST library matching (match factor\u0026thinsp;\u0026gt;\u0026thinsp;85%) with retention index verification.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003c/ol\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2 Spearman method\u003c/h2\u003e\u003cp\u003eThe Spearman's rank correlation method was employed to assess the nonlinear dependencies between 16 variables (pre-production flowback rate, open-flow potential, initial tubing pressure, etc.) and two critical plugging indicators: (i) time to first plugging and (ii) plugging removal frequency. The parameter ranges are summarized in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Notably, three completion methodologies were represented by open-hole section length, liner length, and number of perforation intervals. Categorical variables included: (i) Drilling mud type: Coded as 1 for oil-based mud and 0 for water-based mud (WBM) during target zone drilling. (ii)Downhole anomalies: Coded as 1 for mechanical failures (e.g., tubing misplacement or rupture) and 0 for normal operations. All other parameters were treated as continuous variables. Spearman's method was selected for its distribution-free nature and robustness to outliers, making it particularly suitable for the nonlinear and non-Gaussian data characteristics observed in this study (Wang and Feng. 1993). The mathematical formulation is expressed in Equations (\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) and (\u003cspan refid=\"Equ2\" class=\"InternalRef\"\u003e2\u003c/span\u003e):\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\:{R}_{S1}=1-\\frac{6\\sum\\:{d}_{i}^{2}}{n\\left({n}^{2}-1\\right)}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$$\\:{R}_{S2}=\\frac{\\left[\\left({n}^{3}-n\\right)/6\\right]-\\left(Tx+Ty\\right)-\\sum\\:{d}_{i}^{2}}{\\sqrt{\\left(\\frac{{n}^{3}-n}{6}-2Tx\\right)}\\sqrt{\\left(\\frac{{n}^{3}-n}{6}-2Ty\\right)}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003ewhere \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:n\\)\u003c/span\u003e\u003c/span\u003e denotes the number of observed data points, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{d}_{i}\\)\u003c/span\u003e\u003c/span\u003e represents the rank difference between paired variables (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:x,y\\)\u003c/span\u003e\u003c/span\u003e), and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:Tx\\:\\)\u003c/span\u003e\u003c/span\u003e(or \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:Ty\\)\u003c/span\u003e\u003c/span\u003e) is calculated as \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\sum\\:(t3-t)/12\\)\u003c/span\u003e\u003c/span\u003e, where \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:t\\)\u003c/span\u003e\u003c/span\u003e corresponds to the number of tied ranks in \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:x\\)\u003c/span\u003e\u003c/span\u003e (or \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:y\\)\u003c/span\u003e\u003c/span\u003e). Eq.\u0026nbsp;(\u003cspan refid=\"Equ2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) (denoted as \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{R}_{S2}\\)\u003c/span\u003e\u003c/span\u003e) is applied when \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:x\\)\u003c/span\u003e\u003c/span\u003e or \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:y\\)\u003c/span\u003e\u003c/span\u003e contains tied ranks, whereas Eq.\u0026nbsp;(\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{R}_{S1}\\)\u003c/span\u003e\u003c/span\u003e) is used for datasets without ties. Notably, when \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:Tx\\)\u003c/span\u003e\u003c/span\u003e=\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:Ty\\)\u003c/span\u003e\u003c/span\u003e=0, Equations (\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) and (\u003cspan refid=\"Equ2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) become mathematically equivalent.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eRange of parameters affecting plugging\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"2\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eInfluence factor\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eRange\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePre-production flowback rate, %\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e7.8\u0026minus;73.24\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eOpen-flow potential (OFP), 10\u003csup\u003e4\u003c/sup\u003em\u003csup\u003e3\u003c/sup\u003e/d\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e70\u0026ndash;335\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eInitial tubing pressure, MPa\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e35.36\u0026ndash;47.72\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePre-production shut-in duration, d\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e457\u0026ndash;1245\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eOpen-hole section length, m\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0\u0026minus;1272.5\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eLiner length, m\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0\u0026minus;2087.5\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNumber of sliding sleeves\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0\u0026ndash;9\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNumber of perforation intervals\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0\u0026ndash;3\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTotal stimulation fluid volume, m\u003csup\u003e3\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1020\u0026ndash;3272\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAcid volume used in stimulation, m\u003csup\u003e3\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e720\u0026ndash;2550\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eDiverting agent dosage, kg\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0\u0026minus;4500\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eFiber volume, kg\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0\u0026minus;470\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eDrilling fluid loss volume, m\u003csup\u003e3\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0\u0026minus;503\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCompletion fluid loss volume, m\u003csup\u003e3\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0\u0026minus;427.64\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eDownhole anomalies\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0 or 1\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eDrilling mud type\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0 or 1\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTime to first plugging, d\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e51.7\u0026ndash;355\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePlugging removal frequency, d\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e74\u0026ndash;486\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e2.3 Preferred method of plugging removal fluid\u003c/h2\u003e\u003cp\u003eThe removal efficacy of five distinct plugging removal fluids was systematically evaluated: Fluid A (toluene-dominated formulation), Fluid B (ethanol-based composition), Fluid C (acetone-primary solvent), Fluid D (15% HCl\u0026thinsp;+\u0026thinsp;5.5% high-temperature corrosion inhibitor), and Fluid E (neutral viscosity-reducing fluid synthesized from surfactant-viscosity modifier complexes).\u003c/p\u003e\u003cp\u003eInorganic plugging samples from Well P6 were pulverized, dried in a vacuum oven at 60\u0026deg;C for 24 hours to achieve baseline mass (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{m}}_{1}\\)\u003c/span\u003e\u003c/span\u003e), then subjected to 30-minute reactions with 50 mL of each fluid under 80\u0026deg;C water bath conditions. Post-treatment residues were redried at 60\u0026deg;C to constant mass (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{m}}_{2}\\)\u003c/span\u003e\u003c/span\u003e), with dissolution efficiency (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\eta\\:}\\)\u003c/span\u003e\u003c/span\u003e) calculated as Eq.\u0026nbsp;\u003cspan refid=\"Equ3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003cdiv id=\"Equ3\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ3\" name=\"EquationSource\"\u003e\n$$\\:{\\eta\\:}=\\frac{{\\text{m}}_{1}-{\\text{m}}_{2}}{{\\text{m}}_{1}}\\times\\:100\\text{%}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e3\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eOrganic plugging samples from Well M1 were subjected to rheological characterization using a Brookfield DV2T rotational viscometerto determine baseline apparent viscosity (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\mu\\:}_{0}\\)\u003c/span\u003e\u003c/span\u003e) at room temperature. Each plugging removal fluid (A-E) was mixed with the organic plugging at a 1:1 mass ratio. The reaction was carried out for 30 min at 80\u0026deg;C in a water bath. At the end of the reaction, the apparent viscosity (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\mu\\:}_{1}\\)\u003c/span\u003e\u003c/span\u003e) of the mixture was determined. The rate of viscosity reduction (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\text{R}\\)\u003c/span\u003e\u003c/span\u003e) is shown in Eq.\u0026nbsp;\u003cspan refid=\"Equ4\" class=\"InternalRef\"\u003e4\u003c/span\u003e.\u003cdiv id=\"Equ4\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ4\" name=\"EquationSource\"\u003e\n$$\\:\\text{R}=\\frac{{\\mu\\:}_{0}-{\\mu\\:}_{1}}{{\\mu\\:}_{0}}\\times\\:100\\text{%}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e4\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\u003ch2\u003e2.4 Methodology for quantifying plugging degree(QPD)\u003c/h2\u003e\u003cp\u003eGas well plugging is systematically classified into wellbore plugging (W\u003csub\u003ewellbore\u003c/sub\u003e) and reservoir plugging (W\u003csub\u003ereservoir\u003c/sub\u003e), with the latter comprising blockages in tubing sections, screen annuli, and productive intervals. The fundamental relationship governing plugging severity is defined as Total Plugging Degree (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\varDelta\\:P\\)\u003c/span\u003e\u003c/span\u003e)\u0026thinsp;=\u0026thinsp;W\u003csub\u003ewellbore\u003c/sub\u003e +W\u003csub\u003ereservoir\u003c/sub\u003e, where spatial and temporal plugging patterns are discerned through comparative analysis of W\u003csub\u003ewellbore\u003c/sub\u003e and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\varDelta\\:P\\)\u003c/span\u003e\u003c/span\u003e variations. W\u003csub\u003ewellbore\u003c/sub\u003e is quantified as the integral pressure differential between measured pump pressure during plugging removal operations and theoretical unplugged pump pressure (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Force equilibrium analysis of the wellbore liquid column identifies three dominant components: gravitational force, frictional resistance, and upward thrust from gas influx. In deviated well sections, gravitational potential energy in vertical intervals substantially exceeds frictional losses in inclined segments, justifying the simplified pump pressure model: the pumping pressure\u0026thinsp;=\u0026thinsp;wellbore flow pressure - liquid column pressure, where negative values are considered to zero. While established methods for calculating wellbore flow pressure (Beggs and Brill. 1973. Hagedorn. 1965. Mukherjee and Brill. 1985. Hasan and Kabir. 1983), this study adopts an empirical correlation for gas-dominated systems (Eq.\u0026nbsp;\u003cspan refid=\"Equ5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). Based on the natural rate of pressure drop in the well, the wellhead oil pressure (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{P}_{2}\\)\u003c/span\u003e\u003c/span\u003e) under non-clogging conditions is deduced, and the difference between \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{P}_{2}\\)\u003c/span\u003e\u003c/span\u003e and the current oil pressure (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{P}_{1}\\)\u003c/span\u003e\u003c/span\u003e) is \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\varDelta\\:P\\)\u003c/span\u003e\u003c/span\u003e as in Eq.\u0026nbsp;(\u003cspan refid=\"Equ6\" class=\"InternalRef\"\u003e6\u003c/span\u003e).\u003cdiv id=\"Equ5\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ5\" name=\"EquationSource\"\u003e\n$$\\:{P}_{\\text{i}}={P}_{1}{e}^{\\frac{0.03415\\gamma\\:ℎ}{{T}_{cp}{Z}_{cp}}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e5\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equ6\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ6\" name=\"EquationSource\"\u003e\n$$\\:\\varDelta\\:P={P}_{2}-{P}_{1}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e6\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{P}_{i}\\)\u003c/span\u003e\u003c/span\u003e\u0026mdash;Any well depth flow pressure. γ\u0026mdash;relative density of natural gas. h\u0026mdash;vertical depth, m.\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{T}}_{\\text{c}\\text{p}}\\)\u003c/span\u003e\u003c/span\u003e\u0026mdash;Average wellbore temperature, K. \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{Z}}_{\\text{c}\\text{p}}\\)\u003c/span\u003e\u003c/span\u003e\u0026mdash;Average wellbore compression factor. e\u0026mdash;Natural logarithm. \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\varDelta\\:P\\)\u003c/span\u003e\u003c/span\u003e\u0026mdash;gas well plugging pressure drop. \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{P}_{1}\\)\u003c/span\u003e\u003c/span\u003e\u0026mdash;actual oil pressure. \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{P}_{2}\\)\u003c/span\u003e\u003c/span\u003e\u0026mdash;wellhead oil pressure under non-clogging conditions.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e"},{"header":"3 Results and Discussion","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003e3.1 Plugging Characterization\u003c/h2\u003e\u003cp\u003eAnalysis of 40 well cases compared pressure decline rates during plugging and normal production (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). Some wells exhibiting higher pressure decline rates during plugging suggest instantaneous wellbore blockage or rapid near-wellbore debris accumulation, while lower rates indicate gradual plugging. The average pressure decline rates before and after plugging show an order of magnitude difference (0.025 vs 0.434 MPa/d), with an increase of 17.36 times. A incremental pressure decline rate of \u0026ge;\u0026thinsp;0.02 MPa/d, which is the difference between \u0026ldquo;the baseline pressure decline rate\u0026rdquo; and \u0026ldquo;the plugging-induced pressure decline rate\u0026rdquo;, can be used as the plugging warning threshold.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\u003ch2\u003e3.2 Plugging mechanism\u003c/h2\u003e\u003cdiv id=\"Sec10\" class=\"Section3\"\u003e\u003ch2\u003e3.2.1 Scorch experiment\u003c/h2\u003e\u003cp\u003eThe results are shown in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, the plugging materials in the west Sichuan gas field can be divided into three categories. The first category is organic plugging, with organic matter accounting for more than 70%, and this plugging material presents solid state below 50℃ and molten state above 70℃, and P3 and M1 wells are organic plugging. The second category is compound plugging, with the ratio of organic and inorganic materials from 44.8 to 55.2%, and X1 and P4 wells are compound plugging. The third category is inorganic plugging, the proportion of inorganic matter is more than 80%, and P6 and P5 wells are inorganic plugging.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eSample scorching results\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"8\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSample\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eWell\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eChannels\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eBefore scorching (g)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eAfter scorching (g)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eorganic content (%)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003eInorganic content (%)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c8\"\u003e\u003cp\u003ePlugging type\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eG1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eP3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eSplitter\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e7.6167\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.6677\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e91.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e8.8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003eOrganic\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eG2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eP3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eDownhole tools\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e34.3778\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e9.5364\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e72.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e27.7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003eOrganic\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eG3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eX1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eSand filer\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e10.5772\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e5.6071\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e46.9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e53.1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003eCompound\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eG4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eM1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eSand filer\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e12.5501\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e1.2427\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e90.1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e9.9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003eOrganic\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eG5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eP4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eSplitter\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e1.2354\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.6819\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e44.8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e55.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003eCompound\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eG6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eP6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eSplitter\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e2.3456\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e2.0243\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e13.7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e86.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003eInorganic\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eG7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eP5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eSplitter\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e1.6873\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e1.4224\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e15.7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e84.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003eInorganic\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec11\" class=\"Section3\"\u003e\u003ch2\u003e3.2.2 SEM\u0026thinsp;+\u0026thinsp;EDS\u003c/h2\u003e\u003cp\u003eMicrostructural characterization (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e) demonstrates granular-dominated architectures across all types. Organic plugs (G1) display surface encapsulation features, contrasting with the textural heterogeneity of composite (G5) and inorganic (G6) variants, potentially attributable to declining organic fractions. EDS quantification (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e) identifies C, O, S, Si, Fe, and Ba as primary constituents. Elevated carbon concentrations in G1, G2, and G4 confirm their organic-rich nature, aligning with scorch test mass-loss measurements.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eEDS test results\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"8\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eElement\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"7\" nameend=\"c8\" namest=\"c2\"\u003e\u003cp\u003eAtomic content/Weight content, %\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eG1\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eG2\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eG3\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eG4\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eG5\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003eG6\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c8\"\u003e\u003cp\u003eG7\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eC\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e68.8/54.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e92.4/85\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e28.3/50.6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e49.1/73.4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e41.8/20.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e29.8/14.9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e35.2/16.3\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eO\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e26.1/27.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e3.4/4.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e20.3/27.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e11.6/13.1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e6.7/4.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e40.5/27\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e3.9/2.4\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eN\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e6.2/3.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e0.5/0.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMg\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.2/0.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e0.9/0.9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNa\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e10.4/9.6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e3.2/3.1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e25.0/22.2\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAl\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.18/0.14\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e2.0/2.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSi\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.01/0.02\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.1/0.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.47/0.36\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.6/0.4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.3/0.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e4.5/5.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eS\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.04/0.08\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e3.5/8.6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e6.12/4.09\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e6.6/3.7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e19.7/25.4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e3.1/4.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e20.2/25\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCa\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.03/0.08\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e3.87/2.07\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.9/0.9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e1.5/2.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e0.39/0.6\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eK\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e7.9/13\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMn\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.44/0.17\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eFe\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e4.8/17.7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.4/1.9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e38.7/14.8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e2.3/0.8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e4.1/9.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e1.4/3.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eBa\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.02/0.14\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.66/0.1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.8/4.6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e3.2/18.1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec12\" class=\"Section3\"\u003e\u003ch2\u003e3.2.3 XRF\u003c/h2\u003e\u003cp\u003eX-ray fluorescence (XRF) characterization of the calcined powders (Table\u0026nbsp;4) reveals inorganic constituents dominated by Fe, S, Ba, Si, and transition metals. Samples G1-G3 exhibit elevated iron content coupled with sulfur, suggesting predominant phases of iron oxides in G1/G3 and iron sulfide (FeS) in G2 through stoichiometric parity analysis. Notably, G7 demonstrates a superstoichiometric Ba/S mass ratio of 5.69 versus the theoretical 4.43 for pure BaSO₄, indicating free BaO phase coexistence. Conversely, G3 and G6 display substoichiometric Ba/S ratios (1.2\u0026ndash;1.5) with respective Ba (11.3\u0026ndash;11.7 wt%) and S (7.4\u0026ndash;9.5 wt%) concentrations, consistent with intermediate barium sulfate phases formation. These mineralogical signatures collectively indicate complex assemblages of iron oxides (Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e), sulfides (FeS/FeS\u003csub\u003e2\u003c/sub\u003e), and barium sulfate (BaSO\u003csub\u003e4\u003c/sub\u003e).\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec13\" class=\"Section3\"\u003e\u003ch2\u003e3.2.4 FTIR\u003c/h2\u003e\u003cp\u003eFTIR analysis of pre-sintered samples (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e) identified characteristic functional groups (Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e5\u003c/span\u003e). Broad absorption bands at 3313\u0026ndash;3439 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e correspond to O-H/N-H stretching vibrations. Peaks between 2907\u0026ndash;2952 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e indicate C-H stretching modes in aliphatic chains (-CH\u003csub\u003e3\u003c/sub\u003e, -CH\u003csub\u003e2\u003c/sub\u003e-), confirming alkane presence. The 1600 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e region suggests aromatic C\u0026thinsp;=\u0026thinsp;C, carbonyl (C\u0026thinsp;=\u0026thinsp;O), or amide groups. A distinct C-H bending vibration occurs at 1352 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. Functional group analysis reveals organic constituents dominated by alkanes and aromatic hydrocarbons.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eFunctional group analysis of each sample\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"6\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSample\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eFunctional\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eLocation\u003c/p\u003e\u003cp\u003e(cm\u0026thinsp;\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eSample\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eFunctional\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eLocation\u003c/p\u003e\u003cp\u003e(cm\u0026thinsp;\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"4\" rowspan=\"5\"\u003e\u003cp\u003eG1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eHydroxyl (-OH) or amine (-NH)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e3428\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\" morerows=\"5\" rowspan=\"6\"\u003e\u003cp\u003eG2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eHydroxyl (-OH) or amine (-NH)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e3435\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eAlkyl -CH\u003csub\u003e3\u003c/sub\u003e and -CH\u003csub\u003e2\u003c/sub\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e2952\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eAlkyl -CH\u003csub\u003e3\u003c/sub\u003e and -CH\u003csub\u003e2\u003c/sub\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e2907\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eAmide or benzene ring or carbonyl C\u0026thinsp;=\u0026thinsp;O\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1620\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eAmide or benzene ring or carbonyl C\u0026thinsp;=\u0026thinsp;O\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e1600\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e-C-O-C or -COO\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1206\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eC-H bond\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e1352\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eAromatic or olefinic C-H\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e558\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eether bond\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e1105\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"6\" rowspan=\"7\"\u003e\u003cp\u003eG3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eHydroxyl (-OH) or amine (-NH)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e3439\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eCharacteristic peaks of substitution on the benzene ring\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e620\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eThe -C-H of the benzene ring\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e3058\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\" morerows=\"4\" rowspan=\"5\"\u003e\u003cp\u003eG4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eHydroxyl (-OH) or amine (-NH)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e3419\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eAlkyl -CH\u003csub\u003e3\u003c/sub\u003e and -CH\u003csub\u003e2\u003c/sub\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e2918\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eAlkyl -CH\u003csub\u003e3\u003c/sub\u003e and -CH\u003csub\u003e2\u003c/sub\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e2923\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eAmide or benzene ring or carbonyl C\u0026thinsp;=\u0026thinsp;O\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1600\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eAmide or benzene ring or carbonyl C\u0026thinsp;=\u0026thinsp;O\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e1631\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e-C-O-C or -COO\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1233\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eNaphthalene C-C\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e1459\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSecondary or tertiary alcohols\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1070\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eSecondary or tertiary alcohols\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e1064\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCharacteristic peaks of substitution on the benzene ring\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e702\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\" morerows=\"4\" rowspan=\"5\"\u003e\u003cp\u003eG6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eHydroxyl (-OH) or amine (-NH)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e3384\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"4\" rowspan=\"5\"\u003e\u003cp\u003eG5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eHydroxyl (-OH) or amine (-NH)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e3313\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eAlkyl -CH\u003csub\u003e3\u003c/sub\u003e and -CH\u003csub\u003e2\u003c/sub\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e2925\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eAlkyl -CH\u003csub\u003e3\u003c/sub\u003e and -CH\u003csub\u003e2\u003c/sub\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e2919、2852\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eAmide or benzene ring or carbonyl C\u0026thinsp;=\u0026thinsp;O\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e1592\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eAmide or benzene ring or carbonyl C\u0026thinsp;=\u0026thinsp;O\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1652\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eC-H bond\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e1382\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003ehydroxyl alcohol\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1513\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eether\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e1008\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eEster cyclic ether C-O-C-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1086\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\" morerows=\"3\" rowspan=\"4\"\u003e\u003cp\u003eG7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e-CH\u003csub\u003e2\u003c/sub\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e1459\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e\u003cp\u003eG7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eHydroxyl (-OH) or amine (-NH)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e3313\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e-C-O-C or -COO\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e1251\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eAlkyl -CH\u003csub\u003e3\u003c/sub\u003e and -CH\u003csub\u003e2\u003c/sub\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e2919\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eamide\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e948\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eAmide or benzene ring or carbonyl C\u0026thinsp;=\u0026thinsp;O\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1608\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec14\" class=\"Section3\"\u003e\u003ch2\u003e3.2.5 GC-MS\u003c/h2\u003e\u003cp\u003eAs shown in Table\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e6\u003c/span\u003e, all samples exhibit at least one dominant component: either alkanes (C\u003csub\u003e14\u003c/sub\u003e-C\u003csub\u003e44\u003c/sub\u003e) or aromatic hydrocarbons (e.g., G1/G5 with \u0026gt;\u0026thinsp;70% alkanes; G2/G4 with \u0026gt;\u0026thinsp;89% aromatics). Siloxanes (0.51\u0026ndash;5.65%) are present in all samples except G4 and G5. The elevated aromatic hydrocarbon content suggests contamination from wellbore-introduced materials such as drilling fluid additives.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab5\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 6\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eGC-MS analysis results\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"6\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eOrganic component\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"5\" nameend=\"c6\" namest=\"c2\"\u003e\u003cp\u003eContent (%)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eG1\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eG2\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eG3\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eG4\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eG5\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAlkane (C\u003csub\u003e14\u003c/sub\u003e-C\u003csub\u003e44)\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e73.79\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e4.61\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e35.43\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.33\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e78.14\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSilicone\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0.51\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e4.73\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e5.65\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.02\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eEthers\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e8.1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAldehydes\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e4.83\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eBenzene-containing compounds\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e10.06\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e89.29\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e38.02\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e99.62\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e12.6\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCarboxylic acid-containing hydrocarbons\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e2.33\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e1.25\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e9.75\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec15\" class=\"Section3\"\u003e\u003ch2\u003e3.2.6 Mechanical analysis\u003c/h2\u003e\u003cp\u003eAccording to the results of plugging material analysis (Table\u0026nbsp;\u003cspan refid=\"Tab6\" class=\"InternalRef\"\u003e7\u003c/span\u003e), the plugging material types in the West Sichuan gas field are complex, with three types of plugging: organic, inorganic, and composite. The main components of organic materials are long-chain alkanes and benzene-containing compounds, and the main components of inorganic materials are iron sulphides and oxides, BaSO\u003csub\u003e4\u003c/sub\u003e and clay. Based on the whole-rock analysis, there is no pyrite in the area, and it is judged that the iron sulphides and oxides are mainly from the corrosion products of H\u003csub\u003e2\u003c/sub\u003eS with downhole metal tubing (Chen et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2020\u003c/span\u003e. Ye et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). BaSO\u003csub\u003e4\u003c/sub\u003e originates from barite, a weighting material in drilling fluids, and is inert and insoluble in hydrochloric acid. For the long-chain alkanes of organic materials, most scholars now generally believe that there are two main reasons (Lou and Wu. 2020. Abbasi et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2024\u003c/span\u003e. Lu et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2023\u003c/span\u003e): (1) The reservoir contains organic components such as asphalt. (2) Organic components of the working fluids such as amide, methanol and quaternary ammonium salt of corrosion inhibitors, oil-soluble substances of drilling fluids, fatty acids, fatty acid lipids sulphonated tannin (SMT), sulphonated quebracho ketene (SMK) and polymers such as sulphonated phenolic resins (SMP). We trace the materials of the working fluids and analyse that polyacrylamide mainly originates from polymers such as phenolic resins, sulphonated tannins, polymer blocking agents, temperature-resistant viscosity enhancers, and polyacrylamide of gelling acids in drilling fluids. Long-chain alkanes and phenyl compounds originate from the reservoirs and working fluids. Asphaltenes have been found in cast thin sections of the destination layer of the P-1 well, an exploratory well in the West Sichuan gas field (Wu et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Asphaltenes, defoamers (silicone oils), emulsions, polymer additives, viscosity enhancers in drilling fluids, substances such as aldehydes and amines in completion fluids, and amides, methanol, and quaternary ammonium salts in corrosion inhibitors. These organics generate long-chain alkanes and benzene-containing compounds with a certain viscosity at high temperatures and pressures.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab6\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 7\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eResults of plugging analysis\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"4\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eType\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSample\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003ewell\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003ePlugging components\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e\u003cp\u003eorganic\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eG1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eP3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e91.2% Organic (long-chain alkanes and benzene-containing compounds)\u003c/p\u003e\u003cp\u003e8.8% Inorganic (iron oxides and sulphides, BaSO\u003csub\u003e4\u003c/sub\u003e, clay)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eG2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eP3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e72.3% Organic (benzene-containing compounds and long-chain alkanes)\u003c/p\u003e\u003cp\u003e27.7% Inorganic (iron sulphides, clay)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eG4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eM1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e90.1%Organic (benzene-containing compounds)\u003c/p\u003e\u003cp\u003e9.9% Inorganic (CaSO\u003csub\u003e4\u003c/sub\u003e、FeS、clay)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eCompound\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eG3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eX1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e46.9% Organic (long-chain alkanes and benzene-containing compounds)\u003c/p\u003e\u003cp\u003e53.1% Inorganic (iron oxides and sulphides, BaSO\u003csub\u003e4\u003c/sub\u003e, clay)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eG5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eP4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e44.8% Organic (long-chain alkanes and benzene-containing compounds)\u003c/p\u003e\u003cp\u003e55.2% Inorganic (S, FeS, BaSO\u003csub\u003e4\u003c/sub\u003e)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eInorganic\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eG6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eP6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e86.4% Inorganic (BaSO\u003csub\u003e4\u003c/sub\u003e, FeS, metal oxide)\u003c/p\u003e\u003cp\u003e13.7% Organic (alkanes and benzene-containing compounds)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eG7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eP5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e84.3% Inorganic (BaSO\u003csub\u003e4\u003c/sub\u003e, FeS, metal oxide)\u003c/p\u003e\u003cp\u003e15.7% Organic (benzene-containing compounds and alkanes)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Sec16\" class=\"Section2\"\u003e\u003ch2\u003e3.3 Plugging Correlation Analysis​\u003c/h2\u003e\u003cp\u003eSpearman correlation analysis (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e) delineated the statistical dependencies between 16 parameters and two plugging metrics\u0026mdash;time to first plugging (TFP) and plugging removal frequency (PRF). Following statistical conventions (Zhao et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), correlation strength was classified as: moderate (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\left|\\rho\\:\\right|\\)\u003c/span\u003e\u003c/span\u003e=0.4\u0026ndash;0.59), weak (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\left|\\rho\\:\\right|\\)\u003c/span\u003e\u003c/span\u003e=0.2\u0026ndash;0.39), and negligible (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\left|\\rho\\:\\right|\\)\u003c/span\u003e\u003c/span\u003e\u0026le;0.19). Downhole anomalies exhibited moderate inverse correlations with both metrics (TFP: \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\rho\\:\\)\u003c/span\u003e\u003c/span\u003e=\u0026minus;0.47; PRF: \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\rho\\:\\)\u003c/span\u003e\u003c/span\u003e=\u0026minus;0.43), while drilling fluid loss volume showed moderate anti-correlation with PRF (ρ=\u0026minus;0.45), substantiating the hypothesis of composite plugging formation through physical retention of wellbore-introduced materials (e.g., drilling fluid solids, unbroken fracturing gel) coupled with sulfide coprecipitation. Notably, stimulation fluid volume and acid volume demonstrated weak negative correlations with PRF (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\rho\\:\\)\u003c/span\u003e\u003c/span\u003e=\u0026minus;0.24 and\u0026minus;0.26 respectively), suggesting potential wettability alteration reversal from high-intensity acidizing that enhances particle adhesion in pore throats. Divergent correlations between open-hole section length (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\rho\\:\\)\u003c/span\u003e\u003c/span\u003e=\u0026minus;0.24) and liner length (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\rho\\:\\)\u003c/span\u003e\u003c/span\u003e=0.077) expose open-hole completion risks: the packer-isolated annular spaces in open-hole segments create stagnant zones prone to particulate settling, contrasting with liner-sleeve completions during gas surges.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec17\" class=\"Section2\"\u003e\u003ch2\u003e3.4 Preferred plugging removal fluid\u003c/h2\u003e\u003cp\u003eExperimental evaluations (Table\u0026nbsp;\u003cspan refid=\"Tab7\" class=\"InternalRef\"\u003e8\u003c/span\u003e) demonstrate that \u0026ldquo;Fluid D (15% HCl\u0026thinsp;+\u0026thinsp;5.5% high-temperature corrosion inhibitor)\u0026rdquo; achieves superior efficacy, dissolving\u0026thinsp;\u0026gt;\u0026thinsp;60% of inorganic plugging materials and reducing organic plugging viscosity by \u0026gt;\u0026thinsp;90%. While inorganic solubility remains partial, the solution effectively disrupts plugging matrix integrity by dissolving structural frameworks and destabilizing organic agglomerations, enabling wellbore evacuation through dissolution and mechanical loosening. Field applications in the western Sichuan gas field prioritize this acid-based remediation, though operational constraints, notably ground purification capacity, currently limit maximum treatment volumes to 25 m\u0026sup3;per operation.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab7\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 8\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eDissolving Effectiveness of Five Removal Fluids for plugging\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"3\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePlugging Removal Fluid\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eInorganic plugging\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eOrganic plugging\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eA\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003edissolution efficiency\u0026lt;33%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eviscosity reduction rate\u0026lt;60%\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eB\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003edissolution efficiency\u0026lt;36%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eviscosity reduction rate\u0026lt;58%\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eC\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003edissolution efficiency\u0026lt;30%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eviscosity reduction rate\u0026lt;20%\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eD\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003edissolution efficiency\u0026gt;60%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eviscosity reduction rate\u0026gt;90%\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eE\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003edissolution efficiency\u0026lt;15%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eviscosity reduction rate\u0026gt;90%\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec18\" class=\"Section2\"\u003e\u003ch2\u003e3.5 Optimization of Unplugging Timing​\u003c/h2\u003e\u003cp\u003eStatistical evaluation of 33 well interventions reveals a consistent trend: higher incremental pressure decline rates correlate with shorter unplugging cycle durations and greater post-treatment tubing pressure increase ratios. As empirically illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e, the longest average unplugging interval occurs when interventions are initiated while the incremental pressure decline rate remains\u0026thinsp;\u0026le;\u0026thinsp;0.2 MPa/d. This relationship between incremental pressure decline rate and unplugging interval, highlighting the criticality of timely unplugging for productivity preservation.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec19\" class=\"Section2\"\u003e\u003ch2\u003e3.6 Classified Mitigation Strategies\u003c/h2\u003e\u003cp\u003eBased on the identification of plugging characterization, mechanism, analysis of influencing factors, optimization of plugging removal fluids, unplugging timing, and quantifying plugging degree, this study proposes classified mitigation strategies for plugged wells. As illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e, an initial diagnosis of plugging is indicated when the incremental pressure decline rate reaches or exceeds 0.02 MPa/d. Intervention should be initiated as early as possible while the pressure decline rate remains below 0.2 MPa/d. For wells experiencing their first blockage, the adopted approach involves \u0026ldquo;small dosage injection of removal fluid\u0026thinsp;+\u0026thinsp;flowback of gas transmission process\u0026rdquo;. Previous operational experience revealed that verifying wellbore clearance using water alone proved ineffective for blockage removal. Consequently, the method \u0026ldquo;15 m\u003csup\u003e3\u003c/sup\u003e acid followed by one tubing volume of water\u0026rdquo; is employed, followed by an appropriate shut-in period prior to flowback. Wells exhibiting pump injection overpressure (unable injection) undergo \u0026ldquo;deep plugging removal utilizing coiled tubing (CT) deployment, large-scale acid fluid (\u0026ge;\u0026thinsp;100 m\u003csup\u003e3\u003c/sup\u003e), and controlled blowdown flowback\u0026rdquo;. For wells with two or more prior plugging, the remediation method is optimized based on a quantitative assessment of the current plugging degree.\u003c/p\u003e\u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e, based on the QPD method, gas well plugging degree is classified into Types I through IV. Type I is characterized by a progressively increasing difference between \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\varDelta\\:P\\)\u003c/span\u003e\u003c/span\u003e and W\u003csub\u003ewellbore\u003c/sub\u003e, signifying a gradual increase in W\u003csub\u003ereservoir\u003c/sub\u003e. This represents the most challenging type to remediate. Category II is characterized by a progressively decreasing difference between \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\varDelta\\:P\\)\u003c/span\u003e\u003c/span\u003e and W\u003csub\u003ewellbore\u003c/sub\u003e, indicating a reduction in W\u003csub\u003ereservoir\u003c/sub\u003e. This signifies a progressive shift of the plugging from the reservoir towards the wellbore, reflecting an improving condition. Categories III and IV exhibit consistent trends between \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\varDelta\\:P\\)\u003c/span\u003e\u003c/span\u003e and W\u003csub\u003ewellbore\u003c/sub\u003e, demonstrating that the wellhead pressure decline is primarily governed by wellbore plugging. Consequently, the plugging location is confined to the wellbore, representing a more favorable scenario.\u003c/p\u003e\u003cp\u003e\u003col\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eFor Type I: Displacement rate should be increased to enhance the impingement of the plugging removal fluid on downhole plugging. Acid volume should be increased and delivered via staged displacement, ensuring the acid remains in contact with the lower tubing and annulus for over 30 minutes. Finally, all acid is injected into the reservoir. This approach enhances dissolution efficiency at downhole plugging points but increases tubing corrosion hazards, it is therefore reserved exclusively for Type I scenarios.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eFor Type II: Displacement rate and acid volume should be increased to accelerate the transition of plugging material from the reservoir toward the wellbore.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eFor Type III: Both displacement fluid and acid should be injected at low displacement rates to maximize contact time with wellbore plugging material. Staged displacement reduces the concentration of the initial acid stage. During pump injection overpressure, this mitigates corrosion damage caused by excessively high acid concentration in the wellbore.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eFor Type IV: As plugging conditions progressively improve, low displacement rates are primarily employed to maximize acid contact time with wellbore plugging deposits.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003c/ol\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e"},{"header":"4 Typical well applications","content":"\u003cdiv id=\"Sec21\" class=\"Section2\"\u003e\u003ch2\u003e4.1 P5 well\u003c/h2\u003e\u003cp\u003eThis open-hole staged completion well (OFP: 110.6\u0026times;10\u003csup\u003e4\u003c/sup\u003e m\u0026sup3;/d, initial wellhead pressure: 42.5 MPa) commenced production in January 2024. Initial remediation attempts employed conventional treatment (15\u0026ndash;20 m\u003csup\u003e3\u003c/sup\u003e acid\u0026thinsp;+\u0026thinsp;one tubing-volume water), proving ineffective with short plugging cycles (mean: 50 days) and rapid pressure decline (\u0026gt;\u0026thinsp;0.2 MPa/d). Diagnostic analysis of the 2nd and 3rd plugging events (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003ea) identified Type III. Consequently, the 4th treatment implemented an optimized protocol: Variable-rate pumping\u0026thinsp;+\u0026thinsp;staged fluid displacement\u0026thinsp;+\u0026thinsp;high-volume treatment.\u003c/p\u003e\u003cp\u003eDuring execution, wellbore plugging caused pump overpressure after injecting 5 m\u003csup\u003e3\u003c/sup\u003e acid and 10 m\u003csup\u003e3\u003c/sup\u003e water. Flowback was initiated before completing treatment. Crucially, conventional method would have retained high-concentration acid in the wellbore, risking prolonged tubing corrosion. Through QPD-optimized procedures, the operation succeeded. Post-treatment results (Figs.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003eb-c) show significantly extended effectiveness (\u0026gt;\u0026thinsp;120 days) and reduced pressure decline (0.04 MPa/d). While plugging recurrence occurred, the 4th intervention demonstrated marked improvement over prior attempts.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec22\" class=\"Section2\"\u003e\u003ch2\u003e4.2 X1 well\u003c/h2\u003e\u003cp\u003eThis cased/perforated completion well (OFP: 70\u0026times;10\u003csup\u003e4\u003c/sup\u003e m\u003csup\u003e3\u003c/sup\u003e/d; initial pressure: 40.34 MPa) began production in December 2023. By August 2024, six plugging removal operations had been performed, averaging just 23.6 days of effectiveness. Pumping diagnostics revealed multiple migrating obstruction points from the formation to ~\u0026thinsp;346m inside tubing. The 6th treatment failed due to pump overpressure, confirming untreatable plugging within 1,200m of tubing - necessitating coiled tubing (CT) intervention.\u003c/p\u003e\u003cp\u003eInitial CT operations (Φ44mm milling shoe, 150 L/min) encountered obstruction at 88.8m (subsurface safety valve), stalling at 6-ton resistance. Analysis indicated gas-mobilized plugging material ascending and encapsulating the valve assembly. The small-diameter tool's limited flow prevented circulation. Switching to a Φ54mm nozzle enabled 300 L/min displacement, circulating out safety-valve deposits and successfully penetrating to the formation.\u003c/p\u003e\u003cp\u003ePost-treatment (100m\u0026sup3; HCl\u0026thinsp;+\u0026thinsp;blowdown flowback) recovered\u0026thinsp;~\u0026thinsp;1m\u0026sup3; of solids. Wellhead pressure increased from 36.86 to 42.3 MPa with gas production rising from 7.19 to 12.8\u0026times;10 \u003csup\u003e4\u003c/sup\u003e m\u0026sup3;/d. As of January 2025, production has stabilized\u0026thinsp;\u0026gt;\u0026thinsp;170 days at 19\u0026times;10\u003csup\u003e4\u003c/sup\u003e m\u003csup\u003e3\u003c/sup\u003e/d with minimal pressure decline (0.0125 MPa/d), demonstrating exceptional remediation efficacy (Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e"},{"header":"5 Conclusion","content":"\u003col class=\"decimal_type\"\u003e\n \u003cli\u003ePlugging mechanisms in the West Sichuan gas field are categorized into three primary types: organic (predominantly long-chain alkanes and phenyl compounds originating from reservoirs/work fluids), inorganic (chiefly iron sulfides/oxides, barite, and clay derived from corrosion products and drilling additives), and composite plugging.\u003c/li\u003e\n \u003cli\u003eDiagnostic thresholds establish that an incremental pressure decline rate\u0026nbsp;\u0026ge;0.02 MPa/d indicates initial plugging, mandating intervention initiation before the rate exceeds 0.2 MPa/d.\u003c/li\u003e\n \u003cli\u003eSpearman correlation analysis reveals significant trends: wells exhibiting more Downhole anomalies and drilling fluid loss earlier plugging onset and demonstrate greater remediation complexity.\u003c/li\u003e\n \u003cli\u003eComparative evaluation of five removal fluid types confirms acid fluids as most effective, achieving \u0026gt;60% dissolution efficiency for inorganic deposits and \u0026gt;90% degradation rate for organic accumulations.\u003c/li\u003e\n \u003cli\u003eWellbore plugging degree can be characterized through differential analysis between actual removal fluid pump pressure and theoretical non-plugging pressure profiles. This approach provides a feasible methodology for locating plugging zones and optimizing mitigation strategies. Field applications of the CT-QPD integrated mitigation strategy in Wells P5 and X1 demonstrate substantially extended unplugging validity periods and significantly reduced pressure decline rates, validating the methodology\u0026apos;s efficacy.\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Declarations","content":"\u003cp\u003eDisclosure statement\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e\u003ch2\u003eFunding\u003c/h2\u003e\u003cp\u003eThis paper was supported by Sinopec Southwest Oil and Gas Branch Project (Grant NO. CYQ-104-2403)\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eZ.K.​​ (Zheng Kang): Conceptualization, Methodology, Funding acquisition, Supervision, Writing \u0026ndash; original draft. ​​Y.-T.L.​​ (Yin-Tao Liu): Investigation, Formal analysis, Data curation, Writing \u0026ndash; review \u0026amp; editing. ​​G.-D.Z.​​ (Guo-Dong Zhang): Validation, Visualization. ​​B.S.​​ (Biao Su): Resources, Project administration. ​​X.-F.L.​​ (Xiao-Feng Liu): Investigation, Writing \u0026ndash; review \u0026amp; editing. ​​B.X.​​ (Biao Xia): Formal analysis, Visualization. ​​W.-Z.W.​​ (Wei-zhi Wang): Supervision, Funding acquisition, Writing \u0026ndash; review \u0026amp; editing. All authors critically reviewed and approved the final manuscript.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAbbasi A, Khamehchi E, Khaleghi M R, et al. A new formulation for removing condensate blockage for low permeable gas reservoir. 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Spearman rank correlations analysis of the elemental, mineral concentrations, and mechanical parameters of the Lower Cambrian Niutitang shale: A case study in the Fenggang block, Northeast Guizhou Province, South China. Journal of Petroleum Science and Engineering, 2022, 208: 109550.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":false,"email":"","identity":"journal-of-petroleum-exploration-and-production-technology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Journal of Petroleum Exploration and Production Technology","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"VoR Journals","inReviewEnabled":false,"inReviewRevisionsEnabled":false},"keywords":"plugging, West Sichuan gas field, sour, mitigation strategies, plugging degree","lastPublishedDoi":"10.21203/rs.3.rs-7224036/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7224036/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eSince their commissioning in 2023, eighteen sour gas wells in the West Sichuan Gas Field have experienced over forty significant plugging incidents, severely compromising field productivity. This study employed multidisciplinary experimental methods to analyze plugging mechanism. Spearman correlation analysis identified plugging influencing factors, enabling recognition of plugging characterization and optimal unplugging timing. An optimized plugging removal fluid system was developed alongside a novel Quantitative Plugging Degree (QPD) assessment methodology, forming the basis of a targeted well mitigation strategy. Key findings reveal: (1) Three distinct plugging types\u0026mdash;organic (predominantly long-chain alkanes and benzene compounds), inorganic (iron sulfides/oxides, BaSO\u003csub\u003e4\u003c/sub\u003e, and clays), and composite plugging; (2) Acid demonstrates superior efficacy, with initial plugging diagnosis indicated at incremental pressure decline rates\u0026thinsp;\u0026ge;\u0026thinsp;0.02 MPa/d, necessitating intervention before rates exceed 0.2 MPa/d; (3) The QPD method enables precise plugging location identification, facilitating optimized mitigation strategy. Implemented in Wells P5 and X1, this classified mitigation strategies significantly extended unplugging validity periods with demonstrable field success.\u003c/p\u003e","manuscriptTitle":"Integrated Diagnosis of plugging in Western Sichuan Sour Gas Reservoirs: From Plugging Mechanisms to Mitigation Strategies","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-08-08 12:49:42","doi":"10.21203/rs.3.rs-7224036/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-10-10T07:13:10+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-09-06T15:22:47+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"255710215370677037720160881256591370352","date":"2025-08-27T08:44:09+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-08-20T03:14:49+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"132439045013249916218948279341599651354","date":"2025-08-19T07:36:22+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-08-03T05:37:06+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-07-29T02:39:27+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-07-29T02:38:20+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Petroleum Exploration and Production Technology","date":"2025-07-27T04:13:30+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":false,"email":"","identity":"journal-of-petroleum-exploration-and-production-technology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Journal of Petroleum Exploration and Production Technology","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"VoR Journals","inReviewEnabled":false,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"127f81b5-1657-4d9c-9f1f-29f1d2c81d80","owner":[],"postedDate":"August 8th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2025-11-17T09:23:23+00:00","versionOfRecord":[],"versionCreatedAt":"2025-08-08 12:49:42","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7224036","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7224036","identity":"rs-7224036","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}