The Influence of Pore Throat Structure on Fluid Displacement in Tight Oil Reservoir

The Influence of Pore Throat Structure on Fluid Displacement in Tight Oil Reservoir | 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 The Influence of Pore Throat Structure on Fluid Displacement in Tight Oil Reservoir Xiong Liu, Yirui Ren, Nan Wang, Yueqi Cui, Zhiyuan Du This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8214370/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 10 You are reading this latest preprint version Abstract Based on core imbibition experiments combined with nuclear magnetic resonance technology, this study identifies the dominant governing forces for different pore throat types and quantitatively characterizes the contribution of pore throats at various levels to imbibition-driven oil production. The results show that: Higher permeability correlates with greater fluid displacement rates. In reservoirs with high permeability, gravity dominates the imbibition process, with macropore recovery accounting for 96.27% of total recovery. In reservoirs with lower permeability, both gravitational and capillary imbibition forces are prominent. Fluid displacement primarily occurs during the early imbibition phase, with relatively weaker displacement in the later phase. Macropore recovery accounts for 86.36% of total recovery, while mesopores contribute a minor portion of imbibition recovery. Pinholes and micropores also make negligible contributions. Whether driven by gravitational or capillary forces, macropores and mesopores are the primary contributors to imbibition recovery rates, indicating that oil content and connectivity are critical factors influencing imbibition recovery efficiency. This research provides valuable guidance for enhancing recovery rates through imbibition enhancement in tight sandstones. Clinical Trial Registry :NOT APPLICABLE tight sandstone pore throat structure fluid displacement capillary force imbibition Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 1. INTRODUCTION Tight sandstone reservoirs, as a vital component of unconventional oil and gas resources, have become a key focus in global oil and gas development. Their poor reservoir properties, fine pore-throat structures, and limited connectivity typically result in low recovery rates for crude oil[ 1 – 3 ]. Imbibition refers to the spontaneous replacement of non-wetting phase fluids within pores by wetting phase fluids under capillary forces and gravity. Its driving mechanism, coupled with its compatibility with the micro-pore throat structure of unconventional reservoirs, is key to mobilizing crude oil trapped within pinholes[ 4 ]. However, unconventional reservoirs exhibit complex and diverse throat structures, where factors such as throat size, shape, and connectivity collectively influence fluid flow and replacement[ 5 – 8 ]. Regarding the micro-displacement mechanisms governing imbibition efficiency in pore throat structures, extensive research has been conducted by scholars both domestically and internationally. Wu, Y. et al.[ 9 ] employed techniques such as nuclear magnetic resonance to characterize the microstructural features of tight sandstone reservoirs, concluding that not only do significant differences exist between various reservoirs, but the microstructure within a single reservoir is also highly complex. Xia, Y. et al.[ 10 – 11 ] quantitatively evaluated the distribution characteristics of mobile fluids in three rock types based on the principle of nuclear magnetic resonance mobile fluid testing. Their analysis concluded that reservoirs dominated by residual intergranular pores larger than 10µm and dissolution pores larger than 1µm exhibit higher percentages of mobile fluids in pores larger than 1µm. These reservoirs represent the primary focus for future exploration and development. Hu, B. et al.[ 12 – 13 ] established a porous medium model for tight sandstone based on high-precision digital core images, enabling quantitative characterization of micro-pore throat structures in tight sandstone via scanned images. Results indicate that larger pore throat radii correlate with increased pore throat abundance, higher coordination numbers, and improved connectivity. Yang, C.[ 14 – 15 ] et al. characterized the pore size distribution of tight sandstones using NMR-C, LF-NMR, and micro-CT techniques, investigating the influence of pore structure characteristics and displacement phase properties on self-imbibition. Results indicate that the maximum pore size and its proportion are the primary factors affecting permeability, while the content of micropores and medium pores plays a crucial role in connectivity quality. Zhang, Y. et al.[ 16 – 17 ] elucidated the displacement mechanism and process in imbibition oil recovery based on imbibition dynamics equations, demonstrating that in low-permeability reservoirs, capillary forces primarily drive oil from micropores to large pores before buoyancy forces complete expulsion. Zhou, D.[ 18 ] et al., based on spontaneous imbibition experiments of tight sandstone cores from the Yanchang Formation in the Changqing Oilfield, statistically analyzed the imbibition stabilization time under different parameter conditions. They concluded that the stabilization time exhibits a “V”-shaped relationship with permeability. Ju, M. et al.[ 19 ] utilized nuclear magnetic resonance (NMR) technology to elucidate static imbibition flow patterns in tight rock cores. Comparative analysis demonstrated high consistency between imbibition recovery levels obtained via NMR T2 spectroscopy and those derived from gravimetric methods, thereby validating the applicability of NMR experiments for investigating imbibition mechanisms in tight reservoirs. Shi, L.[ 20 ] et al. conducted imbibition displacement experiments at different injection rates, quantitatively evaluating oil content changes and displacement efficiency characteristics in dual-pore media under varying experimental conditions. Results indicate that porosity, permeability, and maximum pore throat radius positively correlate with imbibition displacement efficiency, while showing weaker correlations with displacement efficiency under combined imbibition and displacement effects. Kashiri, A.[ 21 ] investigated the influence of pH on oil recovery in fractured porous carbonate reservoirs through imbibition experiments. Huang, X.[ 22 ] et al. established the imbibition effect in quartz nanopores via molecular dynamics simulations, examining the impact of various factors on this phenomenon. Results indicate that water flow rates within nanopores correlate with temperature, pore size, and wettability. This study investigates the relationship between permeability and fluid displacement rate in unconventional reservoirs through indoor core imbibition experiments combined with nuclear magnetic resonance (NMR) analysis. By quantitatively characterizing the contribution of different pore scales to total imbibition recovery, it provides theoretical foundations and practical guidance for unconventional reservoir development, particularly in tight sandstone reservoirs. 2. Characterization of Rock Samples For the investigation, five typical rock samples were chosen, and the accompanying table (Table 1 ) presents the physical characteristics of the core in detail: The reservoir's low porosity dense content is shown by its porosity of 5.1%-9.63%, average 6.7%, permeability of 0.055mD-0.176mD, average 0.0982mD, and quartz content of 16%-48.5%, average 37%, feldspar content of 27%-53%, average 36.2%, and clay minerals of 27.4%-47.7%, average 37.08%. Under scanning electron microscopy: The rock sample exhibits a dense structure with interlocking contacts between clastic grains. Fibrillar illite aggregates adhere to the surfaces of clastic grains and fill the spaces between them, with isolated fine intergranular joints visible ( Fig. 1 ). Table 2 displays the results of an X-ray diffraction clay mineral analysis. The results indicate that the immonite mixed layer has an absolute percentage of 21%-56%, with an average of 37.4%; the illite has an absolute percentage of 21%-53%, with an average of 33.4%; the kaolinite has an absolute percentage of 4%-20%, with an average of 8.6%; and the chlorite has an absolute percentage of 17%-28%, with an average of 20.6%. Figure 2 shows the X-ray diffraction patterns of non-clay minerals in whole rock and clay minerals under different conditions. Table 1 Physical parameters of the core. Number Length/cm Diameter/cm Porosity/% Permeability/10 − 3 µm 2 Quartz (%) Potassium feldspar (%) Plagioclase (%) Dolomite (%) Clay minerals (%) 1 4.358 2.514 9.63 0.176 48.5 25.0 2.0 0.0 37.6 2 4.462 2.510 7.44 0.125 51.5 24.5 2.0 33.9 27.4 3 4.340 2.532 6.10 0.055 23.0 46.0 0.5 0.0 42.6 4 4.386 2.500 5.41 0.076 46.0 24.0 4.0 0.0 30.1 5 4.424 2.522 5.10 0.059 16.0 53.0 0.0 0.0 47.7 Table 2 X-ray clay mineral analysis. Number Relative content of clay minerals (%) Mixed layer ratio (% S) Imon mixed layer Elysium kaolinite Chlorite Imon mixed layer 1 31 33 8 28 15 2 21 53 5 21 15 3 56 21 4 19 20 4 38 24 20 18 20 5 41 36 6 17 20 3. Pore Throat Structure and Permeability Correlation Table 3 High-pressure mercury compression experimental data. Number Discharge pressure /MPa Maximum pore throat radius /um Median pressure/MPa Median radius /um Maximum mercury saturation/% Un- saturated mercury saturation/% Residual mercury saturation/% Mercury removal efficiency/% Main- stream throat radius /um Main- stream throat min /um Average throat radius /um 1 2.09 0.35 7.68 0.096 86.78 13.22 72.65 16.28 0.164 0.11 0.132 2 1.48 0.50 19.56 0.038 67.32 32.68 48.37 28.15 0.276 0.19 0.195 3 4.25 0.17 99.97 0.007 21.36 78.64 14.92 30.18 0.163 0.07 0.070 4 4.24 0.17 51.06 0.014 65.04 34.96 44.03 32.30 0.103 0.07 0.077 5 4.25 0.17 99.96 0.007 34.32 65.68 23.66 31.06 0.072 0.03 0.039 From the perspective of permeability and discharge pressure, maximum pore throat radius, maximum mercury feed saturation, residual mercury saturation, mercury withdrawal efficiency, mainstream throat radius, minimum mainstream throat radius, average pore throat radius, median radius, and sorting coefficient, all of them have good correlation, and except for the negative correlation of the discharge pressure and the mercury withdrawal efficiency, the other factors are positively correlated with the permeability, so that the permeability can be used instead of characterizing the pore throat structure. 4. Experimental Study of Imbibition This study employed a real-time monitoring system using a high-precision electronic balance to conduct imbibition experiments. The system primarily consisted of a METTLER TOLEDO electronic balance, a computer, beakers, saturated fluorinated oil cores, and fishing line. Specifically, lightweight fishing line was used to wrap and suspend the core sample from the balance's weighing hook. A beaker containing the experimental fluid was positioned beneath the balance. The arrangement was adjusted to ensure the core was fully submerged in the liquid within the beaker and maintained in a state of free suspension, preventing interference from contact with the container walls. A high-precision electronic balance records the core's weight in real time, while the computer's data acquisition system, linked to the balance, collects weight measurements at different time points. During seepage, the wetting phase displaces the non-wetting phase within the core, causing a phase replacement between them. The principle of this method lies in the displacement between the wetting phase and the non-wetting phase. Since the wetting phase and the non-wetting phase have different densities, this displacement causes a change in the weight of the core. Therefore, by recording the weight changes of the core at different times, the suction condition of the core can be determined. The specific calculation is as follows: Percolation Displacement Volume: Where: ρ w and ρ o are the densities of the wetted and non-wetted phases, respectively; M 0 and M t are the weights of the core at the beginning of the percolation and at moment t, respectively. Therefore, the recovery rate is calculated by the formula: Where: ΔM is the weight difference between the core before and after saturation. The curves of fluid replacement rate versus imbibition time and fluid replacement rate versus permeability are given in Fig. 5 , respectively. It can be seen from the curve patterns: The core exhibits an imbibition recovery pattern that accelerates initially and then decelerates, with higher permeability corresponding to greater fluid displacement. This phenomenon can be attributed to reservoirs with higher permeability typically possessing more developed pore-throat systems, higher porosity connectivity, and larger two-phase flow zones, thereby providing more efficient pathways for oil-water displacement. The longer the fluid replacement time of the core with high permeability, as shown in Fig. 5 a, the No. 1 rock sample still did not reach a stable state after 250 hours of imbibition, while the other four rock samples tended to be stabilized in about 100 hours during the fluid replacement process. Fluid migration pathways in such reservoirs may be more complex, significantly prolonging the time required to achieve equilibrium displacement. In actual production, reservoirs with higher permeability can appropriately extend the steaming duration to fully leverage their imbibition potential. 5. Analysis of Nuclear Magnetic Resonance Experiments Two core samples with notably diverse physical characteristics were used for comparison tests to examine the impact of various pore shapes on imbibition behavior. Core 6 exhibited a gas permeability of 3.892×10⁻³ µm⁻² and a porosity of 11.19%, classifying it as a low-porosity, low-permeability core. Core 7 demonstrated a gas permeability of 0.078×10⁻³ µm⁻² and a porosity of 4.94%, categorizing it as an extremely low-porosity, tight core (Table 4 ). Table 4 Core Physical Parameters. Core number Porosity/% Gas permeability/10 − 3 µm2 Length/cm Diameter/cm Dry weight/g 6 11.19 3.892 4.921 2.534 64.1 7 4.94 0.078 5.033 2.520 65.5 Figure 5 displays the bar charts of the two cores' pore throat distributions. The data indicate that the No. 6 core's pore throat distribution is primarily between 0-0.1 µm, with 45.36% of its pore throats having a diameter of less than 0.1 µm, 21.97% having a diameter between 0.1 µm and 1.0 µm, and 32.67% having a diameter greater than 1.0 µm. Additionally, the No. 7 core's pore throat distribution is likewise in the same position as the distribution of pore throats in the 0-0.1 µm range, and pore throats in core No. 7 are distributed as follows: 26.08% have a diameter between 0.1 and 1.0 µm, 25.46% have a diameter larger than 1.0 µm, and 48.46% have a diameter less than 0.1 µm. Overall data comparison reveals that Core 7's development quality is lower than Core 6's (Fig. 6 ). The following experimental protocol was used in this study to evaluate different kinds of pore throat imbibition properties using a combination of core self-imbibition tests and NMR techniques (MesoMR23-60H-I medium-size NMR splitter): The initial core's basic cleaning and preservation of its original wetting traits; After being cleaned, the cores were put in the replacement apparatus, submerged with distilled water, pressurized until they were completely saturated, and then allowed to stand at a steady pressure. The cores were first scanned using nuclear magnetic resonance (NMR) methods to document the signal properties of the cores after they were completely saturated with distilled water; After the core had been fully saturated with distilled water, replaced it with fluorine oil in the opposite direction until it was with no distilled water discharged and fully rested to guarantee that its internal fluid was in equilibrium under the influence of capillary force. Next, used nuclear magnetic resonance technology to scan the core a second time and recorded its signal characteristics; After setting up the core imbibition experiment apparatus, the fluorine oil-saturated core was vertically submerged in distilled water. Five and ten days later, the core signal characteristics were scanned at various points in time using nuclear magnetic resonance (NMR) technology; The MRI information collected from the aforementioned scans was processed and examined. Figure 7 displays the NMR T2 spectra of core No. 6 under saturated fluorine oil condition, five and ten days of imbibition, respectively. Examine how the spectral lines change: Core No. 6's 0.0065-18.65um pore throats, particularly the 0.16um-18.65um pore throats, are where fluid replacement primarily takes place; macropore pore throats are particularly prevalent during the first five days of imbibition; 5 days later, the rate of core replacement dropped. The micropores are little involved in the oil-water replacement reaction, the macropores are nearly entirely responsible for the oil-water replacement, and the fluid replacement of mesopores and micropores is minimal. We conclude that while capillary force imbibition is not evident, gravity plays a significant role in fluid replacement. By dividing the core pores into four classes—pinholes (pore size ≤ 0.025 um), micropores (pore size 0.025-0.1 um), mesopores (pore size 0.1-1 um), and macropores (pore size > 1 um)—we were able to assess the impact of various pore types on imbibition recovery. According to the findings of the data analysis of the water content in Core 6's various pore types throughout time: The overall water content of No.6 core increased from 3.23% to 41.67% within 240 hours of imbibition, and realized 38.44% of imbibition recovery, in which the water content of macropores increased from 2.3% to 39.31%, and the recovery amounted to 96.27% of the overall recovery, and the water content of mesopores increased from 0.77% to 2.09%, and the recovery amount accounted for 3.45% of the overall oil recovery. The effect of pinholes and micropores on the overall imbibition recovery is very limited and almost negligible (Fig. 8 ). During imbibition oil production, pore structures exhibit significant variations in crude oil mobilization efficiency. Large pores, characterized by their larger throat radii, form the dominant pathways for crude oil migration and constitute the primary contributors to imbibition production. Mesopores, micropores, and pinholes, however, do not serve as effective production conduits. The NMR T2 spectrum curves of the core No. 7 under saturated fluorine oil conditions, five days after imbibition, and ten days following imbibition are displayed in Fig. 9 . A significant amount of the oil-water replacement takes place in macropores, and the data also shows that mesopores, micropores, and even pinholes are actively involved in the replacement process, indicating that gravity and capillary force imbibition is very evident. The replacement process of imbibition in core No. 7 is primarily observed in the 0.001 um-18.65 um pore throat, and the entire replacement process is relatively stable and slow. Within 240 hours of imbibition, the overall water content in core No. 7 rose from the initial 0.82% to 16.58%, achieving a 15.76% recovery rate, according to the data analysis results based on the change of water content over time in core 7 in various pore types. The water content of macropores increased from 0.66% to 14.27%, and the recovery accounted for 86.36% of the overall oil recovery; the water content of mesopores increased from 0.13% to 2.13%, and the recovery accounted for 12.69% of the overall oil recovery; and the recovery of micropores and pinholes accounted for 0.69% and 0.26% of the overall recovery. The mesopore in core No. 7 achieved a higher recovery than the micropore and pinhole (Fig. 10 ). This further confirms the control mechanism of pore structure over imbibition behavior, and indicates that mesopores make a more significant contribution to recovery than anticipated in ultra-low-permeability reservoirs. Core No. 6, characterized by low porosity and low permeability, exhibits a gravity-dominated drainage pattern. Its imbibition recovery is highly concentrated in the macropore throats, with minimal mobilization of mesopores and micropores, resulting in an extremely unbalanced pore mobilization structure. Fluid replacement is primarily controlled by gravity-driven segregation, while capillary imbibition plays a negligible role. Core No. 7, characterized by ultra-low porosity and permeability, exhibited synergistic capillary and gravitational effects. Imbibition occurred not only in the macropores but also demonstrated fluid replacement signals in mesopores, micropores, and even pinholes (total recovery rate approximately 14%). The range of utilized pores was broad, with capillary-driven spontaneous imbibition also playing a role in this process. Therefore, the imbibition efficiency of unconventional reservoirs strongly depends on their microporous structure. Different cores exhibit distinct imbibition patterns, and imbibition behavior can be predicted through detailed characterization of the reservoir's pore structure. 6. CONCLUSIONS Reservoirs with higher permeability exhibit better pore-throat connectivity, resulting in greater fluid displacement rates and longer core fluid displacement times. Gravity is the primary controlling force in the imbibition process, with fluid displacement primarily occurring in macropores (pore size > 1 μm). Macropores contribute the vast majority of imbibition recovery, while contributions from mesopores(pore size 0.1-1 μm), micropores(pore size 0.025-0.1 μm), and pinholes(pore size<0.025μm) to imbibition recovery are negligible In reservoirs with lower permeability, the fluid replacement process is shorter, with imbibition predominantly occurring during the early stages of imbibition, with relatively weaker imbibition in the later stages. Both gravitational and capillary imbibition forces are prominent. Macropores contribute the majority of imbibition recovery, medium pores contribute a minor portion, while micropores and pinholes make negligible contributions. Regardless of whether the dominant driving force is gravity or capillar y action, macropores and mesopores remain the primary contributors to imbibition recovery. This indicates that oil content and connectivity are critical factors influencing imbibition recovery. Declarations Ethics statement: Not Applicable Consent to participate: Not Applicable Consent to Publish: Not Applicable Funding : This work was supported by the National Natural Science Foundation of China (Grant No. 52374038 and U23B2089) and Innovation Capability Support Program of Shaanxi (Program No. 2024ZC-KJXX-064). Conflicts of Interest : The authors declare no conflicts of interest. Declaration of no conflict of interest between co-authors. Data Availability Statement: The original contributions presented in this study are included in the article/supplementary material. Further inquiries can be directed to the corresponding author(s). 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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-8214370","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":561880540,"identity":"cfdd8d07-f249-48d4-94b0-9b1b0b34db48","order_by":0,"name":"Xiong Liu","email":"","orcid":"","institution":"Xi’an Shiyou University","correspondingAuthor":false,"prefix":"","firstName":"Xiong","middleName":"","lastName":"Liu","suffix":""},{"id":561880541,"identity":"1dead827-de6e-4c8f-b00d-d3a4a6faa2d6","order_by":1,"name":"Yirui 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1","display":"","copyAsset":false,"role":"figure","size":788777,"visible":true,"origin":"","legend":"\u003cp\u003eScanning electron microscopy of rock samples.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-8214370/v1/7236d083822d40dbfb593c86.png"},{"id":98625183,"identity":"c913d176-a068-49d0-b27c-831a1f85bc5a","added_by":"auto","created_at":"2025-12-19 17:08:58","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":48261,"visible":true,"origin":"","legend":"\u003cp\u003eX-ray clay mineral analysis.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-8214370/v1/fa4f05f8c052d383fc614348.png"},{"id":98514862,"identity":"011ebcea-cfe0-4be3-aa65-767aa7d4a1c8","added_by":"auto","created_at":"2025-12-18 12:26:07","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":40062,"visible":true,"origin":"","legend":"\u003cp\u003eCorrelation between permeability and pore throat structural parameters.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-8214370/v1/84fe6378a8e88bb766d39914.png"},{"id":98514871,"identity":"a147c4e2-878f-4e9d-9e61-8a0789cdbd7e","added_by":"auto","created_at":"2025-12-18 12:26:07","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":20736,"visible":true,"origin":"","legend":"\u003cp\u003eDiagram of the Imbibition Experiment Apparatus\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-8214370/v1/d9d4f5a5c186c16a7f064930.png"},{"id":98514866,"identity":"eaa9eb30-23a2-4415-a720-e177c21d264b","added_by":"auto","created_at":"2025-12-18 12:26:07","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":61612,"visible":true,"origin":"","legend":"\u003cp\u003eAnalysis of data from imbibition experiments.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-8214370/v1/b2aa37086cba510018b5302e.png"},{"id":98514868,"identity":"21a99afb-af4f-414c-b25e-9091e734495b","added_by":"auto","created_at":"2025-12-18 12:26:07","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":34050,"visible":true,"origin":"","legend":"\u003cp\u003eDistribution of core pore throats.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-8214370/v1/edeb9fcab8a550f9e5e9aae3.png"},{"id":98514873,"identity":"f61aae87-3c1f-4613-aaee-61774e2b67c2","added_by":"auto","created_at":"2025-12-18 12:26:07","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":76624,"visible":true,"origin":"","legend":"\u003cp\u003eNMR curve of rock sample No. 6.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-8214370/v1/247b6e0dfaff9e80eb9c86dc.png"},{"id":98624983,"identity":"6122328a-7345-45df-96db-e047653525fa","added_by":"auto","created_at":"2025-12-19 17:08:52","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":65299,"visible":true,"origin":"","legend":"\u003cp\u003eVariation curves of water content of different types of pore throats with infiltration time for rock sample No. 6.\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-8214370/v1/fe94b74e011bfcca60f6b179.png"},{"id":98624021,"identity":"a24be52e-5060-4390-9c43-46d313857024","added_by":"auto","created_at":"2025-12-19 17:07:54","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":73852,"visible":true,"origin":"","legend":"\u003cp\u003eNMR curve of rock sample No. 7.\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-8214370/v1/c9d5e36accd1ad37488ba531.png"},{"id":98624949,"identity":"a4119fdd-0485-4a1b-9ac2-2c0115b4e3fa","added_by":"auto","created_at":"2025-12-19 17:08:51","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":62961,"visible":true,"origin":"","legend":"\u003cp\u003eVariation curves of water content of different types of pore throats with infiltration time in Core No. 7.\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-8214370/v1/4c6bf8e4b0f1e0d40f57979b.png"},{"id":98775001,"identity":"53e45234-b5e2-4f28-85d3-721fe83a5596","added_by":"auto","created_at":"2025-12-22 12:17:51","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1900811,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8214370/v1/e62e2440-4368-44eb-9ca8-c2451dc70210.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"The Influence of Pore Throat Structure on Fluid Displacement in Tight Oil Reservoir","fulltext":[{"header":"1. INTRODUCTION","content":"\u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eTight sandstone reservoirs, as a vital component of unconventional oil and gas resources, have become a key focus in global oil and gas development. Their poor reservoir properties, fine pore-throat structures, and limited connectivity typically result in low recovery rates for crude oil[\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Imbibition refers to the spontaneous replacement of non-wetting phase fluids within pores by wetting phase fluids under capillary forces and gravity. Its driving mechanism, coupled with its compatibility with the micro-pore throat structure of unconventional reservoirs, is key to mobilizing crude oil trapped within pinholes[\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. However, unconventional reservoirs exhibit complex and diverse throat structures, where factors such as throat size, shape, and connectivity collectively influence fluid flow and replacement[\u003cspan additionalcitationids=\"CR6 CR7\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Regarding the micro-displacement mechanisms governing imbibition efficiency in pore throat structures, extensive research has been conducted by scholars both domestically and internationally. Wu, Y. et al.[\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e] employed techniques such as nuclear magnetic resonance to characterize the microstructural features of tight sandstone reservoirs, concluding that not only do significant differences exist between various reservoirs, but the microstructure within a single reservoir is also highly complex. Xia, Y. et al.[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e] quantitatively evaluated the distribution characteristics of mobile fluids in three rock types based on the principle of nuclear magnetic resonance mobile fluid testing. Their analysis concluded that reservoirs dominated by residual intergranular pores larger than 10\u0026micro;m and dissolution pores larger than 1\u0026micro;m exhibit higher percentages of mobile fluids in pores larger than 1\u0026micro;m. These reservoirs represent the primary focus for future exploration and development. Hu, B. et al.[\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e] established a porous medium model for tight sandstone based on high-precision digital core images, enabling quantitative characterization of micro-pore throat structures in tight sandstone via scanned images. Results indicate that larger pore throat radii correlate with increased pore throat abundance, higher coordination numbers, and improved connectivity. Yang, C.[\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e] et al. characterized the pore size distribution of tight sandstones using NMR-C, LF-NMR, and micro-CT techniques, investigating the influence of pore structure characteristics and displacement phase properties on self-imbibition. Results indicate that the maximum pore size and its proportion are the primary factors affecting permeability, while the content of micropores and medium pores plays a crucial role in connectivity quality. Zhang, Y. et al.[\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e] elucidated the displacement mechanism and process in imbibition oil recovery based on imbibition dynamics equations, demonstrating that in low-permeability reservoirs, capillary forces primarily drive oil from micropores to large pores before buoyancy forces complete expulsion. Zhou, D.[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e] et al., based on spontaneous imbibition experiments of tight sandstone cores from the Yanchang Formation in the Changqing Oilfield, statistically analyzed the imbibition stabilization time under different parameter conditions. They concluded that the stabilization time exhibits a \u0026ldquo;V\u0026rdquo;-shaped relationship with permeability. Ju, M. et al.[\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e] utilized nuclear magnetic resonance (NMR) technology to elucidate static imbibition flow patterns in tight rock cores. Comparative analysis demonstrated high consistency between imbibition recovery levels obtained via NMR T2 spectroscopy and those derived from gravimetric methods, thereby validating the applicability of NMR experiments for investigating imbibition mechanisms in tight reservoirs. Shi, L.[\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e] et al. conducted imbibition displacement experiments at different injection rates, quantitatively evaluating oil content changes and displacement efficiency characteristics in dual-pore media under varying experimental conditions. Results indicate that porosity, permeability, and maximum pore throat radius positively correlate with imbibition displacement efficiency, while showing weaker correlations with displacement efficiency under combined imbibition and displacement effects. Kashiri, A.[\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e] investigated the influence of pH on oil recovery in fractured porous carbonate reservoirs through imbibition experiments. Huang, X.[\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e] et al. established the imbibition effect in quartz nanopores via molecular dynamics simulations, examining the impact of various factors on this phenomenon. Results indicate that water flow rates within nanopores correlate with temperature, pore size, and wettability. This study investigates the relationship between permeability and fluid displacement rate in unconventional reservoirs through indoor core imbibition experiments combined with nuclear magnetic resonance (NMR) analysis. By quantitatively characterizing the contribution of different pore scales to total imbibition recovery, it provides theoretical foundations and practical guidance for unconventional reservoir development, particularly in tight sandstone reservoirs.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e"},{"header":"2. Characterization of Rock Samples","content":"\u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eFor the investigation, five typical rock samples were chosen, and the accompanying table (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) presents the physical characteristics of the core in detail: The reservoir's low porosity dense content is shown by its porosity of 5.1%-9.63%, average 6.7%, permeability of 0.055mD-0.176mD, average 0.0982mD, and quartz content of 16%-48.5%, average 37%, feldspar content of 27%-53%, average 36.2%, and clay minerals of 27.4%-47.7%, average 37.08%. Under scanning electron microscopy: The rock sample exhibits a dense structure with interlocking contacts between clastic grains. Fibrillar illite aggregates adhere to the surfaces of clastic grains and fill the spaces between them, with isolated fine intergranular joints visible ( Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e displays the results of an X-ray diffraction clay mineral analysis. The results indicate that the immonite mixed layer has an absolute percentage of 21%-56%, with an average of 37.4%; the illite has an absolute percentage of 21%-53%, with an average of 33.4%; the kaolinite has an absolute percentage of 4%-20%, with an average of 8.6%; and the chlorite has an absolute percentage of 17%-28%, with an average of 20.6%. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e shows the X-ray diffraction patterns of non-clay minerals in whole rock and clay minerals under different conditions.\u003c/p\u003e \u003c/div\u003e \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\u003ePhysical parameters of the core.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"10\"\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=\"char\" char=\".\" 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=\"char\" char=\".\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNumber\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLength/cm\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eDiameter/cm\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003ePorosity/%\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003ePermeability/10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e\u0026micro;m \u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eQuartz (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003ePotassium feldspar (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003ePlagioclase (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003eDolomite (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c10\"\u003e \u003cp\u003eClay minerals (%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4.358\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.514\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e9.63\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.176\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e48.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e25.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e2.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e0.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e37.6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4.462\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.510\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e7.44\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.125\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e51.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e24.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e2.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e33.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e27.4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4.340\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.532\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e6.10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.055\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e23.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e46.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e0.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e42.6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4.386\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.500\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e5.41\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.076\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e46.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e24.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e4.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e0.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e30.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4.424\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.522\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e5.10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.059\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e16.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e53.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e0.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e0.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e47.7\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \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\u003eX-ray clay mineral analysis.\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=\"char\" char=\".\" 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 \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eNumber\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"4\" nameend=\"c5\" namest=\"c2\"\u003e \u003cp\u003eRelative content of clay minerals (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eMixed layer ratio (% S)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eImon mixed layer\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eElysium\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003ekaolinite\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eChlorite\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eImon mixed layer\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e31\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e33\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e28\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e21\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e53\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e21\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e56\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e21\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e38\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e41\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e36\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"3. Pore Throat Structure and Permeability Correlation","content":"\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\u003eHigh-pressure mercury compression experimental data.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"12\"\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=\"char\" char=\".\" 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=\"char\" char=\".\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c11\" colnum=\"11\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c12\" colnum=\"12\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNumber\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDischarge pressure\u003c/p\u003e \u003cp\u003e/MPa\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMaximum pore throat radius\u003c/p\u003e \u003cp\u003e/um\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMedian pressure/MPa\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eMedian radius\u003c/p\u003e \u003cp\u003e/um\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eMaximum mercury saturation/%\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eUn-\u003c/p\u003e \u003cp\u003esaturated mercury saturation/%\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eResidual mercury saturation/%\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003eMercury removal efficiency/%\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c10\"\u003e \u003cp\u003eMain-\u003c/p\u003e \u003cp\u003estream throat radius\u003c/p\u003e \u003cp\u003e/um\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c11\"\u003e \u003cp\u003eMain-\u003c/p\u003e \u003cp\u003estream throat min\u003c/p\u003e \u003cp\u003e/um\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c12\"\u003e \u003cp\u003eAverage throat radius\u003c/p\u003e \u003cp\u003e/um\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2.09\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.35\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e7.68\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.096\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e86.78\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e13.22\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e72.65\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e16.28\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e0.164\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e \u003cp\u003e0.11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c12\"\u003e \u003cp\u003e0.132\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.48\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e19.56\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.038\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e67.32\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e32.68\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e48.37\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e28.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e0.276\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e \u003cp\u003e0.19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c12\"\u003e \u003cp\u003e0.195\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e99.97\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.007\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e21.36\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e78.64\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e14.92\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e30.18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e0.163\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e \u003cp\u003e0.07\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c12\"\u003e \u003cp\u003e0.070\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4.24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e51.06\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.014\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e65.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e34.96\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e44.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e32.30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e0.103\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e \u003cp\u003e0.07\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c12\"\u003e \u003cp\u003e0.077\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e99.96\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.007\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e34.32\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e65.68\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e23.66\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e31.06\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e0.072\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e \u003cp\u003e0.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c12\"\u003e \u003cp\u003e0.039\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eFrom the perspective of permeability and discharge pressure, maximum pore throat radius, maximum mercury feed saturation, residual mercury saturation, mercury withdrawal efficiency, mainstream throat radius, minimum mainstream throat radius, average pore throat radius, median radius, and sorting coefficient, all of them have good correlation, and except for the negative correlation of the discharge pressure and the mercury withdrawal efficiency, the other factors are positively correlated with the permeability, so that the permeability can be used instead of characterizing the pore throat structure.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"4. Experimental Study of Imbibition","content":"\u003cdiv class=\"BlockQuote\"\u003e\n \u003cp\u003eThis study employed a real-time monitoring system using a high-precision electronic balance to conduct imbibition experiments. The system primarily consisted of a METTLER TOLEDO electronic balance, a computer, beakers, saturated fluorinated oil cores, and fishing line. Specifically, lightweight fishing line was used to wrap and suspend the core sample from the balance\u0026apos;s weighing hook. A beaker containing the experimental fluid was positioned beneath the balance. The arrangement was adjusted to ensure the core was fully submerged in the liquid within the beaker and maintained in a state of free suspension, preventing interference from contact with the container walls. A high-precision electronic balance records the core\u0026apos;s weight in real time, while the computer\u0026apos;s data acquisition system, linked to the balance, collects weight measurements at different time points. During seepage, the wetting phase displaces the non-wetting phase within the core, causing a phase replacement between them. The principle of this method lies in the displacement between the wetting phase and the non-wetting phase. Since the wetting phase and the non-wetting phase have different densities, this displacement causes a change in the weight of the core. Therefore, by recording the weight changes of the core at different times, the suction condition of the core can be determined. The specific calculation is as follows:\u003c/p\u003e\n\u003c/div\u003e\n\u003cp\u003ePercolation Displacement Volume:\u003c/p\u003e\n\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\n \u003cdiv class=\"EquationNumber\"\u003e\u003cimg src=\"data:image/png;base64,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\"\u003e\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003eWhere: \u0026rho;\u003csub\u003ew\u003c/sub\u003e and \u0026rho;\u003csub\u003eo\u003c/sub\u003e are the densities of the wetted and non-wetted phases, respectively; M\u003csub\u003e0\u003c/sub\u003e and M\u003csub\u003et\u003c/sub\u003e are the weights of the core at the beginning of the percolation and at moment t, respectively.\u003c/p\u003e\n\u003cdiv class=\"BlockQuote\"\u003e\n \u003cp\u003eTherefore, the recovery rate is calculated by the formula:\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\n \u003cdiv class=\"EquationNumber\"\u003e\u003cimg src=\"data:image/png;base64,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\"\u003e\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003eWhere: \u0026Delta;M is the weight difference between the core before and after saturation.\u003c/p\u003e\n\u003cdiv class=\"BlockQuote\"\u003e\n \u003cp\u003eThe curves of fluid replacement rate versus imbibition time and fluid replacement rate versus permeability are given in Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e, respectively. It can be seen from the curve patterns: The core exhibits an imbibition recovery pattern that accelerates initially and then decelerates, with higher permeability corresponding to greater fluid displacement. This phenomenon can be attributed to reservoirs with higher permeability typically possessing more developed pore-throat systems, higher porosity connectivity, and larger two-phase flow zones, thereby providing more efficient pathways for oil-water displacement. The longer the fluid replacement time of the core with high permeability, as shown in Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ea, the No. 1 rock sample still did not reach a stable state after 250 hours of imbibition, while the other four rock samples tended to be stabilized in about 100 hours during the fluid replacement process. Fluid migration pathways in such reservoirs may be more complex, significantly prolonging the time required to achieve equilibrium displacement. In actual production, reservoirs with higher permeability can appropriately extend the steaming duration to fully leverage their imbibition potential.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"5. Analysis of Nuclear Magnetic Resonance Experiments","content":"\u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eTwo core samples with notably diverse physical characteristics were used for comparison tests to examine the impact of various pore shapes on imbibition behavior. Core 6 exhibited a gas permeability of 3.892\u0026times;10⁻\u0026sup3; \u0026micro;m⁻\u0026sup2; and a porosity of 11.19%, classifying it as a low-porosity, low-permeability core. Core 7 demonstrated a gas permeability of 0.078\u0026times;10⁻\u0026sup3; \u0026micro;m⁻\u0026sup2; and a porosity of 4.94%, categorizing it as an extremely low-porosity, tight core (Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e \u003c/div\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 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eCore Physical Parameters.\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=\"char\" char=\".\" 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 \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCore number\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePorosity/%\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eGas permeability/10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e\u0026micro;m2\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eLength/cm\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eDiameter/cm\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eDry weight/g\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e11.19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3.892\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e4.921\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.534\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e64.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4.94\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.078\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e5.033\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.520\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e65.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e displays the bar charts of the two cores' pore throat distributions. The data indicate that the No. 6 core's pore throat distribution is primarily between 0-0.1 \u0026micro;m, with 45.36% of its pore throats having a diameter of less than 0.1 \u0026micro;m, 21.97% having a diameter between 0.1 \u0026micro;m and 1.0 \u0026micro;m, and 32.67% having a diameter greater than 1.0 \u0026micro;m. Additionally, the No. 7 core's pore throat distribution is likewise in the same position as the distribution of pore throats in the 0-0.1 \u0026micro;m range, and pore throats in core No. 7 are distributed as follows: 26.08% have a diameter between 0.1 and 1.0 \u0026micro;m, 25.46% have a diameter larger than 1.0 \u0026micro;m, and 48.46% have a diameter less than 0.1 \u0026micro;m. Overall data comparison reveals that Core 7's development quality is lower than Core 6's (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eThe following experimental protocol was used in this study to evaluate different kinds of pore throat imbibition properties using a combination of core self-imbibition tests and NMR techniques (MesoMR23-60H-I medium-size NMR splitter):\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003col\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eThe initial core's basic cleaning and preservation of its original wetting traits;\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eAfter being cleaned, the cores were put in the replacement apparatus, submerged with distilled water, pressurized until they were completely saturated, and then allowed to stand at a steady pressure. The cores were first scanned using nuclear magnetic resonance (NMR) methods to document the signal properties of the cores after they were completely saturated with distilled water;\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eAfter the core had been fully saturated with distilled water, replaced it with fluorine oil in the opposite direction until it was with no distilled water discharged and fully rested to guarantee that its internal fluid was in equilibrium under the influence of capillary force. Next, used nuclear magnetic resonance technology to scan the core a second time and recorded its signal characteristics;\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eAfter setting up the core imbibition experiment apparatus, the fluorine oil-saturated core was vertically submerged in distilled water. Five and ten days later, the core signal characteristics were scanned at various points in time using nuclear magnetic resonance (NMR) technology;\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eThe MRI information collected from the aforementioned scans was processed and examined.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003c/ol\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e displays the NMR T2 spectra of core No. 6 under saturated fluorine oil condition, five and ten days of imbibition, respectively. Examine how the spectral lines change: Core No. 6's 0.0065-18.65um pore throats, particularly the 0.16um-18.65um pore throats, are where fluid replacement primarily takes place; macropore pore throats are particularly prevalent during the first five days of imbibition; 5 days later, the rate of core replacement dropped. The micropores are little involved in the oil-water replacement reaction, the macropores are nearly entirely responsible for the oil-water replacement, and the fluid replacement of mesopores and micropores is minimal. We conclude that while capillary force imbibition is not evident, gravity plays a significant role in fluid replacement.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eBy dividing the core pores into four classes\u0026mdash;pinholes (pore size\u0026thinsp;\u0026le;\u0026thinsp;0.025 um), micropores (pore size 0.025-0.1 um), mesopores (pore size 0.1-1 um), and macropores (pore size\u0026thinsp;\u0026gt;\u0026thinsp;1 um)\u0026mdash;we were able to assess the impact of various pore types on imbibition recovery. According to the findings of the data analysis of the water content in Core 6's various pore types throughout time: The overall water content of No.6 core increased from 3.23% to 41.67% within 240 hours of imbibition, and realized 38.44% of imbibition recovery, in which the water content of macropores increased from 2.3% to 39.31%, and the recovery amounted to 96.27% of the overall recovery, and the water content of mesopores increased from 0.77% to 2.09%, and the recovery amount accounted for 3.45% of the overall oil recovery. The effect of pinholes and micropores on the overall imbibition recovery is very limited and almost negligible (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e). During imbibition oil production, pore structures exhibit significant variations in crude oil mobilization efficiency. Large pores, characterized by their larger throat radii, form the dominant pathways for crude oil migration and constitute the primary contributors to imbibition production. Mesopores, micropores, and pinholes, however, do not serve as effective production conduits.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eThe NMR T2 spectrum curves of the core No. 7 under saturated fluorine oil conditions, five days after imbibition, and ten days following imbibition are displayed in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e. A significant amount of the oil-water replacement takes place in macropores, and the data also shows that mesopores, micropores, and even pinholes are actively involved in the replacement process, indicating that gravity and capillary force imbibition is very evident. The replacement process of imbibition in core No. 7 is primarily observed in the 0.001 um-18.65 um pore throat, and the entire replacement process is relatively stable and slow.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eWithin 240 hours of imbibition, the overall water content in core No. 7 rose from the initial 0.82% to 16.58%, achieving a 15.76% recovery rate, according to the data analysis results based on the change of water content over time in core 7 in various pore types. The water content of macropores increased from 0.66% to 14.27%, and the recovery accounted for 86.36% of the overall oil recovery; the water content of mesopores increased from 0.13% to 2.13%, and the recovery accounted for 12.69% of the overall oil recovery; and the recovery of micropores and pinholes accounted for 0.69% and 0.26% of the overall recovery. The mesopore in core No. 7 achieved a higher recovery than the micropore and pinhole (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e). This further confirms the control mechanism of pore structure over imbibition behavior, and indicates that mesopores make a more significant contribution to recovery than anticipated in ultra-low-permeability reservoirs.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eCore No. 6, characterized by low porosity and low permeability, exhibits a gravity-dominated drainage pattern. Its imbibition recovery is highly concentrated in the macropore throats, with minimal mobilization of mesopores and micropores, resulting in an extremely unbalanced pore mobilization structure. Fluid replacement is primarily controlled by gravity-driven segregation, while capillary imbibition plays a negligible role. Core No. 7, characterized by ultra-low porosity and permeability, exhibited synergistic capillary and gravitational effects. Imbibition occurred not only in the macropores but also demonstrated fluid replacement signals in mesopores, micropores, and even pinholes (total recovery rate approximately 14%). The range of utilized pores was broad, with capillary-driven spontaneous imbibition also playing a role in this process. Therefore, the imbibition efficiency of unconventional reservoirs strongly depends on their microporous structure. Different cores exhibit distinct imbibition patterns, and imbibition behavior can be predicted through detailed characterization of the reservoir's pore structure.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e"},{"header":"6. CONCLUSIONS","content":"\u003col\u003e\n \u003cli\u003eReservoirs with higher permeability exhibit better pore-throat connectivity, resulting in greater fluid displacement rates and longer core fluid displacement times. Gravity is the primary controlling force in the imbibition process, with fluid displacement primarily occurring in macropores (pore size \u0026gt; 1 \u0026mu;m). Macropores contribute the vast majority of imbibition recovery, while contributions from mesopores(pore size 0.1-1 \u0026mu;m), micropores(pore size 0.025-0.1 \u0026mu;m), and pinholes(pore size\u0026lt;0.025\u0026mu;m) to imbibition recovery are negligible\u0026nbsp;\u003c/li\u003e\n \u003cli\u003eIn reservoirs with lower permeability, the fluid replacement process is shorter, with imbibition predominantly occurring during the early stages of imbibition, with relatively weaker imbibition in the later stages. Both gravitational and capillary imbibition forces are prominent. Macropores contribute the majority of imbibition recovery, medium pores contribute a minor portion, while micropores and pinholes make negligible contributions.\u003c/li\u003e\n \u003cli\u003eRegardless of whether the dominant driving force is gravity or capillar\u003cstrong\u003ey\u003c/strong\u003e action, macropores and mesopores remain the primary contributors to imbibition recovery. This indicates that oil content and connectivity are critical factors influencing imbibition recovery.\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthics statement:\u0026nbsp;\u003c/strong\u003eNot Applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to participate:\u003c/strong\u003eNot Applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to Publish:\u0026nbsp;\u003c/strong\u003eNot Applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003cstrong\u003e:\u003c/strong\u003e This work was supported by the National Natural Science Foundation of China (Grant No. 52374038 and U23B2089) and Innovation Capability Support Program of Shaanxi (Program No. 2024ZC-KJXX-064).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflicts of Interest\u003c/strong\u003e\u003cstrong\u003e:\u0026nbsp;\u003c/strong\u003eThe authors declare no conflicts of interest. Declaration of no conflict of interest between co-authors.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability Statement:\u003c/strong\u003eThe original contributions presented in this study are included in the article/supplementary material. Further inquiries can be directed to the corresponding author(s).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgments:\u003c/strong\u003eAuthors gratefully acknowledge the support from the National Natural Science Foundation of China (Grant No. 52374038 and U23B2089) and the Innovation Capability Support Program of Shaanxi (Program No. 2024ZC-KJXX-064).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eGharavi, A.; Abbas, K.A.; Hassan, M.G.; Haddad, M.; Ghoochaninejad, H.; Alasmar, R.; Al-Saegh, S.; Yousefi, P.; Shigidi, I. Unconventional Reservoir Characterization and Formation Evaluation: A Case Study of a Tight Sandstone Reservoir in West Africa. Energies 2023, 16, 7572. 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Effect of pH on the Dominant Mechanisms of Oil Recovery by Low Salinity Water in Fractured Carbonates. Energy \u0026amp; Fuels 2023, 37 (15): 10951-10959. DOI: 10.1021/acs.energyfuels.3c01538\u003c/li\u003e\n\u003cli\u003eHuang, X.M.; Han, D.L.; Lin, W.; Yang, Z.M.; Zhang, Y.P. Study on the influencing factors of imbibition in tight reservoirs based on molecular dynamics simulation[J]. Petrol Explor Prod Technol 2024, 14, 3079\u0026ndash;3090. DOI: 10.1007/s13202-024-01859-8\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"discover-applied-sciences","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Discover Applied Sciences](https://link.springer.com/journal/42452)","snPcode":"42452","submissionUrl":"https://submission.springernature.com/new-submission/42452/3","title":"Discover Applied Sciences","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Discover Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"tight sandstone, pore throat structure, fluid displacement, capillary force, imbibition","lastPublishedDoi":"10.21203/rs.3.rs-8214370/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8214370/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eBased on core imbibition experiments combined with nuclear magnetic resonance technology, this study identifies the dominant governing forces for different pore throat types and quantitatively characterizes the contribution of pore throats at various levels to imbibition-driven oil production. The results show that: Higher permeability correlates with greater fluid displacement rates. In reservoirs with high permeability, gravity dominates the imbibition process, with macropore recovery accounting for 96.27% of total recovery. In reservoirs with lower permeability, both gravitational and capillary imbibition forces are prominent. Fluid displacement primarily occurs during the early imbibition phase, with relatively weaker displacement in the later phase. Macropore recovery accounts for 86.36% of total recovery, while mesopores contribute a minor portion of imbibition recovery. Pinholes and micropores also make negligible contributions. Whether driven by gravitational or capillary forces, macropores and mesopores are the primary contributors to imbibition recovery rates, indicating that oil content and connectivity are critical factors influencing imbibition recovery efficiency. 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