Microemulsion Depressurization and Increasing Injection Technology for Tight Reservoirs

Microemulsion Depressurization and Increasing Injection Technology for Tight Reservoirs | 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 Article Microemulsion Depressurization and Increasing Injection Technology for Tight Reservoirs Yuhang Wu, Li Wang, Siqi He, Yujie Gu, Hong Chen, Wei Huang This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5685514/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Although some microcracks or large cracks occur during fracturing in the tight reservoirs, the average permeability and porosity of the reservoir matrix are relatively low: 0.76×10 − 3 µm 2 and 11.5%, respectively. These values are typical of a typical low-permeability tight reservoir. Currently, the water injection pressure during the development of reservoir water injection is high and exceeds the reopening pressure of a crack. The pressure is close to the formation fracture pressure, which minimizes the phenomenon of water breakthrough and water injection efficiency. The reservoir matrix is substantially under injection. Therefore, a method to reduce the injection pressure and improve the matrix injection capacity is urgently needed. According to the features of tight reservoirs and crude oil, three kinds of microemulsion are screened: 13% AP6 + 4% polyoxyvinyl ether surfactant + 4% sodium petroleum sulfonate + 4% lower alcohol + 6% oil phase + 69% salt solution and 0.5% anti-temperature agent. The maximum soluble capacity of onsite oil is 14%. Microemulsion has excellent temperature resistance; if it is heated for 24 hours at 70°C, it does not break. Microemulsion also has excellent salt and anti-dilution performance. No turbidity occurs after the microemulsion and the formation water are mixed in any proportion for 24 hours. A core displacement experiment using microemulsion was performed in a lab. The results of the research indicate that the water injection pressure is reduced to a minimum of 40% when the injection concentration of the microemulsion is 1% and the injection slug is 5 PV. low permeability reservoir microemulsion depressurization and increasing injection interfacial tension solubilization mechanistic Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 1 Introduction The reservoir porosity and permeability of the tight reservoirs in southern Ordos are low, the connectivity is poor, and the matrix water injection is difficult. The minimum porosity is 7%, the maximum porosity is 17.2%, and the average porosity is 11.5% [ 1 – 2 ] . The minimum permeability is 0.086 mD, the maximum permeability is 1.43 mD, and the average permeability is 0.45 mD. These reservoirs have low porosity and ultralow permeability. The reservoirs develop large cracks or a large number of artificial cracks. The phenomenon of water breaking is very serious. The producing reserves of the formation matrix is low. The reservoir rock surface is weakly water-wet, and the irreducible oil saturation is high; thus, it substantially blocks the seepage channels. Currently, many methods exist for the transformation of low permeability reservoirs inland and abroad, such as acidification, fracturing, and concentrated surfactant displacement [ 3 – 4 ] . The disadvantage of the acidification and fracturing method is that the improved stratigraphication is prone to water breaking and insufficient long-term effectiveness. The high concentrated surfactant can be mixed with crude oil in the formation to spontaneously form a microemulsion. However, the formation conditions of microemulsions are harsh, and the stratum is easily blocked by emulsion [ 5 ] . Compared with the former, microemulsion is a kind of concentrated surfactant that has a stable thermodynamic system. The particle size of a microemulsion ranges between 10–100 nm, which enables particles to easily pass through the percolation channel, and has ultralow interfacial tension [ 6 ] . The microemulsion has excellent solubilization, wetting and penetration ability [ 7 – 8 ] . Therefore, the microemulsion can better clean the irreducible oil in the channel, weaken the influence of the Jamin effect, and improve the water phase permeability [ 9 ] . In this paper, different microemulsion systems were screened; the interfacial tension, solubilization, temperature and salt resistance were used as indicators, and a microemulsion system that is suitable for dense reservoirs in Southern Ordos was selected. 2 Microemulsion depressurization and injection mechanism 2.1 Reduce oil-water interfacial tension and increase or decrease crude oil flow capacity (1) Microemulsion can reduce adhesion work and increase oil washing ability As shown in Fig. 1 , a large amount of residual oil distribution in the site rock sample. The microemulsion can reduce the oil-water interfacial tension and increase the wetting angle of the oil on the rock surface. Thus, the oil droplets have to be pulled away from the rock surface. The adhesion work and residual oil saturation is considerably reduced, and the oil washing ability is improved. (2) Microemulsion increases the number of capillary tubes and improves the oil displacement efficiency [ 10 ] $$\:Nc=\frac{\mu\:wVw}{\phi\:{\sigma\:}_{O/W}}$$ 1 At the end of the water injection development, the NC generally ranges from 10 − 7 -10 − 6 . As indicated by formula (1), as the NC increases, the oil displacement efficiency also increases. Studies have shown that when the NC is increased by three orders of magnitude, the oil displacement efficiency of the residual oil is 50%. If the oil displacement efficiency is 100%, the number of capillary tubes should be increased by four orders of magnitude. (3) Strong solubilization and dispersion, small droplets dispersed, easily passes through microporous medium The O/W type microemulsion can solubilize the oil phase; the crude oil can be dissolved into the micelle by small oil droplets to achieve the effect of mutual solubility with water; and the crude oil is driven out. The microemulsion dispersed droplets have a diameter between 5 nm and 100 nm, which is substantially smaller than the pore radius. This radius prevents the Jamin effect and enables the droplets to smoothly pass through the formation pore [ 11 ] . (4) Dredging the layer An interface is formed between the residual oil of the formation and the water, which creates a pressure difference at the interface. When the applied pressure is greater than ΔP, the residual oil can move. The addition of the microemulsion substantially reduces the interfacial tension, which reduces the injection pressure. 2.2 Reduce oil-water interfacial tension and avoid increasing water injection pressure Low-permeability reservoirs are generally hydrophilic, and capillary forces are the driving force of water-driven oil. Due to the small pores of low-permeability cores and the uneven distribution of pores, the capillary forces in large and small pores vary greatly, and the injection of water easily cuts off the oil flow, which causes water injection. The pressure is constantly rising. The microemulsion reduces the interfacial tension of the oil and water, which reduces the capillary force, uniformly pushes the oil-water interface in the pores of different sizes forward, and eliminates all excessive residual oil after the water flooding. Thus, the injection pressure will gradually decrease. 2.3 Wettability reversal, reducing the possibility of oil droplets readsorption Since the surfactant has two groups—a hydrophilic group and a lipophilic group—it can adsorb on the surface of the rock and reduce the solid-liquid interface energy. Therefore, by injecting a suitable surfactant, the rock surface can be transformed from oleophilic to hydrophilic, which further enhances the water wetness of the rock, prevents the activated crude oil from easily readsorbing, and produces a better antihypertensive effect. 3 Experimental Part 3.1 Materials and instruments (1) Experimental equipment MS12001L/02 Electronic Balance (METTLER TOLEDO Instrument Co., Ltd.); J-HH-4A constant temperature water bath (Shanghai Xinzhuang Instrument Co., Ltd.); TX-500C Rotary Drop Interface Tension Meter (CMG, USA); HKY-1 Multifunctional Core Displacement Device (Jiangsu Hai'an Petroleum Technology Instrument Co., Ltd.); and Vacuum-saturated core device (Jiangsu Hai'an Petroleum Technology Instrument Co., Ltd.). (2) Experimental drugs According to the Schulman method, three kinds of microemulsion systems were constructed in a laboratory [ 12 – 16 ] . The onsite crude oil and kerosene were blended, and the simulated oil that was employed in the laboratory was arranged. The simulated oil density was 0.82 g/cm 3 , and the viscosity (70°C) was 3.73 mPa·s. Distilled water with a conductivity less than 5 µs/cm was utilized. The simulated formation water had a salinity of 49,712.6 mg/L. 3.2 Experimental methods (1) Salt resistance test The three microemulsion systems were each diluted to 10% with formation water. The microemulsions of different systems were diluted with simulated formation water with a salinity of 49712.6 mg/L (microemulsion: formation water = 1:1, 3, 5, 7, 9). for the turbidity was observed for 24 h in a normal temperature environment. (2) Interfacial tension test The interfacial tension of three microemulsion systems (concentration: 10%) was tested at room temperature using a TX-500C rotary drop interfacial tension meter. The interfacial tension between the microemulsion and the crude oil was calculated by measuring the length and width of the microemulsion droplets, the density difference between the microemulsion and the crude oil and the rotational speed. (3) Temperature resistance test The three microemulsion systems were diluted with formation water (microemulsion: formation water = 1:1, 3, 5, 7, 9) and observed in a 70°C water bath for 24 hours to determine if the systems were demulsified. (4) Solubilization performance test In this test, 30 ml of 3 microemulsion systems (concentration: 10%) and 30 ml of crude oil were placed in a measuring cylinder and then placed in a 70°C water bath for 24 hours to observe the volume reduction of the crude oil. (5) Laboratory core displacement experiment Experimental preparation: The natural core (1.98×10 − 3 µm2) was selected from the Chang 9 oilfield and cleaned with Soxhlet extractor. The cleaning solvent was mixed with toluene and ethanol in a ratio of 1:1. After drying and weighing, the core gas phase permeability is obtained using nitrogen pressure to drive the pressure. A core was selected with a similar gas phase permeability to evacuate and saturate the formation water with a salinity of 49712.6 mg/L. The wet weight was determined, and the core pore volume and porosity were calculated. Natural core displacement experimental steps: The core saturated simulated oil was displaced in the 70°C incubator with simulated oil at a flow rate of 0.05 ml/min until the end of the core did not discharge. The core is displaced to the residual oil state with a simulated formation water with a salinity of 49712.6 mg/L at a constant flow rate of 0.05 ml/min until the end of the core end-exit fluid reaches 98% and the displacement is stopped. The water displacement recovery is calculated. The microemulsions were diluted with different solvents of different concentrations, and different injection amounts were injected to investigate the reduction in water injection pressure. 4 Results and Discussion 4.1 Salt resistance performance evaluation The three microemulsion systems were diluted to 10% with formation water. The microemulsions of different systems were diluted with simulated formation water that has a salinity of 49712.6 mg/L, as shown in Table 1 . The three microemulsion systems are stable without turbidity, which indicates that the salt resistance performance satisfies the requirements. Table 1 Salt resistance test sample Dilution ratio (microemulsion: formation water) 1: 1 1: 3 1: 5 1: 7 1: 9 WSC-EM Clarified and transparent Clarified and transparent Clarified and transparent Clarified and transparent Clarified and transparent WSC-OP Clarified and transparent Clarified and transparent Clarified and transparent Clarified and transparent Clarified and transparent WSC-1 Clarified and transparent Clarified and transparent Clarified and transparent Clarified and transparent Clarified and transparent 4.2 Interface tension test The interfacial tension between the three microemulsion systems and the crude oil was measured by a rotary drop interface tension meter. The results are shown in Table 2 . The three systems can reduce the oil-water interfacial tension by two orders of magnitude, and the minimum interfacial tension of the WSC-1 system is 0.0293 Mn/m. Table 2 Interface tension test Sample Number of tests Interfacial tension (minimum) 1 2 3 4 WSC- EM 0.0468 0.0338 0.0328 0.0321 0.0321 WSC-OP 0.0516 0.0386 0.0376 0.0369 0.0369 WSC-1 0.0442 0.0315 0.0301 0.0293 0.0293 4.3 Evaluation of temperature resistance The three microemulsion systems were diluted with different amounts of formation water and then placed in a water bath at 70°C for 24 h. The experimental results are shown in Table 3 . WSC-EM breaks at 70°C, the temperature resistance is not acceptable, the other two systems are kept clear and transparent, and the temperature resistance is excellent. Table 3 Temperature resistance test Sample Dilution ratio (microemulsion: formation water) 1: 1 1: 3 1: 5 1: 7 1: 9 WSC-EM Demulsification, oil film Demulsification, oil film Demulsification, oil film Demulsification, oil film Demulsification, oil film WSC-OP Clarified and transparent Clarified and transparent Clarified and transparent Clarified and transparent Clarified and transparent WSC-1 Clarified and transparent Clarified and transparent Clarified and transparent Clarified and transparent Clarified and transparent 4.4 Solubilization performance evaluation In this experiment, 30 ml of microemulsion (concentration: 10%) and 30 ml of crude oil were placed in a measuring cylinder and then placed in a 70°C water bath for 24 hours. The experimental results are shown in Table 4 . According to the data in the table, all three systems have a certain solubilization effect, and the WSC-1 system can solubilize 4 ml of crude oil. The solubilization of the microemulsion is the solubilization of the micelles to the water-insoluble oil phase. The WSC-1 microemulsion system is a water external phase microemulsion. When the microemulsion is in contact with oil water, the water of the external phase can be mutually miscible with water, and the micelles in the microemulsion are mutually soluble with the crude oil to solubilize the washing oil. As shown in Fig. 1 , the interface between the upper layer crude oil and the lower layer microemulsion in the test tube is clear without turbidity. This finding indicates that the microemulsion enters the formation without causing emulsion blockage. Table 4 Solubilization performance test Sample Initial aqueous phase (ml) Initial oil phase (ml) Soluble aqueous phase (ml) Soluble oil phase (ml) Increased capacity (ml) WSC-EM 30 30 31 29 1 WSC-OP 30 30 32 28 2 WSC-1 30 30 34 26 4 By experimental evaluation, the microemulsion system WSC-1 was selected: 13% AP6 + 4% Polyoxyvinyl ether surfactant + 4% sodium petroleum sulfonate + 4% lower alcohol + 6% oil phase + 69% salt solution and 0.5% anti-temperature agent. 4.5 Laboratory core displacement experiment (1) Since the onsite treatment of produced water is not acceptable, surface water is utilized for the water injection. Therefore, the effect of different dilution solvents on the anti-pressure effect of the microemulsion must be evaluated. Therefore, the concentration of the WSC-1 microemulsion system was diluted to 10% using a formation water, 1% KCl solution and surface water, and the core injection volume was 5 PV. The results of the buck are shown in Figs. 1 to 3 and Table 5 . The microemulsion uses different dilution solvents, which causes the water drive pressure of the core to decrease by varying degrees because the injected microemulsion system has ultralow interfacial tension. When the microemulsion enters the core pore throat, it is in a mixed-phase displacement state. An interface does not exist between oil and water, which reduces the oil-water interfacial tension. The rock gradually changes from oil wetting to water wetting, which increases the wetting angle of the crude oil on the rock surface. Thus, the adhesion work required to pull the crude oil droplets away from the rock surface is considerably reduced, and the washing ability will improve and improve the state of the high residual oil saturation in the formation. Low-permeability reservoirs are generally hydrophilic, and capillary forces are the driving force of water-driven oil. Due to the small pores of low-permeability cores and the uneven distribution of pores, the capillary forces in large and small pores substantially vary, and the injection of water easily stops the oil flow, which causes water injection. The pressure is constantly rising. The microemulsion reduces the interfacial tension of the oil and water, which reduces the capillary force and uniformly pushes the oil-water interface in the pores of different sizes forward, eliminating any excessive residual oil after the water displacement. Thus, the injection pressure will gradually decrease. Since the microemulsion has two groups—a hydrophilic group and a lipophilic group—it can adsorb on the rock surface and reduce the solid-liquid interface energy. Therefore, the microemulsion can transform the rock surface from oleophilic to hydrophilic to further enhance the water wetness of the rock, and the activated crude oil will not be easily readsorbed, which has the positive effect of reducing the injection pressure. In the core displacement experiment shown in Fig. 2 , the surface water was displaced to the residual oil state with 1% KCL solution, the microemulsion was diluted to 10% concentration with 1% KCL solution, and the pressure drop continued with 1% KCL solution displacement. The displacement of the surface water is employed to investigate whether the hydration expansion of clay occurs in the same core with the surface water displacement. As shown in Fig. 3 , the core is displaced by the surface water displacement after 1% KCL solution displacement, and the displacement pressure is gradually increased, which indicates that KCl acts as a stable clay. However, after conversion to the surface water displacement, the surface water has a certain elution effect on KCL, which reduces the long-term stability of KCL to clay stability, which produces an increase in the displacement pressure. Figure 4 shows that the surface water with microemulsion is subsequently displaced by the surface water. The pressure of the subsequent water displacement is lower than that of the residual oil water displacement but the reduction is not large. Figure 5 shows a microemulsion with the simulated formation water. Because the formation water has the best compatibility with the natural core, the maximum pressure drop is 56% after the displacement of 30 PV. Figure 5 Formation water with microemulsion displacement pressure changes with injection volume Table 5 Effect of Different Dilution Solvents on Antihypertensive Effect Core number Water permeability /10 − 3 µm 2 Pore volume /cm 3 Dilution solvent Microemulsion concentration/% Microemulsion injection amount/PV Reduce pressure rate/% C9-5 0.279 5.08 1% KCl solution 10 5 44 C9-4 0.391 5.10 Surface water 10 5 28 C9-1 0.348 5.65 Formation water 10 5 56 (2) The microemulsion was diluted to 10%, 5%, and 1% using a 1% KCl solution. The reduced pressure rate results are shown in Table 6 . As the concentration of the microemulsion system decreases, the rate of depressurization decreases. The microemulsion concentration was 1%, the injection amount was 5 PV, and the pressure rate was reduced to 41%. Table 6 Effect of microemulsion concentration on antihypertensive effect Core number Water permeability/10 − 3 µm 2 Pore volume/cm 3 Microemulsion concentration /% Microemulsion injection amount/PV Reduce pressure rate/% C9-13 0.316 5.17 10 5 52 C9-6 0.335 5.26 5 5 47 C9-7 0.329 5.20 1 5 41 (3) The effect of the amount of microemulsion injected on the water displacement pressure is shown in Table 7 . When the concentration of the microemulsion is constant, the depressurization rate also decreases as the amount of the injection decreases. When a 1% concentration of 1% microemulsion system is injected, the maximum pressure reduction rate is 31%, which satisfies both the oilfield requirements and the cost. Table 7 Effect of microemulsion injection on antihypertensive effect Core number Water permeability/10 − 3 µm 2 Pore volume/cm 3 Microemulsion concentration /% Microemulsion injection amount/PV Reduce pressure rate/% C9-7 0.329 5.20 1 5 41 C9-9 0.500 5.76 1 3 33 C9-3 0.480 5.34 1 1 31 5 Conclusions (1) The preferred microemulsion system has excellent salt resistance, temperature resistance and solubilization performance, and the minimum interfacial tension is 0.0293 Mn/m. (2) The water pressure reduction rate of the core decreases with a decrease in the concentration and injection amount of the system; the minimum rate is 30% at a concentration of 1% and an injection amount of 1 PV. (3) The use of surface water injection at the site is one of the main causes of pressure rise. (4) Periodical injection of a long-lasting clay stabilizer onsite is recommended to reduce the impact of high-water-injection pressure caused by the hydration expansion of clay and the control costs. 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Surfactant-electrolyte interactions in concentrated water-in-oil emulsions. FT-IR spectroscopic and low-temperature differential scanning alorimetric studies. Colloids and Surfaces. 1992, 65(4):243~256 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted 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. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-5685514","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":400516281,"identity":"b92e92be-84d0-4724-9b3a-143eb5aff29a","order_by":0,"name":"Yuhang 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oil distribution map after onsite core water flooding\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-5685514/v1/858fdeb78d01b7f67aaad953.png"},{"id":73650253,"identity":"23299a22-4df6-4428-b816-017750b28018","added_by":"auto","created_at":"2025-01-13 09:30:23","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":85243,"visible":true,"origin":"","legend":"\u003cp\u003eEvaluation of solubilization performance of microemulsion\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-5685514/v1/21886ac81025ade581773ced.png"},{"id":73650255,"identity":"847710f3-030b-4ca9-b8c6-26edc020dfee","added_by":"auto","created_at":"2025-01-13 09:30:23","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":61952,"visible":true,"origin":"","legend":"\u003cp\u003e1% KCl with microemulsion displacement pressure changes with injection volume\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-5685514/v1/5cb18456b4f2335fd81e38de.png"},{"id":73650258,"identity":"1bbef193-6e0a-46fc-a089-f2696da2544a","added_by":"auto","created_at":"2025-01-13 09:30:23","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":67017,"visible":true,"origin":"","legend":"\u003cp\u003eSurface water with microemulsion displacement pressure changes with injection volume\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-5685514/v1/1735c3617ad4a0d01ce7ad7b.png"},{"id":73650803,"identity":"1c2f1b4d-2956-4571-81ef-7ba0762457dd","added_by":"auto","created_at":"2025-01-13 09:38:23","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":68174,"visible":true,"origin":"","legend":"\u003cp\u003eFormation water with microemulsion displacement pressure changes with injection volume\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-5685514/v1/2ca8608a3943e518ea74340d.png"},{"id":83036609,"identity":"1863bca2-321f-4687-9ca9-99308c0d21b9","added_by":"auto","created_at":"2025-05-19 10:02:08","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1417820,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5685514/v1/5e31e1ea-784c-44ae-b31d-dad6c5a0a3b5.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":" Microemulsion Depressurization and Increasing Injection Technology for Tight Reservoirs","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eThe reservoir porosity and permeability of the tight reservoirs in southern Ordos are low, the connectivity is poor, and the matrix water injection is difficult. The minimum porosity is 7%, the maximum porosity is 17.2%, and the average porosity is 11.5%\u003csup\u003e[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]\u003c/sup\u003e. The minimum permeability is 0.086 mD, the maximum permeability is 1.43 mD, and the average permeability is 0.45 mD. These reservoirs have low porosity and ultralow permeability. The reservoirs develop large cracks or a large number of artificial cracks. The phenomenon of water breaking is very serious. The producing reserves of the formation matrix is low. The reservoir rock surface is weakly water-wet, and the irreducible oil saturation is high; thus, it substantially blocks the seepage channels.\u003c/p\u003e \u003cp\u003eCurrently, many methods exist for the transformation of low permeability reservoirs inland and abroad, such as acidification, fracturing, and concentrated surfactant displacement\u003csup\u003e[\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]\u003c/sup\u003e. The disadvantage of the acidification and fracturing method is that the improved stratigraphication is prone to water breaking and insufficient long-term effectiveness. The high concentrated surfactant can be mixed with crude oil in the formation to spontaneously form a microemulsion. However, the formation conditions of microemulsions are harsh, and the stratum is easily blocked by emulsion\u003csup\u003e[\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]\u003c/sup\u003e. Compared with the former, microemulsion is a kind of concentrated surfactant that has a stable thermodynamic system. The particle size of a microemulsion ranges between 10\u0026ndash;100 nm, which enables particles to easily pass through the percolation channel, and has ultralow interfacial tension\u003csup\u003e[\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]\u003c/sup\u003e. The microemulsion has excellent solubilization, wetting and penetration ability\u003csup\u003e[\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]\u003c/sup\u003e. Therefore, the microemulsion can better clean the irreducible oil in the channel, weaken the influence of the Jamin effect, and improve the water phase permeability\u003csup\u003e[\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eIn this paper, different microemulsion systems were screened; the interfacial tension, solubilization, temperature and salt resistance were used as indicators, and a microemulsion system that is suitable for dense reservoirs in Southern Ordos was selected.\u003c/p\u003e"},{"header":"2 Microemulsion depressurization and injection mechanism","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\n \u003ch2\u003e2.1 Reduce oil-water interfacial tension and increase or decrease crude oil flow capacity\u003c/h2\u003e\n \u003cp\u003e(1) Microemulsion can reduce adhesion work and increase oil washing ability\u003c/p\u003e\n \u003cp\u003eAs shown in Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e, a large amount of residual oil distribution in the site rock sample. The microemulsion can reduce the oil-water interfacial tension and increase the wetting angle of the oil on the rock surface. Thus, the oil droplets have to be pulled away from the rock surface. The adhesion work and residual oil saturation is considerably reduced, and the oil washing ability is improved.\u003c/p\u003e\n \u003cp\u003e(2) Microemulsion increases the number of capillary tubes and improves the oil displacement efficiency\u003csup\u003e[\u003cspan class=\"CitationRef\"\u003e10\u003c/span\u003e]\u003c/sup\u003e\u003c/p\u003e\n \u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\n \u003cdiv class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e$$\\:Nc=\\frac{\\mu\\:wVw}{\\phi\\:{\\sigma\\:}_{O/W}}$$\u003c/div\u003e\n \u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\n \u003c/div\u003e\n \u003cp\u003eAt the end of the water injection development, the NC generally ranges from 10\u003csup\u003e\u0026minus;\u0026thinsp;7\u003c/sup\u003e-10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e. As indicated by formula (1), as the NC increases, the oil displacement efficiency also increases. Studies have shown that when the NC is increased by three orders of magnitude, the oil displacement efficiency of the residual oil is 50%. If the oil displacement efficiency is 100%, the number of capillary tubes should be increased by four orders of magnitude.\u003c/p\u003e\n \u003cp\u003e(3) Strong solubilization and dispersion, small droplets dispersed, easily passes through microporous medium\u003c/p\u003e\n \u003cp\u003eThe O/W type microemulsion can solubilize the oil phase; the crude oil can be dissolved into the micelle by small oil droplets to achieve the effect of mutual solubility with water; and the crude oil is driven out. The microemulsion dispersed droplets have a diameter between 5 nm and 100 nm, which is substantially smaller than the pore radius. This radius prevents the Jamin effect and enables the droplets to smoothly pass through the formation pore\u003csup\u003e[\u003cspan class=\"CitationRef\"\u003e11\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e\n \u003cp\u003e(4) Dredging the layer\u003c/p\u003e\n \u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\n \u003cdiv class=\"EquationNumber\"\u003e\u003cimg src=\"https://myfiles.space/user_files/122228_c8a1650c59388082/122228_custom_files/img1736760049.png\"\u003e\u003c/div\u003e\n \u003c/div\u003e\n \u003cp\u003eAn interface is formed between the residual oil of the formation and the water, which creates a pressure difference at the interface. When the applied pressure is greater than \u0026Delta;P, the residual oil can move. The addition of the microemulsion substantially reduces the interfacial tension, which reduces the injection pressure.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\n \u003ch2\u003e2.2 Reduce oil-water interfacial tension and avoid increasing water injection pressure\u003c/h2\u003e\n \u003cp\u003eLow-permeability reservoirs are generally hydrophilic, and capillary forces are the driving force of water-driven oil. Due to the small pores of low-permeability cores and the uneven distribution of pores, the capillary forces in large and small pores vary greatly, and the injection of water easily cuts off the oil flow, which causes water injection. The pressure is constantly rising. The microemulsion reduces the interfacial tension of the oil and water, which reduces the capillary force, uniformly pushes the oil-water interface in the pores of different sizes forward, and eliminates all excessive residual oil after the water flooding. Thus, the injection pressure will gradually decrease.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\n \u003ch2\u003e2.3 Wettability reversal, reducing the possibility of oil droplets readsorption\u003c/h2\u003e\n \u003cp\u003eSince the surfactant has two groups\u0026mdash;a hydrophilic group and a lipophilic group\u0026mdash;it can adsorb on the surface of the rock and reduce the solid-liquid interface energy. Therefore, by injecting a suitable surfactant, the rock surface can be transformed from oleophilic to hydrophilic, which further enhances the water wetness of the rock, prevents the activated crude oil from easily readsorbing, and produces a better antihypertensive effect.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"3 Experimental Part","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Materials and instruments\u003c/h2\u003e \u003cp\u003e(1) Experimental equipment\u003c/p\u003e \u003cp\u003eMS12001L/02 Electronic Balance (METTLER TOLEDO Instrument Co., Ltd.); J-HH-4A constant temperature water bath (Shanghai Xinzhuang Instrument Co., Ltd.); TX-500C Rotary Drop Interface Tension Meter (CMG, USA); HKY-1 Multifunctional Core Displacement Device (Jiangsu Hai'an Petroleum Technology Instrument Co., Ltd.); and Vacuum-saturated core device (Jiangsu Hai'an Petroleum Technology Instrument Co., Ltd.).\u003c/p\u003e \u003cp\u003e(2) Experimental drugs\u003c/p\u003e \u003cp\u003eAccording to the Schulman method, three kinds of microemulsion systems were constructed in a laboratory\u003csup\u003e[\u003cspan additionalcitationids=\"CR13 CR14 CR15\" citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]\u003c/sup\u003e. The onsite crude oil and kerosene were blended, and the simulated oil that was employed in the laboratory was arranged. The simulated oil density was 0.82 g/cm\u003csup\u003e3\u003c/sup\u003e, and the viscosity (70\u0026deg;C) was 3.73 mPa\u0026middot;s. Distilled water with a conductivity less than 5 \u0026micro;s/cm was utilized. The simulated formation water had a salinity of 49,712.6 mg/L.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Experimental methods\u003c/h2\u003e \u003cp\u003e(1) Salt resistance test\u003c/p\u003e \u003cp\u003eThe three microemulsion systems were each diluted to 10% with formation water. The microemulsions of different systems were diluted with simulated formation water with a salinity of 49712.6 mg/L (microemulsion: formation water\u0026thinsp;=\u0026thinsp;1:1, 3, 5, 7, 9). for the turbidity was observed for 24 h in a normal temperature environment.\u003c/p\u003e \u003cp\u003e(2) Interfacial tension test\u003c/p\u003e \u003cp\u003eThe interfacial tension of three microemulsion systems (concentration: 10%) was tested at room temperature using a TX-500C rotary drop interfacial tension meter. The interfacial tension between the microemulsion and the crude oil was calculated by measuring the length and width of the microemulsion droplets, the density difference between the microemulsion and the crude oil and the rotational speed.\u003c/p\u003e \u003cp\u003e(3) Temperature resistance test\u003c/p\u003e \u003cp\u003eThe three microemulsion systems were diluted with formation water (microemulsion: formation water\u0026thinsp;=\u0026thinsp;1:1, 3, 5, 7, 9) and observed in a 70\u0026deg;C water bath for 24 hours to determine if the systems were demulsified.\u003c/p\u003e \u003cp\u003e(4) Solubilization performance test\u003c/p\u003e \u003cp\u003eIn this test, 30 ml of 3 microemulsion systems (concentration: 10%) and 30 ml of crude oil were placed in a measuring cylinder and then placed in a 70\u0026deg;C water bath for 24 hours to observe the volume reduction of the crude oil.\u003c/p\u003e \u003cp\u003e(5) Laboratory core displacement experiment\u003c/p\u003e \u003cp\u003eExperimental preparation: The natural core (1.98\u0026times;10\u0026thinsp;\u0026minus;\u0026thinsp;3 \u0026micro;m2) was selected from the Chang 9 oilfield and cleaned with Soxhlet extractor. The cleaning solvent was mixed with toluene and ethanol in a ratio of 1:1. After drying and weighing, the core gas phase permeability is obtained using nitrogen pressure to drive the pressure. A core was selected with a similar gas phase permeability to evacuate and saturate the formation water with a salinity of 49712.6 mg/L. The wet weight was determined, and the core pore volume and porosity were calculated.\u003c/p\u003e \u003cp\u003eNatural core displacement experimental steps: The core saturated simulated oil was displaced in the 70\u0026deg;C incubator with simulated oil at a flow rate of 0.05 ml/min until the end of the core did not discharge. The core is displaced to the residual oil state with a simulated formation water with a salinity of 49712.6 mg/L at a constant flow rate of 0.05 ml/min until the end of the core end-exit fluid reaches 98% and the displacement is stopped. The water displacement recovery is calculated. The microemulsions were diluted with different solvents of different concentrations, and different injection amounts were injected to investigate the reduction in water injection pressure.\u003c/p\u003e \u003c/div\u003e"},{"header":"4 Results and Discussion","content":"\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e4.1 Salt resistance performance evaluation\u003c/h2\u003e \u003cp\u003eThe three microemulsion systems were diluted to 10% with formation water. The microemulsions of different systems were diluted with simulated formation water that has a salinity of 49712.6 mg/L, as shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The three microemulsion systems are stable without turbidity, which indicates that the salt resistance performance satisfies the requirements.\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\u003eSalt resistance test\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=\"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\u003esample\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"5\" nameend=\"c6\" namest=\"c2\"\u003e \u003cp\u003eDilution ratio (microemulsion: formation water)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1: 1\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1: 3\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1: 5\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1: 7\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1: 9\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWSC-EM\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eClarified and transparent\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eClarified and transparent\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eClarified and transparent\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eClarified and transparent\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eClarified and transparent\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWSC-OP\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eClarified and transparent\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eClarified and transparent\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eClarified and transparent\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eClarified and transparent\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eClarified and transparent\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWSC-1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eClarified and transparent\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eClarified and transparent\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eClarified and transparent\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eClarified and transparent\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eClarified and transparent\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=\"Section2\"\u003e \u003ch2\u003e4.2 Interface tension test\u003c/h2\u003e \u003cp\u003eThe interfacial tension between the three microemulsion systems and the crude oil was measured by a rotary drop interface tension meter. The results are shown in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. The three systems can reduce the oil-water interfacial tension by two orders of magnitude, and the minimum interfacial tension of the WSC-1 system is 0.0293 Mn/m.\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\u003eInterface tension test\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\u003eSample\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"4\" nameend=\"c5\" namest=\"c2\"\u003e \u003cp\u003eNumber of tests\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eInterfacial tension\u003c/p\u003e \u003cp\u003e(minimum)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWSC- EM\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.0468\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.0338\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.0328\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.0321\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.0321\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWSC-OP\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.0516\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.0386\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.0376\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.0369\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.0369\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWSC-1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.0442\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.0315\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.0301\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.0293\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.0293\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=\"Section2\"\u003e \u003ch2\u003e4.3 Evaluation of temperature resistance\u003c/h2\u003e \u003cp\u003eThe three microemulsion systems were diluted with different amounts of formation water and then placed in a water bath at 70\u0026deg;C for 24 h. The experimental results are shown in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. WSC-EM breaks at 70\u0026deg;C, the temperature resistance is not acceptable, the other two systems are kept clear and transparent, and the temperature resistance is excellent.\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\u003eTemperature resistance test\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=\"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\u003eSample\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"5\" nameend=\"c6\" namest=\"c2\"\u003e \u003cp\u003eDilution ratio (microemulsion: formation water)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1: 1\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1: 3\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1: 5\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1: 7\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1: 9\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWSC-EM\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDemulsification, oil film\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eDemulsification, oil film\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eDemulsification, oil film\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eDemulsification, oil film\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eDemulsification, oil film\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWSC-OP\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eClarified and transparent\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eClarified and transparent\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eClarified and transparent\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eClarified and transparent\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eClarified and transparent\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWSC-1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eClarified and transparent\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eClarified and transparent\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eClarified and transparent\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eClarified and transparent\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eClarified and transparent\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=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e4.4 Solubilization performance evaluation\u003c/h2\u003e \u003cp\u003eIn this experiment, 30 ml of microemulsion (concentration: 10%) and 30 ml of crude oil were placed in a measuring cylinder and then placed in a 70\u0026deg;C water bath for 24 hours. The experimental results are shown in Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. According to the data in the table, all three systems have a certain solubilization effect, and the WSC-1 system can solubilize 4 ml of crude oil. The solubilization of the microemulsion is the solubilization of the micelles to the water-insoluble oil phase. The WSC-1 microemulsion system is a water external phase microemulsion. When the microemulsion is in contact with oil water, the water of the external phase can be mutually miscible with water, and the micelles in the microemulsion are mutually soluble with the crude oil to solubilize the washing oil. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, the interface between the upper layer crude oil and the lower layer microemulsion in the test tube is clear without turbidity. This finding indicates that the microemulsion enters the formation without causing emulsion blockage.\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 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eSolubilization performance test\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\u003eSample\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eInitial aqueous phase (ml)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eInitial oil phase (ml)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSoluble aqueous phase (ml)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eSoluble oil phase (ml)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eIncreased capacity (ml)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWSC-EM\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e31\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e29\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWSC-OP\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e32\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\u003e2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWSC-1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e34\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e26\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e4\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\u003eBy experimental evaluation, the microemulsion system WSC-1 was selected: 13% AP6\u0026thinsp;+\u0026thinsp;4% Polyoxyvinyl ether surfactant\u0026thinsp;+\u0026thinsp;4% sodium petroleum sulfonate\u0026thinsp;+\u0026thinsp;4% lower alcohol\u0026thinsp;+\u0026thinsp;6% oil phase\u0026thinsp;+\u0026thinsp;69% salt solution and 0.5% anti-temperature agent.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e4.5 Laboratory core displacement experiment\u003c/h2\u003e \u003cp\u003e(1) Since the onsite treatment of produced water is not acceptable, surface water is utilized for the water injection. Therefore, the effect of different dilution solvents on the anti-pressure effect of the microemulsion must be evaluated. Therefore, the concentration of the WSC-1 microemulsion system was diluted to 10% using a formation water, 1% KCl solution and surface water, and the core injection volume was 5 PV. The results of the buck are shown in Figs.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e to \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e and Table\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. The microemulsion uses different dilution solvents, which causes the water drive pressure of the core to decrease by varying degrees because the injected microemulsion system has ultralow interfacial tension. When the microemulsion enters the core pore throat, it is in a mixed-phase displacement state. An interface does not exist between oil and water, which reduces the oil-water interfacial tension. The rock gradually changes from oil wetting to water wetting, which increases the wetting angle of the crude oil on the rock surface. Thus, the adhesion work required to pull the crude oil droplets away from the rock surface is considerably reduced, and the washing ability will improve and improve the state of the high residual oil saturation in the formation. Low-permeability reservoirs are generally hydrophilic, and capillary forces are the driving force of water-driven oil. Due to the small pores of low-permeability cores and the uneven distribution of pores, the capillary forces in large and small pores substantially vary, and the injection of water easily stops the oil flow, which causes water injection. The pressure is constantly rising. The microemulsion reduces the interfacial tension of the oil and water, which reduces the capillary force and uniformly pushes the oil-water interface in the pores of different sizes forward, eliminating any excessive residual oil after the water displacement. Thus, the injection pressure will gradually decrease. Since the microemulsion has two groups\u0026mdash;a hydrophilic group and a lipophilic group\u0026mdash;it can adsorb on the rock surface and reduce the solid-liquid interface energy. Therefore, the microemulsion can transform the rock surface from oleophilic to hydrophilic to further enhance the water wetness of the rock, and the activated crude oil will not be easily readsorbed, which has the positive effect of reducing the injection pressure. In the core displacement experiment shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, the surface water was displaced to the residual oil state with 1% KCL solution, the microemulsion was diluted to 10% concentration with 1% KCL solution, and the pressure drop continued with 1% KCL solution displacement. The displacement of the surface water is employed to investigate whether the hydration expansion of clay occurs in the same core with the surface water displacement.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, the core is displaced by the surface water displacement after 1% KCL solution displacement, and the displacement pressure is gradually increased, which indicates that KCl acts as a stable clay. However, after conversion to the surface water displacement, the surface water has a certain elution effect on KCL, which reduces the long-term stability of KCL to clay stability, which produces an increase in the displacement pressure. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e shows that the surface water with microemulsion is subsequently displaced by the surface water. The pressure of the subsequent water displacement is lower than that of the residual oil water displacement but the reduction is not large. Figure\u0026nbsp;5 shows a microemulsion with the simulated formation water. Because the formation water has the best compatibility with the natural core, the maximum pressure drop is 56% after the displacement of 30 PV.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure 5 Formation water with microemulsion displacement pressure changes with injection volume\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 5\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eEffect of Different Dilution Solvents on Antihypertensive Effect\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\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=\"left\" 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 \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\u003eWater permeability /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=\"c3\"\u003e \u003cp\u003ePore volume /cm\u003csup\u003e3\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eDilution solvent\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eMicroemulsion concentration/%\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eMicroemulsion injection amount/PV\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eReduce pressure rate/%\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eC9-5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.279\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5.08\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1% KCl solution\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e44\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eC9-4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.391\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5.10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSurface water\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e28\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eC9-1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.348\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5.65\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eFormation water\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e56\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(2) The microemulsion was diluted to 10%, 5%, and 1% using a 1% KCl solution. The reduced pressure rate results are shown in Table\u0026nbsp;\u003cspan refid=\"Tab6\" class=\"InternalRef\"\u003e6\u003c/span\u003e. As the concentration of the microemulsion system decreases, the rate of depressurization decreases. The microemulsion concentration was 1%, the injection amount was 5 PV, and the pressure rate was reduced to 41%.\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 6\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eEffect of microemulsion concentration on antihypertensive effect\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\u003eWater permeability/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=\"c3\"\u003e \u003cp\u003ePore volume/cm\u003csup\u003e3\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMicroemulsion concentration /%\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eMicroemulsion injection amount/PV\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eReduce pressure rate/%\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eC9-13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.316\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5.17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e52\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eC9-6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.335\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5.26\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\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e47\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eC9-7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.329\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5.20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e41\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(3) The effect of the amount of microemulsion injected on the water displacement pressure is shown in Table\u0026nbsp;\u003cspan refid=\"Tab7\" class=\"InternalRef\"\u003e7\u003c/span\u003e. When the concentration of the microemulsion is constant, the depressurization rate also decreases as the amount of the injection decreases. When a 1% concentration of 1% microemulsion system is injected, the maximum pressure reduction rate is 31%, which satisfies both the oilfield requirements and the cost.\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 7\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eEffect of microemulsion injection on antihypertensive effect\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\u003eWater permeability/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=\"c3\"\u003e \u003cp\u003ePore volume/cm\u003csup\u003e3\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMicroemulsion concentration /%\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eMicroemulsion injection amount/PV\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eReduce pressure rate/%\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eC9-7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.329\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5.20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e41\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eC9-9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.500\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5.76\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e33\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eC9-3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.480\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5.34\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e31\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"},{"header":"5 Conclusions","content":"\u003cp\u003e(1) The preferred microemulsion system has excellent salt resistance, temperature resistance and solubilization performance, and the minimum interfacial tension is 0.0293 Mn/m.\u003c/p\u003e \u003cp\u003e(2) The water pressure reduction rate of the core decreases with a decrease in the concentration and injection amount of the system; the minimum rate is 30% at a concentration of 1% and an injection amount of 1 PV.\u003c/p\u003e \u003cp\u003e(3) The use of surface water injection at the site is one of the main causes of pressure rise.\u003c/p\u003e \u003cp\u003e(4) Periodical injection of a long-lasting clay stabilizer onsite is recommended to reduce the impact of high-water-injection pressure caused by the hydration expansion of clay and the control costs.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets generated and/or analysed during the current study are not publicly available due the project has not passed the confidentiality period,but are available from the corresponding author on reasonable request.(Corresponding author email address:[email protected])\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eOptimized oilwell fracturing of moderate-permeability reservoirs. L.K. Britt. SPE14371 . 1985\u003c/li\u003e\n\u003cli\u003e\u0026quot;Refracturing:Observations and Theo-ries\u0026quot;. Elbel,J.L,Mack,M.G. the Production Operations Symposium,SPE 25464 . 1993\u003c/li\u003e\n\u003cli\u003eA new analytical multi-linear solution for gas flow toward fractured horizontal wells with different fracture intensity[J] . Bin Yuan,Yuliang Su,Rouzbeh Ghanbarnezhad Moghanloo,Zhenhua Rui,Wendong Wang,Yangyang Shang. Journal of Natural Gas Science and Engineering . 2015\u003c/li\u003e\n\u003cli\u003eNumerical approach for enhanced oil recovery with surfactant flooding[J] . Sadegh Keshtkar,Morteza Sabeti,Amir H. Mohammadi. Petroleum . 2015\u003c/li\u003e\n\u003cli\u003eScreening Estimation of Recovery Efficiency and Chemical Requirements for Chemical Flooding. LAKE L W,,STOCK L G,and LAWSON J B. SPE Fifth Symposium on Improved Methodes for OiRecovery . 1978\u003c/li\u003e\n\u003cli\u003ePhase Behavior and Microstructure of Microemulsions with a Room-Temperature Ionic Liquid as the Polar Phase. Rob Atkin,Gregory G. Warr. Journal of Physics . 2007\u003c/li\u003e\n\u003cli\u003eInvestigations of capacitance for sodium dodecyl sulfate/benzyl alcohol/H 2 O microemulsion[J] . Rong Guo,Xun Wei,Tiangqing Liu,Weiya Liu. Colloids and Surfaces A: Physicochemical and Engineering Aspects . 2005 (1)\u003c/li\u003e\n\u003cli\u003eCrosslinkedemulsion to be used as fracturing fluids. KAKADJIAN S,RAUSEO O,MARQUEZ R,et al. SPE InternationalSymposium on Oilfield Chemistry . 2001\u003c/li\u003e\n\u003cli\u003eMicroemulsions in Enhanced Oil Recovery: A Review[J] . M.F. Nazar,S.S. Shah,M.A. Khosa. Petroleum Science and Technology . 2011\u003c/li\u003e\n\u003cli\u003eThe Effect of the Capillary Number and its Constituents on Two-Phase Relative Permeability Curves. Fulcher,R. A. Jr. paper SPE 12170 . 1983\u003c/li\u003e\n\u003cli\u003eAmit Kumar,Rohit Kumar Saw,Ajay Mandal. RSM optimization of oil-in-water microemulsion stabilized by synthesized zwitterionic surfactant and its properties evaluation for application in enhanced oil recovery[J]. Chemical Engineering Research and Design,2019,147.\u003c/li\u003e\n\u003cli\u003eSchulman J H, Leja L. Control of contact angles at the oil-water-solid interfaces-emulsions stabilized by solid particles (Ba SO4). Transactions of the Faraday Society articles. 1954, 50:598~605\u003c/li\u003e\n\u003cli\u003eBinks B P, Desforges A, Duff D G. Synergetic stabilization of emulsions by a mixture of surface-active nanoparticles and surfactant. Langmuir. 2007, 23:1098~1106 \u003c/li\u003e\n\u003cli\u003eBinks B P, Rodrigues J A. Synergetic interaction in emulsions stabilized by a mixture of silica nanoparticles and cationic surfactant. Langmuir. 2007, 23:3626~3636\u003c/li\u003e\n\u003cli\u003eHunter R J. Introduction to Modern Colloid Science. Oxford: Oxford University Press, 1993.\u003c/li\u003e\n\u003cli\u003eGanguly S, Mohan V, Krishna, et al. Surfactant-electrolyte interactions in concentrated water-in-oil emulsions. FT-IR spectroscopic and low-temperature differential scanning alorimetric studies. Colloids and Surfaces. 1992, 65(4):243~256\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"low permeability reservoir, microemulsion, depressurization and increasing injection, interfacial tension, solubilization, mechanistic","lastPublishedDoi":"10.21203/rs.3.rs-5685514/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5685514/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eAlthough some microcracks or large cracks occur during fracturing in the tight reservoirs, the average permeability and porosity of the reservoir matrix are relatively low: 0.76\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e \u0026micro;m\u003csup\u003e2\u003c/sup\u003e and 11.5%, respectively. These values are typical of a typical low-permeability tight reservoir. Currently, the water injection pressure during the development of reservoir water injection is high and exceeds the reopening pressure of a crack. The pressure is close to the formation fracture pressure, which minimizes the phenomenon of water breakthrough and water injection efficiency. The reservoir matrix is substantially under injection. Therefore, a method to reduce the injection pressure and improve the matrix injection capacity is urgently needed. According to the features of tight reservoirs and crude oil, three kinds of microemulsion are screened: 13% AP6\u0026thinsp;+\u0026thinsp;4% polyoxyvinyl ether surfactant\u0026thinsp;+\u0026thinsp;4% sodium petroleum sulfonate\u0026thinsp;+\u0026thinsp;4% lower alcohol\u0026thinsp;+\u0026thinsp;6% oil phase\u0026thinsp;+\u0026thinsp;69% salt solution and 0.5% anti-temperature agent. The maximum soluble capacity of onsite oil is 14%. Microemulsion has excellent temperature resistance; if it is heated for 24 hours at 70\u0026deg;C, it does not break. Microemulsion also has excellent salt and anti-dilution performance. No turbidity occurs after the microemulsion and the formation water are mixed in any proportion for 24 hours. A core displacement experiment using microemulsion was performed in a lab. The results of the research indicate that the water injection pressure is reduced to a minimum of 40% when the injection concentration of the microemulsion is 1% and the injection slug is 5 PV.\u003c/p\u003e","manuscriptTitle":" Microemulsion Depressurization and Increasing Injection Technology for Tight Reservoirs","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-01-13 09:30:18","doi":"10.21203/rs.3.rs-5685514/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"9c53e90b-f950-44de-a7cf-abe8ab633600","owner":[],"postedDate":"January 13th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-05-19T09:54:01+00:00","versionOfRecord":[],"versionCreatedAt":"2025-01-13 09:30:18","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-5685514","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5685514","identity":"rs-5685514","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}