Oil displacement agent containing cationic gemini surfactant and application method thereof

Abstract

The invention discloses an oil-displacing agent containing a cationic gemini surfactant and an application method of the oil-displacing agent, the oil-displacing agent comprises a biquaternary ammonium salt type gemini surfactant and is suitable for unconventional oil reservoirs, and the reverse imbibition effect is enhanced through efficient adsorption and water film regulation of the cationic gemini surfactant in micro capillary pores; the result of an imbibition experiment shows that the imbibition liquid recovery rates of 0.15% N, N, N ', N', N 'hexamethyl diammonium dichloride gemini surfactant and 0.15% N, N, N, N', N 'hexamethyl diammonium dichloride gemini surfactant respectively reach 38.15% and 36.05%, and are respectively improved by 8% and 6%, and the imbibition liquid recovery rates of 0.15% N, N, N, N', N ', N' hexamethyl diammonium dichloride gemini surfactant and 0.15% N, N, N, N ', N' hexamethyl diammonium dichloride gemini surfactant respectively reach 38.15% and 36.05%. On-site implementation cases of a new well and an old well show that the recovery rates can be respectively increased by 22.3%-47.15%.

Description

Technical Field

[0001] This invention belongs to the field of unconventional oil reservoir development technology, specifically relating to an oil displacement agent containing cationic gemini surfactant and its application method. Background Technology

[0002] Unconventional oil reservoirs (such as ultra-low permeability reservoirs, tight reservoirs, and shale reservoirs) are characterized by complex pore structures, small pore sizes (dominated by microcapillary pores with a pore radius of less than 0.1 µm), and low permeability (≤1.0 mD). Water drive is ineffective in these reservoirs, and conventional water injection is also ineffective for enhancing oil recovery. Unconventional reservoirs are dominated by microcapillary pores, resulting in significant flow resistance within the rock matrix system. The primary process is reverse adsorption (the direction of water phase entry into the core is opposite to the direction of oil phase exit). In unconventional reservoirs, under reverse adsorption, the oil within the microcapillary pores contributes the majority of the recovery, averaging over 60% of the total recovery. The thickness of the adsorbed water film is crucial for the success of reverse percolation. Under conventional rock conditions, the water film thickness ranges from 0.079 µm to 0.13 µm, which is higher than the throat radius of most micropores in unconventional reservoirs. Without effective measures to reduce the adsorbed water film on the surface of rock micropores, most pore throats will be water-locked. Reducing the water film thickness on the surface of microcapillary pores in unconventional reservoirs, making it smaller than the throat radius, is essential to improving the effective porosity ratio and the recovery rate of unconventional reservoirs through reverse percolation.

[0003] For example, Chinese invention patent CN112892394B discloses a sulfonic acid-based anionic gemini surfactant, its preparation, and its application as a shale oil reservoir percolation displacement agent. The application of the sulfonic acid-based anionic gemini surfactant of this invention as a shale oil reservoir percolation displacement agent changes the surface wettability of shale oil reservoirs, transforms oil-wet cores into hydrophilic ones, and improves the shale oil percolation recovery rate.

[0004] While various surfactants are currently available for enhancing oil recovery, their effectiveness in unconventional reservoirs is limited, particularly in reducing water film thickness and promoting reverse adsorption within microcapillary pores. Therefore, there is an urgent need for a surfactant and oil displacement agent suitable for unconventional reservoirs that can effectively reduce water film thickness on rock surfaces and enhance reverse adsorption, along with their application methods. Summary of the Invention

[0005] The purpose of this invention is to provide an oil displacement agent containing cationic gemini surfactant and its application method, which is suitable for unconventional oil reservoirs. Through the efficient adsorption and water film regulation of cationic gemini surfactant in microcapillary pores, the reverse permeation effect is enhanced, and the recovery rate of unconventional oil reservoirs is significantly improved.

[0006] The technical solution of the present invention is as follows: An oil displacement agent containing cationic gemini surfactants, suitable for unconventional oil reservoirs, wherein the cationic gemini surfactants include bisquaternary ammonium salt type gemini surfactants; the bisquaternary ammonium salt type gemini surfactants chemically link two or more identical or nearly identical surfactant monomers together with a linking group near or around the hydrophilic head group to form a novel surfactant, which is more easily adsorbed on the gas / liquid surface of sandstone, thereby more effectively reducing the surface tension of the aqueous solution, enhancing adsorption and spreading on the sandstone surface, reducing the thickness of the water film on the rock surface, and enhancing reverse percolation.

[0007] Preferably, the bisquaternary ammonium salt type gemini surfactant is N,N,N,N',N',N' hexamethylethylenediammonium dichloride or N,N,N,N',N',N' hexamethylpropanediammonium dichloride; having the structure shown in Formula I or Formula II:

[0008] Formula I

[0009] Formula II The bis-quaternary ammonium salt molecule of this application carries two positive charges, linked by a short carbon chain (ethyl or propyl); it has stronger adsorption capacity and better surface activity than mono-quaternary ammonium salt.

[0010] Preferably, the content of the bisquaternary ammonium salt type gemini surfactant is 0.01% to 1% (by mass).

[0011] Preferably, the content of the bisquaternary ammonium salt type gemini surfactant is 0.1% to 0.3% (by mass).

[0012] Preferably, the total number of carbon atoms in the bisquaternary ammonium salt type gemini surfactant molecule is 8 to 10.

[0013] Preferably, the permeability of the unconventional reservoir is ≤1.0 mD, including ultra-low permeability reservoirs, tight reservoirs, or shale reservoirs.

[0014] A method for applying an oil displacement agent containing a cationic gemini surfactant includes the following steps: S1 Preparation: According to the net mass concentration ratio of cationic gemini surfactant in the wellbore working fluid, add cationic gemini surfactant to the wellbore working fluid using a metering pump; S2 Injection: The working fluid containing the cationic gemini surfactant prepared in step S1 is injected into the unconventional reservoir; S3 Permeation: After injection, shut the well for 30-60 days for oil-water permeation replacement; S4 oil recovery: drainage and oil recovery.

[0015] The beneficial effects of this invention are: The oil displacement agent containing cationic gemini surfactants of this application has the following advantages: 1. The cationic gemini surfactant of this application has a bisquaternary ammonium salt molecule with two positive charges, which are linked by a short carbon chain (ethyl or propyl); it has a stronger adsorption capacity and better surface activity than monoquaternary ammonium salt; its bipolar cationic structure can improve the adsorption strength and efficiency on sandstone surface, enhance adsorption and spreading on sandstone surface, improve surface properties and reduce the amount of surfactant used. 2. The cationic gemini surfactant of this application controls the length of the molecular chain through short carbon chain design, compresses interfacial adsorption, and prevents the increase of the interphase thickness and water film thickness due to excessively long molecular chains; it achieves low intermolecular forces, enhances the fluidity of free water, and promotes the penetration of the aqueous phase into the micropores; at the same time, it adopts a neutral hydrophilic structure to reduce the hydrophilic strength and prevent water molecules from directly adsorbing onto the microporous surface to form a water film. 3. Improved Oil Recovery: Iridulation experiments showed that the recovery rates of the 0.15% N,N,N,N',N',N' hexamethyl ethylenediamine dichloride gemini surfactant permeate and the 0.15% N,N,N,N',N',N' hexamethyl propanediamine dichloride gemini surfactant permeate reached 38.15% and 36.05%, respectively, representing increases of 8% and 6% compared to the highest recovery rate of 30.16% for anionic gemini surfactants in reference document CN112892394B. Field implementation cases demonstrate that: (1). After fracturing, percolation displacement, fluid drainage, and oil production in new wells, the 6-month oil production of conventional percolation fracturing fluid and the 6-month oil production of fracturing fluid with the addition of 0.15% N,N,N,N',N',N' hexamethyl ethylenediamine dichloride gemini surfactant were 309.51 m³ / s, respectively. 3 and 442.26 m 3 In comparison, oil production increased by 132.75 m³. 3 The recovery rate increased by 42.9%; (2). After repeated fracturing, percolation replacement, fluid drainage, and oil production in old wells, the 6-month oil production of conventional percolation fracturing fluid and the 6-month oil production of fracturing fluid with the addition of 0.15% N,N,N,N',N',N' hexamethyl ethylenediamine dichloride gemini surfactant were 260.26 m³ / s, respectively. 3 and 320.37 m 3 In comparison, oil production increased by 60.11 m³. 3 The harvest rate increased by 23%; (3). After repeated fracturing, percolation replacement, fluid drainage, and oil production in old wells, the 6-month oil production of conventional oil displacement percolation fracturing fluid and the 6-month oil production of fracturing fluid with the addition of 0.15% N,N,N,N',N',N' hexamethylmalonium dichloride gemini surfactant were 421.73 m³ / s, respectively. 3 and 515.85 m 3 In comparison, oil production increased by 94.12 m³. 3 The recovery rate increased by 22.3%.

[0016] (4). After enhanced oil recovery, fluid displacement, and oil production in old wells, the 6-month oil production of conventional displacement fluid and the 6-month oil production of fluid with added 0.3% N,N,N,N',N',N' hexamethylmalonium dichloride gemini surfactant were 223.86 m³ / s. 3 and 329.42 m 3 In comparison, oil production increased by 105.56 m³. 3 The harvest rate increased by 47.15%. Detailed Implementation

[0017] The present invention will be further described below with reference to the embodiments, but the scope of protection of the present invention is not limited to the following embodiments.

[0018] 1. Laboratory Evaluation Case 1 Osmosis test method: volumetric method Oilfield A core sample: permeability 0.3-0.7 mD.

[0019] The core samples were placed in crude oil and aged for 3 months at a reservoir temperature of 90°C for later use.

[0020] #1 Fluid: Conventional percolation displacement fluid (water + 0.15% percolation agent currently used in shale oilfields) #2 Permeation Solution: Water + 0.1% N,N,N,N',N',N' hexamethyl ethylenediamine dichloride gemini surfactant #3 Percolation solution: Water + 0.15% N,N,N,N',N',N' hexamethyl ethylenediamine dichloride gemini surfactant #4 Percolation solution: Water + 0.3% N,N,N,N',N',N' hexamethylethylenediamine dichloride gemini surfactant 5# Percolation solution: Water + 0.5% N,N,N,N',N',N' hexamethyl ethylenediamine dichloride gemini surfactant 6# Percolation fluid: Oilfield formation water The aged core was placed in a percolation container, and the amount of crude oil at the top of the container was read at regular intervals. The recovery rate was calculated by calculating the volume of crude oil separated at different times. The experimental data are shown in Tables 1-7.

[0021] Table 1. Core samples and experimental data used in the permeation experiment.

[0022] Table 21# Liquid Immersion Test Data for Oilfield A 115-1

[0023] Table 32# Liquid's percolation test data for Oilfield A 116-1

[0024] Table 43# liquid permeation test data for oilfield A 114-2

[0025] Table 54# liquid's percolation test data for oilfield A, 117-1

[0026] Table 65# liquid permeation test data for oilfield A 113-1

[0027] Table 76# liquid permeation test data for oilfield A 121-1

[0028] As shown in Table 2-7, the final recovery rate of conventional percolation flooding fluid was 6.26%, lower than the 14.66% recovery rate of formation water in the oilfield. However, the recovery rates of percolation fluids containing 0.1%, 0.15%, 0.3%, and 0.5% N,N,N,N',N',N' hexamethyl ethylenediamine dichloride gemini surfactant reached 31.86%, 38.15%, 35.38%, and 35.65%, respectively. In particular, the recovery rate of the 0.15% N,N,N,N',N',N' hexamethyl ethylenediamine dichloride gemini surfactant percolation fluid reached 38.15%.

[0029] 2. Laboratory Evaluation Case 2 Osmosis test method: volumetric method B oilfield core: permeability 0.5-0.8 mD.

[0030] The core samples were placed in crude oil and aged for 3 months at a reservoir temperature of 65 °C for later use.

[0031] 7# Permeation solution: Water + 0.1% N,N,N,N',N',N' hexamethylpropanediammonium dichloride gemini surfactant #8 Percolation solution: Water + 0.15% N,N,N,N',N',N' hexamethylpropanediammonium dichloride gemini surfactant #9 Percolation solution: Water + 0.3% N,N,N,N',N',N' hexamethylpropanediammonium dichloride gemini surfactant 10# Percolation solution: Water + 0.5% N,N,N,N',N',N' hexamethylpropanediammonium dichloride gemini surfactant The aged core was placed in a percolation container, and the amount of crude oil at the top of the container was read at regular intervals. The recovery rate was calculated by calculating the volume of crude oil separated at different times. The experimental data are shown in Tables 8-12.

[0032] Table 8. Core samples and experimental data used in the permeation test.

[0033] Table 97# liquid permeation test data for oilfield B 23-1

[0034] Table 108# liquid permeation test data for oilfield B 60-1

[0035] Table 119# liquid permeation test data for oilfield B 25-1

[0036] Table 1210# liquid permeation test data for oilfield B 17-3

[0037] As shown in Table 8-12, the recovery rates of percolations with 0.1%, 0.15%, 0.3%, and 0.5% N,N,N,N',N',N' hexamethylmalonium dichloride gemini surfactants reached 31.1%, 36.05%, 33.19%, and 33.78%, respectively. In particular, the recovery rate of the percolation with 0.15% N,N,N,N',N',N' hexamethylmalonium dichloride gemini surfactants reached 36.05%.

[0038] Table 13 is derived from the experimental data obtained by combining laboratory evaluation case 1, laboratory evaluation case 2, and the comparative document CN112892394B. The experimental data in Table 13 show that the recovery rates of the 0.15% N,N,N,N',N',N' hexamethyl ethylenediamine dichloride gemini surfactant percolate and the 0.15% N,N,N,N',N',N' hexamethyl propanediamine dichloride gemini surfactant percolate reached 38.15% and 36.05%, respectively, representing increases of 8% and 6% compared to the highest recovery rate of 30.16% for anionic gemini surfactants in comparative document CN112892394B.

[0039] Table 13 Comparison of Immersion Test Data

[0040] 3. On-site Implementation Case 1 Fracturing status of well D4158-1, new well fracturing. Construction plan: Step 1: Add 0.15% N,N,N,N',N',N' hexamethyl ethylenediamine dichloride gemini surfactant to the conventional fracturing fluid (0.35% guar gum fracturing fluid); Step 2: Perform hydraulic fracturing according to the construction design; Step 3: After fracturing, shut the well in for 50 days to allow the fracturing fluid to permeate and replace oil and water in the formation. Step 4: Draining fluids and extracting oil.

[0041] Implementation results: The well was fracturing on September 4, 2024. The fracturing fluid was conventional fracturing fluid plus 0.15% N,N,N,N',N',N' hexamethyl ethylenediamine dichloride gemini surfactant, with a flow rate of 8 m³ / min. 3 / minute, total fluid volume injected into the well: 1180 m³ 3 Add 110m of quartz sand proppant 3 After fracturing, the well is shut in or sealed.

[0042] It commenced production on October 24, 2024, and produced 14.34 cubic meters of liquid and 10.18 cubic meters of oil per day on October 30, with a water content of 29%. On April 23, 2025, the liquid production was 1.93 cubic meters, the oil production was 1.51 cubic meters, and the water content was 22%.

[0043] As of April 23, 2025, the cumulative liquid production was 589.68 m³. 3 Oil production: 442.26 m³ 3 Average daily liquid production: 3.24 m³ 3 Daily oil production 2.43 m 3 .

[0044] Adjacent comparison well: Fracturing and stimulation status of well D4158-5, new well fracturing.

[0045] Well D4158-5 and Well D4158-1 are adjacent wells in the same well site, and have the same fracturing layer.

[0046] Construction plan: Step 1: Prepare conventional oil displacement and percolation fracturing fluid (0.35% guar gum fracturing fluid + 0.15% percolation agent currently used in shale oilfields); Step 2: Perform hydraulic fracturing according to the construction design; Step 3: After fracturing, shut the well in for 50 days to allow the fracturing fluid to permeate and replace oil and water in the formation. Step 4: Draining fluids and extracting oil.

[0047] The well was fracturing on September 20, 2024, using conventional fracturing fluid with a displacement of 8 m³ / s. 3 / minute, total fluid volume injected into the well: 1250 m³ 3 Add 120 m of quartz sand proppant 3 After fracturing, the well is shut in or sealed.

[0048] It commenced production on November 9, 2024, and produced 13.2 cubic meters of liquid and 7.66 cubic meters of oil per day on October 28, with a water content of 42%. On May 8, 2025, the liquid production was 1.55 cubic meters, the oil production was 1.02 cubic meters, and the water content was 34%.

[0049] As of May 8, 2025, the cumulative liquid production was 499.56 m³. 3 Oil production 309.51 m 3 Average daily liquid production: 2.76 m³ 3 Daily oil production 1.71 m 3 .

[0050] The relevant data for Case 1 of this field implementation are shown in Table 14. After fracturing, percolation replacement, fluid drainage, and oil production in a new well, the 6-month oil production of conventional oil displacement percolation fracturing fluid and the 6-month oil production of fracturing fluid with the addition of 0.15% N,N,N,N',N',N' hexamethyl ethylenediamine dichloride gemini surfactant were 309.51 m³ / s, respectively. 3 and 442.26 m 3 In comparison, oil production increased by 132.75 m³. 3 The recovery rate increased by 42.9%.

[0051] Table 14 Comparison of recovery rate between the implemented well D4158-5 and the control well D4158-1

[0052] 4. On-site Implementation Case 2 D4508-1 old well repeated fracturing and renovation.

[0053] The well was perforated and fracturing and put into production on September 3, 2017, with 30m³ of sand added. 3 Sand ratio 35%, displacement 1.8 m³ 3 / min. Initial production of liquid was 6.7 cubic meters, and oil production was 2.01 cubic meters. 3 It contains 70% water.

[0054] The average daily liquid production in August 2024 was 0.664 m³. 3 Daily oil production is 0.31 m³ 3 The average water content is 53%. A decision was made to conduct repeated fracturing.

[0055] Construction plan: Step 1: Add 0.15% N,N,N,N',N',N' hexamethyl ethylenediamine dichloride gemini surfactant to the conventional fracturing fluid (0.35% guar gum fracturing fluid); Step 2: Perform hydraulic fracturing according to the construction design, using hydraulic fracturing to open old cracks, and adding temporary plugging agent midway to temporarily plug the old cracks; Step 3: Continue fracturing. After fracturing, shut the well in for 30 days to allow for oil-water permeation and replacement. Step 4: Draining fluids and extracting oil.

[0056] Implementation results: The well was fracturing on September 28, 2024. The fracturing fluid was conventional fracturing fluid plus 0.15% N,N,N,N',N',N' hexamethyl ethylenediamine dichloride gemini surfactant, with a flow rate of 4 m³ / s. 3 / minute, total fluid volume injected into the well: 410 m³ 3 Add 400 kg of solvent-based temporary plugging agent and 50 m³ of quartz sand proppant. 3 After fracturing, the well is shut in or sealed.

[0057] It commenced production on October 29, 2024, and produced 9.76 cubic meters of liquid and 3.22 cubic meters of oil per day on November 4, with a water content of 67%. On April 28, 2025, the liquid production was 1.89 cubic meters, the oil production was 1.21 cubic meters, and the water content was 36%.

[0058] As of April 28, 2025, the cumulative liquid production was 553.86 m³. 3 Oil production 320.37 m 3 Average daily liquid production: 3.06 m³ 3 Daily oil production 1.77 m 3 .

[0059] Nearby Comparison Well: Construction and Oil Production Status of Well D4508-3 Well D4508-3 and Well D4508-1 are adjacent wells in the same reservoir, with the same fracturing layer. This well was previously perforated and fracturing and put into production on August 11, 2017, with 25 m³ of sand added. 3 Sand ratio 32%, displacement 1.8 m³ 3 / min. Initial production of liquid was 8.1 cubic meters, and oil production was 2.57 cubic meters. 3 It contains 68% water.

[0060] The average daily liquid production in August 2024 was 0.925 m³. 3 Daily oil production is 0.37 m³ 3 The average water content is 60%. A decision was made to conduct repeated fracturing.

[0061] Construction plan: Step 1: Prepare conventional oil displacement and percolation fracturing fluid (0.35% guar gum fracturing fluid + 0.15% percolation agent currently used in shale oilfields); Step 2: Perform hydraulic fracturing according to the construction design, using hydraulic fracturing to open old cracks, and adding temporary plugging agent midway to temporarily plug the old cracks; Step 3: Continue fracturing. After fracturing, shut the well in for 30 days to allow for oil-water permeation and replacement. Step 4: Draining fluids and extracting oil.

[0062] The well was fracturing on September 13, 2024, using conventional fracturing fluid with a displacement of 4 m³ / s. 3 / minute, total fluid volume injected into the well: 360 m³ 3 Add 400 kg of solvent-based temporary plugging agent and 40 m³ of quartz sand proppant. 3 After fracturing, the well is shut in or sealed.

[0063] It commenced production on October 12, 2024, and produced 11.08 cubic meters of liquid and 2.79 cubic meters of oil per day on October 15, with a water content of 75%. On April 11, 2025, the liquid production was 1.14 cubic meters, the oil production was 0.88 cubic meters, and the water content was 23%.

[0064] As of April 11, 2025, the cumulative liquid production was 365.82 m³. 3 Oil production 260.26 m³ 3 Average daily liquid production: 2.01 m³ 3 Daily oil production 1.43 m 3 .

[0065] The relevant data for Case Study 2 are shown in Table 15. After repeated fracturing, percolation replacement, fluid drainage, and oil production in the old well, the 6-month oil production of conventional oil displacement percolation fracturing fluid and the 6-month oil production of fracturing fluid with the addition of 0.15% N,N,N,N',N',N' hexamethyl ethylenediamine dichloride gemini surfactant were 260.26 m³ / s.3 and 320.37 m 3 In comparison, oil production increased by 60.11 m³. 3 The harvest rate increased by 23%.

[0066] Table 15 Comparison of recovery rate between the implemented well D4508-1 and the control well D4508-3

[0067] 5. On-site Implementation Case 3 H73-3 well underwent repeated fracturing and renovation.

[0068] The well was perforated and fracturing and put into production on April 16, 2015, with 25 m³ of sand added. 3 Sand ratio 30%, displacement 2 m 3 / min. Initial production of liquid was 10.29 m³, and oil production was 2.88 m³. 3 It contains 72% water.

[0069] The average daily liquid production in July 2024 was 0.3 m³. 3 Average daily oil production: 0.0 m³ 3 The average water content is 100%. A decision was made to conduct repeated fracturing.

[0070] Construction plan: Step 1: Add 0.15% N,N,N,N',N',N' hexamethylpropanediammonium dichloride gemini surfactant to the conventional fracturing fluid (0.35% guar gum fracturing fluid); Step 2: Perform fracturing according to the construction design, using hydraulic fracturing to open old cracks, and adding temporary plugging agent midway to temporarily plug the old cracks; Step 3: Continue fracturing. After fracturing, shut the well in for 30 days to allow for oil-water permeation and replacement. Step 4: Draining fluids and extracting oil.

[0071] Implementation results: The well was fracturing on August 11, 2024. The fracturing fluid was conventional fracturing fluid plus 0.15% N,N,N,N',N',N' hexamethylpropanediammonium dichloride gemini surfactant, with a flow rate of 3.5 m³ / min. 3 / minute, total fluid volume injected into the well: 370 m³ 3 Add 400 kg of solvent-based temporary plugging agent and 40 m³ of quartz sand proppant. 3 After fracturing, the well is shut in or sealed.

[0072] It commenced production on September 10, 2024, and produced 16.26 cubic meters of liquid and 3.74 cubic meters of oil per day on September 15, with a water content of 77%. On March 9, 2025, the liquid production was 2.83 cubic meters, the oil production was 1.87 cubic meters, and the water content was 34%.

[0073] As of March 9, 2025, the cumulative liquid production was 937.58 m³. 3 Oil production 515.85 m 3 Average daily liquid production: 5.18 m³ 3 Daily oil production 2.85 m 3 .

[0074] Adjacent comparison well: H73-2 well, an old well, was repeatedly fracturing with conventional fracturing fluid.

[0075] Wells H73-2 and H73-3 are adjacent wells in the same reservoir, with the same fracturing layer. This well was previously perforated and fracturing and put into production on March 11, 2015, with 25 m³ of sand added. 3 Sand ratio 30%, displacement 2 m 3 / min. Initial production of liquid was 8.53 m³, and oil production was 3.41 m³. 3 It contains 60% water.

[0076] The average daily liquid production in July 2024 was 0.7 m³. 3 Daily oil production is 0.1 m³ 3 The average water content is 86%. A decision was made to conduct repeated fracturing.

[0077] Construction plan: Step 1: Prepare conventional oil displacement and percolation fracturing fluid (0.35% guar gum fracturing fluid + 0.15% percolation agent currently used in shale oilfields); Step 2: Perform fracturing according to the construction design, using hydraulic fracturing to open old cracks, and adding temporary plugging agent midway to temporarily plug the old cracks; Step 3: Continue fracturing. After fracturing, shut the well in for 30 days to allow for oil-water permeation and replacement. Step 4: Draining fluids and extracting oil.

[0078] The well was fracturing on August 21, 2024, using conventional fracturing fluid at a displacement of 3.5 m³. 3 / minute, total fluid volume injected into the well: 380 m³ 3 Add 400 kg of solvent-based temporary plugging agent and 40 m³ of quartz sand proppant. 3 After fracturing, the well is shut in or sealed.

[0079] It commenced production on September 20, 2024, producing 11.11 cubic meters of liquid and 3.11 cubic meters of oil per day on September 14, with a water content of 72%. On March 19, 2025, the liquid production was 1.89 cubic meters, the oil production was 1.36 cubic meters, and the water content was 28%.

[0080] As of March 19, 2025, the cumulative liquid production was 602.73 m³. 3 Oil production 421.73 m3 Average daily liquid production: 3.33 m³ 3 Daily oil production 2.33 m 3 .

[0081] The relevant data for Case 3 in this field are shown in Table 16. After repeated fracturing, percolation replacement, fluid drainage, and oil production of the old well, the 6-month oil production of conventional oil displacement percolation fracturing fluid and the 6-month oil production of fracturing fluid with the addition of 0.15% N,N,N,N',N',N' hexamethylmalonium dichloride gemini surfactant were 421.73 m³ / s. 3 and 515.85 m 3 In comparison, oil production increased by 94.12 m³. 3 The recovery rate increased by 22.3%.

[0082] Table 16 Comparison of recovery rate between the implemented well H73-3 and the control well H73-2

[0083] 6. On-site Implementation Case 4 H66-5 well is an old well that is being enhanced for seepage-based oil recovery.

[0084] The well was perforated and fracturing and put into production on October 22, 2013, with 30 m³ of sand added. 3 Sand ratio 30%, discharge volume 1.5 m³ 3 / min. Initial production of liquid was 15.06 m³, and oil production was 5.12 m³. 3 It contains 66% water.

[0085] The average daily liquid production in October 2023 was 0.8 m³. 3 Daily oil production is 0.6 m³ 3 The average water content is 25%. It was decided to inject permeate into the formation to replenish formation energy and improve production and recovery rate through oil-water displacement.

[0086] Construction plan: Step 1: Prepare the Gemini surfactant permeation solution with the following ratio: water + 0.3% N,N,N,N',N',N' hexamethylpropanediammonium dichloride Gemini surfactant; Step 2: According to the construction design, at a depth of 0.5 m 3 A low-volume injection of 600 m³ / min into the formation. 3 Gemini surfactant permeation solution; Step 3: After the injection is completed, the well is shut in for 40 days for oil-water permeation and replacement. Step 4: Draining fluids and extracting oil.

[0087] Implementation results: The well was constructed on November 11-12, 2023, and put into production on December 21, 2023. On December 26, it produced 8.11 cubic meters of fluid, 2.27 cubic meters of oil per day, and had a water cut of 72%. On June 20, 2024, the liquid production was 1.57 cubic meters, the oil production was 1.13 cubic meters, and the water content was 28%.

[0088] As of June 20, 2024, the cumulative liquid production was 471.38 m³. 3 Oil production 329.42 m 3 Average daily liquid production: 2.59 m³ 3 Daily oil production 1.81 m 3 .

[0089] Adjacent comparison well: Well H65-3 uses a permeabilizer to enhance permeabilization and oil production in conventional shale oilfields.

[0090] Wells H65-3 and H66-5 are adjacent wells and have the same oil production layer.

[0091] The well was perforated and fracturing and put into production on March 17, 2014, with 30 m³ of sand added. 3 Sand ratio 28%, displacement 1.5 m³ 3 / min. Initial production of liquid was 16.11 cubic meters, and oil production was 5.63 m³. 3 It contains 65.1% water.

[0092] The average daily liquid production in October 2023 was 0.91 m³. 3 Daily oil production is 0.57 m³ 3 The average water content is 40%. It was decided to inject an adsorbent into the formation to replenish formation energy and improve production and recovery rate through oil-water displacement.

[0093] Construction plan: Step 1: Prepare a conventional shale oilfield permeation fluid with the following ratio: water + 0.3% conventional shale oilfield permeation agent; Step 2: According to the construction design, at a depth of 0.5 m 3 A low-volume injection of 600 m³ / min into the formation. 3 Exudate; Step 3: After the injection is completed, the well is shut in for 40 days for oil-water permeation and replacement. Step 4: Draining fluids and extracting oil.

[0094] Implementation results: The well was constructed on November 3-4, 2023, and put into production on December 13, 2023. On December 17, it produced 7.54 cubic meters of fluid, with a daily oil production of 1.81 cubic meters and a water cut of 76%. On June 12, 2024, the liquid production was 1.03 cubic meters, the oil production was 0.81 cubic meters, and the water content was 21.4%.

[0095] As of June 12, 2024, the cumulative liquid production was 291.2 m³. 3 Oil production 223.86 m³ 3 Average daily liquid production: 1.6 m³ 3 Daily oil production 1.23 m 3 .

[0096] The relevant data for Case 4 in this field are shown in Table 17. After the old well was enhanced with percolation replacement, fluid drainage, and oil production, the 6-month oil production of the conventional oil displacement percolation fluid and the 6-month oil production of the percolation fluid after adding 0.3% N,N,N,N',N',N' hexamethylmalonium dichloride gemini surfactant were 223.86 m³ / s. 3 and 329.42 m 3 In comparison, oil production increased by 105.56 m³. 3 The harvest rate increased by 47.15%.

[0097] Table 17 Comparison of recovery rate between the implemented well H66-5 and the control well H65-3

Claims

1. An oil displacement agent containing a cationic gemini surfactant, comprising a cationic gemini surfactant, suitable for unconventional oil reservoirs, characterized in that: The cationic gemini surfactant includes a bisquaternary ammonium salt type gemini surfactant. The bisquaternary ammonium salt type gemini surfactant is a novel surfactant formed by chemically linking two or more identical or nearly identical surfactant monomers together with a linking group near or around the hydrophilic head group. This surfactant is more easily adsorbed on the gas / liquid surface of sandstone, thereby more effectively reducing the surface tension of the aqueous solution, enhancing adsorption and spreading on the sandstone surface, reducing the thickness of the water film on the rock surface, and enhancing reverse osmosis.

2. The oil displacement agent containing cationic gemini surfactant and its application method according to claim 1, characterized in that: The bisquaternary ammonium salt type gemini surfactant is N,N,N,N',N',N' hexamethylethylenediammonium dichloride or N,N,N,N',N',N' hexamethylpropanediammonium dichloride; having the structure shown in Formula I or Formula II: Formula I Formula II The bis-quaternary ammonium salt molecule of this application carries two positive charges, linked by a short carbon chain (ethyl or propyl); it has stronger adsorption capacity and better surface activity than mono-quaternary ammonium salt.

3. The oil displacement agent containing cationic gemini surfactant and its application method according to claim 1, characterized in that: The content of the bisquaternary ammonium salt type gemini surfactant is 0.01%~1% (mass ratio).

4. The oil displacement agent containing cationic gemini surfactant and its application method according to claim 3, characterized in that: The content of the bisquaternary ammonium salt type gemini surfactant is 0.1%~0.3% (by mass).

5. The oil displacement agent containing cationic gemini surfactant and its application method according to claim 1, characterized in that: The total number of carbon atoms in the bisquaternary ammonium salt type gemini surfactant molecule is 8 to 10.

6. The oil displacement agent containing cationic gemini surfactant and its application method according to claim 1, characterized in that: The unconventional reservoirs have a permeability of ≤1.0 mD, including ultra-low permeability reservoirs, tight reservoirs, or shale reservoirs.

7. The method of applying the oil displacement agent containing a cationic gemini surfactant according to any one of claims 1-6, comprising the following steps: S1 Preparation: According to the net mass concentration ratio of cationic gemini surfactant in the wellbore working fluid, add cationic gemini surfactant to the wellbore working fluid using a metering pump; S2 Injection: The working fluid containing the cationic gemini surfactant prepared in step S1 is injected into the unconventional reservoir; S3 Permeation: After injection, shut the well for 30-60 days for oil-water permeation replacement; S4 oil recovery: drainage and oil recovery.

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