A high-efficiency oil displacement system with polystyrene surface salt composite exhibiting unique in-situ emulsification behavior and its application

Abstract

This invention discloses a high-efficiency oil displacement system with polystyrene surface salt composite exhibiting specific in-situ emulsification behavior and its application. In this oil displacement system, the concentration of the associating polymer is 1000-3000 g / L. The surfactant concentration was 0.2-0.4%; the salt concentration was 1.2-1.8%; and the remainder was water. This polysaturated salt flooding system exhibits unique emulsification behavior: it forms a strong, high-viscosity emulsion with the oil phase under high water cut conditions, and a low-viscosity, weakly emulsion or even no emulsification under low water cut conditions. It can form a stable, high-flow-resistance emulsion with crude oil in situ under high water cut conditions in porous, high-permeability channels; and form a low-viscosity, weakly emulsion or even no emulsification under high oil cut conditions in low-permeability areas, resulting in low flow resistance under high oil cut conditions. It has stronger heterogeneity control capabilities, higher sweep and washout efficiency in low-permeability areas, and significantly increases high and low-permeability oil recovery rates. It is expected to achieve intelligent in-situ emulsification flooding in high-water-cut, highly heterogeneous reservoirs, significantly increasing sweep efficiency and washout efficiency, thereby greatly improving oil recovery rates.

Description

Technical Field

[0001] This invention relates to the field of oilfield chemical enhanced oil recovery technology, specifically to a high-efficiency oil displacement system with unique in-situ emulsification behavior and its application. Background Technology

[0002] In reservoirs with high heterogeneity, existing chemical flooding systems can displace and recover most of the oil in high-permeability zones, while recovery rates in relatively low-permeability zones are low or even unusable. This means the displacing fluid preferentially reaches high-permeability reservoirs, with minimal or no reach in relatively low-permeability zones, resulting in ineffective circulation of the displacing fluid. This poses a significant challenge to further improving the recovery rate of existing chemical flooding systems. To address this issue, moderating the flooding system in conjunction with techniques to expand sweep efficiency and enhance recovery has become a research hotspot in recent years. In-situ emulsification of the formation crude oil for moderating the flooding system is a key research area.

[0003] With long-term water injection development of oil reservoirs, low oil saturation in high-permeability zones and high oil saturation in low-permeability zones are inevitable. Existing in-situ emulsification flooding systems tend to form high-viscosity water-in-oil emulsions at higher oil saturation levels and low-viscosity oil-in-water emulsions at lower oil levels. Sepideh Palizdan demonstrated using a glass etching model that when high-acid-value crude oil and brine are injected in equal volumes, ultra-viscosity W / O emulsions (>500 mPa·s) are easily formed in situ, leading to a sharp increase in injection pressure, which is detrimental to improving EOR (oil-to-oil ratio). Mostafa Borji used CT scanning to demonstrate the comparability of emulsification in test tubes and core samples, finding that under high oil-cut conditions, emulsion droplets tend to form a continuous oil phase in porous media, hindering the flow of the water phase. Although the in-situ emulsification behavior of the above-mentioned flooding systems is beneficial for oil displacement, it further exacerbates the heterogeneity of displacement in high-water-cut, high-permeability zones and low-water-cut, low-permeability zones, making it difficult to achieve ideal balanced displacement, and the problem of ineffective circulation of the displacement fluid may be more prominent. Ideally, an in-situ emulsification flooding system should achieve high-viscosity in-situ emulsification of formation crude oil under high permeability and high water cut conditions, while exhibiting no emulsification or low-viscosity emulsification under low permeability and low water cut conditions. Wanfen Pu developed a composite emulsification system applicable to high-temperature, high-salinity, and acidic reservoirs. This system can change the wettability of rocks from oil-wet to water-wet, achieving maximum emulsion viscosity at a water cut of 70%, thus realizing viscosity-enhancing effects at different oil-water ratios. Subsequent displacement experiments have demonstrated that the in-situ formed emulsion can stabilize the displacement front and improve sweep efficiency.

[0004] Maintaining the kinetic stability of polymeric emulsions with low internal phase and high external phase is a research challenge. To address this issue, this invention develops an associative polymer / surfactant / salt flooding system. This system can achieve high-viscosity emulsification with crude oil at high water cuts, and non-emulsification or low-viscosity emulsification at low water cuts. This profile control system can simultaneously achieve the dual functions of "profile control in high-permeability, high-water-cut conditions and displacement in low-permeability, low-water-cut conditions" in heterogeneous parallel sand-filled tubular flooding experiments, providing a new technical strategy and pathway for significantly improving oil recovery through chemical flooding in high-water-cut heterogeneous reservoirs after waterflooding. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a high-efficiency oil displacement system with specific in-situ emulsification behavior, consisting of a polystyrene composite and its application. In this oil displacement system, the concentration of the associating polymer is 1000-3000 mg / L. The surfactant concentration was 0.2-0.4%; the salt concentration was 1.2-1.8%; and the remainder was water. This polysaturated salt flooding system exhibits unique emulsification behavior: it forms a strong, high-viscosity emulsion with the oil phase under high water cut conditions, and a low-viscosity, weakly emulsion or even no emulsification under low water cut conditions. It can form a stable, high-flow-resistance emulsion in situ with crude oil under high water cut conditions in porous, high-permeability channels; and form a low-viscosity, weakly emulsion or even no emulsification under high oil cut conditions in low-permeability areas, resulting in low flow resistance under high oil cut conditions. It has stronger heterogeneity control capabilities, higher sweep and washout efficiency in low-permeability areas, and significantly increases high and low-permeability oil recovery rates. It is expected to achieve intelligent in-situ emulsification flooding in high-water-cut, highly heterogeneous reservoirs, significantly increasing sweep efficiency and washout efficiency, thereby greatly improving oil recovery rates.

[0006] To achieve the above technical effects, the following technical solution is adopted:

[0007] A high-efficiency oil displacement system with polystyrene surface salt composite exhibiting unique in-situ emulsification behavior, the formulation of which is as follows:

[0008] The concentration of the associative polymer was 1000-3000 mg / L; the concentration of the surfactant was 0.2-0.4%; the concentration of the salt was 1.2-1.8%; and the solvent was water.

[0009] Furthermore, the formulation of the polystyrene composite high-efficiency oil displacement system is as follows:

[0010] The concentration of the associative polymer was 1860 mg / L; the concentration of the surfactant was 0.3%; the concentration of the salt was 1.6%; and the solvent was water.

[0011] Furthermore, the molecular structure of the associative polymer is as follows:

[0012] ;

[0013] Where x, y, z, s, t and n are the number of repeating units in the molecular chain, and R is a methyl group.

[0014] Furthermore, the method for preparing the associative polymer is as follows:

[0015] Acrylamide (AM), 2-acrylamido-2-methylpropanesulfonic acid (AMPS), associating monomer (DH), and emulsifying monomer (RH) were added at a molar ratio of 100:2-4:0.5-1.5:1-2. A mixed solution with a total monomer concentration of 20-35% was prepared using ultrapure water. Disodium ethylenediaminetetraacetate (EDTA) was added to the reaction vessel at a ratio of 0.005%-0.01% of the total mass of the reaction system, and sodium formate was added at a ratio of 0.03%-0.05% of the total mass of the reaction system. The mixture was stirred thoroughly. Next, the pH of the system was adjusted to 7.0-7.5 by adding sodium hydroxide, and then the mixture was cooled to 0°C. A composite initiator prepared by ammonium persulfate, sodium bisulfite and hydrogen peroxide in a molar ratio of 1:1:0.3 was added to the mixture for adiabatic polymerization for 7-9 hours. The amount of the composite initiator added was 0.01%-0.02% of the mass of the reaction system. The resulting colloid was hydrolyzed with sodium hydroxide, then dried, pulverized and sieved to obtain a white polymer powder, which is the associative polymer.

[0016] The molecular structural formula of the associating monomer DH is:

[0017] ;

[0018] The molecular structural formula of the emulsifying monomer RH is:

[0019] ;

[0020] Where n is the number of repeating units, and R is a methyl group;

[0021] Furthermore, the molecular weight of the associative polymer is 8-12 million.

[0022] Furthermore, the surfactant is a novel petroleum sulfonate with a purity of 50%, manufactured by Daqing Petrochemical; its product number is QY-0903.

[0023] Furthermore, the salt is one or more of sodium chloride, sodium sulfate, potassium chloride, and potassium sulfate.

[0024] A method for preparing a high-efficiency oil displacement system with polystyrene surface salt composite exhibiting specific in-situ emulsification behavior, specifically as follows:

[0025] Step (1): Add the associative polymer evenly to water and stir continuously to prepare the polymer mother liquor;

[0026] Step (2): After the polymer mother liquor is prepared, it is subjected to aging treatment.

[0027] Step (3): Mix the fully matured polymer mother liquor with the salt solution and surfactant, and dilute the compound with water to the desired target concentration;

[0028] Step (4): The compound is continuously stirred to obtain a polymer / surfactant / salt ternary solution, which is a high-efficiency oil displacement system with specific in-situ emulsification behavior of polymer-surfactant-salt composite.

[0029] Furthermore, the concentration of the polymer mother liquor is 4000-5000 mg / L; the concentration of the salt solution is 10%-30%.

[0030] Furthermore, the oil displacement system is used in the fields of intelligent in-situ emulsification and regulation of high water-cut and highly heterogeneous reservoirs, as well as in the field of enhanced oil recovery in heterogeneous reservoirs.

[0031] The beneficial effects of this invention are as follows:

[0032] This invention discloses a high-efficiency oil displacement system with polystyrene surface salt composite exhibiting specific in-situ emulsification behavior and its application. In this oil displacement system, the concentration of the associating polymer is 1000-3000 g / L. The surfactant concentration was 0.2-0.4%; the salt concentration was 1.2-1.8%; and the remainder was water. This polysaturated salt flooding system exhibits unique emulsification behavior: it forms a strong, high-viscosity emulsion with the oil phase under high water cut conditions, and a low-viscosity, weakly emulsion or even no emulsification under low water cut conditions. It can form a stable, high-flow-resistance emulsion in situ with crude oil under high water cut conditions in porous, high-permeability channels; and form a low-viscosity, weakly emulsion or even no emulsification under high oil cut conditions in low-permeability areas, resulting in low flow resistance under high oil cut conditions. It has stronger heterogeneity control capabilities, higher sweep and washout efficiency in low-permeability areas, and significantly increases high and low-permeability oil recovery rates. It is expected to achieve intelligent in-situ emulsification flooding in high-water-cut, highly heterogeneous reservoirs, significantly increasing sweep efficiency and washout efficiency, thereby greatly improving oil recovery rates.

[0033] This system can achieve high-viscosity emulsification with crude oil at high water cuts, and non-emulsification or low-viscosity emulsification at low water cuts. In heterogeneous parallel sand-filled tubular oil displacement experiments, this profile control system can simultaneously achieve the dual functions of "profile control in high-permeability and high-water-cut conditions and displacement in low-permeability and low-water-cut conditions," providing a new technical strategy and path for significantly improving oil recovery through chemical flooding in high-water-cut heterogeneous reservoirs after waterflooding. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1This is a schematic diagram of the molecular structure of the associative polymer described in the embodiments of the present invention;

[0036] Figure 2 This is a schematic diagram of the flat sand-filled model according to an embodiment of the present invention;

[0037] Figure 3 This is a schematic diagram of the displacement device according to an embodiment of the present invention;

[0038] Figure 4 Viscosity diagrams of APSS and PSS of polymers with different concentrations as described in the embodiments of the present invention;

[0039] Figure 5 The figure shows a comparison of the emulsification of a novel petroleum sulfonate surfactant at a concentration of 0.3% under different oil-water ratios over 1-6 hours. The oil-water ratios in the graduated cylinder from left to right are (9:1), (8:2), (7:3), (6:4), (3:7), (2:8), and (1:9).

[0040] Figure 6 The graph shows the emulsification of sodium chloride at a concentration of 1.6% at different oil-water ratios over 1-6 hours. The water-oil ratios in the graduated cylinder from left to right are (9:1), (8:2), (7:3), (6:4), (3:7), (2:8), and (1:9).

[0041] Figure 7 The figure shows a comparison of the emulsification of a novel petroleum sulfonate surfactant with a concentration of 0.3% and a sodium chloride concentration of 1.6% at different oil-water ratios over 1-6 hours. The water-oil ratios in the graduated cylinder from left to right in the figure are (9:1), (8:2), (7:3), (6:4), (3:7), (2:8), and (1:9).

[0042] Figure 8 The figure shows a comparison of emulsification at different oil-water ratios over 1-6 hours when the concentration of the associative polymer alone is 1860 mg / L. The oil-water ratios in the graduated cylinders from left to right are (9:1), (8:2), (7:3), (6:4), (3:7), (2:8), and (1:9).

[0043] Figure 9 The figure shows a comparison of emulsification at different oil-water ratios over 1-6 hours when the concentration of the associative polymer is 1860 mg / L and the sodium chloride concentration is 1.6%. The oil-water ratios in the graduated cylinder from left to right are (9:1), (8:2), (7:3), (6:4), (3:7), (2:8) and (1:9).

[0044] Figure 10The figure shows a comparison of emulsification at different oil-water ratios over 1-6 hours when the concentration of the associative polymer is 1860 mg / L and the concentration of the novel petroleum sulfonate surfactant is 0.3%. The oil-water ratios in the graduated cylinder from left to right are (9:1), (8:2), (7:3), (6:4), (3:7), (2:8), and (1:9).

[0045] Figure 11 The figure shows a comparison of emulsification at different oil-water ratios over 1-6 hours when the concentration of the associative polymer is 1860 mg / L, the concentration of the surfactant SDS is 0.3%, and the concentration of sodium chloride is 1.6%. The water-oil ratios in the graduated cylinder from left to right in the figure are (9:1), (8:2), (7:3), (6:4), (3:7), (2:8), and (1:9).

[0046] Figure 12 The figure shows a comparison of emulsification at different oil-water ratios over 1-6 hours when the concentration of the associative polymer is 1860 mg / L, the concentration of the novel petroleum sulfonate surfactant is 0.3%, and the concentration of sodium chloride is 1.6% (APSS). The water-oil ratios in the graduated cylinder from left to right in the figure are (9:1), (8:2), (7:3), (6:4), (3:7), (2:8), and (1:9).

[0047] Figure 13 The figure shows the emulsification of HPAM polymer concentration of 2000 mg / L, surfactant concentration of novel petroleum sulfonate of 0.3%, and sodium chloride concentration of 1.6% (PSS) at different oil-water ratios over 1-6 hours. The water-oil ratios in the graduated cylinder from left to right in the figure are (9:1), (8:2), (7:3), (6:4), (3:7), (2:8), and (1:9).

[0048] Figure 14 The figure shows a comparison of the emulsification of a novel petroleum sulfonate surfactant at a concentration of 0.3% under different oil-water ratios over 24 hours. The water-oil ratios in the graduated cylinder from left to right are (9:1), (8:2), (7:3), (6:4), (3:7), (2:8), and (1:9).

[0049] Figure 15 The figure shows a comparison of the emulsification of sodium chloride at different oil-water ratios over 24 hours when the concentration of sodium chloride alone is 1.6%. The water-oil ratios in the graduated cylinder from left to right in the figure are (9:1), (8:2), (7:3), (6:4), (3:7), (2:8) and (1:9).

[0050] Figure 16The figure shows a comparison of the emulsification of a novel petroleum sulfonate surfactant with a concentration of 0.3% and a sodium chloride concentration of 1.6% over 24 hours at different oil-water ratios. The water-oil ratios in the graduated cylinder from left to right in the figure are (9:1), (8:2), (7:3), (6:4), (3:7), (2:8), and (1:9).

[0051] Figure 17 The figure shows a comparison of the emulsification of the polymer at different oil-water ratios over 24 hours when the concentration of the polymer alone is 1860 mg / L. The oil-water ratios in the graduated cylinder from left to right in the figure are (9:1), (8:2), (7:3), (6:4), (3:7), (2:8) and (1:9).

[0052] Figure 18 The figure shows a comparison of the emulsification of the associative polymer at a concentration of 1860 mg / L and sodium chloride at a concentration of 1.6% over 24 hours at different oil-water ratios. The water-oil ratios in the graduated cylinder from left to right in the figure are (9:1), (8:2), (7:3), (6:4), (3:7), (2:8) and (1:9).

[0053] Figure 19 The figure shows a comparison of the emulsification of a novel petroleum sulfonate surfactant at different oil-water ratios over 24 hours when the concentration of the associated polymer is 1860 mg / L and the concentration of the surfactant is 0.3%. The water-oil ratios in the graduated cylinder from left to right in the figure are (9:1), (8:2), (7:3), (6:4), (3:7), (2:8) and (1:9).

[0054] Figure 20 The figure shows a comparison of the emulsification of the associative polymer at a concentration of 1860 mg / L, the surfactant SDS at a concentration of 0.3%, and the sodium chloride at a concentration of 1.6% over 24 hours at different oil-water ratios. The oil-water ratios in the graduated cylinder from left to right in the figure are (9:1), (8:2), (7:3), (6:4), (3:7), (2:8), and (1:9).

[0055] Figure 21 The figure shows a comparison of the emulsification of the associative polymer concentration of 1860 mg / L, the concentration of the novel petroleum sulfonate surfactant of 0.3%, and the concentration of sodium chloride of 1.6% (APSS) at different oil-water ratios over 24 hours. The water-oil ratios in the graduated cylinder from left to right in the figure are (9:1), (8:2), (7:3), (6:4), (3:7), (2:8), and (1:9).

[0056] Figure 22The figure shows a comparison of the emulsification of HPAM polymer concentration (2000 mg / L), novel petroleum sulfonate surfactant concentration (0.3%), and sodium chloride concentration (1.6%) under different oil-water ratios over 24 hours. The water-oil ratios in the graduated cylinder from left to right in the figure are (9:1), (8:2), (7:3), (6:4), (3:7), (2:8), and (1:9).

[0057] Figure 23 Comparison of emulsified viscosity over 24 hours at different oil-water ratios when the concentration of the novel petroleum sulfonate surfactant alone is 0.3%.

[0058] Figure 24 A comparison of emulsified viscosity over 24 hours at different oil-water ratios when the sodium chloride concentration of the salt alone is 1.6%.

[0059] Figure 25 Comparison of emulsified viscosity over 24 hours for a novel petroleum sulfonate surfactant with a concentration of 0.3% and a sodium chloride concentration of 1.6% at different oil-water ratios;

[0060] Figure 26 A comparison of emulsified viscosity over 24 hours at different oil-water ratios when the concentration of the associative polymer alone is 1860 mg / L.

[0061] Figure 27 A comparison of emulsified viscosity over 24 hours at different oil-water ratios when the associative polymer concentration is 1860 mg / L and the sodium chloride concentration is 1.6%.

[0062] Figure 28 A comparison of emulsified viscosity over 24 hours at different oil-water ratios when the concentration of the associative polymer is 1860 mg / L and the concentration of the novel petroleum sulfonate surfactant is 0.3%.

[0063] Figure 29 The image shows a comparison of the emulsified viscosity over 24 hours at different oil-water ratios when the associative polymer concentration is 1860 mg / L, the surfactant SDS concentration is 0.3%, and the sodium chloride concentration is 1.6%.

[0064] Figure 30 Comparison of emulsified viscosity (APSS) over 24 hours at different oil-water ratios when the concentration of the associative polymer is 1860 mg / L, the concentration of the novel petroleum sulfonate surfactant is 0.3%, and the concentration of sodium chloride is 1.6%.

[0065] Figure 31 The figure shows a comparison of the emulsified viscosity over 24 hours when the HPAM polymer concentration is 2000 mg / L, the surfactant novel petroleum sulfonate concentration is 0.3%, and the sodium chloride concentration is 1.6% (PSS) at different oil-water ratios.

[0066] Figure 32 APSS emulsion stress scan;

[0067] Figure 33 Stress scan of PSS emulsion;

[0068] Figure 34 Frequency sweep curves of emulsions formed by simulated oil emulsification in the APSS system with different oil-water ratios;

[0069] Figure 35 Frequency sweep curves of emulsions formed by simulated oil emulsification in the PSS system with different oil-water ratios;

[0070] Figure 36 The diagrams show the microscopic seepage characteristics of APSS and PSS at 3000 md. Figure 36 a is the pressure diagram of the APSS pressure measurement point; Figure 36 b is the pressure diagram at the PSS pressure measurement point; Figure 36 c is the APSS pressure gradient diagram; Figure 36 d represents the PSS pressure gradient diagram;

[0071] Figure 37 The diagrams show the microscopic seepage characteristics of APSS and PSS at 1400 md, where... Figure 36 a is the pressure diagram of the APSS pressure measurement point; Figure 36 b is the pressure diagram at the PSS pressure measurement point; Figure 36 c is the APSS pressure gradient diagram; Figure 36 d represents the PSS pressure gradient diagram;

[0072] Figure 38 The diagrams show the microscopic seepage characteristics of APSS and PSS at 580 md. Figure 36 a is the pressure diagram of the APSS pressure measurement point; Figure 36 b is the pressure diagram at the PSS pressure measurement point; Figure 36 c is the APSS pressure gradient diagram; Figure 36 d represents the PSS pressure gradient diagram;

[0073] Figure 39 The diagram shows the pressure drop, shunt rate, and recovery rate of the fixed-injection APSS slug under the Type 1 range model.

[0074] Figure 40 The diagram shows the pressure drop, shunt rate, and recovery rate of the fixed-injection APSS slug under the Type 2 range model.

[0075] Figure 41 The diagram shows the pressure drop, shunt rate, and recovery rate of the fixed-injection APSS slug under the Type 3 range model.

[0076] Figure 42 High and low osmotic recovery rates for fixed-injection APSS slugs under the Type 1 range model;

[0077] Figure 43 High and low osmotic recovery rates for fixed-injection APSS slugs under the Type 2 range model;

[0078] Figure 44 High and low osmotic recovery rates for fixed-injection APSS slugs under the Type 3 range model;

[0079] Figure 45 The diagram shows the pressure drop, shunt rate, and recovery rate of the fixed-injection PSS slug under the Type 1 range model.

[0080] Figure 46 Figures showing pressure drop, shunt rate, and recovery rate of a fixed-injection PSS slug under the Type 2 range model;

[0081] Figure 47 Figures showing pressure drop, shunt rate, and recovery rate of a fixed-injection PSS slug under the Type 3 range model;

[0082] Figure 48 The high and low osmotic recovery rates of a fixed-injection PSS slug under the Type 1 range model;

[0083] Figure 49 High and low osmotic recovery rates for a fixed-injection PSS slug under the Type 2 range model;

[0084] Figure 50 This is a graph showing the high and low osmotic recovery rates of a fixed-injection PSS slug under the Type 3 range model. Detailed Implementation

[0085] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0086] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments of the present invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, and / or combinations thereof.

[0087] Example 1:

[0088] Experimental preparation:

[0089] 1. Medicines and Instruments

[0090] Partially hydrolyzed polyacrylamide (HPAM), molecular weight 10 million, manufactured by Daqing Petrochemical Company; Associative polymer (AP), self-made, molecular weight 10 million, polymer molecular structure as follows. Figure 1 As shown. Novel petroleum sulfonate, 50% purity, Daqing Refining & Chemical Co., Ltd. (commodity number QY-0903); NaCl (purity > 99%), Chengdu Kelong; prepared into a 20% solution; the oil used was prepared from Daqing dehydrated crude oil and kerosene, with a viscosity of 10 mPa·s at 45℃.

[0091] MCR301 Anton-Paar rheometer, Anton-Paar GmbH, Germany; Laser confocal scanning microscope (CLSM), Leica STELLARIS 5, Germany; DV-Ⅲ viscometer, Brookfield Instruments, USA; HJ-6 multi-head magnetic stirrer, Jiangsu Kexi Instrument Co., Ltd.; DGH-9240 electric heating drying oven, Shanghai Yiheng Scientific Instrument Co., Ltd.; S-90C constant speed stirrer, Shanghai Shensheng Biotechnology Co., Ltd.; TX-500C rotary drop interfacial tensiometer, Beijing Pinzhi Chuangsi Precision Instrument Co., Ltd.; Sand packing tube, Chengdu Core Company, Sichuan; DQT-2 multifunctional core displacement device, Haian Petroleum Research Instrument Co., Ltd.; Constant temperature oscillator, Shanghai Yuying Instrument Co., Ltd.

[0092] To closely approximate the actual situation on site, the in-situ emulsification flooding system was prepared using the process of preparing diluted wastewater from oilfield production wastewater. Specifically, wastewater simulating water 1 was used to prepare the polymer mother liquor, and simulated water 2 and other chemical agents were used to prepare the required system. The specific composition is shown in Table 1.

[0093] Table 1. Simulated water composition table

[0094]

[0095] The preparation process of the in-situ emulsified oil displacement system is as follows:

[0096] (1) Using simulated water 1, stir continuously for 2 hours at a speed of 400 rpm to prepare a polymer mother liquor with a concentration of 5000 ppm.

[0097] (2) After preparation, the polymer mother liquor is aged and left to stand for more than 12 hours for later use.

[0098] (3) Mix the fully matured polymer mother liquor with the aforementioned 20% NaCl solution and the novel petroleum sulfonate surfactant, and dilute the compound with simulated water 2 to the required target concentration solution.

[0099] (4) The mixture was stirred continuously at 400 rpm for 2 hours and kept at 45°C to obtain a polymer / surfactant / salt ternary solution. The specific composition of this in-situ emulsification displacement system is shown in Table 3.

[0100] Specifically, the polymer / surfactant / salt solution in-situ emulsification oil displacement system containing associative polymers (AP) is named APSS; the polymer / surfactant / salt solution in-situ emulsification oil displacement system containing polyacrylamide (HPAM) is named PSS.

[0101] 2. Interface tension test

[0102] The oil-water interfacial tension was measured using the rotating drop method. In the experiment, the oil phase was simulated crude oil, and the water phase was a mono-, binary, or ternary system solution composed of polymers, surfactants, and salts. The oil-water interfacial tension was measured using a TX-500C rotating drop interfacial tension meter at a test temperature of 45℃.

[0103] 3. Solution viscosity and emulsion emulsion viscosity test

[0104] Viscosity test: The prepared mono-, binary, or ternary system solution composed of polymer, surfactant, and salt was tested on a DV-3 viscometer at a viscosity of 7.34 s⁻¹. -1 The viscosity was tested by shear rate at a temperature of 45℃.

[0105] Emulsion viscosity test: Add simulated crude oil and a mono-, binary, or ternary system solution composed of polymer, surfactant, and salt to a 50ml colorimetric tube according to different oil / water ratios. Seal the port and emulsify at a constant temperature of 45℃ for 24 hours in a constant temperature shaker. Immediately remove the tube and test the emulsion viscosity in a viscometer.

[0106] 4. Emulsification Behavior Analysis

[0107] A mono-, binary, or ternary system solution composed of polymers, surfactants, and salts was mixed with simulated crude oil at different oil-water ratios and emulsified in a constant-temperature shaker at 45°C for 24 hours. The mixture was then removed and allowed to stand for different periods of time to analyze the emulsification behavior.

[0108] 5. Emulsion rheological behavior

[0109] Simulated crude oil with different oil-water ratios was heated in a water bath at 45°C for 2 hours with a ternary emulsion displacement system. The mixture was then emulsified at a constant speed of 400 rpm for 30 minutes to obtain APSS or PSS emulsions with different oil-water ratios. The rheological behavior of the emulsions was immediately tested using a Physica MCR301 advanced rheometer. The tests were conducted using a CP75-1 cone-plate system and the Rheoplus software system. The stress scan test frequency was kept constant at 1 Hz, with a stress scan range of 0.01–10 Pa. The viscoelastic test stress was kept constant at 0.1 Pa, with a frequency range of 0.1–10 Hz, and the test temperature was 45°C.

[0110] 6. Two-phase permeation behavior of oil / oil displacement system in multi-point pressure plate sand-filled model

[0111] The seepage behavior of APSS and PSS systems in low-oil-content porous media was studied using a multi-point pressure plate sand-filled seepage model. This indirectly examines whether the oil displacement system emulsifies the crude oil in situ through seepage shear in the porous media. Figure 2 This is a schematic diagram of a flat sand-filled model. The sand in the model has dimensions of 24cm × 1.5cm × 0.15cm. The model has five pressure sensor ports arranged sequentially from the inlet to the outlet. To eliminate the influence of external factors and end-face effects on seepage, the two pressure measurement points are placed inside the sand-filled body (2cm away from the injection port and the production port, respectively). During the injection of the oil displacement system, it flows through the injection end sequentially, filling the guide channel before entering the sand body, allowing the oil displacement system to advance parallel within the sand body. After flowing through the five pressure production points, it flows out from the guide channel at the outlet end. Thus, four pressure differential gradients can be calculated from the five pressure production points. The model is sealed and compacted by air pressure to ensure that the sand body is fixed and maintains uniformity.

[0112] The experimental steps are as follows:

[0113] (1) Select quartz sand of a specific mesh size for sand laying, bolt on, assemble the model and weigh it, seal the model and place it in an oven, adjust the temperature to 45℃, apply ring pressure and test the sealing performance of the model.

[0114] (2) The model was saturated with simulated salt water. After saturation for 30 minutes, the wet weight of the model was measured. Based on this, the porosity and pore volume of each sand mesh size were determined, and the permeability of the model was determined.

[0115] (3) The simulated brine and the prepared poly / surface / salt flooding system are loaded into an intermediate container for later use;

[0116] (4) Start the micro constant flow pump and inject simulated oil and simulated water at an oil-water ratio of 3:7. Close the simulated water pipeline valve, open the polymer solution valve, adjust the injection speed to 3m / d, and inject the polymer / surface / salt flooding system until the pressure monitored by each pressure sensor stabilizes at 10PV and then stop the experiment;

[0117] (5) Record the pressure data of five pressure sensors (sensor 1, sensor 2, sensor 3, sensor 4, and sensor 5) and plot the curves between pressure and pressure gradient and the number of injected PV.

[0118] 7. Parallel heterogeneous sand-filled pipe oil displacement experiment

[0119] To simulate the high water cut in high-permeability zones and low water cut in low-permeability zones after waterflooding in heterogeneous reservoirs, a parallel sand-filled model was constructed with high oil saturation in low-permeability zones and low oil saturation in high-permeability zones. This model was used to verify the feasibility of using an in-situ emulsion flooding system to improve sweep efficiency and enhance oil recovery. Relevant data from the constructed parallel model with multiple permeability ranges are shown in Table 3. The sand-filled model used in the flooding experiment was a uniform cylinder (φ2.5×20 cm), with a flooding rate of 3 m / d. A schematic diagram of the displacement device is shown in [Figure 1]. Figure 3 During the oil displacement process, the injection pressure, water cut at high and low permeability levels, and recovery rate are recorded in real time.

[0120] The displacement experiment process is as follows:

[0121] (1) Simulated formation water was injected at a rate of 1 mL / min, and the permeability was measured as shown in Formula 1.

[0122] (2) Simulated crude oil was injected into the sand-filled pipe until it was fully saturated, and its oil saturation was measured. It was then aged at 45°C for 12 hours.

[0123] (3) Three parallel experiments with different oil saturation levels were designed. Simulated formation water was injected at a rate of 1 mL / min to achieve an oil saturation of 70% in low-permeability and 30% in high-permeability.

[0124] (4) Parallel sand-filled pipes are used to inject 1.5PV of oil displacement system.

[0125] (5) Proceed with subsequent water drive until the pressure remains constant.

[0126] (6) Demulsify the produced fluid and calculate the recovery rate.

[0127] (Formula 1)

[0128] In the formula, Q is the displacement rate (mL / min); L is the length of the sand-filled tube (cm); μ is the fluid viscosity (mPa·s); A is the cross-sectional area of ​​the sand-filled tube model; and ΔP is the injection pressure difference (MPa).

[0129] Table 2 Permeability Model Data Table

[0130]

[0131] Results and Discussion:

[0132] 1. Construction of a composite oil displacement system

[0133] The viscosities of APSS and PSS of polymers with different concentrations were tested. The results are as follows: Figure 4 As shown, the viscosity-enhancing ability of APSS is slightly greater than that of PSS in any range. Based on this, two oil displacement systems with apparent viscosity close to that of crude oil and comparable interfacial tension were constructed. The specific parameters of the oil displacement systems used are shown in Table 3.

[0134] Table 3 Composition of the in-situ emulsification oil displacement system

[0135]

[0136] 2. Emulsification and thickening behavior of oil displacement systems

[0137] 1) Comparison of emulsification in different systems over 1-6 hours

[0138] from Figures 5-13 As can be seen, APSS exhibits oil-water separation at oil contents of 80% and 90% within 1-2 hours, while the system remains largely unseparated at other oil-water ratios within the same timeframe. However, weak oil-water separation is observed between 2-6 hours, with the lower layer being relatively darker in color. This phenomenon clearly demonstrates the strong emulsifying properties of APSS emulsions. This is likely due to the molecular structure of APSS and its adsorption characteristics at the oil-water interface, which helps maintain reduced interfacial tension, enhances interfacial modulus strength, increases emulsion stability, and promotes better dispersion of oil in the aqueous phase. For PSS, an emulsion band appears in the lower layer after 1 hour. However, after 1 hour, oil-water separation rapidly occurs in all PSS concentrations, with the lower layer being relatively lighter in color. This indicates that PSS emulsions have poor stability; surfactant molecules, under the influence of electrolytes, tend to migrate towards the oil phase, failing to maintain emulsion stability and leading to phase separation within a short time. For other systems, phase separation occurred in most systems with different water-oil ratios after 6 hours. For systems that did not experience phase separation, the higher the water content, the worse the emulsification, while the higher the oil content, the better the emulsification effect. This is completely different from the APSS system, which has the characteristics of emulsification with high water content and no emulsification with low water content.

[0139] 2) Comparison of emulsification of different systems over 24 hours

[0140] from Figures 14-22As can be seen, the phase behavior is similar in the presence of surfactants and surfactant / salt binary systems, but the presence of salt alters the migration of surfactants at the oil / water interface, resulting in slightly different trends in emulsion viscosity. When only AP polymers are present, obvious emulsion bands appear in colorimetric tubes with oil content ranging from 30% to 70%, with higher oil saturation indicating stronger emulsification. The highest viscosity is observed at 70% oil content. This may be due to the presence of long amphiphilic molecular chains in the polymer molecules, which enhances their adsorption capacity at the oil-water interface, thus promoting the stability of the emulsion band. When only salt is present, emulsion bands exist at oil content ranging from 60% to 90%. When AP / salt and AP / surfactant are present, oil-water separation is significant at oil contents of 10% and 20%.

[0141] However, APSS emulsifies with high water content but not with low water content; while PSS exhibits significant oil-water separation under any oil-water ratio conditions, indicating weak emulsification. This suggests that APSS emulsions have better stability.

[0142] 3) Comparison of viscosity of different systems after 24 hours of emulsification

[0143] from Figures 23-31 As can be seen, the emulsion viscosity of APSS and PSS, as well as that of simulated crude oil, is higher than that of simulated crude oil (10 mPa·s) and the oil displacement system. The emulsion viscosity exhibits a downward-opening bell-shaped curve, first increasing and then decreasing as the water / oil ratio decreases. However, the magnitude of the emulsion viscosity and its trend with the oil / water ratio differ significantly between the two systems. The emulsion viscosity of APSS is much greater than that of PSS. The peak of the bell-shaped curve of the APSS system's emulsion viscosity / water-oil ratio shifts towards higher water content, reaching its maximum at an oil content of 30%-40%, exceeding 200 mPa·s, which is more than 20 times that of simulated crude oil. Even at water contents of 90% and 80%, the emulsion viscosity is still 5-10 times higher than that of crude oil and several times higher than that of the oil displacement system. However, at higher oil content, especially when the oil saturation exceeds 50%, the emulsion viscosity decreases significantly. At oil content of 70%-90%, the emulsion viscosity is only close to that of the displacement system or crude oil. Therefore, APSS exhibits the characteristic of emulsification at high water content and non-emulsification at low water content. In contrast, the peak of the bell-shaped curve of the PSS system's emulsion viscosity / water-oil ratio shifts towards lower water content. Its viscosity is highest at oil-water ratios of 5:5 and 4:6, reaching 37 mPa·s, but this is only about four times that of simulated crude oil and about twice that of the displacement system. At high water content (above 70%) and high oil content (above 70%), the emulsion viscosity is only close to that of crude oil or the displacement fluid. The emulsion viscosity of other systems under different water-oil ratio conditions is similar to that of the PSS system and will not be elaborated further.

[0144] 3. Microstructure testing of ternary systems

[0145] Emulsion rheological behavior: Viscoelastic fluids can significantly improve oil recovery. In order to study the rheological behavior of emulsions with different oil-water ratios, the oil displacement system and crude oil were mixed and stirred at 400 rpm for 30 min at 45℃ to form an emulsion. Then, stress scanning and viscoelasticity tests were performed on the emulsion.

[0146] Emulsion stress scanning: APSS exhibits the highest composite modulus at an oil content of 30%, and within a certain shear stress range, it shows a similar composite modulus, indicating a multi-level plateau phenomenon in the composite modulus. This suggests that its structure is a multi-stage fluid. Figure 32 As shown; however, the composite modulus changes less when the oil content of APSS is 70% or 50%. Analysis suggests that the three-tiered plateau in APSS is caused by collisions between oil and water droplets, hydrophobic association between molecules, and the combined effect of the entanglement between the filamentous emulsion and the oil and water. Figure 33 As shown, the modulus of PSS is close and it has no special function. Its emulsion is mainly caused by the collision between oil and water droplets, which further proves that the high viscosity of APSS emulsion is related to the formation of a multi-level structure.

[0147] Emulsion viscoelasticity test: Viscoelasticity test can reflect the microstructure of emulsion. Figure 34 and Figure 35 Frequency sweep curves of the APSS and PSS systems with different oil-water ratios and simulated oil emulsions are shown. For the APSS system, at oil contents of 30% and 50%, the elastic modulus of the emulsion is always greater than the viscous modulus, and the two do not intersect throughout the entire frequency range, except for an intersection point at an oil saturation of 70%. Therefore, it can be considered that the emulsion formed by APSS and crude oil at high water content is a viscoelastic fluid dominated by elasticity. For the PSS system, in the low frequency range, the viscous modulus (G'') > the elastic modulus (G'), indicating that this emulsion is mainly viscous and has an unstable internal structure. However, as the frequency increases, the elastic modulus continuously increases; at high frequencies, the elastic modulus approaches and exceeds the viscous modulus. Comparing the two, at low frequencies (0.1-1Hz), the APSS system exhibits viscosity and elasticity 1-2 orders of magnitude higher than PSS at oil contents of 30% and 50%. At high frequencies, their viscosity and elasticity values ​​are similar, and the APSS system also shows slightly higher elasticity and viscosity at an oil content of 70%. This indicates that APSS emulsions formed at oil contents of 30% and 50% have unique microstructures.

[0148] 4. Two-phase permeation behavior of the oil / oil displacement system in a multi-point pressure plate sand-filled model

[0149] Seepage behavior can reveal the fluid transport mechanism at the pore scale and provide direct insights into interpore pressure changes, which is instructive for research on enhanced oil recovery. To investigate whether an oil displacement system can form an in-situ emulsion under seepage shear and other forces during oil / water co-perfusion at high water cut, the co-perfusion behavior of the oil displacement system / crude oil was studied under a fixed oil-water ratio of 3:7. The test results at three permeabilities are as follows. Figures 36-38 As shown, there are significant differences in injection pressure across the three permeability levels. For APSS, a peak injection pressure is observed at 3000 md, with subsequent pressures differing from the peak by 1-2 times. At 1400 md and 580 md, the overall pressure is relatively high, with subsequent pressures remaining relatively high. For PSS, a peak injection pressure is present at all permeability levels. This indicates that APSS has a good ability to maintain seepage resistance. The pressure gradient along the flow path of APSS increases with the increase of seepage distance, which is an interesting phenomenon. This may indicate that as the APSS oil displacement system and simulated crude oil seep further together, the in-situ emulsion formed under the action of seepage shear and other forces becomes more stable, and the seepage resistance increases. In contrast, the pressure gradient along the flow path of PSS is only about 50% of that of APSS. Moreover, the pressure gradient along the flow path only shows a higher pressure gradient in the second segment than in the first segment as the seepage distance increases. The pressure gradients in the third and fourth segments basically do not increase and show a sawtooth fluctuation. This indicates that the PSS system can also emulsify in situ with crude oil under the action of seepage shear, but the stability of the emulsion is poor and the seepage resistance is relatively low.

[0150] In a high-permeability 3000md medium, both APSS and PSS exhibited a linear pressure increase from 0 to 2 PV, after which the pressures rapidly decreased. After 4 PV, the pressure of APSS was 3-4 times higher than that of PSS, and the change in APSS was more uniform. The pressure gradient curves show that APSS is more likely to form a high pressure differential at the distal end, with its peak pressure differential differing by nearly four times. This indicates that APSS is more suitable for forming high flow resistance and is easier to control.

[0151] The pressure curves of APSS and PSS at 1400 md show that APSS pressure increases rapidly from 0-2 PV, then plateaus from 2-5 PV, and then decreases slightly. Its stable pressure is almost twice that of PSS, indicating that its ability to build high flow resistance decreases slightly with decreasing permeability, possibly due to the viscosity decrease caused by the shear of the porous medium. PSS, on the other hand, rises rapidly from 0-2 PV, then suddenly increases, decreases from 3-6 PV, and then plateaus.

[0152] At 580md, the pressure change of APSS was more pronounced, with the pressure rapidly reaching its peak, entering the pressure equilibrium zone, and maintaining a relatively high pressure, resulting in a significant increase in pressure differential. The pressure gradient of PSS, however, followed a similar pattern to that of high-permeability systems. The pressure gradient of APSS was 4-8 times higher than that of PSS, indicating that even at low permeability and high water cut, APSS also possesses the ability to maintain higher flow resistance, which is beneficial for profile control. In contrast, PSS exhibits relatively low flow resistance at low permeability, which may be beneficial for injection flushing, but not for profile control.

[0153] In summary, APSS exhibits higher flow resistance when co-permeating with oil in porous media under high water cut conditions, and the flow resistance increases sequentially along the flow path. This indirectly proves that APSS can form a relatively stable emulsion with high flow resistance when emulsified in situ with crude oil in porous media under high water cut conditions, while PSS forms an unstable emulsion with relatively low flow resistance. This suggests that APSS may be more effective in regulating and plugging heterogeneous reservoirs under high water cut conditions.

[0154] 5. Heterogeneous oil displacement experiments of composite oil displacement system

[0155] Under heterogeneous conditions, expanding the sweep of low-permeability areas is key to improving oil recovery. To verify the recovery rate under different permeability ranges, three parallel experiments with multiple ranges were designed (experimental conditions such as permeability are shown in Table 2), and the final oil displacement results are shown in Table 4.

[0156] APSS-based drive experiment:

[0157] Figure 39 , Figure 40 , Figure 41Table 2 shows the model pressure drop, split rate, and recovery rate of a 1.5PV fixed-injection APSS slug under three range models (Type 1, Type 2, and Type 3). Comparing the recovery rates of parallel double-filled sand pipe models with different permeabilities reveals significant differences in the enhanced oil recovery rates among the three combinations. The pressure drop initially increases rapidly in all three models, but the pressure drop in Type 1 and Type 3 models decreases slightly in the later stages, while the pressure drop in Type 2 decreases more significantly. The pressure drop in Type 3 remains consistently higher than the other two models. The total recovery rates of Type 1 and Type 3 models are 92.7% and 89.7%, respectively, showing good recovery rates, while the total recovery rate of Type 2 is lower at 47%. Type 1 and Type 3 models maintain large low-permeability split rates, with maximums of 36.1% and 42%, respectively, while the split rate of Type 2 model is lower, with a maximum of only 7.5%. This may be because in the early stages of injection, the oil saturation at the oil-water front is low, and emulsification gradually occurs through shearing in the porous medium, forming a high-viscosity emulsion, allowing some of the displacing fluid to enter the low-permeability zone. In the low-permeability zone, shearing also forms a low-viscosity emulsion, and the combined effect of these two factors results in a higher pressure drop. However, the Type 2 model has a larger permeability range, with a smaller low-permeability fraction. The low-permeability fraction may not even have time to emulsify, and the high-permeability fraction is completely displaced by the APSS, leading to a rapid decrease in the system pressure drop.

[0158] Figure 42 , Figure 43 , Figure 44 The high-permeability and low-permeability fractional recovery rates of the three models are shown. High-permeability areas are almost completely displaced in all three models, while low-permeability recovery rates vary significantly. Looking at the same permeability range, Type 1's high-permeability and low-permeability recovery rates are 91.4% and 93.3%, respectively, higher than Type 3's 97.3% and 85.6%. This is because the low-permeability zone in Type 1 has higher permeability, making it easier for APSS to penetrate. Type 2 has a larger permeability range, with high-permeability and low-permeability recovery rates of only 98.5% and 23%, respectively. The low-permeability fractionation is smaller, and the pressure drop of the high-permeability emulsion formation is much lower than the low-permeability initiation pressure, resulting in lower recovery rates. Clearly, the APSS system can simultaneously achieve the dual effects of high-permeability emulsification and profile control, and low-permeability emulsification and displacement, but it is only suitable for applications with relatively low permeability ranges. Larger permeability ranges make APSS less suitable for application.

[0159] PSS-driven experiment:

[0160] The PSS adjustment and drive test of three groups of parallel double-filled sand pipes was evaluated, and the results are as follows: Figure 45 , Figure 46 , Figure 47The figure shows the model pressure drop, split rate, and recovery rate of a 1.5PV fixed-injection PSS slug under three ranges. The results are shown in the figure. Comparing the recovery rates of parallel double-filled sand pipe models with different permeabilities, it was found that the enhanced oil recovery rates of the three combinations differed significantly. The pressure drop of all three models initially increased rapidly, then decreased slightly in the later stages, with Type 3 consistently showing a higher pressure drop than the other two models. The Type 1 model had a better overall recovery rate of 80%, while Type 2 and Type 3 had lower recovery rates of 32% and 34.5%, respectively. The Type 1 model had the highest low-permeability split rate at 23.5%, while the Type 2 and Type 3 models had almost zero low-permeability split rates, and the split rates of all three models were consistently lower than those of PSS. This may be because, in the early stages of injection, the viscosity of the emulsion formed by shearing through the porous medium is low, preventing more displacing fluid from entering the low-permeability zone, resulting in a much lower pressure drop for PSS compared to APSS. In contrast, the Type 3 model has a lower low-permeability, making it difficult for PSS to enter, and the high-permeability emulsion maintains a relatively high pressure drop.

[0161] Figure 48 , Figure 49 , Figure 50 The high-permeability and low-permeability partial recovery rates of the three models are shown. High-permeability areas are almost completely displaced in all three models, while the recovery rates for low-permeability areas vary significantly. Looking at the same permeability range, the high-permeability and low-permeability recovery rates for Type 1 are 94.6% and 73.3%, respectively. In comparison, the high-permeability and low-permeability recovery rates for Type 2 are 93.8% and 5.6%, and for Type 3, they are 93.6% and 7%. The higher low-permeability recovery rate of Type 1 is because the low-permeability zone in the Type 1 model has higher permeability, making it easier for the PSS (Potentially Surface-Suppressed Surface) to penetrate. Clearly, the PSS system can achieve good displacement function under suitable permeability and permeability range conditions, and permeability greatly affects the application of PSS.

[0162] Table 4 summarizes the recovery rates of the APSS and PSS systems. APSS exhibits good recovery rates within a 5-fold permeability range, simultaneously recovering oil from both low-permeability and high-permeability areas. In contrast, PSS significantly improves recovery rates even under a 10-fold permeability range. PSS shows good recovery rates only under suitable permeability ranges, with a significantly smaller application effect and scope compared to the APSS system. In conclusion, APSS can form high-viscosity emulsions in high-permeability areas with high water content and low-viscosity emulsions in low-permeability areas with low water content, thus creating an intelligent profile control system that simultaneously achieves intelligent profile control in high-permeability areas, broadens sweep potential in low-permeability areas, and facilitates oil washing.

[0163] Table 4 Summary of Improved Recovery Rate

[0164]

[0165] Therefore, the APSS system provides continuous phase rigidity and spatial constraint through the synergistic effect of the polymer three-dimensional network; the surfactant regulates the interfacial polymerization path to achieve filamentous emulsion selectivity; the salt enhances network association and intensifies continuous phase gelation, realizing the coexistence of multi-level structures and achieving intelligent thickening under different oil-water ratios.

[0166] This system can achieve high-viscosity emulsification with crude oil at high water cuts, and non-emulsification or low-viscosity emulsification at low water cuts. In heterogeneous parallel sand-filled tubular oil displacement experiments, this profile control system can simultaneously achieve the dual functions of "profile control in high-permeability and high-water-cut conditions and displacement in low-permeability and low-water-cut conditions," providing a new technical strategy and path for significantly improving oil recovery through chemical flooding in high-water-cut heterogeneous reservoirs after waterflooding.

[0167] Therefore, those skilled in the art will recognize that although embodiments of the present invention have been shown and described in detail herein, many other variations or modifications conforming to the principles of the present invention can be directly determined or derived from the disclosure of the present invention without departing from the spirit and scope of the invention. Therefore, the scope of the present invention should be understood and recognized as covering all such other variations or modifications.

Claims

1. A high-efficiency oil displacement system with polystyrene surface salt composite exhibiting unique in-situ emulsification behavior, characterized in that, The formulation of the polystyrene composite high-efficiency oil displacement system is as follows: The concentration of the associative polymer was 1000-3000 mg / L; the concentration of the surfactant was 0.2-0.4%; the concentration of the salt was 1.2-1.8%; and the solvent was water. The method for preparing the associative polymer is as follows: Acrylamide (AM), 2-acrylamido-2-methylpropanesulfonic acid (AMPS), associating monomer (DH), and emulsifying monomer (RH) were added at a molar ratio of 100:2-4:0.5-1.5:1-2. A mixed solution with a total monomer concentration of 20-35% was prepared using ultrapure water. Disodium ethylenediaminetetraacetate (EDTA) was added to the reaction vessel at a ratio of 0.005%-0.01% of the total mass of the reaction system, and sodium formate was added at a ratio of 0.03%-0.05% of the total mass of the reaction system. The mixture was stirred thoroughly. Next, the pH of the system was adjusted to 7.0-7.5 by adding sodium hydroxide, and then the mixture was cooled to 0°C. A composite initiator prepared by ammonium persulfate, sodium bisulfite and hydrogen peroxide in a molar ratio of 1:1:0.3 was added to the mixture for adiabatic polymerization for 7-9 hours. The amount of the composite initiator added was 0.01%-0.02% of the mass of the reaction system. The resulting colloid was hydrolyzed with sodium hydroxide, then dried, pulverized and sieved to obtain a white polymer powder, which is the associative polymer. The molecular structural formula of the associating monomer DH is: ； The molecular structural formula of the emulsifying monomer RH is: ； Where n is the number of repeating units, and R is a methyl group; The molecular weight of the associative polymer is 8-12 million; The surfactant is a novel petroleum sulfonate with a purity of 50%, manufactured by Daqing Petrochemical; its product number is QY-0903. The salt is one or more of sodium chloride, sodium sulfate, potassium chloride, and potassium sulfate.

2. The polystyrene-based high-efficiency oil displacement system with specific in-situ emulsification behavior as described in claim 1, characterized in that, The specific method for preparing the oil displacement system is as follows: Step (1): Add the associative polymer evenly to water and stir continuously to prepare the polymer mother liquor; Step (2): After the polymer mother liquor is prepared, it is subjected to aging treatment. Step (3): Mix the fully matured polymer mother liquor with the salt solution and surfactant, and dilute the compound with water to the desired target concentration; Step (4): The compound is continuously stirred to obtain a polymer / surfactant / salt ternary solution, which is a high-efficiency oil displacement system with specific in-situ emulsification behavior of polymer-surfactant-salt composite.

3. The polystyrene-based high-efficiency oil displacement system with specific in-situ emulsification behavior as described in claim 2, characterized in that, The concentration of the polymer mother liquor is 4000-5000 mg / L; the concentration of the salt solution is 10%-30%.

4. A high-efficiency oil displacement system with specific in-situ emulsification behavior as described in any one of claims 1-3, characterized in that, The oil displacement system is used in the fields of intelligent in-situ emulsification and regulation of high water-cut and highly heterogeneous reservoirs, as well as in the field of enhanced oil recovery in heterogeneous reservoirs.

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