An ultra-low interfacial tension water-based microsphere flooding system and its application

Abstract

The present invention relates to a kind of ultra-low interfacial tension water-based microsphere adjustment and displacement system, belonging to the field of oil and water well adjustment and displacement, profile control and water plugging. The system includes a first segment plug and a second segment plug, and one or more of core-shell self-intertwining water-based microspheres or pre-crosslinked gel swellable particles are dissolved in oil field reinjection water at a concentration of 3-6wt% to form a first segment plug; a mixture of a surfactant and ultra-low interfacial tension water-based microspheres is dissolved in oil field reinjection water at a concentration of 4-8wt%, forming a second segment plug. The system is used for oil and water well adjustment and displacement process, the first segment plug enters a high permeability layer and a large pore, adjusts the water absorption profile, the second segment plug enters the deep part of the formation, and the water-based microspheres are filled with the formation pores after expansion to form a piston-shaped front, and then the surfactant is released for oil displacement. The present invention has the advantages of simple injection process, strong migration ability, low interfacial tension, etc., by adjusting the component concentration and the segment plug dosage, the injection speed is controlled, the injection well is stabilized and oil and water are controlled, and the recovery rate is greatly improved.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and water well flooding, profile control and water plugging, and specifically relates to an ultra-low interfacial tension water-based microsphere flooding system and its application in oil field flooding, profile control and water plugging. Background Art

[0002] After the oilfield entered the water injection development, there were problems such as rapid increase of water content and serious inrush of injected water. Profile control and displacement control technology have become important means to stabilize oil and control water in the oilfield. Due to the small processing radius, profile control cannot enter deep profile control, and focuses on plugging the high permeability strip near the wellbore and improving the contradiction between layers, which can easily cause high injection pressure, injection difficulties and damage to the medium and low permeability layers, resulting in unsatisfactory results. The existing displacement control means focus on solving plane contradictions, with a long construction period, occupying platform operating space, and a large one-time investment.

[0003] In recent years, deep liquid flow diversion technology has played an important role in water control and oil stabilization measures in high water-content oilfields. Among them, ultra-low interfacial tension water-based microsphere deep liquid flow diversion technology is a new technology developed on the basis of ordinary water-based microsphere profile control and drive control technology. It can maximize the role of secondary oil recovery while carrying out limited tertiary oil recovery.

[0004] Chinese patent CN115806813A discloses a sustained-release polymer water-based microsphere recovery agent with a core-shell heterogeneous structure. The recovery agent has multiple functions of ordinary polymer water-based microspheres, organic resin plugging agents, crude oil dissociation agents, and surfactant oil-displacing agents. It has the multi-effect characteristics of blocking water when encountering water (profile adjustment), emulsifying crude oil when encountering oil (oil washing), and combining plugging and flooding. It solves the problems of polymer water-based microspheres not being resistant to shearing, short profile adjustment distance, large formation adsorption of surfactant oil-displacing agents, and reduced deep oil washing effects in the polymer water-based microsphere + surfactant flooding process in oil fields. However, the production process of the recovery agent is complicated, resulting in high cost of the agent, and it is not suitable for large-scale promotion and application. Chinese patent CN115873173B discloses a nano polymer water-based microsphere for flooding, which has the characteristics of high apparent viscosity and high shear resistance, but poor temperature and salt resistance, is not suitable for high temperature or heavy oil reservoirs, and has a narrow range of application. Chinese patent CN103073679A discloses a polyacrylamide water-based microsphere water plugging agent, which is prepared by weighing raw materials acrylamide, salt-resistant monomer, N,N-methylenebisacrylamide, Span 80, potassium persulfate, cyclohexane and deionized water; stirring and mixing dispersant and cyclohexane in the polymerized monomer; initiating polymerization to form a water plugging agent. Since cyclohexane is used as the continuous phase, the cost is relatively high, and it will stratify after standing, and the stability is poor, and the salt resistance is only 30,000 degrees of mineralization. Chinese patent CN104231168A discloses a polymer water-based microsphere temporary plugging agent with ultra-low interfacial tension and a preparation method thereof. The microsphere temporary plugging agent is prepared from raw materials such as white oil, acrylamide monomer, acrylic acid, dehydrated sorbitan fatty acid ester, N,N-methylenebisacrylamide, ammonium persulfate, sodium bisulfite, hydrophilic surfactant, water, etc., and its salt resistance is only 50,000 degrees of mineralization. Summary of the invention

[0005] The purpose of the present invention is to provide an ultra-low interfacial tension water-based microsphere flooding system, which has the advantages of simple injection process, strong migration ability, low interfacial tension, swelling when encountering water and no change when encountering oil, low raw material cost, controllable preparation process, and broad market application prospects.

[0006] Another object of the present invention is to provide an application of the ultra-low interfacial tension water-based microsphere flooding system in oil field flooding, wherein the slugs constituting the system are injected sequentially, and the injection rate is controlled by adjusting the component concentration and the amount of slugs, so as to achieve stable oil and water control in water wells or chemical flooding injection wells, thereby improving the recovery rate.

[0007] In order to achieve the above technical objectives, the present invention adopts the following technical solutions.

[0008] The present invention firstly uses a water-based core-shell self-intertwined water-based microsphere or pre-crosslinked gel swellable particles with a size of 0.5 to 70 microns as the first plug, which preferentially enters the high permeability layer and large pores in the formation, adjusts the water absorption profile, and expands the sweep coefficient. Then, a surfactant and an ultra-low interfacial tension water-based microsphere are used as the second plug, which not only plays a role in stabilizing the system, but also plays a role in oil displacement. Under the action of subsequent water displacement, the ultra-low interfacial tension water-based microspheres relatively quickly enter the deep part of the formation with the injected water and migrate; because the water-based microspheres swelled by water can fill the formation pores, form a piston-shaped front, and release the ultra-low interfacial tension surfactant to drive oil, which plays a dual role in adjusting the water absorption profile and driving oil.

[0009] The invention discloses an ultra-low interfacial tension water-based microsphere control and displacement system, comprising a first section plug and a second section plug. One or more of core-shell self-interlinked water-based microspheres or pre-crosslinked gel expansion particles are dissolved in oilfield reinjection water at a concentration of 3-6wt% to form the first section plug; a mixture of a surfactant and ultra-low interfacial tension water-based microspheres is dissolved in oilfield reinjection water at a concentration of 4-8wt% to form the second section plug. In the mixture, the surfactant accounts for 15-20wt% and the ultra-low interfacial tension water-based microspheres account for 80-85wt%.

[0010] The surfactant is sodium 3-allyloxy-2-hydroxy-1-propane sulfonate.

[0011] The ultra-low interfacial tension water-based microspheres are composed of the following substances in parts by weight: 10-100 parts of polyethylene glycol I, 10-500 parts of polyethylene glycol II, 10-100 parts of special polyether, 10-500 parts of (amphoteric) hexafluoropropylene oxide trimer, 10-500 parts of dioctyl sodium sulfosuccinate (OT penetrant), 100-500 parts of calcium chloride, 0-50 parts of 30-40wt% sodium hydroxide solution, 100-500 parts of acrylamide, 1-50 parts of acrylic acid, 0.1-10 parts of ammonium persulfate, 10-200 parts of ethylene glycol, 1-10 parts of N,N-methylenebisacrylamide, 1-50 parts of emulsifier, 0.1-10 parts of azobisisobutyronitrile, 0.1-10 parts of sodium bisulfite, and 100-500 parts of deionized water.

[0012] The polyethylene glycol type I is polyethylene glycol 400.

[0013] The polyethylene glycol type II is polyethylene glycol 4000, polyethylene glycol 6000 or polyethylene glycol 8000.

[0014] The special polyether is one or more of isooctyl alcohol polyoxyethylene ether, 12-14 alcohol polyoxyethylene ether, 16-18 alcohol polyoxyethylene ether, dodecyl primary amine polyoxyethylene ether, and octadecyl primary amine polyoxyethylene ether.

[0015] The calcium chloride may not be added during summer construction.

[0016] The emulsifier is one or more of Span 60, Span 80, Tween 60 and Tween 80.

[0017] The OT type of penetrant has excellent foaming, wettability and washing properties, strong, rapid and uniform penetration ability. After being treated with the penetrant, its penetration ability will no longer be affected by changes in temperature, acidity and alkali.

[0018] The ultra-low interfacial tension water-based microspheres are prepared by the following process:

[0019] (1) Add deionized water to reactor No. 1, then add polyethylene glycol type I, polyethylene glycol type II, special polyether, hexafluoropropylene oxide trimer, and sodium dioctyl sulfosuccinate in sequence, stir evenly, introduce nitrogen to the top of reactor No. 1, then add ethylene glycol and emulsifier, and continue to stir evenly;

[0020] (2) adding deionized water to reactor No. 2, adding solid anhydrous calcium chloride in small amounts and multiple times while stirring, stirring evenly and pumping the mixture into reactor No. 1;

[0021] (3) adding deionized water, acrylamide, acrylic acid, and sodium hydroxide solution to reactor No. 2, stirring evenly, introducing nitrogen, and then adding N,N-methylenebisacrylamide and ammonium persulfate to the reactor, stirring for 1-3 hours;

[0022] (4) Open the valve at the bottom of reactor No. 1 and continue to introduce nitrogen into reactor No. 1 from the bottom until bubbles rise;

[0023] (5) adding azobisisobutyronitrile to reactor No. 2 and sodium bisulfite to reactor No. 1;

[0024] (6) After the two reactors are stirred for 1-3 hours respectively, the monomer aqueous solution in reactor No. 2 is pumped into reactor No. 1 by a drop-feeding pump and stirred rapidly. The mixture is reacted for 1-5 hours, cooled, washed, and dried to obtain ultra-low interfacial tension water-based microspheres.

[0025] The present invention discloses a water-based microsphere with ultra-low interfacial tension, which uses acrylamide and acrylic acid as comonomers, N,N-methylenebisacrylamide as a crosslinker, ammonium persulfate and sodium bisulfite as redox initiators, polyethylene glycol and water as continuous phases, and Span series or Tween series and hydrophilic surfactant as composite emulsifiers. At the same time, a fluorine surfactant is introduced, which can greatly reduce the surface tension and interfacial tension. The ultra-low interfacial tension water-based microsphere is synthesized by inverse emulsion polymerization. Analysis shows that the microsphere is a new type of polymer microsphere with ultra-low interfacial tension, and its interfacial tension can reach 2×10 -3mN / N, and the salt resistance can reach 250000mg / L, which improves the problem of high interfacial tension of existing polymer microspheres.

[0026] The oil displacement mechanism of ultra-low interfacial tension water-based microspheres is not to increase the viscosity of the displacement fluid to increase the swept volume to improve the oil displacement efficiency, but to improve the flow resistance of the dominant channel at the microscopic level, improve the water injection profile, and then improve the oil washing efficiency and thus the recovery rate through the emulsification properties of surfactants, reduce the oil-water interfacial tension, and reduce the residual oil saturation.

[0027] After the microspheres are injected into the formation, they will first enter the dominant channel with relatively high permeability along with the injected water, and gradually absorb water and expand at a certain temperature. When the breakthrough pressure reaches the critical pressure difference, the liquid flow will be redirected step by step, so that the injected water enters the channel with relatively low permeability, that is, the formation with more residual oil, improving the contradictions between and within the layers, reducing the advance of the injected water caused by the extreme difference, thereby realizing the piston-like advancement of the water injection front, achieving deep profile adjustment, and maximizing the swept volume of the injected liquid.

[0028] When the surfactant system enters the formation after the water injection profile is improved, the interaction between the surfactant and the formation oil reservoir and the reservoir fluid reduces the tension of the oil-water interface, changes the emulsification characteristics of the oil, and also changes the wettability of the formation rock surface. On the one hand, a relatively stable oil-water emulsion can be formed, and on the other hand, the adhesion of the oil to the formation surface can be reduced, thereby improving the oil washing ability. Since the emulsified oil is not easy to re-adhere to the formation surface during the forward movement, and the action of the surfactant increases the electrostatic repulsion between the oil droplets and the formation rock surface, the oil droplets are easily carried away by the displacement medium, thereby improving the oil washing efficiency. As more and more oil is washed down from the formation surface, they may collide with each other and form an oil belt when moving forward. When the oil belt moves forward, it will continuously gather the scattered oil it encounters, causing the oil belt to expand continuously and finally be extracted from the oil well.

[0029] The application of the ultra-low interfacial tension water-based microsphere flooding system in oilfield flooding refers to injecting a first plug and a second plug in sequence, wherein the first plug first enters the high permeability layer and large pores in the formation to adjust the water absorption profile, and the second plug enters the deep formation along with the injected water. The water-based microspheres swell when encountering water and fill the pores in the formation to form a piston-shaped front, and then release surfactants to drive oil, thereby greatly improving the recovery rate.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) The first plug preferentially enters the high permeability layer and large pores in the formation, adjusts the water absorption profile, and expands the sweep coefficient. Under the action of subsequent water flooding, the second plug, due to its low friction resistance, can relatively quickly enter the deep formation with the injected water and migrate, and after expansion, fill the formation pores to form a piston-shaped front and release surfactants, thereby playing a dual role of adjusting the water absorption profile and displacing oil.

[0032] (2) Surfactants play a role in stabilizing the system and displacing oil. They are added as bottom materials in the polymerization process to play an emulsifying and dispersing role, and can also participate in the polymerization, forming well-controlled molecular segments, with a wide distribution of particle diameters and low foaming properties. They can be polymerized in a low pH or highly acidic monomer environment. The resin system has no surfactant migration and has excellent chemical and mechanical properties.

[0033] (3) Super interfacial tension water-based microspheres have the characteristics of simple production process, low cost of reagents, wide application range, strong migration ability, low interfacial tension, swelling when in contact with water, and unchanged when in contact with oil. Compared with traditional water-based microspheres, they can absorb water and swell, migrate continuously, and achieve deep formation plugging. By controlling the particle size, they can meet the technical requirements of low-permeability and ultra-low-permeability oil reservoir profile control, with a plugging strength of more than 13MPa / m, a temperature resistance of up to 120°C, a mineralization resistance of up to 250,000mg / L, and an interfacial tension of up to 2×10 -3 mN / m.

[0034] (4) During the synthesis process, ultra-low interfacial tension water-based microspheres utilize their own exothermic reaction process to achieve energy conservation and consumption reduction. At the same time, the material viscosity is low during the reaction process, and the reaction is easy to transfer heat and control. After polymerization, only simple separation, cleaning and drying are required to obtain pure and uniform water-based microsphere products, which is conducive to large-scale production and industrial application. DETAILED DESCRIPTION

[0035] The present invention will be further described below in conjunction with specific implementations and examples, and the advantages and various effects of the present invention will be more clearly presented. It should be understood by those skilled in the art that these specific implementations and examples are for illustrating the present invention, rather than limiting the present invention.

[0036] Unless otherwise specifically stated, the terms used herein should be understood as having the same meanings as commonly used in the art.

[0037] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0038] Embodiment 1:

[0039] An ultra-low interfacial tension water-based microsphere, the raw materials for preparation include, by weight:

[0040] (1) Water: 100 parts;

[0041] (2) Polyethylene glycol type I: polyethylene glycol 400, 10 parts;

[0042] (3) Polyethylene glycol II: polyethylene glycol 4000, 10 parts;

[0043] (4) Special polyether: polyoxyethylene isooctanol ether, 10 parts;

[0044] (5) Hexafluoropropylene oxide trimer: 10 parts;

[0045] (6) dioctyl sodium sulfosuccinate: 10 parts;

[0046] (7) calcium chloride: 100 parts;

[0047] (8) 30 wt% sodium hydroxide solution: 1 part;

[0048] (9) acrylamide: 100 parts;

[0049] (10) acrylic acid: 1 part;

[0050] (11) ammonium persulfate: 0.1 part;

[0051] (12) N,N-methylenebisacrylamide: 1 part;

[0052] (13) ethylene glycol: 10 parts;

[0053] (14) Emulsifier: Span 60, 1 part;

[0054] (15) azobisisobutyronitrile: 0.1 part;

[0055] (16) Sodium bisulfite: 0.1 part.

[0056] The production steps are as follows:

[0057] (1) Add distilled water or deionized water to the No. 1 reactor, and then add polyethylene glycol type I, polyethylene glycol type II, special polyether, hexafluoropropylene oxide trimer, and OT penetrant in sequence. After stirring evenly, introduce nitrogen to the top of the No. 1 reactor, then add ethylene glycol and emulsifier, and continue to stir evenly;

[0058] (2) adding distilled water or deionized water to reactor No. 2, adding solid anhydrous calcium chloride in small amounts and multiple times under stirring, stirring evenly and pumping the mixture into reactor No. 1;

[0059] (3) Add distilled water or deionized water, acrylamide, acrylic acid, and sodium hydroxide aqueous solution (add acid first and then alkali) to the No. 2 reaction kettle, stir evenly, introduce nitrogen, add N,N-methylenebisacrylamide and ammonium persulfate to the kettle, and stir for 1 hour;

[0060] (4) Open the valve at the bottom of reactor No. 1 and continue to introduce nitrogen into reactor No. 1 from the bottom until bubbles rise;

[0061] (5) adding azobisisobutyronitrile to reactor No. 2 and sodium bisulfite to reactor No. 1;

[0062] (6) After the two kettles were stirred for 1 hour each, the monomer aqueous solution in the No. 2 reactor was pumped into the No. 1 reactor by a drop-feeding pump and stirred rapidly. The mixture was reacted for 1 hour, cooled, washed, and dried to obtain ultra-low interfacial tension water-based microspheres.

[0063] The construction method of the ultra-low interfacial tension water-based microsphere flooding system comprises the following steps:

[0064] (1) Injecting the first plug into the water well or chemical flooding injection well: core-shell self-interlinked water-based microspheres (nano-scale polymer microspheres WQ50 / WQ100 for flooding, Xi'an Wande Energy Chemical Co., Ltd.), prepared with oilfield reinjection wastewater, with a concentration of 3 wt%;

[0065] (2) Injecting a second plug into a water well or a chemical flooding injection well: a mixture of sodium 3-allyloxy-2-hydroxy-1-propane sulfonate and the above-mentioned ultra-low interfacial tension water-based microspheres in a concentration ratio of 15:85, prepared with oilfield reinjection wastewater, with a concentration of 4 wt%.

[0066] The above-mentioned ultra-low interfacial tension water-based microsphere flooding system was applied to 6 well groups in Block A of a domestic oil field. After the measures were taken, the daily oil production of the 6 well groups increased by 14.2 tons, the water cut decreased by 6.8 percentage points, and the cumulative oil production increased by 3,425 tons. The measures were effective.

[0067] Embodiment 2:

[0068] An ultra-low interfacial tension water-based microsphere, the raw materials for preparation include, by weight:

[0069] (1) Water: 500 parts;

[0070] (2) Polyethylene glycol type I: polyethylene glycol 400, 100 parts;

[0071] (3) Polyethylene glycol II: polyethylene glycol 6000, 500 parts;

[0072] (4) Special polyether: 12-14 alcohol polyoxyethylene ether, 100 parts;

[0073] (5) Hexafluoropropylene oxide trimer: 500 parts;

[0074] (6) dioctyl sodium sulfosuccinate: 100 parts;

[0075] (7) Calcium chloride: 500 parts;

[0076] (8) sodium hydroxide solution 40wt%: 50 parts;

[0077] (9) acrylamide: 500 parts;

[0078] (10) acrylic acid: 50 parts;

[0079] (11) ammonium persulfate: 10 parts;

[0080] (12) N,N-methylenebisacrylamide: 10 parts;

[0081] (13) ethylene glycol: 200 parts;

[0082] (14) Emulsifier: Span 80, 50 parts;

[0083] (15) azobisisobutyronitrile: 10 parts;

[0084] (16) Sodium bisulfite: 10 parts.

[0085] The production steps are as follows:

[0086] (1) Add distilled water or deionized water to the No. 1 reactor, and then add polyethylene glycol type I, polyethylene glycol type II, special polyether, hexafluoropropylene oxide trimer, and OT penetrant in sequence. After stirring evenly, introduce nitrogen to the top of the No. 1 reactor, then add ethylene glycol and emulsifier, and continue to stir evenly;

[0087] (2) adding distilled water or deionized water to reactor No. 2, adding solid anhydrous calcium chloride in small amounts and multiple times under stirring, stirring evenly and pumping the mixture into reactor No. 1;

[0088] (3) Add distilled water or deionized water, acrylamide, acrylic acid, and sodium hydroxide aqueous solution (add acid first and then alkali) to the No. 2 reaction kettle, stir evenly, introduce nitrogen, add N,N-methylenebisacrylamide and ammonium persulfate to the kettle, and stir for 3 hours;

[0089] (4) Open the valve at the bottom of reactor No. 1 and continue to introduce nitrogen into reactor No. 1 from the bottom until bubbles rise;

[0090] (5) adding azobisisobutyronitrile to reactor No. 2 and sodium bisulfite to reactor No. 1;

[0091] (6) After the two kettles were stirred for 3 hours each, the monomer aqueous solution in the No. 2 reactor was pumped into the No. 1 reactor with a drop-feeding pump and stirred rapidly. The reaction was continued for 5 hours, and then cooled, washed, and dried to obtain ultra-low interfacial tension water-based microspheres.

[0092] The construction method of the ultra-low interfacial tension water-based microsphere flooding system comprises the following steps:

[0093] (1) Injecting the first plug into a water well or a chemical flooding injection well: anion-cation self-crosslinked water-based microspheres, prepared with oilfield reinjection wastewater, with a concentration of 6 wt%;

[0094] (2) Injecting a second plug into a water well or a chemical flooding injection well: a mixture of sodium 3-allyloxy-2-hydroxy-1-propane sulfonate and the above-mentioned ultra-low interfacial tension water-based microspheres in a concentration ratio of 20:80, prepared with oilfield reinjection wastewater, with a concentration of 8 wt%.

[0095] The above-mentioned ultra-low interfacial tension water-based microsphere flooding system was applied to 9 well groups in Block B of a domestic oil field. After the measures were taken, the daily oil production of the 9 well groups increased by 21.7 tons, the water cut decreased by 5.2 percentage points, and the cumulative oil production increased by 4,212 tons. The measures were effective.

[0096] Embodiment 3:

[0097] An ultra-low interfacial tension water-based microsphere, the raw materials for preparation include, by weight:

[0098] (1) Water: 300 parts;

[0099] (2) Polyethylene glycol type I: polyethylene glycol 400, 30 parts;

[0100] (3) Polyethylene glycol II: polyethylene glycol 8000, 300 parts;

[0101] (4) Special polyether: 16-18 alcohol polyoxyethylene ether, 30 parts;

[0102] (5) Hexafluoropropylene oxide trimer: 300 parts;

[0103] (6) dioctyl sodium sulfosuccinate: 50 parts;

[0104] (7) Calcium chloride: 300 parts;

[0105] (8) 35% sodium hydroxide solution: 30 parts;

[0106] (9) Acrylamide: 300 parts;

[0107] (10) acrylic acid: 30 parts;

[0108] (11) ammonium persulfate: 5 parts;

[0109] (12) N,N-methylenebisacrylamide: 5 parts;

[0110] (13) ethylene glycol: 100 parts;

[0111] (14) Emulsifier: Tween 60, 30 parts;

[0112] (15) azobisisobutyronitrile: 5 parts;

[0113] (16) Sodium bisulfite: 5 parts.

[0114] The production steps are as follows:

[0115] (1) Add distilled water or deionized water to the No. 1 reactor, and then add polyethylene glycol type I, polyethylene glycol type II, special polyether, hexafluoropropylene oxide trimer, and OT penetrant in sequence. After stirring evenly, introduce nitrogen to the top of the No. 1 reactor, then add ethylene glycol and emulsifier, and continue to stir evenly;

[0116] (2) adding distilled water or deionized water to reactor No. 2, adding solid anhydrous calcium chloride in small amounts and multiple times under stirring, stirring evenly and pumping the mixture into reactor No. 1;

[0117] (3) Add distilled water or deionized water, acrylamide, acrylic acid, and sodium hydroxide aqueous solution (add acid first and then alkali) to the No. 2 reaction kettle, stir evenly, introduce nitrogen, add N,N-methylenebisacrylamide and ammonium persulfate to the kettle, and stir for 2 hours;

[0118] (4) Open the valve at the bottom of reactor No. 1 and continue to introduce nitrogen into reactor No. 1 from the bottom until bubbles rise;

[0119] (5) adding azobisisobutyronitrile to reactor No. 2 and sodium bisulfite to reactor No. 1;

[0120] (6) After the two kettles were stirred for 2 hours each, the monomer aqueous solution in the No. 2 reactor was pumped into the No. 1 reactor with a drop-feeding pump and stirred rapidly. The reaction was continued for 3 hours, and then cooled, washed, and dried to obtain ultra-low interfacial tension water-based microspheres.

[0121] The construction method of the ultra-low interfacial tension water-based microsphere flooding system comprises the following steps:

[0122] (1) Injecting the first plug into a water well or a chemical flooding injection well: pre-crosslinked gel expansion particles (pre-crosslinked gel expansion particles for oil production profile control agent YX-Ⅰ, Shenyang Yongxin Fine Chemical Co., Ltd.), prepared with oilfield reinjection wastewater, with a concentration of 4wt%;

[0123] (2) Injecting a second plug into a water well or a chemical flooding injection well: a mixture of sodium 3-allyloxy-2-hydroxy-1-propane sulfonate and the above-mentioned ultra-low interfacial tension water-based microspheres in a ratio of 18:82, prepared with oilfield reinjection wastewater, with a concentration of 6 wt%.

[0124] The above-mentioned ultra-low interfacial tension water-based microsphere flooding system was applied to four well groups in Block C of a domestic oil field. After the measures were taken, the daily oil production of the four well groups increased by 16.5 tons, the water cut decreased by 3.4 percentage points, and the cumulative oil production increased by 1,225 tons. The measures were effective.

[0125] Embodiment 4:

[0126] An ultra-low interfacial tension water-based microsphere, the raw materials for preparation include, by weight:

[0127] (1) Water: 300 parts;

[0128] (2) Polyethylene glycol type I: polyethylene glycol 400, 20 parts;

[0129] (3) Polyethylene glycol II: polyethylene glycol 4000, 200 parts;

[0130] (4) Special polyether: dodecaprimaryamine polyoxyethylene ether, 20 parts;

[0131] (5) Hexafluoropropylene oxide trimer: 200 parts;

[0132] (6) dioctyl sodium sulfosuccinate: 60 parts;

[0133] (7) Calcium chloride: 250 parts;

[0134] (8) 36% sodium hydroxide solution: 25 parts;

[0135] (9) Acrylamide: 300 parts;

[0136] (10) acrylic acid: 25 parts;

[0137] (11) ammonium persulfate: 2 parts;

[0138] (12) N,N-methylenebisacrylamide: 6 parts;

[0139] (13) ethylene glycol: 200 parts;

[0140] (14) Emulsifier: Span 60, 25 parts;

[0141] (15) azobisisobutyronitrile: 4 parts;

[0142] (16) Sodium bisulfite: 6 parts.

[0143] The production steps are as follows:

[0144] (1) Add distilled water or deionized water to the No. 1 reactor, and then add polyethylene glycol type I, polyethylene glycol type II, special polyether, hexafluoropropylene oxide trimer, and OT penetrant in sequence. After stirring evenly, introduce nitrogen to the top of the No. 1 reactor, then add ethylene glycol and emulsifier, and continue to stir evenly;

[0145] (2) adding distilled water or deionized water to reactor No. 2, adding solid anhydrous calcium chloride in small amounts and multiple times under stirring, stirring evenly and pumping the mixture into reactor No. 1;

[0146] (3) Add distilled water or deionized water, acrylamide, acrylic acid, and sodium hydroxide aqueous solution (add acid first and then alkali) to reaction kettle No. 2, stir evenly, introduce nitrogen, add N,N-methylenebisacrylamide and ammonium persulfate to the kettle, and stir for 2.5 hours;

[0147] (4) Open the valve at the bottom of reactor No. 1 and continue to introduce nitrogen into reactor No. 1 from the bottom until bubbles rise;

[0148] (5) adding azobisisobutyronitrile to reactor No. 2 and sodium bisulfite to reactor No. 1;

[0149] (6) After the two kettles were stirred for 2.5 hours each, the monomer aqueous solution in the No. 2 reactor was pumped into the No. 1 reactor by a drop-feeding pump and stirred rapidly. The reaction was continued for 2.5 hours, and then cooled, washed, and dried to obtain ultra-low interfacial tension water-based microspheres.

[0150] After the ultra-low interfacial tension water-based microspheres were placed in the oilfield reinjection wastewater at a constant temperature for 24 hours, their water absorption and expansion performance under different temperature conditions was investigated. The water absorption expansion multiple is usually used to evaluate the stability and physical blocking ability of the particles. The water absorption capacity of the particle gel uses the water absorption per unit mass of particles as the standard (i.e., the water absorption expansion multiple), and the calculation formula is C = (M / ρ) + H0-H1 / (M / ρ), where: C is the sample expansion multiple; M is the sample mass, g; ρ is the sample density, g / cm 3 ; H1 is the remaining water volume after sample expansion, ml; H0 is the initial volume of water, ml.

[0151] A large water absorption expansion multiple indicates that the ultra-low interfacial tension water-based microspheres have a strong expansion capacity and a strong ability to block pores in the formation; a small expansion multiple indicates that the ultra-low interfacial tension water-based microspheres have a weak expansion capacity and a weak ability to block pores in the formation.

[0152] The experimental results are shown in Table 1. The ultra-low interfacial tension water-based microspheres provided in this embodiment have a temperature resistance of up to 120°C, which is fully capable of adapting to the temperature conditions of domestic high-temperature oil reservoirs. At the same time, the water absorption expansion multiple of the ultra-low interfacial tension water-based microspheres increases with increasing temperature. According to the law of molecular thermal motion, an increase in temperature will lead to enhanced molecular thermal motion, and thus the binding force between particle molecules will decrease with increasing temperature.

[0153] Table 1 Effect of temperature on water absorption and expansion multiples of ultra-low interfacial tension water-based microspheres

[0154] Temperature, °C 60 70 80 90 100 110 120 130 Water absorption expansion ratio 7.9 8.1 8.1 8.3 8.4 8.5 8.7 Hydration

[0155] The ultra-low interfacial tension water-based microspheres were prepared using the reinjection wastewater with a mineralization of 250,000 mg / L from an oil field in the west. After being placed at different temperatures for 24 hours, the interfacial tension between the microspheres and the simulated oil was measured using a TX500 spinning drop interfacial tension meter. As can be seen from Table 2, the interfacial tension between the surfactant solution and the crude oil first decreases and then increases with increasing temperature. The interfacial tension value is the lowest at about 120°C. When the temperature continues to rise to 130°C, it can still reach an ultra-low interfacial tension level (10 -3 m N / m order of magnitude), indicating that the surfactant has good temperature and salt resistance.

[0156] Table 2 Effect of temperature on water absorption and expansion multiples of ultra-low interfacial tension water-based microspheres

[0157] Temperature, °C 60 70 80 90 100 110 120 130 <![CDATA[Interfacial tension, 10 -3 mN / m]]> 17.5 14.2 12.3 10.5 8.6 5.4 2.1 25.8

[0158] Embodiment 5:

[0159] An ultra-low interfacial tension water-based microsphere, the raw materials for preparation include, by weight:

[0160] (1) Water: 250 parts;

[0161] (2) Polyethylene glycol type I: polyethylene glycol 400, 50 parts;

[0162] (3) Polyethylene glycol II: polyethylene glycol 6000, 300 parts;

[0163] (4) Special polyether: octadecyl primary amine polyoxyethylene ether, 50 parts;

[0164] (5) Hexafluoropropylene oxide trimer: 300 parts;

[0165] (6) dioctyl sodium sulfosuccinate: 40 parts;

[0166] (7) calcium chloride: 100 parts;

[0167] (8) Sodium hydroxide solution 30%: 30 parts;

[0168] (9) acrylamide: 200 parts;

[0169] (10) acrylic acid: 30 parts;

[0170] (11) ammonium persulfate: 5 parts;

[0171] (12) N,N-methylenebisacrylamide: 8 parts;

[0172] (13) ethylene glycol: 100 parts;

[0173] (14) Emulsifier: Tween 80, 30 parts;

[0174] (15) azobisisobutyronitrile: 5 parts;

[0175] (16) Sodium bisulfite: 5 parts.

[0176] The production steps are as follows:

[0177] (1) Add distilled water or deionized water to the No. 1 reactor, and then add polyethylene glycol type I, polyethylene glycol type II, special polyether, hexafluoropropylene oxide trimer, and OT penetrant in sequence. After stirring evenly, introduce nitrogen to the top of the No. 1 reactor, then add ethylene glycol and emulsifier, and continue to stir evenly;

[0178] (2) adding distilled water or deionized water to reactor No. 2, adding solid anhydrous calcium chloride in small amounts and multiple times under stirring, stirring evenly and pumping the mixture into reactor No. 1;

[0179] (3) Add distilled water or deionized water, acrylamide, acrylic acid, and sodium hydroxide aqueous solution (add acid first and then alkali) to the No. 2 reaction kettle, stir evenly, introduce nitrogen, add N,N-methylenebisacrylamide and ammonium persulfate to the kettle, and stir for 2 hours;

[0180] (4) Open the valve at the bottom of reactor No. 1 and continue to introduce nitrogen into reactor No. 1 from the bottom until bubbles rise;

[0181] (5) adding azobisisobutyronitrile to reactor No. 2 and sodium bisulfite to reactor No. 1;

[0182] (6) After the two kettles were stirred for 2 hours each, the monomer aqueous solution in the No. 2 reactor was pumped into the No. 1 reactor by a drop-feeding pump and stirred rapidly. The mixture was reacted for 2 hours, cooled, washed, and dried to obtain ultra-low interfacial tension water-based microspheres.

[0183] Use a balance to weigh 500g of quartz sand with a median particle size of 0.3mm to 0.5mm and 40g of the above-mentioned ultra-low interfacial tension water-based microspheres. Mix the two evenly and fill them into a Φ25mm×500mm stainless steel sand filling tube. Fill and compact while filling until full, and seal both ends with a fine mesh. Then use distilled water for water flooding at an injection rate of 1.0mL / min and a temperature of 60°C. Record the pressure changes during the water flooding process. After the water flooding is completed, the core model is placed at 60°C for 30 days, and then distilled water is used for water flooding again, and the pressure data is recorded. The injection pressure changes of ultra-low interfacial tension water-based microspheres in the core are shown in Table 3 below:

[0184] Table 3 Changes in injection pressure of ultra-low interfacial tension water-based microspheres

[0185]

[0186] It can be seen that as the expansion time increases, the injection pressure gradually increases, and the ultra-low interfacial tension water-based microspheres have a strong retention capacity in the core, which can achieve a good profile control effect. And after the ultra-low interfacial tension water-based microspheres are placed for a period of time, the injection pressure of the core water drive has basically not changed, indicating that the ultra-low interfacial tension water-based microspheres have good stability.

[0187] Embodiment 6:

[0188] A super interfacial tension water-based microsphere, the raw materials for preparation include, by weight:

[0189] (1) Water: 250 parts;

[0190] (2) Polyethylene glycol type I: polyethylene glycol 400, 60 parts;

[0191] (3) Polyethylene glycol II: polyethylene glycol 8000, 300 parts;

[0192] (4) Special polyether: isooctyl alcohol polyoxyethylene ether, 60 parts;

[0193] (5) Hexafluoropropylene oxide trimer: 300 parts;

[0194] (6) dioctyl sodium sulfosuccinate: 80 parts;

[0195] (7) calcium chloride: 100 parts;

[0196] (8) 40% sodium hydroxide solution: 30 parts;

[0197] (9) acrylamide: 200 parts;

[0198] (10) acrylic acid: 30 parts;

[0199] (11) ammonium persulfate: 5 parts;

[0200] (12) N,N-methylenebisacrylamide: 8 parts;

[0201] (13) ethylene glycol: 100 parts;

[0202] (14) Emulsifier: Span 60, 30 parts;

[0203] (15) azobisisobutyronitrile: 5 parts;

[0204] (16) Sodium bisulfite: 5 parts.

[0205] The production steps are as follows:

[0206] (1) Add distilled water or deionized water to the No. 1 reactor, and then add polyethylene glycol type I, polyethylene glycol type II, special polyether, hexafluoropropylene oxide trimer, and OT penetrant in sequence. After stirring evenly, introduce nitrogen to the top of the No. 1 reactor, then add ethylene glycol and emulsifier, and continue to stir evenly;

[0207] (2) adding distilled water or deionized water to reactor No. 2, adding solid anhydrous calcium chloride in small amounts and multiple times under stirring, stirring evenly and pumping the mixture into reactor No. 1;

[0208] (3) Add distilled water or deionized water, acrylamide, acrylic acid, and sodium hydroxide aqueous solution (add acid first and then alkali) to the No. 2 reaction kettle, stir evenly, introduce nitrogen, add N,N-methylenebisacrylamide and ammonium persulfate to the kettle, and stir for 2 hours;

[0209] (4) Open the valve at the bottom of reactor No. 1 and continue to introduce nitrogen into reactor No. 1 from the bottom until bubbles rise;

[0210] (5) adding azobisisobutyronitrile to reactor No. 2 and sodium bisulfite to reactor No. 1;

[0211] (6) After the two kettles were stirred for 2 hours each, the monomer aqueous solution in the No. 2 reactor was pumped into the No. 1 reactor by a drop-feeding pump and stirred rapidly. The mixture was reacted for 2 hours, cooled, washed, and dried to obtain ultra-low interfacial tension water-based microspheres.

[0212] The ultra-low interfacial tension water-based microspheres prepared as above were subjected to a core single-tube simulation experiment to examine their plugging strength to the formation. Table 4 reflects the plugging strength of ultra-low interfacial tension water-based microspheres. The plugging strength of ultra-low interfacial tension water-based microspheres can be described by breakthrough pressure. The determination procedure is as follows: ① Saturate the core with water; ② Inject a certain amount of plugging agent at a certain flow rate. The test process is a conventional process with external pressure and a constant temperature water bath; ③ Place the core injected with the plugging agent in a closed container and place it in a constant temperature water bath at a set temperature for a period of time; ④ Under the conditions of the set temperature and the same external pressure, inject water at a certain flow rate until the first drop of liquid flows out of the outlet of the core holder and liquid continues to flow out. At this time, the reading of the pressure gauge at the inlet end is the breakthrough pressure P of the plugging agent. t .

[0213] Table 4 Plugging strength of ultra-low interfacial tension water-based microspheres

[0214] Core number Length (cm) Injection plugging agent (VP) Liquid outlet pressure (MPa) Breakthrough pressure (MPa / m) 2023-25 5.3 0.5 0.72 13.6 2023-26 4.9 0.5 0.68 13.9

[0215] It can be seen from Table 4 that the plugging strength of the ultra-low interfacial tension water-based microspheres screened out in the experiment is above 13 MPa / m, which can meet the requirements of on-site profile control and flooding control and has a very high plugging strength.

Claims

1. An ultra-low interfacial tension water-based microsphere flooding system, comprising a first section plug and a second section plug, wherein one or more of core-shell self-crosslinked water-based microspheres or pre-crosslinked gel swellable particles are dissolved in oilfield reinjection water at a concentration of 3-6wt% to form the first section plug; a mixture of a surfactant and ultra-low interfacial tension water-based microspheres is dissolved in oilfield reinjection water at a concentration of 4-8wt% to form the second section plug, wherein the surfactant is 15-20wt% in the mixture, the ultra-low interfacial tension water-based microspheres are 80-85wt%, the surfactant is sodium 3-allyloxy-2-hydroxy-1-propane sulfonate, and the ultra-low interfacial tension water-based microspheres are prepared by the following process: (1) Add deionized water to the No. 1 reaction kettle, and then add polyethylene glycol type I, polyethylene glycol type II, special polyether, hexafluoropropylene oxide trimer, and sodium dioctyl sulfosuccinate in sequence, stir evenly, introduce nitrogen to the top of the No. 1 reaction kettle, and then add ethylene glycol and emulsifier, and continue to stir evenly, wherein the special polyether is one or more of isooctyl alcohol polyoxyethylene ether, 12-14 alcohol polyoxyethylene ether, 16-18 alcohol polyoxyethylene ether, dodecyl primary amine polyoxyethylene ether, and octadecyl primary amine polyoxyethylene ether; (2) Add deionized water to reactor No. 2, add anhydrous calcium chloride in small amounts and multiple times while stirring, stir evenly, and then pump into reactor No. 1; (3) Add deionized water, acrylamide, acrylic acid, and sodium hydroxide solution to the No. 2 reactor, stir evenly, and then introduce nitrogen. Then add N,N-methylenebisacrylamide and ammonium persulfate to the reactor, and stir for 1-3 hours. The acrylamide is 100-500 parts by weight, and the acrylic acid is 1-50 parts by weight. (4) Open the bottom valve of reactor No. 1 and continue to introduce nitrogen into reactor No. 1 from the bottom until bubbles rise; (5) Add azobisisobutyronitrile to reactor No. 2 and add sodium bisulfite to reactor No. 1; (6) After the two reactors are stirred for 1-3 hours respectively, the monomer aqueous solution in reactor No. 2 is poured into reactor No. 1 and stirred rapidly. The mixture is reacted for 1-5 hours, cooled, washed and dried to obtain ultra-low interfacial tension water-based microspheres.

2. The ultra-low interfacial tension water-based microsphere flooding system according to claim 1, characterized in that: The ultra-low interfacial tension water-based microspheres are composed of the following substances in parts by weight: 10-100 parts of polyethylene glycol I, 10-500 parts of polyethylene glycol II, 10-100 parts of special polyether, 10-500 parts of hexafluoropropylene oxide trimer, 10-500 parts of sodium dioctyl sulfosuccinate, 100-500 parts of calcium chloride, 0-50 parts of 30-40wt% sodium hydroxide solution, 100-500 parts of acrylamide, 1-50 parts of acrylic acid, 0.1-10 parts of ammonium persulfate, 10-200 parts of ethylene glycol, 1-10 parts of N,N-methylenebisacrylamide, 1-50 parts of emulsifier, 0.1-10 parts of azobisisobutyronitrile, 0.1-10 parts of sodium bisulfite, and 100-500 parts of deionized water.

3. The ultra-low interfacial tension water-based microsphere flooding system according to claim 2, characterized in that: The polyethylene glycol type I is polyethylene glycol 400, and the polyethylene glycol type II is polyethylene glycol 4000, polyethylene glycol 6000 or polyethylene glycol 8000.

4. The ultra-low interfacial tension water-based microsphere flooding system according to claim 2, characterized in that: The emulsifier is one or more of Span 60, Span 80, Tween 60 and Tween 80.

5. The ultra-low interfacial tension water-based microsphere flooding system according to claim 2, characterized in that: The ultra-low interfacial tension water-based microspheres do not require the addition of calcium chloride during summer construction.

6. The application of the ultra-low interfacial tension water-based microsphere flooding system as described in claim 1, 2, 3, 4 or 5 in an oil field refers to injecting a first plug and a second plug in sequence, the first plug enters the high permeability layer and the large pores to adjust the water absorption profile, the second plug enters the deep formation, the water-based microspheres swell when encountering water and fill the formation pores to form a piston-shaped front, and then release surfactants to drive oil, thereby greatly improving the recovery rate.

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