Pre-crosslinked particle gel for self-crosslinking regrowth of hypersalinity reservoir and application method of pre-crosslinked particle gel

Abstract

The invention discloses pre-crosslinked particle gel for self-crosslinking regrowth of a hypersalinity reservoir. The pre-crosslinked particle gel is prepared from the following raw materials in percentage by mass: 60%-65% of carboxylic acid functional group-containing monomers, 8%-10% of sulfonic acid functional group-containing monomers, 0.5%-1.5% of a bifunctional group-containing crosslinking agent, 0.1%-0.5% of a free radical initiator and the balance of water. The number of raw material components for preparing the pre-crosslinked particle gel is small, and the introduced carboxylic acid functional group-containing monomer and the sulfonic acid functional group-containing monomer can promote the pre-crosslinked particles to respond to divalent cations in formation water to generate self-crosslinking and regrowth to form block gel with higher strength under a high-salinity oil reservoir condition; and the problem that the traditional polymer is dewatered and degraded too early due to the influence of divalent cations in a high-salinity reservoir is avoided. The invention also discloses a preparation method and an application method of the pre-crosslinked granular gel.

Description

Technical Field

[0001] The present invention relates to the technical field of water plugging agents used in oil and gas field development, specifically to pre-crosslinked particle gels with self-crosslinking and regrowth in high salinity reservoirs, and also to a preparation method and an application method of the above-mentioned pre-crosslinked particle gels with self-crosslinking and regrowth in high salinity reservoirs. Background Art

[0002] During the process of oil and gas field development, the gel system profile control and water plugging technology is often used to block the dominant channeling channels to increase the water injection swept volume, thereby improving the oil and gas recovery rate. Since the conventional liquid gels have problems such as insufficient plugging strength and short water control effective period when used for plugging water in high permeability channels with strong water washing and fracture-type channeling channels; thus, the pre-crosslinked particle technology for blocking the dominant channeling channels is proposed. However, the existing pre-crosslinked particle water plugging system has the problem of insufficient strength. Especially during the plugging process of fracture-type water channeling channels, since the particles cannot be completely cemented into a block gel, it is easy to cause subsequent water flooding to break through the plugging layer. Therefore, a new technical system is needed to improve the plugging effect.

[0003] The present invention has developed pre-crosslinked particle gels with self-crosslinking and regrowth in high salinity reservoirs, which can greatly improve the water flooding effect, optimize the oilfield development process, and enhance the oil and gas recovery rate, and has broad application prospects. Summary of the Invention

[0004] The purpose of the present invention is to provide pre-crosslinked particle gels with self-crosslinking and regrowth in high salinity reservoirs, which can effectively solve the problems of poor injectability and unstable water control effect encountered by conventional polymer gels and pre-crosslinked particles in oilfield applications. Especially in high salinity reservoirs, the pre-crosslinked particle gels of the present invention can form a water control gel system with low viscosity and good injectability after being mixed with metal ion crosslinking agents without swelling.

[0005] The second purpose of the present invention is to provide a preparation method of the above-mentioned pre-crosslinked particle gels.

[0006] The third purpose of the present invention is to provide an application method of the above-mentioned pre-crosslinked particle gels.

[0007] The first technical solution adopted by the present invention is that the pre-crosslinked particle gels with self-crosslinking and regrowth in high salinity reservoirs are composed of the following raw materials in terms of molar percentage: 60%-65% of carboxylic acid functional group-containing monomers, 8%-10% of sulfonic acid functional group-containing monomers, 0.5%-1.5% of bifunctional crosslinking agents, 0.1%-0.5% of free radical initiators, and the balance is water.

[0008] The characteristics of the first technical solution of the present invention also lie in: The molar ratio of the carboxylic acid functional group-containing monomers to the sulfonic acid functional group-containing monomers is 6-7:1.

[0009] The carboxylic acid functional group-containing monomer is any one or two of acrylic acid, methacrylic acid, hydroxyacrylic acid, polyvinyl alcohol formal, and 2-hydroxypropionic acid; The sulfonic acid functional group-containing monomer is any one or two of vinylsulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, methylvinylsulfonic acid, and sulfonated polyvinyl alcohol.

[0010] The bifunctional crosslinking agent is any one of N,N'-methylenebisacrylamide, polyethylene glycol diacrylate, divinylbenzene, and tripropylene glycol diacrylate; The radical initiator is any one of sodium persulfate, hydrogen peroxide, ammonium persulfate, di-tert-butyl peroxide, and benzoyl peroxide.

[0011] The second technical solution adopted in the present invention is a preparation method of a pre-crosslinked particle gel for self-crosslinking and regrowth in high salinity reservoirs. The specific preparation process is as follows: Step 1: Weigh the following raw materials according to the molar percentage: 60%-65% of the carboxylic acid functional group-containing monomer, 8%-10% of the sulfonic acid functional group-containing monomer, 0.5%-1.5% of the bifunctional crosslinking agent, 0.1%-0.5% of the radical initiator, and the balance is water; Step 2: Divide the water weighed in Step 1 into two equal parts. Dissolve the carboxylic acid functional group-containing monomer in one part of the water and stir until completely dissolved to obtain Solution A. Dissolve the sulfonic acid functional group-containing monomer in the other part of the water and stir until completely dissolved to obtain Solution B. Then mix Solution A and Solution B evenly to form a monomer solution; Step 3: Add the bifunctional crosslinking agent and the radical initiator to the monomer solution in sequence. Control the pH value of the reaction system to be 5-7 and the reaction temperature to be 50°C-70°C, and stir and polymerize for 2 hours-6 hours until a bulk gel is formed to obtain a pre-crosslinked gel; Step 4: Cut the pre-crosslinked gel into pieces, repeatedly dry and wash it, and then freeze or dry it to make it hard. Then crush it into particles and screen it through a sieve to obtain a pre-crosslinked particle gel with a particle size of 10μm-200μm.

[0012] The characteristics of the second technical solution of the present invention also lie in: The carboxylic acid functional group-containing monomer is any one or two of acrylic acid AA, methacrylic acid, hydroxyacrylic acid, polyvinyl alcohol formal, and 2-hydroxypropionic acid; The sulfonic acid functional group-containing monomer is any one or two of vinylsulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, methylvinylsulfonic acid, and sulfonated polyvinyl alcohol; The bifunctional crosslinking agent is any one of N,N'-methylenebisacrylamide, polyethylene glycol diacrylate, divinylbenzene, and tripropylene glycol diacrylate; The free radical initiator is any one of sodium persulfate, hydrogen peroxide, ammonium persulfate, di-tert-butyl peroxide, and benzoyl peroxide; The molar ratio of the carboxylic acid functional group-containing monomer to the sulfonic acid functional group-containing monomer is 6-7:1.

[0013] The third technical solution adopted in the present invention is an application method of a pre-crosslinked particle gel for self-crosslinking and regrowth in a high salinity reservoir. The prepared pre-crosslinked particle gel is used in a water plugging, profile control, and water control system in the oil and gas field development field as a water plugging agent.

[0014] The characteristics of the third technical solution of the present invention also lie in: The specific usage method of the pre-crosslinked particle gel is as follows: The pre-crosslinked particle gel is prepared into an aqueous solution with a mass concentration of 0.1% - 0.3% and directly injected into an indoor physical model saturated with high salinity brine or into a high salinity reservoir as a water plugging agent.

[0015] The specific usage method of the pre-crosslinked particle gel is as follows: The pre-crosslinked particle gel is mixed with a high-valent metal ion crosslinking agent with a mass concentration of 0.1% - 0.5% to prepare a profile control and water plugging agent, which is injected into the preferential channel of fluid breakthrough as a water plugging agent.

[0016] The high-valent metal ion crosslinking agent is a chromium ion crosslinking agent, a zirconium ion crosslinking agent, or an aluminum ion crosslinking agent.

[0017] The beneficial effects of the present invention are: (1) The raw material components of the pre-crosslinked particle gel prepared in the present invention are few in number and the synthesis method is simple; the introduced carboxylic acid functional group-containing monomer and sulfonic acid functional group-containing monomer can promote the pre-crosslinked particles to respond to divalent cations in formation water under high salinity reservoir conditions to undergo self-crosslinking and regrowth to form a bulk gel with higher strength, avoiding problems such as premature dehydration and degradation of traditional polymers affected by divalent cations in high salinity reservoirs. In reservoirs with normal salinity, metal ion crosslinking agents most commonly used in oilfield operations can be selected to achieve the purpose of self-crosslinking and regrowth of gel particles in the reservoir.

[0018] (2) The pre-crosslinked particle gel of the present invention can be mixed with the crosslinking agent without swelling and directly injected into the reservoir. The system has a low initial viscosity, thus having good injectability and avoiding the problem of too high initial viscosity caused by the need for polymers to swell sufficiently during the preparation of conventional liquid gels; (3) The pre-crosslinked particle gel of the present invention can undergo re-crosslinking with the participation of the introduced metal ion crosslinking agents (such as zirconium ion crosslinking agents, chromium ion crosslinking agents, and aluminum ion crosslinking agents), causing the gaps between the pre-crosslinked particles to regrow after stacking and plugging, thereby avoiding subsequent injected water from breaking through the gaps and effectively improving the water control effect of the system. Description of the Drawings

[0019] Figure 1 It is the water flooding fractional flow curve before and after plugging the high - permeability sand - packed tube by the pre - crosslinked particle gel in the parallel sand - packed tubes filled with saturated CaCl₂ and MgCl₂ mixed brine in Example 5 of the present invention. Detailed Description of the Invention

[0020] The present invention will be described in detail below in conjunction with the drawings and specific embodiments.

[0021] The pre - crosslinked particle gel for self - crosslinking and regrowth in high - salinity reservoirs of the present invention is composed of the following raw materials in terms of molar percentage: carboxylic - functional - group - containing monomer 60% - 65%, sulfonic - functional - group - containing monomer 8% - 10%, bifunctional crosslinking agent 0.5% - 1.5%, free - radical initiator 0.1% - 0.5%, and the balance is water. The functions of the raw materials of the above - mentioned components are as follows: The carboxylic - functional - group - containing monomer provides carboxyl functional groups for crosslinking with divalent cations (Ca²⁺, Mg²⁺). Its carboxylic acid group (-COOH) can form a complex or coordination structure with divalent cations, and this coordination or complex structure can stabilize crosslinking. Especially in a high - salinity water environment, it can effectively crosslink with calcium and magnesium ions. The sulfonic - functional - group - containing monomer provides sulfonic acid functional groups, enhancing the binding ability and stability of the pre - crosslinked particles with ions in high - salinity water. The bifunctional crosslinking agent, as a crosslinking agent, is used to form a crosslinking network structure, improving the mechanical strength and crosslinking stability of the particles. The free - radical initiator, as an initiator, generates free radicals to initiate the polymerization reaction of monomers. Water provides a reaction medium, dissolves monomers, crosslinking agents and initiators, ensuring a uniform polymerization reaction.

[0022] The carboxylic - functional - group - containing monomer is any one or two of acrylic acid AA, methacrylic acid, hydroxyacrylic acid, polyvinyl alcohol - formal, 2 - hydroxypropionic acid; the sulfonic - functional - group - containing monomer is any one or two of vinylsulfonic acid, 2 - acrylamide - 2 - methylpropanesulfonic acid, methylvinylsulfonic acid, sulfonated polyvinyl alcohol. The bifunctional crosslinking agent is any one of N,N'-methylenebisacrylamide, polyethylene glycol diacrylate, divinylbenzene, tripropylene glycol diacrylate; the free - radical initiator is any one of sodium persulfate, hydrogen peroxide, ammonium persulfate, di - tert - butyl peroxide, benzoyl peroxide. The molar ratio of the carboxylic - functional - group - containing monomer to the sulfonic - functional - group - containing monomer is 6 - 7:1.

[0023] The preparation method of the above - mentioned pre - crosslinked particle gel for self - crosslinking and regrowth in high - salinity reservoirs is as follows: Step 1: Weigh the following raw materials according to the molar percentage: 60%-65% of carboxylic acid functional group-containing monomers, 8%-10% of sulfonic acid functional group-containing monomers, 0.5%-1.5% of difunctional crosslinking agents, 0.1%-0.5% of free radical initiators, and the balance is water; the carboxylic acid functional group-containing monomers are any one or two of acrylic acid AA, methacrylic acid, hydroxyacrylic acid, polyvinyl alcohol-formaldehyde, and 2-hydroxypropionic acid; the sulfonic acid functional group-containing monomers are any one or two of vinylsulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, methylvinylsulfonic acid, and sulfonated polyvinyl alcohol. The difunctional crosslinking agent is any one of N,N'-methylenebisacrylamide, polyethylene glycol diacrylate, divinylbenzene, and tripropylene glycol diacrylate; the free radical initiator is any one of sodium persulfate, hydrogen peroxide, ammonium persulfate, di-tert-butyl peroxide, and benzoyl peroxide.

[0024] Step 2: Divide the water weighed in Step 1 into two equal parts. Dissolve the carboxylic acid functional group-containing monomers in one part of the water and stir until completely dissolved to obtain Solution A. Dissolve the sulfonic acid functional group-containing monomers in the other part of the water and stir until completely dissolved to obtain Solution B. Then mix Solution A and Solution B evenly to form a monomer solution; Step 3: Add the difunctional crosslinking agent and the free radical initiator to the monomer solution in sequence. Control the pH value of the reaction system to be 5-7 and the reaction temperature to be 50°C-70°C, and stir and polymerize for 2 hours-6 hours until a block gel is formed to obtain a pre-crosslinked gel; in this step, the difunctional crosslinking agent is a crosslinking agent that promotes the polymerization reaction and forms a crosslinked structure, which is used to strengthen the crosslinking degree of the monomers. During the polymerization reaction, the monomers form a network structure through crosslinking reactions; at the same time, functional groups (carboxylic acid groups and sulfonic acid groups) for crosslinking divalent cations (such as Ca 2+ 、Mg 2+ etc.) or polyvalent metal ion-based crosslinking agents (such as zirconium, chromium ion-based crosslinking agents, etc.) are introduced into the polymer chain.

[0025] Step 4: Cut the pre-crosslinked gel into pieces, repeatedly dry and wash it, and then freeze or dry it to make it hard. Then crush it into particles and sieve it through a sieve to obtain pre-crosslinked granular gel with a particle size of 10μm-200μm. Usually, the pre-crosslinked gel is cut into small pieces with a volume of about 1 cm 3 and is repeatedly dried and washed to remove solvents, unreacted monomers, and small molecule impurities. The substance used for washing is anhydrous ethanol, and the temperature during the drying process is set at 40-60°C.

[0026] The application method of the pre-crosslinked particle gel with self-crosslinking and regrowth in the above high salinity reservoir is to use the prepared pre-crosslinked particle gel in the water plugging and profile control water control system in the oil and gas field development field as a water plugging agent. In this application, two methods of using the pre-crosslinked particle gel with self-crosslinking and regrowth in the high salinity reservoir as a water plugging agent are specifically disclosed. The first method is as follows: The pre-crosslinked particle gel is formulated into an aqueous solution with a mass concentration of 0.1% - 0.3% and directly injected into an indoor physical model saturated with high salinity brine or into a high salinity reservoir as a water plugging agent. The second method is as follows: The specific usage method of the pre-crosslinked particle gel is as follows: The pre-crosslinked particle gel is mixed with a high-valence metal ion crosslinking agent with a mass concentration of 0.1% - 0.5% to prepare a profile control and water plugging agent, which is injected into the dominant channel of fluid channeling as a water plugging agent. The high-valence metal ion crosslinking agent is a chromium ion crosslinking agent, a zirconium ion crosslinking agent, or an aluminum ion crosslinking agent.

[0027] The technical solution of the present invention will be further described below through specific examples: Example 1 According to the molar percentage, the composition of the raw materials in this example is as follows: acrylic acid (AA) 60%, vinylsulfonic acid (VSA) 10%, N,N'-methylenebisacrylamide (MBAA) 1.5%, sodium persulfate (SPS) 0.5%, and the balance is water.

[0028] The water is divided into two equal parts. Acrylic acid (AA) is dissolved in one part of the water and stirred until completely dissolved to obtain solution A; vinylsulfonic acid (VSA) is added to the other part of the water and stirred until completely dissolved to obtain solution B; solution A and solution B are mixed and stirred continuously to form a uniform monomer solution; N,N'-methylenebisacrylamide (MBAA) and sodium persulfate (SPS) are added to the monomer solution and stirred thoroughly until the solution is uniform; the pH of the reaction system is adjusted to 6 with dilute hydrochloric acid, the reaction temperature is 60 °C, and polymerization is carried out for 4 hours to form a bulk gel and obtain a pre-crosslinked gel.

[0029] The pre-crosslinked gel is cut into small pieces with a volume of 1m 3 and repeatedly washed and dried with absolute ethanol to remove solvents, unreacted monomers, and small molecule impurities. After being thoroughly washed, the pre-crosslinked gel is subjected to low-temperature drying treatment at 40 °C to make it hard, and then it is crushed into particles using a ball mill. The crushed particles are screened using a standard sieve to control the particle size range, and pre-crosslinked particle gel with a particle size of 10 - 200 μm is obtained.

[0030] Add a mixed brine of 0.5% mass fraction of CaCl2 and MgCl2 (CaCl2:MgCl2 = 1:1) to the pre-crosslinked particle gel. The mixed brine covers the pre-crosslinked particle gel. Then put it into a reagent bottle and place it in an oven at 60°C for more than 12 h. The pre-crosslinked particles crosslink and self-grow into a bulk gel.

[0031] Example 2 According to the molar percentage, the composition of the raw materials in this example is as follows: methacrylic acid (MAA) 63%, 2-acrylamido-2-methylpropanesulfonic acid (AMPS) 9%, polyethylene glycol diacrylate (PEGDA) 1.5%, hydrogen peroxide (H2O2) 0.1%, and the balance is water.

[0032] Divide the water into two equal parts. Dissolve methacrylic acid (MAA) in one part of the water and stir until completely dissolved to obtain solution A; add 2-acrylamido-2-methylpropanesulfonic acid (AMPS) to the other part of the water and stir until completely dissolved to obtain solution B; mix solution A and solution B and continue to stir to form a uniform monomer solution; add polyethylene glycol diacrylate (PEGDA) and hydrogen peroxide (H2O2) to the monomer solution and stir thoroughly until the solution is uniform; adjust the pH of the reaction system to 5 with dilute hydrochloric acid, the reaction temperature is 50°C, and polymerize for 6 hours to form a bulk gel and obtain a pre-crosslinked gel.

[0033] Cut the pre-crosslinked gel into small pieces with a volume of 1m 3 and wash and dry it repeatedly with absolute ethanol to remove solvents, unreacted monomers and small molecule impurities. After being thoroughly washed, the pre-crosslinked gel is subjected to low-temperature drying treatment at 50°C to make it hard, and then it is crushed into particles using a ball mill. The crushed particles are screened using a standard sieve to control the particle size range, and pre-crosslinked particle gel with a particle size of 10 - 200 μm is obtained.

[0034] Add a chromium acetate crosslinking agent solution with a mass fraction of 0.5% to the pre-crosslinked particle gel. The chromium acetate crosslinking agent solution covers the pre-crosslinked particle gel. Then put it into a reagent bottle and place it in an oven at 60°C for more than 12 h. The pre-crosslinked particles crosslink and self-grow into a bulk gel.

[0035] Example 3 According to the molar percentage, the composition of the raw materials in this example is as follows: hydroxyacrylic acid (HPAA) 65%, methallyl sulfonic acid 10%, divinylbenzene (DVB) 1.2%, ammonium persulfate (APS) 0.3%, and the balance is water.

[0036] Divide the water into two equal parts. Dissolve hydroxyacrylic acid (HPAA) in one part of the water and stir until completely dissolved to obtain solution A; add methallyl sulfonic acid to the other part of the water and stir until completely dissolved to obtain solution B; mix solution A and solution B and continue stirring to form a uniform monomer solution; add divinylbenzene (DVB) and ammonium persulfate (APS) to the monomer solution and stir well until the solution is uniform; adjust the pH of the reaction system to 7 with dilute hydrochloric acid, keep the reaction temperature at 70 °C, and polymerize for 2 hours to form a bulk gel, obtaining a pre-crosslinked gel.

[0037] Cut the pre-crosslinked gel into small pieces with a volume of 1 m 3 and wash and dry it repeatedly with absolute ethanol to remove solvents, unreacted monomers and small molecule impurities. After being thoroughly washed, the pre-crosslinked gel is dried at a low temperature of 60 °C to make it hard, and then it is crushed into particles using a ball mill. The crushed particles are screened using a standard sieve to control the particle size range, obtaining pre-crosslinked granular gel with a particle size of 10 - 200 μm.

[0038] Add a zirconium acetate crosslinking agent with a mass fraction of 0.5% to the pre-crosslinked granular gel to submerge the pre-crosslinked granular gel, put it into a reagent bottle, and place it in an oven at 60 °C and let it stand for more than 12 h. The pre-crosslinked particles crosslink and self-grow into a bulk gel.

[0039] Example 4: According to the molar percentage, the composition of the raw materials in this example is as follows: polyvinyl alcohol formal (PVA-F) 60%, sulfonated polyvinyl alcohol 8%, tripropylene glycol diacrylate (TMPTA) 0.5%, di-tert-butyl peroxide (DTBP) 0.5%, and the balance is water.

[0040] Divide the water into two equal parts. Dissolve polyvinyl alcohol formal (PVA-F) in one part of the water and stir until completely dissolved to obtain solution A; add sulfonated polyvinyl alcohol to the other part of the water and stir until completely dissolved to obtain solution B; mix solution A and solution B and continue stirring to form a uniform monomer solution; add tripropylene glycol diacrylate (TMPTA) and di-tert-butyl peroxide (DTBP) to the monomer solution and stir well until the solution is uniform; adjust the pH of the reaction system to 6 with dilute hydrochloric acid, keep the reaction temperature at 60 °C, and polymerize for 5 hours to form a bulk gel, obtaining a pre-crosslinked gel.

[0041] Cut the pre-crosslinked gel into small pieces with a volume of 1 m 3The pre-crosslinked gel was cut into small pieces of 1 m

[0042] The pre-crosslinked granular gel was covered with an aluminum acetate crosslinking agent with a mass fraction of 0.5%, placed in a reagent bottle, and put into an oven at 60 °C and left standing for more than 12 h. The pre-crosslinked particles crosslinked and self-grew into a bulk gel.

[0043] Example 5 According to the molar percentage, the composition of the raw materials in this example is as follows: 65% 2-hydroxypropionic acid, 10% sulfonated polyvinyl alcohol, 0.5% tripropylene glycol diacrylate (TMPTA), 0.5% benzoyl peroxide (BPO), and the balance is water.

[0044] The water was divided into two equal parts. 2-Hydroxypropionic acid was dissolved in one part of the water and stirred until completely dissolved to obtain solution A; sulfonated polyvinyl alcohol was added to the other part of the water and stirred until completely dissolved to obtain solution B; solution A and solution B were mixed and stirred continuously to form a uniform monomer solution; tripropylene glycol diacrylate (TMPTA) and benzoyl peroxide (BPO) were added to the monomer solution and stirred thoroughly until the solution was uniform; the pH of the reaction system was adjusted to 6 with dilute hydrochloric acid, the reaction temperature was 60 °C, and polymerization was carried out for 5 h to form a bulk gel and obtain a pre-crosslinked gel.

[0045] The pre-crosslinked gel was cut into small pieces with a volume of 1 m 3 The small pieces were repeatedly washed and dried with absolute ethanol to remove the solvent, unreacted monomers and small molecule impurities. After being thoroughly washed, the pre-crosslinked gel was subjected to low-temperature drying at 50 °C to make it hard, and then it was crushed into particles using a ball mill. The crushed particles were screened using a standard sieve to control the particle size range, and pre-crosslinked granular gel with a particle size of 10 - 200 μm was obtained.

[0046] Two sand-packed tubes with different permeabilities were filled with quartz sand of 40-60 mesh and 80-120 mesh respectively. A mixed brine of CaCl2 and MgCl2 (CaCl2:MgCl2 = 1:1) was used for displacement, and the fractional flow rates of the high-permeability and low-permeability sand-packed tubes during the displacement process were recorded. After continuously injecting 10 PV of the mixed brine, a pre-crosslinked particle gel solution with a mass fraction of 0.5% was directly (without swelling) injected into the sand-packed tube saturated with the mixed brine of CaCl2 and MgCl2 (CaCl2:MgCl2 = 1:1) (5 PV), and waited for 12 h for the pre-crosslinked particles of the present invention to form stable crosslinking and self-growth with divalent cations (such as Ca 2+ 、Mg 2+ etc.) in the high salinity water to achieve high plugging of the high-permeability channels; continued to switch to brine displacement, and recorded the fractional flow rate results of the high-permeability and low-permeability sand-packed tubes during the displacement process as Figure 1 shown.

[0047] Example 6 According to the molar percentage, the composition of the raw materials in this example is as follows: polyvinyl alcohol formal (PVA-F) 62%, sulfonated polyvinyl alcohol 10%, tripropylene glycol diacrylate (TMPTA) 0.5%, di-tert-butyl peroxide (DTBP) 0.5%, and the balance is water.

[0048] The water was divided into two equal parts. Polyvinyl alcohol formal (PVA-F) was dissolved in one part of the water and stirred until completely dissolved to obtain solution A; sulfonated polyvinyl alcohol was added to the other part of the water and stirred until completely dissolved to obtain solution B; solution A and solution B were mixed and stirred continuously to form a uniform monomer solution; tripropylene glycol diacrylate (TMPTA) and di-tert-butyl peroxide (DTBP) were added to the monomer solution and stirred thoroughly until the solution was uniform; the pH of the reaction system was adjusted to 6 with dilute hydrochloric acid, the reaction temperature was 60 °C, and polymerization was carried out for 5 hours to form a block gel to obtain a pre-crosslinked gel.

[0049] The pre-crosslinked gel was cut into small blocks with a volume of 1 m 3 and repeatedly washed and dried with absolute ethanol to remove solvents, unreacted monomers and small molecule impurities. After being thoroughly washed, the pre-crosslinked gel was subjected to low-temperature drying treatment at 50 °C to make it hard, and then it was crushed into particles using a ball mill. The crushed particles were sieved using a standard sieve to control the particle size range, and pre-crosslinked particle gels with a particle size of 10-200 μm were obtained.

[0050] Two sand-packed tubes with different permeabilities were filled with quartz sand of 40-60 mesh and 80-120 mesh respectively. A mixed brine of CaCl2 and MgCl2 (CaCl2:MgCl2 = 1:1) was used for displacement, and the fractional flow rates of the high-permeability and low-permeability sand-packed tubes during the displacement process were recorded. After continuously injecting 10 PV of the mixed brine, a gelling agent formed by mixing a pre-crosslinked particle gel solution with a mass fraction of 0.5% and a chromium acetate crosslinking agent with a mass fraction of 0.5 was directly (without swelling) injected into the sand-packed tube saturated with the mixed brine of CaCl2 and MgCl2 (CaCl2:MgCl2 = 1:1) (5 PV). Wait for 12 h for the pre-crosslinked particles of the present invention to form stable crosslinking and self-growth with chromium acetate to achieve high plugging of the high-permeability channels.

[0051] Example 7 According to the molar percentage, the composition of the raw materials in this example is as follows: hydroxyacrylic acid (HPAA) 63%, methallyl sulfonic acid 9%, divinylbenzene (DVB) 1.2%, ammonium persulfate (APS) 0.3%, and the balance is water.

[0052] The water was divided into two equal parts. Hydroxyacrylic acid (HPAA) was dissolved in one part of the water and stirred until completely dissolved to obtain solution A; methallyl sulfonic acid was added to the other part of the water and stirred until completely dissolved to obtain solution B; solution A and solution B were mixed and stirred continuously to form a uniform monomer solution; divinylbenzene (DVB) and ammonium persulfate (APS) were added to the monomer solution and stirred thoroughly until the solution was uniform; the pH of the reaction system was adjusted to 7 with dilute hydrochloric acid, the reaction temperature was 70 °C, and polymerization was carried out for 2 hours to form a bulk gel to obtain a pre-crosslinked gel.

[0053] The pre-crosslinked gel was cut into small pieces with a volume of 1 m 3 and repeatedly washed and dried with absolute ethanol to remove the solvent and unreacted monomers and small molecule impurities. The pre-crosslinked gel after being thoroughly cleaned was frozen to make it hard, and then it was crushed into particles using a ball mill. The crushed particles were screened using a standard sieve to control the particle size range, and pre-crosslinked particle gel with a particle size of 10-200 μm was obtained.

[0054] Two sand-packed tubes with different permeability were filled with quartz sand of 40-60 mesh and 80-120 mesh respectively. A mixed brine of CaCl2 and MgCl2 (CaCl2:MgCl2 = 1:1) was used for displacement, and the fractional flow rates of the high-permeability and low-permeability sand-packed tubes during the displacement process were recorded. After continuously injecting 10 PV of the mixed brine, a gelling agent formed by mixing a pre-crosslinked particle gel with a mass fraction of 0.5% and a zirconium acetate crosslinking agent with a mass fraction of 0.5 was directly (without swelling) injected into the sand-packed tube saturated with the mixed brine of CaCl2 and MgCl2 (CaCl2:MgCl2 = 1:1) (5 PV). After waiting for 12 h for the pre-crosslinked particle gel of the present invention to form stable crosslinking and self-growth with zirconium acetate, high-permeability channels were highly plugged.

Claims

1. Pre-crosslinked particle gel for self-crosslinking and regrowth in high salinity reservoirs, characterized in that, It consists of the following raw materials by mole percentage: 60%-65% of carboxylic acid functional group-containing monomers, 8%-10% of sulfonic acid functional group-containing monomers, 0.5%-1.5% of difunctional crosslinking agents, 0.1%-0.5% of free radical initiators, and the balance is water.

2. The pre-crosslinked particle gel for self-crosslinking and regrowth in a high salinity reservoir according to claim 1, characterized in that, The molar ratio of the carboxylic acid functional group-containing monomers to the sulfonic acid functional group-containing monomers is 6-7:

1.

3. The pre-crosslinked particle gel for self-crosslinking and regrowth in high salinity reservoirs according to claim 1, characterized in that, The carboxylic acid functional group-containing monomers are any one or two of acrylic acid, methacrylic acid, hydroxyacrylic acid, polyvinyl formal, and 2-hydroxypropionic acid; the sulfonic acid functional group-containing monomers are any one or two of vinylsulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, methylvinylsulfonic acid, and sulfonated polyvinyl alcohol.

4. The pre-crosslinked particle gel for self-crosslinking and regrowth in a high salinity reservoir according to any one of claims 1-3, characterized in that, The difunctional crosslinking agent is any one of N,N'-methylenebisacrylamide, polyethylene glycol diacrylate, divinylbenzene, and tripropylene glycol diacrylate; the free radical initiator is any one of sodium persulfate, hydrogen peroxide, ammonium persulfate, di-tert-butyl peroxide, and benzoyl peroxide.

5. Preparation method of pre-crosslinked particle gel with self-crosslinking and regrowth in high salinity reservoirs, characterized in that, The specific preparation process is as follows: Step 1: Weigh the following raw materials according to the mole percentage: 60%-65% of carboxylic acid functional group-containing monomers, 8%-10% of sulfonic acid functional group-containing monomers, 0.5%-1.5% of difunctional crosslinking agents, 0.1%-0.5% of free radical initiators, and the balance is water; Step 2: Divide the water weighed in Step 1 into two equal parts. Dissolve the carboxylic acid functional group-containing monomers in one part of the water and stir until completely dissolved to obtain Solution A. Dissolve the sulfonic acid functional group-containing monomers in the other part of the water and stir until completely dissolved to obtain Solution B. Then mix Solution A and Solution B evenly to form a monomer solution; Step 3: Add the difunctional crosslinking agent and the free radical initiator to the monomer solution in sequence, control the pH value of the reaction system to be 5-7, the reaction temperature to be 50°C-70°C, and stir and polymerize for 2 hours-6 hours until a block gel is formed to obtain a pre-crosslinked gel; Step 4: Cut the pre-crosslinked gel into pieces, repeatedly dry and wash it, and then freeze or dry it to make it hard. Then crush it into particles and screen it through a sieve to obtain pre-crosslinked granular gel with a particle size of 10μm-200μm.

6. The preparation method of the pre-crosslinked particle gel with self-crosslinking and regrowth in high salinity reservoirs according to claim 5, characterized in that, The carboxylic acid functional group-containing monomers are any one or two of acrylic acid AA, methacrylic acid, hydroxyacrylic acid, polyvinyl formal, and 2-hydroxypropionic acid; the sulfonic acid functional group-containing monomers are any one or two of vinylsulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, methylvinylsulfonic acid, and sulfonated polyvinyl alcohol; the difunctional crosslinking agent is any one of N,N'-methylenebisacrylamide, polyethylene glycol diacrylate, divinylbenzene, and tripropylene glycol diacrylate; the free radical initiator is any one of sodium persulfate, hydrogen peroxide, ammonium persulfate, di-tert-butyl peroxide, and benzoyl peroxide, and the molar ratio of the carboxylic acid functional group-containing monomers to the sulfonic acid functional group-containing monomers is 6-7:

1.

7. Application method of pre-crosslinked particle gel with self-crosslinking and regrowth in high salinity reservoir, characterized in that, The prepared pre-crosslinked granular gel is used in the water plugging, profile control, and water control system in the oil and gas field development field and is used as a water plugging agent.

8. The application method of the pre-crosslinked particle gel with self-crosslinking and regrowth in high salinity reservoirs according to claim 7, characterized in that, The specific application method is as follows: Prepare the pre-crosslinked particle gel into an aqueous solution with a mass concentration of 0.1% - 0.3%, and directly inject it into an indoor physical model saturated with high salinity brine or into a high salinity reservoir as a water plugging agent.

9. The application method of the pre-crosslinked particle gel with self-crosslinking and regrowth in high salinity reservoirs according to claim 7, characterized in that, The specific usage method is as follows: Mix the pre-crosslinked particle gel with a high-valent metal ion crosslinking agent with a mass concentration of 0.1% - 0.5% to prepare a profile control and water plugging agent, and inject it into the preferential channel of fluid breakthrough as a water plugging agent.

10. The application method of the pre-crosslinked particle gel with self-crosslinking and regrowth in high salinity reservoirs according to claim 9, characterized in that, The high-valent metal ion crosslinking agent is a chromium ion crosslinking agent, a zirconium ion crosslinking agent or an aluminum ion crosslinking agent.

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