Temperature-resistant and salt-resistant in-situ plugging reinforced gel composition, gel and preparation method and application thereof

Abstract

The invention relates to the technical field of oilfield chemistry, and discloses a temperature-resistant and salt-resistant in-situ plugging reinforced gel composition, gel, and a preparation method and application thereof. The gel composition contains a first monomer, a second monomer, a first cross-linking agent, a second cross-linking agent, an initiator, a reinforcing agent and water, optionally, the composition also contains a third monomer. The gel provided by the invention can be re-crosslinked under the stimulation of high temperature and CO2 acidic conditions to form blocky integral gel, so that the problems of crosslinking uncertainty, chromatographic separation, easiness in causing reservoir damage and the like of an underground crosslinking system are avoided, and meanwhile, the enhancement of the plugging capacity under the in-situ reservoir condition is realized.

Description

Technical Field

[0001] The invention relates to the technical field of oilfield chemistry, and in particular to a temperature-resistant and salt-resistant in-situ plugging enhancement gel composition, the gel, and a preparation method and application thereof. Background Art

[0002] Geological resources such as crude oil, natural gas, natural gas hydrates, and geothermal fluids are all stored in underground reservoirs. To achieve efficient development, fluids (such as water, CO2, steam, and polymer solutions) must be injected into the ground to replenish the formation's energy, thereby extracting the resources from the ground. Furthermore, underground space utilization technologies such as carbon sequestration and gas storage also require the injection of fluids into underground reservoirs to ensure stable storage. The successful application of these technologies requires that the injected fluids be able to achieve balanced migration and distribution within the reservoir.

[0003] However, geological reservoirs are often highly heterogeneous due to the influence of multiple factors such as sedimentation, structure, diagenesis, and fluid. After fluid is injected into the underground, it is very easy for crossflow and leakage to occur along faults, natural cracks, artificial cracks, microcracks, and high permeability layers. This is an important reason that restricts the efficient development of geological energy and the safe utilization of underground space.

[0004] To address these channeling and fluid leakage issues, gels are used to plug channeling and leakage pathways, a method widely considered cost-effective for reducing reservoir heterogeneity. Underground crosslinking systems are widely used in oilfields. Typically, a gel solution consisting of polymers, crosslinkers, and other chemicals is injected underground. The gel forms at a specific formation temperature, sealing the formation.

[0005] However, this type of gel faces some uncertainties during the gelation process, resulting in poor sealing effects. On the one hand, the gelling liquid is easy to enter non-target layers after being injected underground, causing reservoir damage after gelation; on the other hand, when this type of gel passes through the porous medium of the formation, the various components in the gelling liquid interact differently with the rock surface, resulting in different migration speeds. This chromatographic separation phenomenon affects the subsequent gelation performance of the gel system.

[0006] Unlike the aforementioned channeling-blocking systems, the pre-crosslinked particle gel system is formed into gel particles after surface gelation. These gel particles are then formulated into a suspension and injected underground, avoiding the uncertainty of gelation reactions under formation conditions. Currently, various particle gel-based channeling-blocking systems have been proposed both domestically and internationally to address formation heterogeneity.

[0007] CN116023917A discloses a CO2-responsive gel system, its preparation method, and a method for preventing CO2 leakage in oil reservoirs. The system has low viscosity in the absence of CO2, making it easy to inject. Upon reacting with CO2, it forms a carbamate-bridged gel structure, effectively blocking CO2. During CO2 flooding or storage, the CO2-responsive gel is injected into a leaking or leak-prone formation to effectively prevent CO2 leakage from the reservoir.

[0008] CN119529180A discloses a dual-network CO2-responsive particle gel and its application method. The system components include 15%-20% acrylamide, 5%-10% zwitterionic monomer, 5%-10% CO2-responsive monomer, 0.25%-1% emulsifier, 0.05%-0.25% cross-linker, 0.075%-0.15% initiator, and the balance water. The CO2-responsive monomer is composed of vinyl pyridine and N,N-dimethylaminoethyl methacrylate in a mass ratio of (0.5-1):1. Indoor core flooding experiments revealed that the gel particles achieved a 99.0% plugging rate when CO2 was applied to a core at 60°C, with a 10% salinity in the mineralized water, and a fracture width of 0.3 mm.

[0009] CN105504158A discloses a smart gel particle that can be re-crosslinked under formation conditions and a preparation method thereof. After the gel particles enter the formation, under formation conditions, the particles can be re-crosslinked to form a high-strength gel, thereby achieving effective plugging. The smart gel particle is mainly used to solve oilfield profile control and water plugging, filtration control and / or plugging problems during drilling and completion.

[0010] CN112839994A discloses a re-crosslinked particle gel for controlling CO2 consistency and preventing CO2 leakage. This technology provides a CO2-resistant particle gel that can be re-crosslinked under underground conditions to improve the consistency of CO2 flow and control CO2 leakage problems.

[0011] While these technical solutions have the potential to address fluid crossflow and leakage to a certain extent, projects such as oil and gas exploration, storage, and CO2 flooding and storage often develop strong crossflow channels, such as high-permeability fractures and cavities. While traditional granular gels can reduce the permeability of high-permeability zones, fractures, and large pores, they are limited by the matching relationship between their particle size and crossflow channels, as well as the inherent properties of the gel particles. This makes effective plugging difficult, especially in harsh reservoir environments such as high temperature, high salinity, and supercritical CO2 acid corrosion. The resulting plugging effect is short-lived, reducing the economic viability of geo-energy development and underground space utilization technologies.

[0012] Furthermore, traditional gel design relies on empirical trial-and-error methods, which are subject to long cycles, high costs, and difficulty in global optimization. This is especially true in complex reservoir environments characterized by multiple factors, including high temperature, high salinity, and acidic CO₂. Nonlinear interactions between components make molecular structure design and formulation optimization inefficient.

[0013] In recent years, artificial intelligence (AI) technology has provided a new approach for the efficient design of functionalized gels by establishing quantitative predictive models for material composition, structure, and properties. However, existing patents have not yet addressed AI-driven methods for the targeted design of temperature- and salt-tolerant, CO2-responsive gels. Summary of the Invention

[0014] The purpose of the present invention is to solve the problem that traditional particle gels are difficult to withstand multiple harsh environments such as high temperature, high salinity, and supercritical CO2 acid corrosion in geological reservoirs, and the plugging effect period is too short.

[0015] In order to achieve the above-mentioned object, the first aspect of the present invention provides a composition for a temperature-resistant and salt-resistant in-situ plugging and reinforcing gel, wherein the composition comprises a first monomer, a second monomer, a first cross-linking agent, a second cross-linking agent, an initiator, a reinforcing agent, and water; optionally, the composition further comprises a third monomer; The first monomer is selected from at least one of 2-acrylamido-2-methylpropanesulfonic acid, sodium styrenesulfonate, vinylsulfonic acid, p-styrenesulfonic acid, 4-styrylbenzenesulfonic acid, sulfoethyl methacrylate, and hydroxypropanesulfonic acid; The second monomer is selected from at least one of N-vinyl pyrrolidone, diethylaminoethyl acrylate, dimethylaminoethyl methacrylate, vinyl imidazole, vinyl pyridine, and hydroxyethyl methacrylate; The third monomer is selected from at least one of N-isopropyl acrylamide, hydroxyethyl acrylate, and N-(3-aminopropyl) methacrylamide; The first cross-linking agent is selected from at least one of polyethylene imine, borate compounds, dialdehyde cellulose, N,N'-methylenebisacrylamide, and polyethylene glycol diacrylate; The second cross-linking agent is selected from a second acid-sensitive cross-linking agent and / or a second temperature-sensitive cross-linking agent; Based on the total weight of the composition, the content of the first monomer is 5wt%-40wt%, the content of the second monomer is 5wt%-30wt%, the content of the third monomer is 0wt%-10wt%, the content of the first cross-linking agent is 0.01wt%-1wt%, the content of the second cross-linking agent is 0.01wt%-1wt%, the content of the enhancer is 0.01wt%-10wt%, the content of the initiator is 0.01wt%-1wt%, and the balance is water.

[0016] The second aspect of the present invention provides a method for preparing a heat-resistant and salt-resistant in-situ plugging enhancement gel. The method is performed using the composition described in the first aspect, and comprises: mixing and contacting the components in the composition to obtain the gel.

[0017] The third aspect of the present invention provides the gel prepared by the second aspect.

[0018] The fourth aspect of the present invention provides an application of the gel described in the third aspect in at least one of the fields selected from the group consisting of oil field exploitation, underground CO2 crossflow blocking, and CO2 geological storage.

[0019] The heat-resistant and salt-resistant in-situ plugging reinforcement gel prepared by the solution of the present invention can be pre-crosslinked to form gel particles under ground conditions. After being prepared into a suspension with formation water and injected into the reservoir, it can gather in strong cross-flow channels such as cracks, large pores and fissure holes. Under the stimulation of high temperature and CO2 acidic conditions in the formation, the gel particles are re-crosslinked to form a block-shaped integral gel.

[0020] The solution provided by the present invention avoids the problems of uncertainty, chromatographic separation, and reservoir damage caused by underground cross-linking systems, while achieving enhanced plugging capacity under in-situ reservoir conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a physical picture of the temperature-resistant and salt-resistant in-situ plugging enhancement gel Gel-1; Figure 2 These are the injectability test results of the temperature-resistant and salt-resistant in-situ plugging enhancement gel Gel-1. DETAILED DESCRIPTION

[0022] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0023] It should be noted that, in various aspects of the present invention, for the same components in various aspects, the present invention is only described once in one aspect without repeated description, which should not be understood by those skilled in the art as a limitation of the present invention.

[0024] As mentioned above, the first aspect of the present invention provides a composition for a heat-resistant and salt-resistant in-situ plugging and reinforcing gel, the composition comprising a first monomer, a second monomer, a first cross-linking agent, a second cross-linking agent, an initiator, a reinforcing agent, and water; optionally, the composition further comprises a third monomer; The first monomer is selected from at least one of 2-acrylamido-2-methylpropanesulfonic acid, sodium styrenesulfonate, vinylsulfonic acid, p-styrenesulfonic acid, 4-styrylbenzenesulfonic acid, sulfoethyl methacrylate, and hydroxypropanesulfonic acid; The second monomer is selected from at least one of N-vinyl pyrrolidone, diethylaminoethyl acrylate, dimethylaminoethyl methacrylate, vinyl imidazole, vinyl pyridine, and hydroxyethyl methacrylate; The third monomer is selected from at least one of N-isopropyl acrylamide, hydroxyethyl acrylate, and N-(3-aminopropyl) methacrylamide; The first cross-linking agent is selected from at least one of polyethylene imine, borate compounds, dialdehyde cellulose, N,N'-methylenebisacrylamide, and polyethylene glycol diacrylate; The second cross-linking agent is selected from a second acid-sensitive cross-linking agent and / or a second temperature-sensitive cross-linking agent; Based on the total weight of the composition, the content of the first monomer is 5wt%-40wt%, the content of the second monomer is 5wt%-30wt%, the content of the third monomer is 0wt%-10wt%, the content of the first cross-linking agent is 0.01wt%-1wt%, the content of the second cross-linking agent is 0.01wt%-1wt%, the content of the reinforcing agent is 0.01wt%-10wt%, the content of the initiator is 0.01wt%-1wt%, and the balance is water.

[0025] Preferably, based on the total weight of the composition, the content of the first monomer is 10wt%-35wt%, the content of the second monomer is 8wt%-20wt%, the content of the third monomer is 0wt%-5wt%, the content of the first cross-linking agent is 0.05wt%-0.5wt%, the content of the second cross-linking agent is 0.05wt%-0.5wt%, the content of the enhancer is 0.05wt%-5wt%, the content of the initiator is 0.05wt%-0.5wt%, and the balance is water.

[0026] Preferably, the second acid-sensitive crosslinking agent is selected from at least one of phenylboronic acid pinacol ester, tri-n-butyl borate, triethyl borate, diglycerol borate, and trimethyl borate.

[0027] Preferably, the second temperature-sensitive crosslinking agent is at least one selected from 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, hexamethylene diisocyanate-butanone oxime end-capping product, and bis(trimethylsilyl)aminopropyltriethoxysilane.

[0028] According to a particularly preferred embodiment, the first monomer is 2-acrylamido-2-methylpropanesulfonic acid; the second monomer is N-vinyl pyrrolidone and / or dimethylaminoethyl methacrylate; the first cross-linking agent is polyethylene glycol diacrylate; and the second cross-linking agent is phenylboronic acid pinacol ester. The inventors of the present invention have found that, in this preferred embodiment, after the gel provided by the present invention enters the underground reservoir, it can absorb water and swell in a supercritical CO2 acidic environment, and the CO2 response group is protonated to become a positively charged ammonium salt, and the molecular chain stretches, promoting gel swelling and exposing cross-linking sites. The inventors believe that the gel provided in the preferred embodiment of the present invention may have the following mechanism of action: under acidic conditions, the second cross-linking agent is hydrolyzed to release active sites, and the free boric acid re-forms dynamic covalent bonds with the newly exposed vicinal diol groups from polyethylene glycol diacrylate, achieving re-cross-linking to form an overall block structure, thereby achieving enhanced plugging ability under in-situ reservoir conditions.

[0029] According to a particularly preferred embodiment, the first monomer is 2-acrylamido-2-methylpropanesulfonic acid; the second monomer is N-vinyl pyrrolidone and / or dimethylaminoethyl methacrylate; the third monomer is N-isopropylacrylamide; the first crosslinker is polyethylene glycol diacrylate; and the second crosslinker is 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane. The inventors of the present invention have discovered that in this preferred embodiment, after the gel provided by the present invention enters the underground reservoir, at high temperatures, the 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane gradually hydrolyzes, exposing crosslinking sites. The hydrophilic groups in some polymers extend into the water, promoting water absorption and expansion. The inventors believe that the gel provided in the preferred embodiment of the present invention may have the following mechanism of action: under high temperature conditions, the second crosslinker hydrolyzes to release active sites, which then react with surrounding amino / carboxyl groups after ring opening to achieve re-crosslinking, forming an overall block structure, thereby enhancing the plugging ability under in situ reservoir conditions.

[0030] The present invention has no particular requirements for the weight average molecular weight of the polyethyleneimine, which may be, for example, 1500-10000 g / mol.

[0031] Preferably, the reinforcing agent is a nanoparticle material with an average particle diameter of 10 nm to 500 nm.

[0032] More preferably, the reinforcing agent is a nanoparticle material with an average particle diameter of 10 nm to 200 nm. The inventors have found that in this preferred embodiment, the mechanical strength of the re-crosslinked plugging gel provided by the present invention is better.

[0033] Further preferably, the reinforcing agent is selected from at least one of nano-bentonite, nano-silicon dioxide, nano-titanium oxide, nano-aluminum oxide, nano-calcium carbonate, carbon nanotubes, and graphene.

[0034] Further preferably, the reinforcing agent is selected from at least one of nano-bentonite, nano-silicon dioxide, nano-titanium oxide, nano-aluminum oxide, and nano-calcium carbonate.

[0035] Preferably, the initiator is selected from at least one of ammonium persulfate, sodium persulfate, potassium persulfate, tetramethylethylenediamine, and azobisisobutyronitrile.

[0036] More preferably, the initiator is selected from at least one of ammonium persulfate, potassium persulfate, and sodium persulfate.

[0037] The inventors of this invention have discovered that a gel design method that integrates artificial intelligence can significantly shorten the R&D cycle and guide the creation of high-performance combinations that are difficult to discover using traditional methods. The method includes: (a) Construct a parameterized database containing the first monomer, second monomer, first crosslinker, second crosslinker, initiator, enhancer, and water, and collect their molecular descriptors (e.g., functional group type, number of hydrophilic / hydrophobic groups, molecular weight, charge density) and process conditions; (b) Establishing a mapping model between molecular structure and composition and gel properties (recrosslinking time, breakthrough pressure, and plugging rate) through machine learning algorithms; (c) Use optimization algorithms to search for the optimal formula that meets the target performance within the component constraint space.

[0038] As mentioned above, the second aspect of the present invention provides a method for preparing a heat-resistant and salt-resistant in-situ plugging enhancement gel. The method is performed using the composition described in the first aspect, comprising: mixing and contacting the components in the composition to obtain the gel.

[0039] Preferably, the step of performing the mixed contact comprises: (1) In the presence of water, the enhancer is subjected to ultrasonic dispersion treatment to obtain solution 1; (2) contacting the solution 1 with a monomer material containing a first monomer and a second monomer to obtain a solution 2; the monomer material optionally further contains a third monomer; (3) adding a first crosslinking agent, a second crosslinking agent, and an initiator to the solution 2 in sequence for a second contact, and subjecting the obtained solution 3 to a gelling treatment to obtain an intermediate 1; (4) Drying the intermediate 1 to obtain the gel.

[0040] Preferably, in step (1), the ultrasonic dispersion treatment time is 20 min-60 min.

[0041] According to a particularly preferred embodiment, the method further comprises, in step (1), before performing the ultrasonic dispersion treatment, introducing an inert gas into the water for 10-40 minutes, and then performing the ultrasonic dispersion treatment.

[0042] Preferably, in step (2), the conditions for the first contact include: temperature of 20-60°C, time of 0.5-3h, and stirring speed of 500-1500rpm.

[0043] Preferably, in step (3), the second contacting conditions include: a temperature of 20-60°C, a time of 1-6 hours, and a stirring speed of 500-1500 rpm; and the gelling treatment temperature is 30-90°C, and the time is 4-24 hours. The inventors of the present invention have found that, in this preferred embodiment, the in-situ plugging enhancement gel provided by the present invention has a three-dimensional network structure and good water absorption and swelling capacity.

[0044] The present invention has no particular limitation on the conditions for the gelling treatment in step (3). Those skilled in the art may adopt the operation and process conditions known in the art. For example, the treatment may be carried out under static conditions.

[0045] Preferably, in step (4), the drying conditions include: a temperature of 40-90°C and a time of 20-72 hours.

[0046] According to a particularly preferred embodiment, the method further comprises, in step (2), adjusting the pH value of the solution 2 to 7-8 after the first contact, and then performing step (3). The inventors of the present invention have found that, in this preferred embodiment, the CO2-responsive group in the second monomer described in the solution of the present invention can be in a non-ionic state under this pH environment, thereby facilitating the shielding of the cross-linking sites, avoiding the uncertainty of the underground cross-linking system, and achieving enhanced plugging capacity under in-situ reservoir conditions.

[0047] Preferably, the method further comprises, in step (4), after the drying treatment, pulverizing the dried product to obtain the gel having a particle diameter of 20 nm to 10 mm. The inventors of the present invention have found that, in this preferred case, the mineralizable plugging gel provided by the scheme of the present invention has better CO2 plugging efficiency. In addition, the gel synthesis method described in the scheme of the present invention is a one-pot method, and the synthesized block gel is difficult to reach the nanometer level after mechanical crushing; however, under the same synthesis conditions, by using the reverse microemulsion method, by controlling the water-oil ratio to optimize the particle size, nanometer-level (minimum 20 nm) gel particles can be synthesized. The present invention has no special requirements for the conditions of the reverse microemulsion method. For example, reference can be made to the method in Energy & Fuels, 2018 32 (3), 3068-3076 (DOI: 10.1021 / acs.energyfuels.7b03649.).

[0048] As mentioned above, the third aspect of the present invention provides the gel prepared by the second aspect.

[0049] As mentioned above, the fourth aspect of the present invention provides the use of the gel described in the third aspect in at least one of the fields selected from the oil field exploitation, underground CO2 crossflow blocking, and CO2 geological storage.

[0050] The present invention will be described in detail below by way of examples. In the following examples, unless otherwise specified, all instruments and raw materials used are commercially available.

[0051] The first monomer I: 2-acrylamido-2-methylpropanesulfonic acid, purchased from Shanghai Jizhi Biochemical Technology Co., Ltd., brand TCI-A0926-100G.

[0052] The first monomer II: sodium styrene sulfonate (SSS), purchased from Beijing Huawei Ruike Chemical Technology Co., Ltd., brand HWG00338.

[0053] The second monomer I: N-vinyl pyrrolidone, purchased from Shanghai Jizhi Biochemical Technology Co., Ltd., brand V20730.

[0054] The second monomer II: dimethylaminoethyl methacrylate, purchased from Beijing Inokai Technology Co., Ltd., brand R004180.

[0055] The third monomer: N-isopropylacrylamide, purchased from Beijing Inokai Technology Co., Ltd., brand T77704.

[0056] The first cross-linking agent: polyethylene glycol diacrylate (PEGDA), purchased from Shanghai Titan Technology Co., Ltd., brand P17544.

[0057] The second acid-sensitive crosslinking agent: phenylboronic acid pinacol ester, purchased from Shanghai Titan Technology Co., Ltd., brand GC37247.

[0058] The second temperature-sensitive crosslinking agent: 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, purchased from Beijing Xinbaohai Chemical Technology Co., Ltd., brand E156231.

[0059] Initiator: ammonium persulfate.

[0060] Reinforcement agent I: nano-silicon dioxide, with an average particle diameter of 20 nm, purchased from Beijing Yinuokai Technology Co., Ltd.

[0061] Enhancer II: nano-silica, with an average particle diameter of 500 nm, purchased from Shanghai MacLean Biochemical Technology Co., Ltd.

[0062] The room temperature or normal temperature mentioned herein means 25±2°C.

[0063] Example 1 (1) Nitrogen was introduced into water for 30 min, and then an enhancer was added and ultrasonic dispersion was performed for 30 min to obtain solution 1; (2) adding a monomer material containing the first monomer I and the second monomer I to the solution 1 at 40° C. for first contact, and then adjusting the pH value with 40% NaOH to obtain a solution 2 having a pH value of 7.5; the stirring speed of the first contact is 1200 rpm, and the stirring time is 2 h; (3) At 40°C, the first cross-linking agent, the second cross-linking agent, and the initiator were sequentially added to the solution 2 to perform a second contact. The stirring speed of the second contact was 1200 rpm and the stirring time was 2 h. The obtained solution 3 was subjected to a gelling treatment to obtain an intermediate 1. The gelling treatment was performed under the condition of standing at 40°C for 12 h. (4) The intermediate 1 was dried at 80°C for 24 hours, and then pulverized to obtain a temperature-resistant and salt-resistant in-situ plugging enhancement gel, named Gel-1, with an average particle diameter of 100 μm.

[0064] The remaining specific process parameters of this embodiment are shown in Table 1.

[0065] Figure 1 This is a photo of the heat-resistant and salt-tolerant in-situ plugging enhancement gel Gel-1. Figure 1 shows the block-shaped gel, and Figure 2 shows the crushed gel particles.

[0066] Example 2 The same process as in Example 1 was adopted, except that the monomer material also contained a third monomer (N-isopropylacrylamide). The remaining steps were the same as in Example 1 to obtain a particle gel named Gel-2.

[0067] The remaining specific process parameters of this embodiment are shown in Table 1.

[0068] Example 3-Example 7 The same process as Example 1 was adopted, except that the type / amount of raw materials or process parameters were different, as shown in Table 1, to obtain a temperature-resistant and salt-resistant in-situ plugging enhancement gel.

[0069] Example 8 The same process as in Example 1 was used, except that the amounts of the raw materials were different. The amounts of the raw materials were obtained by the following method: The formulation data and performance indicators of Examples 1 to 7 and Comparative Example 1 were collected (Table 2 and Table 3), and the following features were extracted: monomer type, content, number of cross-linking agent functional groups, reinforcing agent particle size, and process parameters (temperature, time); With re-cross-linking time, CO2 breakthrough pressure, and plugging rate as output targets, the random forest algorithm was used to train the prediction model, and the optimization targets were set as follows: re-cross-linking time ≤ 5h at 150°C, breakthrough pressure ≥ 6.0MPa / m, and plugging rate ≥ 99%; The optimized formula is obtained by searching within the component range of claim 1 through a genetic algorithm.

[0070] The remaining specific process parameters of this embodiment are shown in Table 1.

[0071] Table 1

[0072] Comparative Example 1 This comparative example was carried out using a method similar to that of Example 1, except that in step (3), 0.3 g of the first cross-linking agent was added, and no second cross-linking agent was added. The temperature of the gelation treatment after the second contact was increased to 80°C. The remaining steps were the same as those of Example 1, and a particle gel was obtained, named KN-1.

[0073] Comparative Example 2 This comparative example was carried out using a method similar to that of Example 1, except that in step (3), 0.3 g of the second cross-linking agent was added, and the first cross-linking agent was not added. The remaining steps were the same as those of Example 1. The product prepared using this method failed to form a gel.

[0074] Test Example 1 Comparison of re-crosslinking time: Using a high-precision electronic balance, 5 g of the gel particles provided in Examples 1 to 7 were respectively weighed, placed in a beaker filled with the same volume of 10 wt % NaCl, and sealed with plastic wrap; The beaker containing the gel sample was placed in a thermostat at 150°C. t 0, recording the time when weak cross-linking occurs between gel particles t 1, and the time when the boundaries between particles disappear t 2.

[0075] Table 2 shows the re-cross-linking time of the temperature-resistant and salt-resistant in situ plugging enhancement gels Gel-1 to Gel-7 at 50°C, 100°C, and 150°C. As shown in Table 2, increasing the temperature helps shorten the re-cross-linking time. At the same temperature, Gel-1 has the shortest re-cross-linking time. When the particle diameter of the enhancer is too large, the temperature sensitivity to the re-cross-linking reaction is reduced, and the difference in re-cross-linking time at different temperatures becomes smaller. The re-cross-linking time of Gel-AI at 50°C is 3.1 h, which is close to the predicted value (3 h).

[0076] Table 2

[0077] Test Example 2 Injectability test: The present invention exemplarily provides the test results of the in-situ plugging enhancement gel in Example 1.

[0078] Experimental device: high temperature and high pressure core displacement device.

[0079] Experimental materials: the in-situ plugging enhancement gel provided in Example 1 (particle diameter is 80-100 mesh, i.e., 150-177 μm).

[0080] Test steps: 1) Using a high-precision electronic balance, weigh 10 g of gel particles and place them in a 1 L beaker filled with 10 wt% NaCl for swelling. Leave the swollen gel particles at room temperature for 24 h. Remove the swollen gel particles and remove the free water on the surface. 2) placing the processed particle gel in an intermediate container; 3) preparing fracture cores with different fracture openings, including 0.1 mm, 0.3 mm, 0.5 mm, 1 mm, and 2 mm, and placing the fracture cores in a core holder; 4) Turn on the constant temperature system of the experimental device and control the experimental temperature at 150°C; 5) Start the constant-speed and constant-pressure pump and inject the expanded gel particles from the intermediate container into the fracture core at a constant rate of 0.5 mL / min until particles are produced and the injection pressure reaches equilibrium. Record the pressure gradient during the gel injection process.

[0081] Figure 2 The injectability test results of the heat-resistant and salt-resistant in-situ plugging enhancement gel Gel-1 are Figure 2 It can be seen that Gel-1 has good injection performance. During the injection process, the gel particles do not undergo obvious re-crosslinking to reduce the injection performance.

[0082] Test Example 3 CO2 breakthrough pressure test: Experimental device and experimental materials: the same as those in Test Example 2.

[0083] Test steps: 1) Using a high-precision electronic balance, weigh 10 g of the gel particles and place them in a 1 L beaker filled with 1 wt% NaCl to swell. Leave the swelled gel particles at room temperature for 24 h. Remove the swollen gel particles and remove the free water on the surface.

[0084] 2) Place the processed particle gel in a core holder.

[0085] 3) Start the constant speed and pressure pump and inject the expanded gel particles from the intermediate container into the fracture core at a constant rate of 0.5 mL / min until particles are produced and the injection pressure reaches equilibrium.

[0086] 4) The device temperature was raised to 150 °C and 0.1 fracture volume (FPV) of CO2 was injected to allow the gel particles to re-crosslink within the fractures. The re-crosslinking time is shown in Table 2.

[0087] 5) After the gel particles are completely cross-linked, a CO2 displacement experiment is performed.

[0088] 6) Using constant pressure mode, inject CO2 at a constant pressure of 0.05 MPa. Place the outlet line in the aqueous solution to observe whether CO2 breaks through. Specifically, the generation of bubbles indicates CO2 breakthrough. If no bubbles are generated at the outlet after 5 minutes, increase the CO2 injection pressure by 0.05 MPa each time until bubbles appear at the outlet.

[0089] Table 3 shows the CO2 breakthrough pressure test results of the temperature-resistant and salt-resistant in situ plugging enhancement gels Gel-1 to Gel-7 and KN-1. It can be seen from Table 3 that compared with KN-1 which has no re-cross-linking ability, once the re-cross-linking reaction occurs, the gel particles of Gel-1 to Gel-7 adhere to each other and have better sealing tightness; the CO2 breakthrough pressure of Gel-AI is 6.7 MPa / m, which is close to the predicted value (6.8 MPa / m).

[0090] Table 3

[0091] Test Example 4 Plugging performance test: After the completion of Test Example 3, the gel's ability to block CO2 under high temperature and high pressure conditions was further investigated.

[0092] Experimental device and experimental materials: the same as those in Test Example 3.

[0093] Test steps: 1) Set the back pressure to 30 MPa and control the experimental temperature to above 150°C.

[0094] 2) Inject CO2 into the plugged fracture core at a constant rate of 0.5 mL / min, and record the pressure values ​​at both ends of the fracture core during the CO2 injection process.

[0095] 3) After the pressure at both ends of the core stabilizes, stop CO2 injection and maintain high temperature and high pressure CO2 conditions to allow the gel in the fractures to re-crosslink. Refer to Table 2 for the re-crosslinking time.

[0096] 4) Restart CO2 injection, maintaining a constant injection rate (0.5 mL / min) and record the core pressure values ​​at both ends of the core.

[0097] 5) The crack blocking rate of the gel before and after cross-linking is calculated using equations (1) and (2).

[0098] Formula (1), Formula (2), Where, F rr is the residual resistance coefficient, dimensionless; K pregel is the permeability before gel injection, D; K postgel is the permeability after gel injection, D; is the pressure difference between the two ends of the core after gel injection, MPa; is the pressure difference between the two ends of the core before gel injection, MPa; E P is the gel blocking efficiency.

[0099] Calculated by formula (1) and formula (2), the crack plugging rates of the heat-resistant and salt-resistant in-situ plugging enhancement gel Gel-1 were 85.5% and 99.9% before and after re-crosslinking, respectively, indicating that the gel has in-situ self-enhanced plugging performance under high temperature (150°C) and acidic CO2 (pH 1.5-2) environments; the plugging efficiency of Gel-AI after re-crosslinking was 99.98%, which is close to the predicted value (99.99%).

[0100] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A composition for heat-resistant and salt-resistant in-situ plugging enhancement gel, characterized in that: The composition contains a first monomer, a second monomer, a first crosslinking agent, a second crosslinking agent, an initiator, a reinforcing agent and water; optionally, the composition further contains a third monomer; The first monomer is selected from at least one of 2-acrylamido-2-methylpropanesulfonic acid, sodium styrenesulfonate, vinylsulfonic acid, p-styrenesulfonic acid, 4-styrylbenzenesulfonic acid, sulfoethyl methacrylate, and hydroxypropanesulfonic acid; The second monomer is selected from at least one of N-vinyl pyrrolidone, diethylaminoethyl acrylate, dimethylaminoethyl methacrylate, vinyl imidazole, vinyl pyridine, and hydroxyethyl methacrylate; The third monomer is selected from at least one of N-isopropyl acrylamide, hydroxyethyl acrylate, and N-(3-aminopropyl) methacrylamide; The first cross-linking agent is selected from at least one of polyethylene imine, borate compounds, dialdehyde cellulose, N,N'-methylenebisacrylamide, and polyethylene glycol diacrylate; The second cross-linking agent is selected from a second acid-sensitive cross-linking agent and / or a second temperature-sensitive cross-linking agent; Based on the total weight of the composition, the content of the first monomer is 5wt%-40wt%, the content of the second monomer is 5wt%-30wt%, the content of the third monomer is 0wt%-10wt%, the content of the first cross-linking agent is 0.01wt%-1wt%, the content of the second cross-linking agent is 0.01wt%-1wt%, the content of the reinforcing agent is 0.01wt%-10wt%, the content of the initiator is 0.01wt%-1wt%, and the balance is water.

2. The composition according to claim 1, characterized in that Based on the total weight of the composition, the content of the first monomer is 10wt%-35wt%, the content of the second monomer is 8wt%-20wt%, the content of the third monomer is 0wt%-5wt%, the content of the first cross-linking agent is 0.05wt%-0.5wt%, the content of the second cross-linking agent is 0.05wt%-0.5wt%, the content of the reinforcing agent is 0.05wt%-5wt%, the content of the initiator is 0.05wt%-0.5wt%, and the balance is water; And / or, the second acid-sensitive cross-linking agent is selected from at least one of phenylboronic acid pinacol ester, tri-n-butyl borate, triethyl borate, diglycerol borate, and trimethyl borate; And / or, the second temperature-sensitive crosslinking agent is at least one selected from 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, hexamethylene diisocyanate-butanone oxime end-capping product, and bis(trimethylsilyl)aminopropyltriethoxysilane.

3. The composition according to claim 1, characterized in that The reinforcing agent is a nanoparticle material with an average particle diameter of 10nm-200nm; And / or, the reinforcing agent is selected from at least one of nano-bentonite, nano-silicon dioxide, nano-titanium oxide, nano-aluminum oxide, nano-calcium carbonate, carbon nanotubes, and graphene.

4. The composition according to claim 3, characterized in that The initiator is selected from at least one of ammonium persulfate, sodium persulfate, potassium persulfate, tetramethylethylenediamine, and azobisisobutyronitrile.

5. A method for preparing a heat-resistant and salt-resistant in-situ plugging enhancement gel, characterized in that: The method is carried out using the composition according to any one of claims 1 to 4, and comprises: mixing and contacting the components in the composition to obtain the gel.

6. The method according to claim 5, characterized in that The step of performing the mixed contact comprises: (1) In the presence of water, the enhancer is subjected to ultrasonic dispersion treatment to obtain solution 1; (2) contacting the solution 1 with a monomer material containing a first monomer and a second monomer to obtain a solution 2; the monomer material optionally further contains a third monomer; (3) adding a first cross-linking agent, a second cross-linking agent, and an initiator to the solution 2 in sequence for a second contact, and subjecting the obtained solution 3 to a gelling treatment to obtain an intermediate 1; (4) Drying the intermediate 1 to obtain the gel.

7. The method according to claim 6, characterized in that In step (1), the ultrasonic dispersion treatment time is 20 min-60 min; And / or, in step (2), the conditions of the first contact include: temperature of 20-60°C, time of 0.5-3h, stirring speed of 500-1500rpm; And / or, in step (3), the conditions of the second contact include: temperature of 20-60°C, time of 1-6 hours, stirring speed of 500-1500 rpm; the temperature of the gelling treatment is 30-90°C, time of 4-24 hours; And / or, in step (4), the drying treatment conditions include: temperature of 40-90°C and time of 20-72h.

8. The method according to claim 6, characterized in that The method further comprises, in step (2), adjusting the pH value of the solution 2 to 7-8 after the first contact, and then performing step (3).

9. A gel prepared by the method according to any one of claims 5 to 8.

10. Use of the gel according to claim 9 in at least one of the fields selected from the group consisting of oil field exploitation, underground CO2 crossflow blocking, and CO2 geological storage.

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