An organic-inorganic composite material system for preventing / controlling CO2 formation leakage, its preparation method and application

Abstract

This invention discloses an organic-inorganic composite material system for preventing / controlling CO2 formation leakage. The organic-inorganic composite material system includes organic comonomers, tannic acid, a composite initiator, a binary crosslinking agent pair, sodium alginate-gum arabic@sodium silicate microcapsules, thiourea, and other raw materials. The organic comonomers are dissolved in water, and the composite initiator is added to obtain a solution. Tannic acid, the binary crosslinking agent pair, sodium alginate-gum arabic@sodium silicate microcapsules, and thiourea are then added to the solution to obtain an organic-inorganic composite solution. In application, a sodium alginate-gum arabic@sodium silicate microcapsule suspension and a calcium chloride solution are injected alternately in multiple rounds, followed by the injection of the organic-inorganic composite solution. This forms a gel radial barrier above the shallow formation-caprock interface or above the leakage path at weak points within the caprock, forcing the leaked CO2 to accumulate laterally and generate mineral precipitates in situ, sealing and solidifying cracks, thereby reducing the amount of CO2 leakage and achieving long-term safe CO2 containment.

Description

Technical Field

[0001] This invention relates to the field of CO2 formation leakage prevention and control technology, and in particular to an organic-inorganic composite material system for preventing and controlling CO2 leakage in the caprock of a CO2 geological storage system, its preparation method and application. Background Technology

[0002] CO2 capture and storage (CCS) technology refers to the capture, purification, compression, transportation, and injection of CO2 generated in industrial production into deep geological storage, achieving permanent isolation of CO2 from the atmosphere. Currently, the main CO2 storage technologies used on a large scale are injecting CO2 into oil reservoirs for oil displacement and storing it in saline aquifers. Injecting large amounts of CO2 into saline aquifers / oil reservoirs necessitates consideration of CO2 leakage risks. Existing research indicates that CO2 leakage along the caprock is the greatest risk threatening the long-term safe storage of CO2. There are two main leakage paths along the caprock: ① Fracture propagation to the caprock. When a large amount of CO2 is stored in the reservoir, and the bottomhole pressure exceeds the formation fracture pressure, CO2 leaks upwards to the caprock-reservoir interface. Pore pressure accumulates at the interface, causing shear failure, and the fracture extends into the caprock; ② Fault activation within the caprock. A rapid increase in pore pressure activates faults (the caprock contains faults or fault failure extends into the caprock).

[0003] Currently used technologies for preventing and controlling CO2 leaks in caprock mainly include geological site selection for CO2 storage facilities, computer-simulated CO2 leak risk assessment, CO2 leak monitoring technology, real-time adjustment of construction parameters, and chemical prevention and control methods. Among these, chemical prevention and control methods primarily include CO2 foam, CO2 reactive slurry, CO2-responsive polymers, CO2-responsive worm-like micelles, polymer gels, nanoparticles, microbially induced calcium carbonate precipitation, and hydraulic barriers.

[0004] CO2 foam reduces CO2 migration and flow rate by controlling gas mobility and expands CO2 sweep volume through fluid diversion. However, the foam has low mechanical strength, and the high temperature, high pressure, and high salinity conditions of the reservoir accelerate the drainage rate of the liquid film, reducing foam stability, and foam collapse is irreversible. On-site construction is difficult; foam formed on the surface has poor injectability, while foam formed underground has poor foaming performance, foam life, and stability. CO2 reactive slurry injects silicate aqueous solution into the formation to react with dissolved CO2, generating amorphous SiO2 precipitates to fill and seal cracks. However, the generated precipitates cannot completely seal leakage channels, and CO2 gas can easily escape. Silicate aqueous solutions settle immediately upon contact with CO2, and the sedimentation time is too fast to achieve precise prevention / control. CO2-responsive polymers / CO2-responsive worm-like micelles transform from low-viscosity aqueous solutions into flowable high-viscosity polymers / worm-like micelles upon encountering CO2, but their mechanical strength is inferior to solid gels, making long-term storage impossible. Furthermore, the system is sensitive to CO2 stimulation and responds rapidly. Upon encountering CO2 near the wellbore, it reacts as a high-viscosity solution, making it unable to penetrate deep into the caprock for prevention / control. The polymer gel forms new diversions after in-situ gelation under underground temperature and pressure conditions, reducing CO2 leakage. However, it is generally not acid-resistant and is prone to shrinkage, breakage, degradation, and instability in low-pH CO2 environments. Additionally, there is a contradiction between control intensity and displacement pressure differential, and between injection capacity and prevention / control range. Nanoparticles, by mixing CO2 and injecting them into the reservoir, increase the density difference between saturated CO2 brine and lower brine, reducing the time to unstable flow and accelerating convective mixing. However, nanoparticles are expensive and have complex preparation processes. Microbial-induced calcium carbonate precipitation involves the catalytic hydrolysis of urea and Ca by urease in bacteria. 2+ The reaction produces calcium carbonate precipitation in situ, sealing and reinforcing microcracks. However, this technology is still relatively immature, with problems such as high cost of bacteria and nutrient solution, uneven distribution of calcium carbonate precipitation, significant impact of supercritical CO2 and high-temperature environment on bacterial activity, and inability to repair larger-scale cracks. The hydraulic barrier method creates a hydraulic barrier by setting up a water injection well on one side of the CO2 injection well, preventing the CO2 plume from migrating upwards. However, this method lacks selectivity; to ensure complete blocking of CO2 migration, the injection length in the upper reservoir must exceed the CO2 plume thickness, requiring the injection of a large amount of brine. The prevention / control effect is affected by the distance between the leaking well and the injection well.

[0005] In summary, current chemical methods for preventing and controlling CO2 leakage in caprock formations all have various shortcomings, affecting their effectiveness to varying degrees. Therefore, it is necessary to develop a low-viscosity, delayed-crosslinking, high-strength, strong-adhesive, and self-adhesive material system for preventing and controlling CO2 leakage in caprock formations. This material must simultaneously meet the requirements of "easy injection, long-distance travel, durable performance, long-lasting plugging, and efficient and precise leakage prevention and control" in caprock formations in remote well areas of CO2 geological storage systems. Summary of the Invention

[0006] To address the shortcomings of current chemical methods used in CO2 leak prevention and control, which directly affect the effectiveness of CO2 leak prevention and control in caprock formations, this invention provides an organic-inorganic composite material system for preventing and controlling CO2 formation leaks, along with its preparation method and application. This organic-inorganic composite material system can simultaneously meet the requirements of "easy injection, long reach, durable, long-lasting plugging, and highly efficient and precise leak prevention and control" in caprocks in remote well areas of CO2 geological storage systems.

[0007] The organic-inorganic composite material system for preventing / controlling CO2 formation leakage provided by this invention comprises the following raw material components: organic comonomer, tannic acid, composite initiator, binary crosslinking agent pair, sodium alginate-gum arabic@sodium silicate microcapsules, thiourea, and deionized water solvent. The mass percentage concentration of each raw material component is as follows:

[0008] Based on the total mass of the organic-inorganic composite solution, the mass percentage concentration of the organic comonomer is 5-10 wt%, the mass percentage concentration of the composite initiator is 0.05-0.1 wt%, the mass percentage concentration of the binary crosslinking agent pair is 0.015-0.03 wt%, the mass percentage concentration of tannic acid is 0.5-1 wt%, the mass percentage concentration of sodium silicate is 5-10 wt%, and the mass percentage concentration of thiourea is 0.05-0.1 wt%.

[0009] The preparation method of the sodium alginate-gum arabic@sodium silicate microcapsules is as follows:

[0010] (1) Mix gum arabic (GA) solution with sodium silicate (Na2O·3SiO2) solution and stir thoroughly to obtain GA / Na2O·3SiO2 solution; add the compound nonionic surfactants Span 80 and Tween 80 dropwise to GA / Na2O·3SiO2 solution and emulsify at high speed at 70℃ for 5 h to obtain O / W emulsion, namely GA / Na2O·3SiO2 emulsion.

[0011] (2) Add sodium alginate (SA) to the GA / Na2O·3SiO2 emulsion at 70℃, add glacial acetic acid dropwise to adjust the pH of the solution to 4.2, stir until fully mixed, and obtain GA / SA / Na2O·3SiO2 emulsion.

[0012] (3) The GA / SA / Na2O·3SiO2 emulsion was slowly and uniformly added to the calcium chloride solution in the form of spherical droplets, and stirred and solidified for 1 h to obtain a Ca / SA / GA@Na2O·3SiO2 suspension. The mass percentage concentration of the calcium chloride solution was 6.0-12.0 wt%.

[0013] (4) After the Ca / SA / GA@Na2O·3SiO2 suspension was allowed to stand, it was filtered, washed and dried to obtain Ca / SA / GA@Na2O·3SiO2 microcapsules.

[0014] The organic comonomers are acrylamide (AM) and 2-acrylamide-2-methylpropanesulfonic acid (AMPS). Preferably, the mass ratio of acrylamide to 2-acrylamide-2-methylpropanesulfonic acid is (4-5):1.

[0015] The composite initiator is a compound of ammonium persulfate-sodium bisulfite redox initiator and azobisisobutyronitrile, belonging to the low-temperature-high-temperature composite initiator category. Preferably, the mass ratio of ammonium persulfate-sodium bisulfite redox initiator to azobisisobutyronitrile is 4:1. The mass ratio of ammonium persulfate to sodium bisulfite in the redox initiator is 1:1.

[0016] The binary crosslinking agent is a compound of hexamethylenetetramine (HMTA) and resorcinol (RE). Preferably, the mass ratio of hexamethylenetetramine to resorcinol is (1-5):1.

[0017] This invention also provides a method for preparing an organic-inorganic composite material system for preventing / controlling CO2 formation leakage, the steps of which are as follows:

[0018] S1. Acrylamide and 2-acrylamide-2-methylpropanesulfonic acid are mixed in a certain proportion and dissolved in deionized water. The mixture is mechanically stirred until fully dissolved. The pH of the solution is adjusted to 6.0. Under N2 purging conditions, ammonium persulfate, sodium bisulfite, and azobisisobutyronitrile are added sequentially to obtain an AM-AMPS solution (solution A). The pH adjusting agents are glacial acetic acid and sodium hydroxide.

[0019] S2. Add tannic acid (TA) to solution A and stir mechanically until fully mixed to obtain AM-AMPS / TA solution (solution B).

[0020] S3. Mix hexamethylenetetramine and resorcinol in a certain proportion and add them to solution B to obtain an organic solution.

[0021] S4. Preparation of sodium alginate-gum arabic@sodium silicate microcapsules.

[0022] S5. Add sodium alginate-gum arabic@sodium silicate microcapsules and thiourea to an organic solution to obtain an organic-inorganic composite solution.

[0023] After continuously and uniformly introducing CO2 into the organic-inorganic composite solution prepared by the above method, it is quickly sealed and placed at 40°C. oThe reaction occurs in the oven at temperature C. In the solution, organic free radical polymerization, inorganic acid-base neutralization, and silicic acid condensation occur, leading to cross-linking and entanglement between organic and inorganic polymer chains, forming an organic-inorganic interpenetrating three-dimensional network structure. This indicates that the organic-inorganic composite solution can undergo a solution-sol-gel transition under CO2 acidic conditions and a temperature greater than or equal to 40°C, generating a non-flowing gel.

[0024] This invention also provides a method for applying the aforementioned organic-inorganic composite material system for preventing / controlling CO2 formation leakage, the steps of which are as follows:

[0025] Step 1: Injection of Sodium Silicate-Isolation Fluid-Calcium Chloride Solution: Before or after a CO2 leak is detected, the main agent, sodium alginate-gum arabic@sodium silicate microcapsule suspension, and the auxiliary agent, calcium chloride solution, are injected alternately in multiple rounds into the weak zone or leaked path of the caprock through a CO2 injection well. Brine is also injected as an isolation slug to promote the deep migration of both agents. The injection sequence for each round is: isolation slug - main agent - isolation slug - auxiliary agent - isolation slug. In this step, the injection of sodium alginate-gum arabic@sodium silicate microcapsules and calcium chloride into the formation is to generate mineral precipitation.

[0026] Step 2: Injection of the organic-inorganic composite solution: The organic-inorganic composite solution is injected into the formation. An isolation slug is injected to propel the solution deeper into the formation, filling the weak points within the caprock at the shallow formation-caprock interface / leakage path. In this step, the sodium alginate-gum arabic@sodium silicate microcapsules in the organic-inorganic composite solution serve to generate an organic-inorganic interpenetrating network composite gel and to delay gel formation.

[0027] Step 3, Well Shutdown: Shut down the well for a period of time to allow the system to react. Sodium silicate as the main agent and calcium chloride as the auxiliary agent meet at the target location in the far-wellbore zone. Upon encountering leaked CO2, they generate mineral precipitates in situ, filling and sealing weak points / vertical micro-fractures / faults in the caprock, cementing and reinforcing loose clay particles inside. The organic-inorganic composite solution migrates deep into the caprock, where it encounters leaked CO2 above potential / already leaked paths, forming a gel radial barrier that forces the leaked CO2 to accumulate laterally.

[0028] Step 4, CO2 injection: After the system reaction is complete, open the CO2 injection well and continuously inject CO2 into the reservoir for permanent storage.

[0029] Preferably, in step 1, the sodium alginate-gum arabic@sodium silicate microcapsule suspension is obtained by adding sodium alginate-gum arabic@sodium silicate microcapsules to an aqueous solution and mechanically stirring until uniformly suspended; wherein the mass concentration of sodium alginate-gum arabic@sodium silicate microcapsules in the sodium alginate-gum arabic@sodium silicate microcapsule suspension is 5-15 wt%. The mass concentration of calcium chloride in the calcium chloride solution is 3.5-12.0 wt%. The brine is a 5 wt% potassium chloride solution.

[0030] The working principle of the organic-inorganic composite material system of the present invention is as follows:

[0031] When CO2 is absent at the surface, the initial viscosity of the organic-inorganic composite solution is close to that of water, making it easy to inject. During CO2 geological sequestration, the organic-inorganic composite solution is injected into the formation, and the system migrates deep into the formation to the shallow formation-caprock interface above weak points within the caprock or above leakage paths. Upon encountering CO2 escaping from the top of the caprock, hexamethylenetetramine hydrolyzes under the acidic heating environment of CO2, releasing formaldehyde, which then reacts stepwise at two active sites of resorcinol. Acrylamide-2-acrylamide-2-methylpropanesulfonic acid undergoes a free radical polymerization reaction to form an organic AM-AMPS copolymer chain; silicate undergoes an acid-base neutralization reaction with carbonic acid to condense and form inorganic polysilicic acid chains. The intermediate products of formaldehyde and resorcinol, the organic AM-AMPS copolymer chain, and the hydroxyl ends of the inorganic polysilicic acid chains associate and crosslink to form an organic-inorganic interpenetrating network structure. After a period of well shut-in, the organic-inorganic composite solution responds in situ to form an impermeable gel radial barrier, preventing CO2 from rising and migrating and forcing CO2 to accumulate laterally below the dense caprock.

[0032] Compared with the prior art, the advantages of the present invention are:

[0033] (1) To solve the technical problem of "injection," this invention utilizes the stimulation response of CO2 to organic / inorganic components to achieve intelligent self-defense / control of the system. When the low-viscosity organic-inorganic composite solution injected from the ground encounters leaked CO2 in the caprock, the solution system undergoes a sol-gel transformation underground, resulting in a non-flowing gel. A radial sealing barrier is formed above the potential or already leaked path within the caprock, forcing subsequent CO2 to deflect, thereby improving CO2 sequestration efficiency.

[0034] (2) In this invention, acrylamide is copolymerized with the acid-resistant monomer 2-acrylamide-2-methylpropanesulfonic acid. The organic comonomer forms an organic AM-AMPS copolymer chain through a free radical polymerization reaction, and sodium silicate and carbonic acid form an inorganic polysilicic acid chain through acid-base neutralization and silicic acid condensation reaction. Finally, the two polymer chains associate and crosslink at both ends to form an organic-inorganic interpenetrating network structure composite gel.

[0035] (3) To address the technical issue of "durability," this invention incorporates silicone as a rigid framework interwoven into a gel network structure composed of acrylamide-2-acrylamide-2-methylpropanesulfonic acid. The polyacrylamide-2-acrylamide-2-methylpropanesulfonic acid chains intertwine with the polysilicic acid, exhibiting the flexibility of organic gels and the toughness of inorganic gels. This endows the system with excellent mechanical properties, resulting in an organic / inorganic composite material system with higher mechanical strength, better elasticity, and stronger toughness after gelation.

[0036] (4) In order to solve the technical problem of “going far”, the present invention introduces a binary crosslinking agent pair and coats the surface of sodium silicate with gum arabic-sodium alginate, thereby achieving stepwise crosslinking of hexamethylenetetramine-resorcinol and delayed release of sodium silicate under CO2 stimulation, thereby extending the gelation time of the system.

[0037] (5) To solve the technical problem of "long-lasting plugging", this invention uses tannic acid as an adhesive and introduces catechol and pyrogallol groups to build a strong and tough bonding interface between the system and the rock through physical actions such as hydrogen bonding and hydrophobic interaction. After the solution system enters the caprock in the far-well zone, it is activated by leaked CO2, solidifies and bonds within the leakage channel, and firmly adheres to the caprock wall to form a high-strength integral plugging layer. This significantly improves the system's pressure resistance and makes it resistant to long-term repeated scouring by CO2, achieving permanent CO2 sealing.

[0038] (6) To achieve efficient and precise prevention / control, this invention proposes to alternately inject sodium alginate-gum arabic@sodium silicate microcapsule suspension and calcium chloride solution into the formation, and inject small doses of the solution into the isolation slug in multiple rounds. The two are mixed above the leakage path in the caprock in the far well zone. Calcium chloride reacts with sodium silicate and carbonic acid to deposit calcium carbonate mineral precipitate in situ. Part of the precipitate fills the weak parts / microcracks / faults in the caprock to seal the leak, thereby reducing the permeability of the leak. The other part adheres to the surface of the loose clay particles inside the leak to cement and reinforce the leak, thereby increasing the activation pressure of the fault.

[0039] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0040] Figure 1 A schematic diagram of the process by which organic-inorganic polymer chains form an interpenetrating network structure.

[0041] Figure 2 (a) Schematic diagram of CO2 leakage along the caprock in a CO2 geological storage system; (b) Schematic diagram of the mechanism of CO2 leakage prevention / control of the organic-inorganic composite material system of the present invention.

[0042] Figure 3The graph shows the initial viscosity versus gelation time of organic-inorganic composite solutions with different organic and inorganic monomer contents.

[0043] Figure 4 The diagram shows the mechanical properties of organic-inorganic composite material systems: (a) and (d) compressive strength; (b) puncture strength; (c) fatigue fracture; (e) tensile strength; (f) shear strength; and (g) flexural strength.

[0044] Figure 5 This is a schematic diagram showing the adhesive strength between the organic-inorganic composite material system and the rock core.

[0045] Figure 6 (a) Products with different ratios of sodium silicate to calcium chloride; (b)-(e) Mineral precipitates filling and sealing the cracks; (f) Mineral precipitates cemented with loose clay; (g) Schematic diagram of mineral precipitates cemented with loose quartz sand. Detailed Implementation

[0046] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0047] Example 1

[0048] 4.0 g of acrylamide and 1.0 g of 2-acrylamide-2-methylpropanesulfonic acid were dissolved in 76.9 mL of deionized water and mechanically stirred for 10 min until fully mixed. The pH of the solution was adjusted to 6.0 with a measured amount of sodium hydroxide and glacial acetic acid. Under N2 purging, 0.02 g of ammonium persulfate, 0.02 g of sodium bisulfite, and 0.01 g of azobisisobutyronitrile were added sequentially, and the mixture was mechanically stirred for 50 min to obtain an AM-AMPS monomer solution (solution A). 0.5 g of tannic acid was added to solution A, and the mixture was mechanically stirred for 60 min to obtain an AM-AMPS / TA solution (solution B). 0.01 g of hexamethylenetetramine and 0.005 g of resorcinol were mixed thoroughly and dissolved in 10 mL of deionized water. The mixture was mechanically stirred for 30 min to obtain a binary crosslinking agent-HMTA-RE solution. The binary crosslinking agent-HMTA-RE solution was added to solution B to obtain an organic solution. 5.0 g of sodium silicate with a modulus of 3.0 was weighed, and 1.0 g of gum arabic and 1.0 g of sodium alginate were coated onto the surface of the sodium silicate. The mixture was then added to a 6 wt% calcium chloride solution for curing, thus preparing calcium alginate-gum arabic@sodium silicate microcapsules. The obtained calcium alginate-gum arabic@sodium silicate microcapsules and 0.05 g of thiourea were added to an organic solution and mechanically stirred until completely dissolved for 60 min, yielding an organic-inorganic composite solution. In the organic-inorganic composite solution, the total mass of the organic and inorganic monomers accounted for 10 wt% of the total solution mass. The organic monomers refer to acrylamide and 2-acrylamide-2-methylpropanesulfonic acid, and the inorganic monomer refers to silicic acid.

[0049] To verify the gelation time, mechanical properties, and adhesive strength of the system of the present invention after exposure to CO2 stimulation, CO2 was continuously and uniformly introduced into the organic-inorganic composite solution for 30 min, and then the system was placed at 40°C. o The organic-inorganic interpenetrating network composite gel is generated in an oven at temperature C until the final gel strength is reached under an acidic CO2 environment.

[0050] Figure 1This is a schematic diagram illustrating the process of organic-inorganic polymer chains forming an interpenetrating network structure. Under heating conditions, the composite initiator generates hydroxyl radicals, which react with free acrylamide and 2-acrylamido-2-methylpropanesulfonic acid monomer molecules in solution to generate organic AM-AMPS copolymer chains. Hexamethylenetetramine hydrolyzes under acidic CO2 heating, releasing formaldehyde. The formaldehyde reacts stepwise at two active sites of resorcinol, generating 4-(hydroxymethyl)benzene-1,3-diol and 4,6-bis(hydroxymethyl)benzene-1,3-diol intermediates. Silicates undergo acid-base neutralization with carbonic acid, condensing to form inorganic polysilicic acid chains. The hydroxyl ends of 4-(hydroxymethyl)benzene-1,3-diol, 4,6-bis(hydroxymethyl)benzene-1,3-diol, and the organic AM-AMPS copolymer chains associate and crosslink with the hydroxyl ends of the inorganic polysilicic acid chains, forming an organic-inorganic interpenetrating network structure. Hydrogen bonds are formed between the catechol and pyrogallol functional groups in tannic acid.

[0051] The specific preparation method of the calcium alginate-gum arabic@sodium silicate microcapsules is as follows:

[0052] (1) Dissolve 1.0 g of gum arabic in 20.0 mL of deionized water to obtain GA solution; dissolve 5.0 g of sodium silicate with a modulus of 3.0 in 72.0 mL of deionized water to obtain Na2O·3SiO2 solution; mix GA solution and Na2O·3SiO2 solution and stir thoroughly to obtain GA / Na2O·3SiO2 solution; slowly add 0.8 g of Span 80 and 0.2 g of Tween 80 dropwise to GA / Na2O·3SiO2 solution and emulsify at high speed at 70℃ for 5 h to obtain O / W emulsion, i.e. GA / Na2O·3SiO2 emulsion;

[0053] (2) Add 1.0 g of sodium alginate to the GA / Na2O·3SiO2 emulsion at 70℃, add glacial acetic acid dropwise to adjust the pH of the solution to 4.2, stir until fully mixed, and obtain GA / SA / Na2O·3SiO2 emulsion.

[0054] (3) The GA / SA / Na2O·3SiO2 emulsion was slowly and uniformly added to a 6wt% calcium chloride solution in the form of spherical droplets, and stirred and solidified for 1 h to obtain a Ca / SA / GA@Na2O·3SiO2 suspension.

[0055] (4) After the Ca / SA / GA@Na2O·3SiO2 suspension was allowed to stand, it was filtered, washed and dried to obtain Ca / SA / GA@Na2O·3SiO2 microcapsules.

[0056] Example 2

[0057] Dissolve 6.0 g of acrylamide and 1.5 g of 2-acrylamide-2-methylpropanesulfonic acid in 70.3 mL of deionized water and stir mechanically for 10 min until fully mixed. Adjust the pH of the solution to 6.0 with a measured amount of sodium hydroxide and glacial acetic acid. Under N2 purging, add 0.03 g of ammonium persulfate, 0.03 g of sodium bisulfite, and 0.015 g of azobisisobutyronitrile sequentially and stir mechanically for 50 min to obtain an AM-AMPS monomer solution (solution A). Add 0.75 g of tannic acid to solution A and stir mechanically for 60 min to obtain an AM-AMPS / TA solution (solution B). Mix 0.015 g of hexamethylenetetramine and 0.0075 g of resorcinol thoroughly and dissolve in 10 mL of deionized water. Stir mechanically for 30 min to obtain a binary crosslinking agent-HMTA-RE solution. Add the binary crosslinking agent-HMTA-RE solution to solution B to obtain an organic solution. 7.5 g of sodium silicate with a modulus of 3.0 was weighed, and 1.5 g of gum arabic and 1.5 g of sodium alginate were coated onto the surface of the sodium silicate. The mixture was then added to a 9 wt% calcium chloride solution for curing, thus preparing calcium alginate-gum arabic@sodium silicate microcapsules. The obtained calcium alginate-gum arabic@sodium silicate microcapsules and 0.075 g of thiourea were added to an organic solution and mechanically stirred for 60 min until completely dissolved, yielding an organic-inorganic composite solution. In the organic-inorganic composite solution, the total mass of the organic and inorganic monomers accounted for 15 wt% of the total solution mass. The organic monomers were acrylamide and 2-acrylamide-2-methylpropanesulfonic acid, and the inorganic monomer was silicic acid.

[0058] To verify the gelation time, mechanical properties, and adhesive strength of the system of the present invention after exposure to CO2 stimulation, CO2 was continuously and uniformly introduced into the solution for 30 min, and then the system was placed at 40°C. o The reaction is carried out in an oven at C until the final gel strength is reached, and a composite gel with an inorganic-organic interpenetrating network structure is generated under an acidic CO2 environment.

[0059] The specific preparation method of the calcium alginate-gum arabic@sodium silicate microcapsules is as follows:

[0060] (1) Dissolve 1.5 g of gum arabic in 20.0 mL of deionized water to obtain GA solution; dissolve 7.5 g of sodium silicate with a modulus of 3.0 in 68.0 mL of deionized water to obtain NaO·3SiO2 solution; mix GA solution and Na2O·3SiO2 solution and stir thoroughly to obtain GA / Na2O·3SiO2 solution; slowly add 1.2 g of Span 80 and 0.3 g of Tween 80 dropwise to GA / Na2O·3SiO2 solution and emulsify at high speed at 70℃ for 5 h to obtain O / W emulsion, i.e. GA / Na2O·3SiO2 emulsion;

[0061] (2) Add 1.5 g of sodium alginate to the GANa2O·3SiO2 emulsion at 70℃, add glacial acetic acid dropwise to adjust the pH of the solution to 4.2, stir until fully mixed, and obtain GA / SA / Na2O·3SiO2 emulsion.

[0062] (3) The GA / SA / Na2O·3SiO2 emulsion was slowly and uniformly added to a 9wt% calcium chloride solution in the form of spherical droplets, and stirred and solidified for 1 h to obtain a Ca / SA / GA@Na2O·3SiO2 suspension.

[0063] (4) After the Ca / SA / GA@Na2O·3SiO2 suspension was allowed to stand, it was filtered, washed and dried to obtain Ca / SA / GA@Na2O·3SiO2 microcapsules.

[0064] Example 3

[0065] Dissolve 8.0 g acrylamide and 2.0 g 2-acrylamide-2-methylpropanesulfonic acid in 62.9 mL of deionized water and stir mechanically for 10 min until fully mixed. Adjust the pH of the solution to 6.0 with a measured amount of sodium hydroxide and glacial acetic acid. Under N2 purging, add 0.04 g ammonium persulfate, 0.04 g sodium bisulfite, and 0.02 g azobisisobutyronitrile sequentially, and stir mechanically for 50 min to obtain an AM-AMPS monomer solution (solution A). Add 1.0 g tannic acid to solution A and stir mechanically for 60 min to obtain an AM-AMPS / TA solution (solution B). Mix 0.02 g hexamethylenetetramine and 0.01 g resorcinol thoroughly and dissolve in 10 mL of deionized water. Stir mechanically for 30 min to obtain a binary crosslinking agent-HMTA-RE solution. Add the binary crosslinking agent-HMTA-RE solution to the AM-AMPS / TA solution to obtain an organic solution. 10.0 g of sodium silicate with a modulus of 3.0 was weighed, and 2.0 g of gum arabic and 2.0 g of sodium alginate were coated onto the surface of the sodium silicate. The coated microcapsules were then solidified in a 12 wt% calcium chloride solution to prepare calcium alginate-gum arabic@sodium silicate microcapsules. The obtained calcium alginate-gum arabic@sodium silicate microcapsules and 1.0 g of thiourea were added to an organic solution and mechanically stirred until completely dissolved for 60 min to obtain an organic-inorganic composite solution. In the organic-inorganic composite solution, the total mass of the organic and inorganic monomers accounted for 20 wt% of the total solution mass. The organic monomers were acrylamide and 2-acrylamido-2-methylpropanesulfonic acid, and the inorganic monomer was silicic acid.

[0066] To verify the gelation time, mechanical properties, and adhesive strength of the system of the present invention after exposure to CO2 stimulation, CO2 was continuously and uniformly introduced into the solution for 30 min, and then the system was placed at 40°C. oThe reaction is carried out in an oven at C until the final gel strength is reached, and an organic-inorganic interpenetrating network composite gel is generated under an acidic CO2 environment.

[0067] The specific preparation method of the calcium alginate-gum arabic@sodium silicate microcapsules is as follows:

[0068] (1) Dissolve 2.0 g gum arabic in 20.0 mL of deionized water to obtain GA solution; dissolve 10.0 g sodium silicate with a modulus of 3.0 in 64.0 mL of deionized water to obtain Na2O·3SiO2 solution; mix GA solution and Na2O·3SiO2 solution and stir thoroughly to obtain GA / Na2O·3SiO2 solution; slowly add 1.6 g Span 80 and 0.4 g Tween 80 dropwise into GA / Na2O·3SiO2 solution and emulsify at high speed at 70℃ for 5 h to obtain O / W emulsion, i.e. GA / Na2O·3SiO2 emulsion;

[0069] (2) Add 2.0 g of sodium alginate to the GA / Na2O·3SiO2 emulsion at 70℃, add glacial acetic acid dropwise to adjust the pH of the solution to 4.2, stir until fully mixed, and obtain GA / SA / Na2O·3SiO2 emulsion.

[0070] (3) The GA / SA / Na2O·3SiO2 emulsion was slowly and uniformly added to a 12wt% calcium chloride solution in the form of spherical droplets, and stirred and solidified for 1 h to obtain a Ca / SA / GA@Na2O·3SiO2 suspension.

[0071] (4) After the Ca / SA / GA@Na2O·3SiO2 suspension was allowed to stand, it was filtered, washed and dried to obtain Ca / SA / GA@Na2O·3SiO2 microcapsules.

[0072] Figure 2 (a) is a schematic diagram of CO2 leakage along the caprock in a CO2 geological sequestration system. Figure 2 (b) is a schematic diagram illustrating the mechanism of CO2 leakage prevention / control of the organic-inorganic composite material system of the present invention. Sodium alginate-gum arabic@sodium silicate microcapsule suspension and calcium chloride solution are alternately injected into the formation. The two solutions mix in the caprock in the far-wellbore zone, reacting with CO2 to form mineral precipitates in situ, sealing and solidifying weak zones, micro-fractures, or faults within the caprock. After the organic-inorganic composite solution is injected into the formation, the solution system migrates to the deeper parts of the far-wellbore zone, above potential or existing leakage paths within the caprock. After a period of well shut-in, upon encountering CO2 escaping from the top of the caprock, an impermeable gel radial barrier is formed in situ, preventing CO2 from rising and forcing it to accumulate laterally. This reduces CO2 leakage, enhances CO2 sequestration efficiency, and achieves long-term, safe CO2 sequestration.

[0073] Performance testing:

[0074] (1) Initial viscosity test of organic-inorganic composite solution: The initial viscosity of the organic-inorganic composite solutions in Examples 1-3 at 25 °C was measured using a Brookfield DV-Ⅲ+ Pro rotational viscometer (Brookfield Laboratories, USA). o Initial viscosity under condition C (shear rate 7.34 s⁻¹) 1 The experimental results are shown in [link to experimental results]. Figure 3 It can be seen that when the content of organic and inorganic monomers is 10-20 wt%, the initial viscosity of the organic-inorganic composite solution is close to that of water, below 5.0 mPa·s. This indicates that the solution is easy to inject at the surface and has good flow properties under formation conditions.

[0075] (2) Gelation time test of organic-inorganic composite solution:

[0076] The gelation time of the organic-inorganic composite solutions in Examples 1-3 at 60°C was determined using the visual coding method. In this invention, gelation time refers to the time elapsed after CO2 introduction for the system to change from polymer solution strength A to its final strength (Sydansk gel strength code, see Table 1). Experimental results are shown below. Figure 3 It can be seen that the gelation time of the organic-inorganic composite solution decreases with increasing organic + inorganic monomer content. When the organic + inorganic monomer content is 10-20 wt%, the gelation time of the system is greater than 20 h. The ultra-long gelation time ensures that the system maintains low viscosity in the near-wellbore area without encountering leaking CO2, enabling deep migration. The strength of the organic-inorganic composite solution in Example 1 after gelation with CO2 is grade H, while the strength of the organic / inorganic composite solutions in Examples 2 and 3 after gelation with CO2 is grade I. All three solutions are in a non-flowing state after gelation, indicating good leakage prevention / control effects.

[0077] Table 1 Sydansk Gel Strength Code Table

[0078]

[0079] (3) Mechanical property testing of organic-inorganic interpenetrating network composite gel:

[0080] The organic-inorganic interpenetrating network composite gel formed in Example 3 was used for intuitive mechanical property testing. Figure 4 This is a schematic diagram illustrating the mechanical properties. The rigid mechanical properties of the inorganic cross-linked network endow the system with high compressive strength, puncture strength, and shear strength. For example... Figure 4 As shown in (a) and (d), the gel can support a 2 kg weight without breaking; as Figure 4As shown in (c), the gel can lift a 0.2 kg weight without breaking. The energy dissipation properties of the organic cross-linked network endow the system with high fatigue fracture resistance, tensile strength, and flexural strength. Figure 4 As shown in (e), a 4.5 cm long sample was stretched, and the gel could be stretched to 400% strain and immediately recovered to its original strain after the stress was removed.

[0081] (4) Adhesive strength test of organic-inorganic interpenetrating network composite gel:

[0082] The adhesive strength of the organic-inorganic interpenetrating network composite gel formed in Example 2 was characterized intuitively, and the results are shown in [Figure 2]. Figure 5 As shown in the figure, the gel adheres firmly to the core wall, forming a high-strength integral sealing layer.

[0083] (5) Filling and cementing properties of mineral precipitates:

[0084] Figure 6 (a) is a schematic diagram of mineral precipitation. Sodium silicate and calcium chloride were mixed in 10 mL test tubes at mass ratios of 3:1, 2:1, 4:3, 5:4, and 1:1, respectively, and the morphology of the products was observed after standing for 10 h. Figure 6 In (a), the ratios from left to right are 3:1, 2:1, 4:3, 5:4, and 1:1, respectively. Figure 6 (a) It is known that when the ratio of sodium silicate to calcium chloride is 3:1-2:1, a white dispersed flocculent is formed; when the ratio of sodium silicate to calcium chloride is 4:3, a white solid precipitate is formed and deposited at the bottom, and the mineral precipitates are cemented together to form cubic crystals; when the ratio of sodium silicate to calcium chloride is 5:4-1:1, a milky white integral gel cluster is formed and suspended in water. Therefore, the preferred ratio of sodium silicate to calcium chloride is 4:3.

[0085] A core sample with a diameter of 2.5 cm and a height of 5.0 cm was cut in half using wire cutting technology. A pair of stainless steel washers with a thickness of 0.1 mm were adhered to the edges of the fracture surface to construct a fracture model with an aperture of 0.1 mm. The core sample was first soaked in a 3.8 wt% calcium chloride solution for 12 h, and then immersed in a 5.0 wt% sodium silicate solution for 12 h. The core sample was then removed, and the distribution of mineral precipitation in the fracture was observed. Figure 6 As shown in (b)-(e), the mineral precipitation fills the ends, sides and interior of the cracks, thus blocking CO2.

[0086] A 3.8 wt% calcium chloride solution and a 5.0 wt% sodium silicate solution were sequentially added dropwise to the clay / quartz sand. After standing for 24 hours, the morphology of the clay / quartz sand was observed. Figure 6As shown in (f) and (g), mineral precipitation encapsulates loose particles and binds them together with clay / quartz sand particles to form a whole, reinforcing weak particle interlayers and improving crack cohesion, compressive strength and shear strength.

[0087] To achieve a system that is "easy to inject, long-range, durable, long-lasting, and efficiently and precisely prevents / controls leaks" within the caprock in remote well areas, this invention incorporates silica gel as a rigid framework interwoven into a gel network structure composed of acrylamide-2-acrylamide-2-methylpropanesulfonic acid, leveraging the flexibility of organic gels and the toughness of inorganic gels. The system's intelligent self-protection / control is achieved by utilizing the stimulation response of CO2 to both organic and inorganic unit components. By introducing a binary crosslinking agent pair and coating the sodium silicate surface with gum arabic / sodium alginate, the binary crosslinking agent pair undergoes stepwise crosslinking, delaying the release of silicates. Tannic acid is used as an adhesive, and catechol and pyrogallol groups are introduced to construct a strong and tough adhesive interface between the system and the caprock. In application, this invention involves repeatedly injecting a sodium alginate-gum arabic@sodium silicate microcapsule suspension and calcium chloride solution alternately into weak zones or leaked paths within the caprock, followed by the injection of brine as an isolation plug. When the two meet at the target location in the distant well area, the leaked CO2 reacts in situ to form mineral precipitates, which fill and seal the weak zones, micro-fractures, or faults in the caprock, cementing and reinforcing loose clay particles. Then, a low-viscosity organic-inorganic composite solution is injected. The system migrates deep into the caprock to the shallow strata-caprock interface above the weak points or above the leak path, forming a radial gel barrier that forces the leaked CO2 to accumulate laterally beneath the dense caprock. This reduces CO2 leakage, enhances CO2 sequestration efficiency, and achieves long-term, safe CO2 sequestration.

[0088] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. An organic-inorganic composite material system for preventing / controlling CO2 leakage from a formation, characterized by, The raw material components include: organic copolymer monomer, tannic acid, composite initiator, binary crosslinking agent pair, sodium alginate-arabic gum@sodium silicate microcapsule, thiourea, and deionized water solvent; The mass percentage concentration of each raw material component is as follows: The mass percentage concentration of the organic copolymer monomer is 5-10 wt% based on the total mass of the organic-inorganic composite solution, the mass percentage concentration of the composite initiator is 0.05-0.1 wt%, the mass percentage concentration of the binary crosslinking agent pair is 0.015-0.03 wt%, the mass percentage concentration of the tannic acid is 0.5-1 wt%, the mass percentage concentration of the sodium silicate is 5-10 wt%, and the mass percentage concentration of the thiourea is 0.05-0.1 wt%; The preparation method of the sodium alginate-arabic gum@sodium silicate microcapsule is as follows: Step (1), mix the arabic gum solution and the sodium silicate solution, stir thoroughly, and obtain a GA / Na2O·3SiO2 solution; slowly add the compounded non-ionic surfactant into the GA / Na2O·3SiO2 solution, emulsify at a high speed for 5 h at 70°C, and obtain an O / W emulsion, i.e., a GA / Na2O·3SiO2 emulsion; Step (2), add sodium alginate into the GA / Na2O·3SiO2 emulsion at 70°C, add glacial acetic acid into the solution to adjust the pH of the solution to 4.2, stir until fully mixed, and obtain a GA / SA / Na2O·3SiO2 emulsion; Step (3), slowly and uniformly add the GA / SA / Na2O·3SiO2 emulsion in the form of spherical droplets into a calcium chloride solution with a mass percentage concentration of 6.0-12.0 wt%, stir and solidify for 1 h, and obtain a Ca / SA / GA@Na2O·3SiO2 suspension; Step (4), filter, wash, and dry the Ca / SA / GA@Na2O·3SiO2 suspension after standing to obtain Ca / SA / GA@Na2O·3SiO2 microcapsules; The organic copolymer monomer is acrylamide and 2-acrylamide-2-methylpropanesulfonic acid; The composite initiator is compounded from an ammonium persulfate-sodium bisulfite redox initiator and azobisisobutyronitrile; The binary crosslinking agent pair is compounded from hexamethylenetetramine and resorcinol; The compounded non-ionic surfactant is a compound of Span 80 and Tween 80.

2. The organic-inorganic composite material system for preventing / controlling CO2 formation leakage according to claim 1, wherein In the preparation method of the sodium alginate-arabic gum@sodium silicate microcapsule, arabic gum and sodium alginate are used as the coating wall material, and the total mass fraction of the coating wall material is 1.5-2.5 wt%, wherein the mass ratio of arabic gum to sodium alginate is (1-4):

1.

3. The organic-inorganic composite material system for preventing / controlling CO2 formation leakage according to claim 2, wherein The mass fraction of the compounded non-ionic surfactant is 0.5-2 wt%, wherein the mass ratio of Span 80 to Tween 80 is (3-4):

1.

4. The organic-inorganic composite material system for preventing / controlling CO2 formation leakage according to claim 1, wherein In the organic copolymer monomer, the mass ratio of acrylamide to 2-acrylamide-2-methylpropanesulfonic acid is (4-5):

1.

5. The organic-inorganic composite material system for preventing / controlling CO2 formation leakage according to claim 1, wherein In the composite initiator, the mass ratio of ammonium persulfate-sodium bisulfite redox initiator to azobisisobutyronitrile is 4:1, and the mass ratio of ammonium persulfate to sodium bisulfite in the redox initiator is 1:

1.

6. The organic-inorganic composite material system for preventing / controlling CO2 formation leakage according to claim 1, wherein The mass ratio of hexamethylenetetramine and resorcinol in the binary crosslinking agent is (1-5):

1.

7. A method for preparing the organic-inorganic composite material system for preventing / controlling CO2 leakage from a formation according to any one of claims 1 to 6, characterized in that, The steps are as follows: S1, acrylamide and 2-acrylamide-2-methylpropanesulfonic acid are dissolved in deionized water, mechanically stirred until fully dissolved, the pH of the solution is adjusted to 6.0, and the composite initiator is added under N2 conditions to obtain an AM-AMPS solution, namely solution A; S2, tannic acid is added to solution A, and mechanically stirred until fully mixed to obtain an AM-AMPS / TA solution, namely solution B; S3, the binary crosslinking agent pair is added to solution B to obtain an organic solution; S4, prepare sodium alginate-arabic gum@sodium silicate microcapsules; S5, add sodium alginate-arabic gum@sodium silicate microcapsules and thiourea to the organic solution to obtain an organic-inorganic composite solution.

8. The method for using the organic-inorganic composite material system for preventing / controlling CO2 leakage from the formation according to any one of claims 1 to 6, characterized in that, The steps are as follows: Step 1, inject sodium silicate-sealing fluid-calcium chloride solution: before CO2 leakage or after monitoring CO2 leakage, the main agent sodium alginate-arabic gum@sodium silicate microcapsule suspension and the auxiliary agent calcium chloride solution are alternately injected into the weak zone of the caprock or the leaked path by CO2 injection wells, and salt water is injected as a sealing slug to promote the deep migration of the two; the injection sequence of each round is: sealing slug-main agent-sealing slug-auxiliary agent-sealing slug; the sodium alginate-arabic gum@sodium silicate microcapsule suspension is prepared by adding sodium alginate-arabic gum@sodium silicate microcapsules to water; Step 2, inject organic-inorganic composite solution: inject the organic-inorganic composite solution into the formation, and inject a sealing slug to promote the deep migration of the organic-inorganic composite solution to the shallow formation-caprock interface above the weak part in the caprock or the point above the leaked path; Step 3, shut in: shut in and wait for the system to react, the main agent sodium alginate-arabic gum@sodium silicate microcapsule suspension and the auxiliary agent calcium chloride meet at the target location in the far-well zone, in situ generate mineral precipitates in the presence of leaked CO2, fill and plug in the weak part of the caprock or microfractures or faults, and cement the internal loose clay particles; the organic-inorganic composite solution migrates deep into the caprock, forms a gel radial barrier in the presence of CO2 above the potential leakage or leaked path in the caprock, and forces the leaked CO2 to aggregate laterally; Step 4, inject CO2: after the system reaction is complete, open the CO2 injection well, and continuously inject CO2 into the reservoir for permanent storage.

9. The method of using the organic-inorganic composite material system for preventing / controlling CO2 formation leakage according to claim 8, wherein, The salt water is a 5 wt% potassium chloride solution.

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