A composite gel material, its preparation method and use

Abstract

The application belongs to the technical field of lost circulation control gels, and particularly relates to a composite gel material and a preparation method and application thereof. The composite gel material comprises the following raw materials: a quaternary ammonium salt type cationic modified copolymer, carboxymethyl chitosan, silane modified basalt fiber, an initiator, N,N-methylene bisacrylamide, inorganic nano filler, octadecyl methacrylate and a flame retardant. The composite gel material has excellent plugging compactness, mechanical bearing capacity, environmental adaptability and long-term stability, can quickly adapt to the complex working conditions such as low pressure, fracture development and multiple media in the broken goaf, can form a firm plugging barrier through physical interception and chemical adsorption, can resist the erosion of drilling fluid and the impact of formation pressure, and can endow the material with self-repairing, anti-pollution and flame-retardant properties through dynamic bonding and functional groups, so as to solve the technical problems of weak interface bonding, easy peeling, poor crack resistance and narrow application range of the traditional lost circulation control materials.

Description

Technical Field

[0001] This invention belongs to the field of sealing gel technology, specifically relating to a composite gel material, its preparation method, and its application. Background Technology

[0002] A fractured goaf refers to the underground cavity formed after the mining of underground mineral resources, along with the surrounding rock mass that has fractured and become unstable due to mining disturbance. Its spatial extent typically includes the goaf itself and a certain depth of surrounding fractured rock, representing a typical geological defect left by the strata after mining. The formation of this area is closely related to the mining method, rock mass properties, and changes in geological stress: During underground mining, the removal of underground ore bodies disrupts the original stress balance of the strata. The surrounding rock above and around the goaf loses its support. Under the combined action of self-weight stress, tectonic stress, and mining disturbance stress, the surrounding rock undergoes elastic deformation, plastic yielding, or even brittle fracture, forming numerous interconnected fissures. Over time, some unstable rock masses further collapse and fracture, together with the goaf, forming a complex geological body composed of fractured rock blocks, a network of fissures, loose media, and cavities—the fractured goaf. Its core characteristics are as follows: its spatial morphology is extremely irregular, with no fixed boundaries or geometric shapes; the rock mass structure is extremely loose, with large differences in the size of the broken rock fragments, dense internal fissures with strong connectivity, forming multi-level seepage channels; its mechanical stability is extremely poor, the surrounding rock is prone to continuous creep and collapse, the formation pressure is unevenly distributed and fluctuates frequently; the medium composition is complex, often containing groundwater, water accumulated in the goaf or residual mining waste, and some areas also contain harmful gases such as methane, making the geological environment extremely uncertain.

[0003] During drilling operations, encountering fractured goaf areas poses serious hazards due to their complex geological features. On the one hand, the high porosity and strong connectivity of goaf areas and fractured zones cause drilling fluid to rapidly infiltrate the formation under pressure differential, resulting in large-scale leakage. This not only leads to an exponential increase in drilling fluid consumption and significantly increases drilling costs, but also causes a sharp drop in hydrostatic pressure due to the loss of drilling fluid, disrupting the wellbore pressure balance. On the other hand, pressure imbalance can further induce wellbore instability, and the fractured rock mass is prone to collapse and bury the drill bit, leading to drilling accidents such as stuck drill bit and dropped drill bit. In severe cases, it can even cause a blowout, threatening the lives of workers and the safety of equipment and property. In addition, the large-scale leakage of drilling fluid may also pollute groundwater resources and the formation environment. Furthermore, the irregularity and dynamic changes of the leakage channels make it difficult for conventional plugging measures to form an effective sealing barrier, further prolonging the operation cycle and increasing construction risks.

[0004] The plugging problem in such formations has always been a core challenge restricting drilling efficiency and safety. Therefore, developing a plugging material that combines high density, strong mechanical properties, excellent environmental adaptability, long-term stability, and self-healing function has become a key technical problem that urgently needs to be solved in the field of drilling engineering. Summary of the Invention

[0005] This application provides a composite gel material, its preparation method, and its application, aiming to solve the technical problems of existing composite gel materials under complex working conditions in fractured goaf areas, such as weak interfacial bonding, easy peeling, poor crack resistance, narrow environmental adaptability, and lack of self-healing ability.

[0006] The first aspect of this application provides a composite gel material comprising the following raw materials in parts by weight: 30-50 parts of quaternary ammonium salt-type cationic modified copolymer, 10-20 parts of carboxymethyl chitosan, 5-15 parts of silane-modified basalt fiber, 0.1-0.5 parts of initiator, 0.5-2.0 parts of N,N-methylenebisacrylamide, 1-5 parts of inorganic nanofiller, 2-8 parts of octadecyl methacrylate, and 3-10 parts of flame retardant.

[0007] According to some embodiments of the composite gel material described in this application, the initiator includes one or more of ammonium persulfate, potassium persulfate, azobisisobutyronitrile, and benzoyl peroxide.

[0008] According to some embodiments of the composite gel material described in this application, the inorganic nanofiller includes one or more of nano-silica, nano-calcium carbonate, and nano-montmorillonite.

[0009] According to some embodiments of the composite gel material described in this application, the flame retardant includes one or more of aluminum hydroxide, magnesium hydroxide, ammonium polyphosphate, pentaerythritol, melamine, and triphenyl phosphate.

[0010] The second aspect of this application provides a method for preparing the composite gel material described in the first aspect of this application, comprising the following steps: mixing a quaternary ammonium salt-type cationic modified copolymer, carboxymethyl chitosan, silane-modified basalt fiber, an initiator, N,N-methylenebisacrylamide, an inorganic nanofiller, octadecyl methacrylate, and a flame retardant to obtain the composite gel material.

[0011] According to some embodiments of the method for preparing the composite gel material described in this application, the method further includes the step of preparing a quaternary ammonium salt-type cationic modified copolymer;

[0012] The preparation method of the quaternary ammonium salt-type cationic modified copolymer includes the following steps: Step 1: Diethylaminoethyl methacrylate, acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, dispersant, initiator and first solvent are mixed to carry out the first reaction to obtain a copolymer solution; Step 2: The copolymer solution, 5-chloromethylfuran-2-carboxaldehyde, 4-chloromethylstyrene, catalyst, and second solvent are mixed to carry out a second reaction to obtain a quaternary ammonium salt-type cationic modified copolymer.

[0013] According to some embodiments of the preparation method of the composite gel material described in this application, in step one, the dispersant includes one or more of polyethylene glycol, polyvinyl alcohol and poly(ethylene glycol) methacrylate, the initiator includes ammonium persulfate and / or sodium bisulfite, and the first solvent includes water and / or ethanol.

[0014] According to some embodiments of the preparation method of the composite gel material described in this application, the initiator includes ammonium persulfate and sodium bisulfite in a molar ratio of 1:(0.8-1.2).

[0015] According to some embodiments of the preparation method of the composite gel material described in this application, the first solvent includes water and ethanol in a volume ratio of (40-50):1; According to some embodiments of the preparation method of the composite gel material described in this application, the molar ratio of diethylaminoethyl methacrylate, acrylamide and 2-acryloylamino-2-methylpropanesulfonic acid is 1:(3-3.5):(1-1.2).

[0016] According to some embodiments of the preparation method of the composite gel material described in this application, the amount of the dispersant is 0.2%-0.4% of the total mass of diethylaminoethyl methacrylate, acrylamide and 2-acryloylamino-2-methylpropanesulfonic acid.

[0017] According to some embodiments of the preparation method of the composite gel material described in this application, the amount of the initiator is 0.5%-0.7% of the total mass of diethylaminoethyl methacrylate, acrylamide and 2-acrylamido-2-methylpropanesulfonic acid.

[0018] According to some embodiments of the preparation method of the composite gel material described in this application, the total mass concentration of the reaction solution formed by diethylaminoethyl methacrylate, acrylamide, 2-acryloylamino-2-methylpropanesulfonic acid and the first solvent is 25%-35%.

[0019] According to some embodiments of the preparation method of the composite gel material described in this application, the temperature of the first reaction is 50-70°C, and the time of the first reaction is 4-8 hours.

[0020] According to some embodiments of the preparation method of the composite gel material described in this application, in step two, the catalyst includes one or more of potassium iodide, sodium iodide and tetrabutylammonium bromide, and the second solvent includes one or more of N,N-dimethylformamide, N-methyl-2-pyrrolidone and dimethyl sulfoxide.

[0021] According to some embodiments of the preparation method of the composite gel material described in this application, the molar ratio of 5-chloromethylfuran-2-carboxaldehyde and 4-chloromethylstyrene is 1:(1-1.1).

[0022] According to some embodiments of the preparation method of the composite gel material described in this application, the molar ratio of the diethylamino unit in the copolymer solution to the total molar ratio of 5-chloromethylfuran-2-carboxaldehyde and 4-chloromethylstyrene is 1:(1.3-1.4).

[0023] According to some embodiments of the preparation method of the composite gel material described in this application, the amount of the catalyst is 1%-1.5% of the total molar amount of the 5-chloromethylfuran-2-carboxaldehyde and 4-chloromethylstyrene.

[0024] According to some embodiments of the preparation method of the composite gel material described in this application, the temperature of the second reaction is 60-90°C, and the time of the second reaction is 6-12 hours.

[0025] According to some embodiments of the preparation method of the composite gel material described in this application, the method further includes the steps of mixing the reaction solution of the second reaction with anhydrous ethanol, filtering, collecting the precipitate, washing with anhydrous ethanol, and drying to obtain the quaternary ammonium salt type cationic modified copolymer.

[0026] According to some embodiments of the method for preparing the composite gel material described in this application, the method further includes the step of preparing silane-modified basalt fibers; The preparation method of the silane-modified basalt fiber includes the following steps: a. Basalt fibers are calcined and acid-leached sequentially to obtain pretreated fibers; b. Mix coupling agent KH570, coupling agent KH550 and solvent, adjust the pH of the mixture to acidic, and obtain silane hydrolysate; c. The pretreated fibers and silane hydrolysate are mixed and reacted to obtain silane-modified basalt fibers.

[0027] According to some embodiments of the preparation method of the composite gel material described in this application, in step a, the calcination temperature is 500-600℃ and the calcination time is 2-3h.

[0028] According to some embodiments of the preparation method of the composite gel material described in this application, the acid leaching treatment includes soaking the calcined basalt fiber in a hydrochloric acid solution with a mass concentration of 5%-10% for 6-12 hours; after soaking, washing with deionized water and drying to obtain the pretreated fiber.

[0029] According to some embodiments of the preparation method of the composite gel material described in this application, in step b, the solvent includes water and ethanol in a volume ratio of 1:(3-5).

[0030] According to some embodiments of the preparation method of the composite gel material described in this application, the mass ratio of the coupling agent KH570 to the coupling agent KH550 is 1:(1-2).

[0031] According to some embodiments of the preparation method of the composite gel material described in this application, in step b, the total mass concentration of coupling agent KH570 and coupling agent KH550 in the mixture is 1%-2%.

[0032] In some embodiments of the preparation method of the composite gel material according to this application, in step b, the pH of the mixture is adjusted to 3-5; preferably, acetic acid is used to adjust the pH of the mixture.

[0033] According to some embodiments of the preparation method of the composite gel material described in this application, the total amount of coupling agent KH570 and coupling agent KH550 is 3%-8% of the mass of basalt fiber.

[0034] According to some embodiments of the preparation method of the composite gel material described in this application, the temperature of the mixing reaction in step c is 50-70°C, and the mixing reaction time is 2-4 hours.

[0035] The third aspect of this application provides an application of the composite gel material described in the first aspect of this application or the composite gel material prepared by the method described in the second aspect of this application in drilling operations for plugging leaks in broken goaf areas.

[0036] The beneficial effects of this application include: the composite gel material described in this application, through the synergistic modification and functional complementarity of multiple components such as quaternary ammonium salt-type cationic modified copolymers, silane-modified basalt fibers, and carboxymethyl chitosan, constructs a multi-scale interpenetrating three-dimensional structure consisting of a rigid fiber skeleton, a flexible gel network, and nanoparticle filling. The composite gel material described in this application possesses excellent sealing and compaction properties, mechanical load-bearing capacity, environmental adaptability, and long-term stability. It can quickly adapt to complex working conditions such as low pressure, fracture development, and multiple media in fractured goaf areas. It can form a robust sealing barrier through physical interception and chemical adsorption, resisting drilling fluid erosion and formation pressure impact. Through dynamic bonding and functional groups, the material is endowed with extended properties such as self-healing, anti-pollution, and flame retardancy, solving the technical problems of traditional plugging materials such as weak interfacial bonding, easy peeling, poor crack resistance, and narrow applicability. Detailed Implementation

[0037] The embodiments of the present invention are described in detail below. These embodiments are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0038] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0039] This application provides a composite gel material comprising the following raw materials in parts by weight: 30-50 parts of quaternary ammonium salt-type cationic modified copolymer, 10-20 parts of carboxymethyl chitosan, 5-15 parts of silane-modified basalt fiber, 0.1-0.5 parts of initiator, 0.5-2.0 parts of N,N-methylenebisacrylamide, 1-5 parts of inorganic nanofiller, 2-8 parts of octadecyl methacrylate, and 3-10 parts of flame retardant.

[0040] The composite gel material described in this application integrates the strong adsorption properties of quaternary ammonium salt-type cationic modified copolymers, the rigid support of silane-modified basalt fibers, the dynamic cross-linking function of carboxymethyl chitosan, and the micro-nano filling effect of inorganic nanofillers to construct a multi-scale interpenetrating three-dimensional fiber-reinforced composite gel material for drilling and plugging leaks in broken goaf areas.

[0041] In some embodiments of this application, the initiator includes one or more of ammonium persulfate, potassium persulfate, azobisisobutyronitrile, and benzoyl peroxide.

[0042] In some embodiments of this application, the inorganic nanofiller includes one or more of nano-silica, nano-calcium carbonate, and nano-montmorillonite.

[0043] In some embodiments of this application, the flame retardant includes one or more of aluminum hydroxide, magnesium hydroxide, ammonium polyphosphate, pentaerythritol, melamine, and triphenyl phosphate.

[0044] In addition to forming strong electrostatic adsorption with negatively charged rock cuttings and clay, the quaternary ammonium salt-type cationic modified copolymer in the composite gel material described in this application can also neutralize the negative charge on the surface of clay minerals, inhibit clay hydration and swelling, and reduce the sealing failure of formation pores caused by clay swelling from the root cause. At the same time, the presence of quaternary ammonium salt groups improves the ionic strength adaptability of the gel material. In high-salinity drilling fluid systems, its cationic properties can resist the ion shielding effect, maintain stable electrostatic adsorption and gel structure, and ensure effective sealing in complex salt mineral formations.

[0045] As a natural biomass derivative, carboxymethyl chitosan possesses key technological advantages through the synergistic effect of hydroxyl, carboxyl, and amino groups in its molecular structure: First, the amino groups undergo Schiff base cross-linking with the aldehyde groups of the quaternary ammonium salt copolymer, forming an interpenetrating structure with the main gel network, significantly improving the cross-linking density and structural stability, and preventing leakage caused by the loose structure of the sealing layer; Second, the hydroxyl and carboxyl groups form multiple hydrogen bonds with the amide and sulfonic acid groups of the copolymer and the amino groups on the surface of the modified basalt fiber, strengthening the interfacial bonding force of each phase, reducing interfacial voids, and improving the sealing performance and anti-peeling ability of the sealing layer; Third, its good biocompatibility and hydrophilicity improve the interfacial wetting effect between the material and the formation rock mass, making the sealing layer adhere more tightly to the formation pore walls, shortening the sealing onset time, and reducing fluid permeation channels, making it particularly suitable for humid or hydrophilic formations.

[0046] The dynamic reversibility of Schiff base bonds formed by quaternary ammonium salt-type cationic modified copolymers and carboxymethyl chitosan endows the material with environmental responsiveness. In different formation pH environments (such as acidic fracture water and alkaline drilling fluid), Schiff base bonds can dynamically adjust the density of the gel network through breakage and recombination. Under acidic conditions, the bonding degree is enhanced, improving the density of the sealing layer; under alkaline conditions, moderate dissociation is achieved, avoiding excessive rigidity of the gel leading to brittleness and ensuring a tight fit to formation pores in complex formation environments. The self-healing performance of the material depends on the fact that when the sealing layer develops micro-cracks due to formation creep or pressure fluctuations, the molecular chains on both sides of the crack can re-entwine through thermal motion, and hydrogen bonds and Schiff base bonds recombine simultaneously, achieving self-healing of the crack without the need for additional grouting operations, significantly reducing maintenance costs and extending the sealing period.

[0047] Inorganic nanofillers, with their high specific surface area and surface-active groups, can form physical cross-linking points with polymer chains, constructing micro-nano reinforcing phases within the gel network. Besides filling microscopic defects, nanoparticles can disperse stress concentrations. When the sealing layer is subjected to formation pressure, the nanoparticles absorb energy through deformation and slippage, significantly improving the material's toughness and crack resistance, preventing the sealing layer from rupturing due to minor formation deformation. Furthermore, the high thermal stability and chemical inertness of nanoparticles improve the temperature resistance and corrosion resistance of the gel material, extending the service life of the sealing layer, making it particularly suitable for deep, high-temperature, fractured goaf areas.

[0048] This application also provides a method for preparing a composite gel material, comprising the following steps: mixing a quaternary ammonium salt-type cationic modified copolymer, carboxymethyl chitosan, silane-modified basalt fiber, an initiator, N,N-methylenebisacrylamide, an inorganic nanofiller, octadecyl methacrylate, and a flame retardant to obtain the composite gel material.

[0049] The composite gel material described in this application uses carboxymethyl chitosan, basalt fiber, halogen-free flame retardant, and other environmentally friendly components. After drilling is completed, it can be naturally degraded or is compatible with the formation medium, and will not cause secondary pollution, which is in line with the development trend of green drilling.

[0050] In some embodiments of this application, the step of preparing a quaternary ammonium salt-type cationic modified copolymer is also included; The preparation method of the quaternary ammonium salt-type cationic modified copolymer includes the following steps: Step 1: Diethylaminoethyl methacrylate, acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, dispersant, initiator and first solvent are mixed to carry out the first reaction to obtain a copolymer solution; Step 2: The copolymer solution, 5-chloromethylfuran-2-carboxaldehyde, 4-chloromethylstyrene, catalyst, and second solvent are mixed to carry out a second reaction to obtain a quaternary ammonium salt-type cationic modified copolymer.

[0051] After copolymerization with monomers such as diethylaminoethyl methacrylate and acrylamide, and then quaternization modification with 5-chloromethylfuran-2-carboxaldehyde and 4-chloromethylstyrene, amide and sulfonic acid groups are introduced into the copolymer to strengthen molecular chain entanglement and hydrogen bonding. Furthermore, the quaternary ammonium salt cations achieve the following effects: forming strong electrostatic adsorption with negatively charged rock fragments and clay, improving the bonding strength between the sealing layer and the formation; neutralizing the negative charge on the surface of clay minerals, inhibiting clay hydration and swelling, and preventing sealing failure due to clay expansion in formation pores; improving the material's ionic strength adaptability in high-mineralization environments, resisting the salt ion shielding effect, and ensuring that it can maintain a stable gel structure and sealing performance in complex salt mine formations.

[0052] In some embodiments of this application, in step one, the dispersant includes one or more of polyethylene glycol, polyvinyl alcohol, and poly(ethylene glycol) methacrylate, the initiator includes ammonium persulfate and / or sodium bisulfite, and the first solvent includes water and / or ethanol.

[0053] In some embodiments of this application, the initiator includes ammonium persulfate and sodium bisulfite in a molar ratio of 1:(0.8-1.2), such as 1:0.8, 1:0.9, 1:1.0, 1:1.2, etc.

[0054] In some embodiments of this application, the first solvent comprises water and ethanol in a volume ratio of (40-50):1; for example, 40:1, 43:1, 45:1, 48:1, 50:1, etc.

[0055] In some embodiments of this application, the molar ratio of diethylaminoethyl methacrylate, acrylamide, and 2-acrylamido-2-methylpropanesulfonic acid is 1:(3-3.5):(1-1.2), for example 1:3:1, 1:3:1.1, 1:3:1.2, 1:3.2:1, 1:3.2:1.1, 1:3.2:1.2, 1:3.5:1, 1:3.5:1.1, 1:3.5:1.2, etc.

[0056] In some embodiments of this application, the amount of the dispersant is 0.2%-0.4% of the total mass of the diethylaminoethyl methacrylate, acrylamide, and 2-acrylamido-2-methylpropanesulfonic acid; for example, 0.2%, 0.25%, 0.3%, 0.38%, 0.4%, etc.

[0057] In some embodiments of this application, the amount of the initiator is 0.5%-0.7% of the total mass of diethylaminoethyl methacrylate, acrylamide, and 2-acrylamido-2-methylpropanesulfonic acid; for example, 0.5%, 0.57%, 0.6%, 0.63%, 0.7%, etc.

[0058] In some embodiments of this application, the total mass concentration of the reaction solution formed by diethylaminoethyl methacrylate, acrylamide, 2-acryloylamino-2-methylpropanesulfonic acid, and the first solvent is 25%-35%; for example, 25%, 28%, 33%, 35%, etc.

[0059] In some embodiments of this application, the temperature of the first reaction is 50-70°C, such as 50°C, 58°C, 60°C, 65°C, 70°C, etc., and the reaction time is 4-8 hours, such as 4 hours, 5 hours, 6 hours, 8 hours, etc.

[0060] In some embodiments of this application, the catalyst includes one or more of potassium iodide, sodium iodide, and tetrabutylammonium bromide, and the second solvent includes one or more of N,N-dimethylformamide, N-methyl-2-pyrrolidone, and dimethyl sulfoxide.

[0061] In some embodiments of this application, the molar ratio of 5-chloromethylfuran-2-carboxaldehyde and 4-chloromethylstyrene is 1:(1-1.1); for example, 1:1, 1:1.08, 1:1.1, etc.

[0062] In some embodiments of this application, the molar ratio of the diethylamino unit in the copolymer solution to the total molar ratio of 5-chloromethylfuran-2-carboxaldehyde and 4-chloromethylstyrene is 1:(1.3-1.4); for example, 1:1.3, 1:1.32, 1:1.35, 1:1.38, 1:1.4, etc.

[0063] In some embodiments of this application, the amount of the catalyst is 1%-1.5% of the total molar amount of the 5-chloromethylfuran-2-carboxaldehyde and 4-chloromethylstyrene; for example, 1%, 1.2%, 1.3%, 1.5%, etc.

[0064] In some embodiments of this application, the temperature of the second reaction is 60-90°C, such as 60°C, 68°C, 73°C, 76°C, 85°C, 90°C, etc., and the time of the second reaction is 6-12h, such as 6h, 8h, 9h, 11h, 12h, etc.

[0065] In some embodiments of this application, the method further includes the steps of mixing the reaction solution of the second reaction with anhydrous ethanol, filtering, collecting the precipitate, washing with anhydrous ethanol, and drying to obtain the quaternary ammonium salt-type cationic modified copolymer.

[0066] In some embodiments of this application, the step of preparing silane-modified basalt fibers is also included; The preparation method of the silane-modified basalt fiber includes the following steps: a. Basalt fibers are calcined and acid-leached sequentially to obtain pretreated fibers; b. Mix coupling agent KH570, coupling agent KH550 and solvent, adjust the pH of the mixture to acidic, and obtain silane hydrolysate; c. The pretreated fibers and silane hydrolysate are mixed and reacted to obtain silane-modified basalt fibers.

[0067] After high-temperature calcination, hydrochloric acid etching, and dual modification with silane coupling agents, basalt fibers undergo a transformation from simple physical mixing to chemical anchoring. The composite modification endows the fiber surface with both double bonds and amino groups, which form stable chemical connections with the gel matrix through free radical polymerization, Schiff base reaction, or hydrogen bonding, respectively. This completely solves the problems of fiber agglomeration and shedding caused by physical mixing. The short-cut fibers form an interwoven network, which not only serves as a rigid skeleton to effectively transmit and disperse formation pressure and resist deformation and rupture of the sealing layer, but also intercepts drilling fluid solid particles, further filling tiny gaps and improving the overall compactness and interception effect of the sealing layer, providing long-term stable mechanical support for the material.

[0068] In some embodiments of this application, basalt fibers are cut into 1-5mm short fibers and then calcined. The three-dimensional random distribution of the 1-5mm short fibers forms an interwoven network, which can effectively block the migration of solid particles in the drilling fluid, further fill the tiny gaps between the fiber skeleton and the formation pores, and improve the interception effect and overall compactness of the sealing layer.

[0069] In some embodiments of this application, in step a, the calcination temperature is 500-600℃, such as 500℃, 520℃, 550℃, 580℃, 600℃, etc., and the calcination time is 2-3h, such as 2h, 2.5h, 2.8h, 3h, etc.

[0070] In some embodiments of this application, the acid leaching treatment includes immersing the calcined basalt fibers in a 5%-10% hydrochloric acid solution for 6-12 hours; after immersion, the fibers are washed with deionized water and dried to obtain the pretreated fibers. High-temperature calcination of the basalt fibers removes surface organic impurities, and hydrochloric acid etching increases the surface hydroxyl density, providing sufficient binding sites for silane coupling agents KH570 and KH550.

[0071] In some embodiments of this application, in step b, the solvent includes water and ethanol in a volume ratio of 1:(3-5); for example, 1:3, 1:4, 1:5, etc.

[0072] In some embodiments of this application, the mass ratio of coupling agent KH570 to coupling agent KH550 is 1:(1-2); for example, 1:1, 1:1.5, 1:1.8, 1:2, etc. The double bond of KH570 can participate in the free radical polymerization reaction of the copolymer, and the amino group of KH550 can form covalent bonds or hydrogen bonds with the aldehyde and carboxyl groups of the copolymer, realizing the chemical anchoring of the fiber and the gel matrix, completely avoiding the fiber agglomeration and shedding problems caused by physical mixing, and ensuring the continuous support of the rigid skeleton.

[0073] In some embodiments of this application, in step b, the total mass concentration of coupling agent KH570 and coupling agent KH550 in the mixture is 1%-2%; for example, 1%, 1.2%, 1.5%, 2%, etc.

[0074] In some embodiments of this application, in step b, the pH of the mixture is adjusted to 3-5; preferably, acetic acid is used to adjust the pH of the mixture.

[0075] In some embodiments of this application, the total amount of coupling agent KH570 and coupling agent KH550 is 3%-8% of the mass of basalt fiber; for example, 3%, 4%, 5%, 6%, 8%, etc.

[0076] In some embodiments of this application, the temperature of the mixing reaction in step c is 50-70°C, such as 50°C, 58°C, 60°C, 63°C, 67°C, 70°C, etc., and the time of the mixing reaction is 2-4 hours, such as 2 hours, 2.5 hours, 3 hours, 3.8 hours, 4 hours, etc.

[0077] This application also provides an application of the composite gel material described in the first aspect of this application or the composite gel material prepared by the method described in the second aspect of this application in drilling operations for plugging leaks in fractured goaf areas. The composite gel material described in this application possesses strong electrostatic adsorption, inhibition of clay expansion, excellent mechanical strength, temperature and salt resistance, self-healing properties, and flame retardant characteristics, effectively sealing the complex fracture network in fractured goaf areas and solving technical problems such as weak interfacial bonding in existing technologies.

[0078] The technical solution of this application will be further described below with reference to specific embodiments.

[0079] Example 1 A method for preparing a composite gel material includes the following steps: S1. Preparation of quaternary ammonium salt-type cationic modified copolymers Diethylaminoethyl methacrylate, acrylamide, and 2-acrylamido-2-methylpropanesulfonic acid were added to a mixed solvent of deionized water and anhydrous ethanol and stirred until completely dissolved. Then, polyethylene glycol was added as a dispersant, along with the composite initiators ammonium persulfate and sodium bisulfite. After passing high-purity nitrogen gas through the mixture for 30 minutes, the temperature was raised to 50°C and reacted for 4 hours. The mixture was then distilled under reduced pressure and dried under vacuum to obtain the copolymer solution. The molar ratio of diethylaminoethyl methacrylate, acrylamide, and 2-acrylamido-2-methylpropanesulfonic acid is 1:3:1; the volume ratio of the mixed solvent is deionized water: anhydrous ethanol = 46:1; the total mass concentration of the three monomers is 25wt%; the amount of polyethylene glycol as a dispersant is 0.2% of the total monomer mass; the molar ratio of ammonium persulfate to sodium bisulfite in the composite initiator is 1:0.8; and the amount of the composite initiator is 0.5% of the total monomer mass. The copolymer solution was added to N,N-dimethylformamide solvent along with 5-chloromethylfuran-2-carboxaldehyde and 4-chloromethylstyrene. Potassium iodide was then added as a catalyst. The mixture was stirred until completely dissolved, heated to 60°C, and refluxed for 6 hours. After the reaction was completed, the reaction solution was poured into anhydrous ethanol to precipitate the precipitate. The precipitate was collected by filtration, washed with anhydrous ethanol, and dried under vacuum to obtain the quaternary ammonium salt cationic modified copolymer. The molar ratio of 5-chloromethylfuran-2-carboxaldehyde to 4-chloromethylstyrene is 1:1, and the total molar ratio of diethylamino units to the two chloromethyl compounds in the copolymer solution is 1:1.3; the amount of potassium iodide catalyst is 1% of the total molar amount of the chloromethyl compounds.

[0080] S2. Preparation of silane-modified basalt fibers Basalt fibers were cut into 1mm short fibers, calcined in a muffle furnace at 500℃ for 2 hours, cooled to room temperature, soaked in 5wt% hydrochloric acid solution for 8 hours, washed with deionized water until the pH of the washing solution was neutral, and then vacuum dried for later use. KH570 and KH550 were mixed at a mass ratio of 1:1 and then a mixed solvent of deionized water and ethanol at a volume ratio of 1:3 was added. The total mass concentration of the coupling agent was 1.25%. The pH of the system was adjusted to 3 using acetic acid. The coupling agent was hydrolyzed by stirring at room temperature (25°C) for 30 minutes to obtain a silane hydrolysate. Pretreated basalt fibers were added to a silane hydrolysate, with the total amount of coupling agent being 3% of the mass of the basalt fibers. The mixture was heated to 50°C and stirred at a constant temperature for 2 hours. After modification, the fibers were separated by filtration, washed three times with anhydrous ethanol, and dried under vacuum to obtain silane-modified basalt fibers.

[0081] The composite gel material is obtained by mixing 30g of the above-mentioned quaternary ammonium salt cationic modified copolymer, 10g of carboxymethyl chitosan, 5g of silane-modified basalt fiber, 0.1g of initiator, 0.5g of N,N-methylenebisacrylamide, 1g of inorganic nanofiller, 2g of octadecyl methacrylate, and 3g of flame retardant; wherein the initiator is a mixture of ammonium persulfate and potassium persulfate in a mass ratio of 1:1; the inorganic nanofiller is a mixture of nano-silica and nano-calcium carbonate in a mass ratio of 1:1; and the flame retardant is a mixture of aluminum hydroxide and magnesium hydroxide in a mass ratio of 1:1.

[0082] Example 2 A method for preparing a composite gel material includes the following steps: The composite gel material was obtained by mixing 50g of quaternary ammonium salt-type cationic modified copolymer, 20g of carboxymethyl chitosan, 15g of silane-modified basalt fiber, 0.5g of initiator, 2.0g of N,N-methylenebisacrylamide, 5g of inorganic nanofiller, 8g of octadecyl methacrylate, and 10g of flame retardant. The initiator was a mixture of ammonium persulfate and potassium persulfate in a 1:1 mass ratio; the inorganic nanofiller was a mixture of nano-silica and nano-calcium carbonate in a 1:1 mass ratio; and the flame retardant was a mixture of aluminum hydroxide and magnesium hydroxide in a 1:1 mass ratio. The preparation methods for the quaternary ammonium salt-type cationic modified copolymer and the silane-modified basalt fiber are the same as in Example 1.

[0083] Example 3 A method for preparing a composite gel material includes the following steps: The composite gel material was obtained by mixing 40g of quaternary ammonium salt-type cationic modified copolymer, 15g of carboxymethyl chitosan, 10g of silane-modified basalt fiber, 0.3g of initiator, 1.2g of N,N-methylenebisacrylamide, 3g of inorganic nanofiller, 5g of octadecyl methacrylate, and 6g of flame retardant. The initiator was a mixture of ammonium persulfate and potassium persulfate in a 1:1 mass ratio; the inorganic nanofiller was a mixture of nano-silica and nano-calcium carbonate in a 1:1 mass ratio; and the flame retardant was a mixture of aluminum hydroxide and magnesium hydroxide in a 1:1 mass ratio. The preparation methods for the quaternary ammonium salt-type cationic modified copolymer and the silane-modified basalt fiber are the same as in Example 1.

[0084] Comparative Example 1 The only difference between the preparation method of the composite gel material in Comparative Example 1 and Example 1 is that a copolymer is used instead of a quaternary ammonium salt-type cationic modified copolymer in the preparation process of the composite gel material in Comparative Example 1.

[0085] The specific operating steps include: S1. Preparation of copolymers Diethylaminoethyl methacrylate, acrylamide, and 2-acrylamido-2-methylpropanesulfonic acid were added to a mixed solvent of deionized water and anhydrous ethanol and stirred until completely dissolved. Then, polyethylene glycol was added as a dispersant, along with the composite initiators ammonium persulfate and sodium bisulfite. After passing high-purity nitrogen gas through the mixture for 30 minutes, the temperature was raised to 50°C and reacted for 4 hours. The mixture was then distilled under reduced pressure and dried under vacuum to obtain the copolymer solution. The molar ratio of diethylaminoethyl methacrylate, acrylamide, and 2-acrylamido-2-methylpropanesulfonic acid is 1:3:1; the volume ratio of the mixed solvent is deionized water: anhydrous ethanol = 46:1; the total mass concentration of the three monomers is 25wt%; the amount of polyethylene glycol dispersant is 0.2% of the total mass of the monomers; the molar ratio of ammonium persulfate to sodium bisulfite in the composite initiator is 1:0.8; and the amount of the composite initiator is 0.5% of the total mass of the monomers.

[0086] Comparative Example 2 The only difference between the preparation method of the composite gel material in Comparative Example 2 and that in Example 1 is that carboxymethyl chitosan was not used in the preparation process of the composite gel material in Comparative Example 2.

[0087] Comparative Example 3 The only difference between the preparation method of the composite gel material described in Comparative Example 3 and that in Example 1 is that pretreated basalt fibers are used instead of silane-modified basalt fibers in the preparation process of the composite gel material described in Comparative Example 3.

[0088] The specific operating steps are as follows: S2. Preparation of pretreated basalt fibers Basalt fibers were cut into 1mm short fibers, calcined in a muffle furnace at 500℃ for 2 hours, cooled to room temperature, soaked in 5wt% hydrochloric acid solution for 8 hours, washed with deionized water until the pH of the washing solution was neutral, and vacuum dried for later use.

[0089] Comparative Example 4 The preparation method of the composite gel material described in Comparative Example 4 includes the following steps: 40g of sodium bentonite, 15g of partially hydrolyzed polyacrylamide (molecular weight 8 million), 3g of phenolic resin crosslinking agent, 10g of fine walnut shell particles (40-60 mesh), 5g of mica flakes (20-40 mesh) and 27g of water were mixed and stirred into a paste to obtain the composite gel material.

[0090] Comparative Example 5 The only difference between the preparation method of the composite gel material described in Comparative Example 5 and that in Example 1 is that the quaternary ammonium salt-type cationic modified copolymer was not used in the preparation process of the composite gel material described in Comparative Example 5.

[0091] Comparative Example 6 The only difference between the preparation method of the composite gel material described in Comparative Example 6 and Example 1 is that acrylamide was not used in the preparation of the quaternary ammonium salt cationic modified copolymer in the preparation process of the composite gel material described in Comparative Example 6.

[0092] Comparative Example 7 The only difference between the preparation method of the composite gel material described in Comparative Example 7 and that in Example 1 is that the quaternary ammonium salt-type cationic modified copolymer in the preparation process of the composite gel material described in Comparative Example 7 did not use diethylaminoethyl methacrylate as a raw material.

[0093] Comparative Example 8 The only difference between the preparation method of the composite gel material described in Comparative Example 8 and Example 1 is that, in the preparation process of the composite gel material described in Comparative Example 8, only the coupling agent KH570 is used to modify the pretreated fibers during the preparation of the silane-modified basalt fibers.

[0094] Performance Study of the Composite Gel Materials Described in Examples 1-3 and Comparative Examples 1-8 of this Application Sealing strength test: Using a high temperature and high pressure sand bed filtration instrument, composite gel material was injected into a model containing quartz sand of different particle sizes at 80℃ and 3.5MPa pressure difference. The leakage rate within 30 minutes and the pressure bearing capacity of the final sealing layer were measured.

[0095] Compressive strength and elastic modulus testing: The composite gel material was made into a standard cylindrical sample, and after curing, its uniaxial compressive strength and elastic modulus were tested using a universal testing machine.

[0096] Self-healing performance test: Mechanical damage was applied to the cured composite gel material sample, and after curing in formation water at 60℃ for 24 hours, the crack healing was observed and the compressive strength recovery rate of the repaired sample was tested.

[0097] Temperature and salt resistance test: After the composite gel material was placed in a medium with different temperatures (room temperature, 100℃, 150℃) and saturated sodium chloride solution for 72h, its volume expansion rate and gel strength retention rate were tested.

[0098] Flame retardancy test: The flame retardancy rating of the composite gel material was evaluated using the vertical burning method (UL-94).

[0099] The test results are shown in Table 1.

[0100] Table 1

[0101] As shown in Table 1, under simulated fractured formation conditions, the composite gel material described in this application exhibits extremely low leakage and high sealing layer breakthrough pressure. This means the composite gel material can quickly penetrate and effectively seal multi-level fractures and pores, forming a dense, high-strength isolation barrier. Furthermore, the compressive strength and elastic modulus of the composite gel material are significantly higher than all comparative examples, indicating its strong resistance to formation pressure and deformation, effectively supporting fractured rock masses and preventing wellbore instability. Under the extreme dual tests of 150℃ high temperature and saturated brine, the composite gel material of this invention still maintains more than 85% of its gel strength, with extremely low volume expansion and structural stability. This means the composite gel material can adapt to deep, high-temperature mines and highly mineralized formation environments. Based on dynamically reversible Schiff base bonds, the material possesses environmental responsiveness and can achieve efficient self-healing, significantly reducing downhole maintenance needs and risks. In addition, the composite gel material of this application meets the V-0 flame retardant standard, effectively reducing the risk of downhole fires.

[0102] Although the above embodiments have been shown and described, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Any changes, modifications, substitutions and variations made to the above embodiments by those skilled in the art are within the protection scope of the present invention.

Claims

1. A composite gel material, characterized in that, The raw materials include the following parts by weight: 30-50 parts of quaternary ammonium salt cationic modified copolymer, 10-20 parts of carboxymethyl chitosan, 5-15 parts of silane-modified basalt fiber, 0.1-0.5 parts of initiator, 0.5-2.0 parts of N,N-methylenebisacrylamide, 1-5 parts of inorganic nanofiller, 2-8 parts of octadecyl methacrylate, and 3-10 parts of flame retardant.

2. The composite gel material according to claim 1, characterized in that, The initiator includes one or more of ammonium persulfate, potassium persulfate, azobisisobutyronitrile, and benzoyl peroxide; And / or, the inorganic nanofiller includes one or more of nano-silica, nano-calcium carbonate and nano-montmorillonite; And / or, the flame retardant includes one or more of aluminum hydroxide, magnesium hydroxide, ammonium polyphosphate, pentaerythritol, melamine, and triphenyl phosphate.

3. The method for preparing the composite gel material according to any one of claims 1-2, characterized in that, Includes the following steps: The composite gel material is obtained by mixing a quaternary ammonium salt-type cationic modified copolymer, carboxymethyl chitosan, silane-modified basalt fiber, initiator, N,N-methylenebisacrylamide, inorganic nanofiller, octadecyl methacrylate, and flame retardant.

4. The method for preparing the composite gel material according to claim 3, characterized in that, It also includes the step of preparing quaternary ammonium salt-type cationic modified copolymers; The preparation method of the quaternary ammonium salt-type cationic modified copolymer includes the following steps: Step 1: Diethylaminoethyl methacrylate, acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, dispersant, initiator and first solvent are mixed to carry out the first reaction to obtain a copolymer solution; Step 2: The copolymer solution, 5-chloromethylfuran-2-carboxaldehyde, 4-chloromethylstyrene, catalyst, and second solvent are mixed to carry out a second reaction to obtain a quaternary ammonium salt-type cationic modified copolymer.

5. The method for preparing the composite gel material according to claim 4, characterized in that, In step one, the dispersant includes one or more of polyethylene glycol, polyvinyl alcohol, and poly(ethylene glycol) methacrylate, the initiator includes ammonium persulfate and / or sodium bisulfite, and the first solvent includes water and / or ethanol; Preferably, the initiator comprises ammonium persulfate and sodium bisulfite in a molar ratio of 1:(0.8-1.2); Preferably, the first solvent comprises water and ethanol in a volume ratio of (40-50):1; And / or, the molar ratio of diethylaminoethyl methacrylate, acrylamide, and 2-acryloylamino-2-methylpropanesulfonic acid is 1:(3-3.5):(1-1.2); And / or, the amount of the dispersant is 0.2%-0.4% of the total mass of the diethylaminoethyl methacrylate, acrylamide, and 2-acrylamido-2-methylpropanesulfonic acid; And / or, the amount of the initiator is 0.5%-0.7% of the total mass of the diethylaminoethyl methacrylate, acrylamide, and 2-acrylamido-2-methylpropanesulfonic acid; And / or, the total mass concentration of the reaction solution formed by the diethylaminoethyl methacrylate, acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and the first solvent is 25%-35%; And / or, the temperature of the first reaction is 50-70℃, and the reaction time is 4-8h.

6. The method for preparing the composite gel material according to claim 4, characterized in that, In step two, the catalyst includes one or more of potassium iodide, sodium iodide, and tetrabutylammonium bromide, and the second solvent includes one or more of N,N-dimethylformamide, N-methyl-2-pyrrolidone, and dimethyl sulfoxide. And / or, the molar ratio of the 5-chloromethylfuran-2-carboxaldehyde and 4-chloromethylstyrene is 1:(1-1.1). And / or, the molar ratio of the diethylamino unit in the copolymer solution to the total molar ratio of the 5-chloromethylfuran-2-carboxaldehyde and 4-chloromethylstyrene is 1:(1.3-1.4). And / or, the amount of the catalyst used is 1%-1.5% of the total molar amount of the 5-chloromethylfuran-2-carboxaldehyde and 4-chloromethylstyrene; And / or, the temperature of the second reaction is 60-90℃, and the time of the second reaction is 6-12h; And / or, it further includes the steps of mixing the reaction solution of the second reaction with anhydrous ethanol, filtering, collecting the precipitate, washing with anhydrous ethanol, and drying to obtain the quaternary ammonium salt-type cationic modified copolymer.

7. The method for preparing the composite gel material according to claim 4, characterized in that, It also includes the step of preparing silane-modified basalt fibers; The preparation method of the silane-modified basalt fiber includes the following steps: a. Basalt fibers are calcined and acid-leached sequentially to obtain pretreated fibers; b. Mix coupling agent KH570, coupling agent KH550 and solvent, adjust the pH of the mixture to acidic, and obtain silane hydrolysate; c. The pretreated fibers and silane hydrolysate are mixed and reacted to obtain silane-modified basalt fibers.

8. The method for preparing the composite gel material according to claim 7, characterized in that, In step a, the calcination temperature is 500-600℃, and the calcination time is 2-3 hours; And / or, the acid leaching treatment includes immersing the calcined basalt fiber in a hydrochloric acid solution with a mass concentration of 5%-10% for 6-12 hours; after immersion, washing with deionized water and drying to obtain the pretreated fiber; And / or, in step b, the solvent comprises water and ethanol in a volume ratio of 1:(3-5); And / or, the mass ratio of coupling agent KH570 to coupling agent KH550 is 1:(1-2); And / or, in step b, the total mass concentration of coupling agent KH570 and coupling agent KH550 in the mixture is 1%-2%; And / or, in step b, the pH of the mixture is adjusted to 3-5; preferably, acetic acid is used to adjust the pH of the mixture.

9. The method for preparing the composite gel material according to claim 7, characterized in that, The total amount of coupling agent KH570 and coupling agent KH550 is 3%-8% of the mass of basalt fiber; And / or, the temperature of the mixing reaction in step c is 50-70°C, and the time of the mixing reaction is 2-4 hours.

10. The application of the composite gel material according to any one of claims 1-2 or the composite gel material obtained by the preparation method according to any one of claims 3-9 in drilling operations for plugging leaks in broken goaf areas.

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