Controlled release type coal seam anti-reflection acid oxidant material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of coal mining and coal bed gas development, and particularly discloses a controlled-release type coal bed anti-reflection acid oxidant material and a preparation method and application thereof. The material comprises a porous carrier, solid acid, a solid oxidant and a delayed trigger, the porous carrier is functionally modified by a sulfonic acid group, and the delayed trigger is a composite system of a pH response and temperature ion strength response polymer. The preparation method comprises the following steps: pre-treating the porous carrier, functionally modifying, carrying out vacuum impregnation to realize gradient loading of the active components, and finally sequentially coating the dual-response polymer layers. The material can be used for deep chemical anti-reflection of the low-permeability coal seam, has the advantages of targeted slow release, no equipment corrosion and efficient and long-acting anti-reflection, and can accurately solve the problems of quick loss of active components and poor deep action in the traditional technology; the preparation method is controllable in process, stable in product structure, and suitable for industrial production and application, and all steps synergistically guarantee the material performance.

Description

Technical Field

[0001] This application relates to the fields of coal mining and coalbed methane development technology, and more specifically, to a controlled-release coal seam permeability-enhancing acid oxidant material, its preparation method, and its application. Background Technology

[0002] In coalbed methane extraction and coalbed gas control, coal seam permeability is a key factor restricting development efficiency and control effectiveness. Deep coal seams, in particular, generally suffer from dense pores and extremely low permeability, necessitating the use of chemical permeability enhancement technologies to improve their permeability. Chemical permeability enhancement typically involves reacting acids or oxidants with coal seam minerals to dissolve blockages in pore throats and expand fracture channels, thereby improving coal seam permeability and creating favorable conditions for gas drainage or coalbed methane extraction. Therefore, chemical permeability enhancement materials and their supporting application methods have significant application value in deep coal seam development.

[0003] Existing chemical permeation enhancement technologies for coal seams mostly employ the direct injection of liquid acid or oxidant materials into the coal seam. However, these materials have significant technical drawbacks. On the one hand, liquid acids or oxidants are highly corrosive, directly corroding downhole equipment and surface pipelines during injection into the wellbore and pumping process, increasing equipment maintenance costs and safety hazards. On the other hand, the liquid active ingredients are prone to rapid diffusion and loss after injection, making it difficult to accurately reach the target area deep within the coal seam. Furthermore, the release process of the active ingredients is uncontrollable, resulting in the permeation enhancement effect being concentrated in shallow coal seams, with poor permeation enhancement effects and short duration of action in deep coal seams. Among these problems, the core contradiction of existing chemical permeation enhancement materials—the inability to simultaneously address the corrosion protection requirements of equipment and the need for long-range, slow-release, targeted permeation enhancement in deep coal seams—severely restricts their widespread application in deep coal seam permeation enhancement projects. Summary of the Invention

[0004] To address the technical problems of severe corrosion of wellbore equipment caused by liquid injection materials of strong acids / strong oxidants in the prior art, and the inability to achieve controllable slow-release permeability enhancement in deep coal seams, this application provides a controlled-release coal seam permeability enhancement acid oxidant material, its preparation method, and its application.

[0005] This application provides a controlled-release coal seam permeability-enhancing acid oxidant material using the following technical solution: In a first aspect, this application provides a controlled-release coal seam permeability-enhancing acid oxidant material, employing the following technical solution: A controlled-release coal seam permeability-enhancing acid oxidant material comprises the following components in parts by weight: 40-60 parts porous carrier, 5-15 parts solid acid, 5-15 parts solid oxidant, and 10-25 parts delayed triggering agent.

[0006] By employing the above technical solution, this controlled-release solid acid oxidant material achieves precise permeability enhancement deep within coal seams through the synergistic combination of specific components and structural design. The porous carrier is selected from porous diatomaceous earth or modified coal-based materials. Its rich pore structure and excellent adsorption performance provide a stable loading substrate for the solid acid and solid oxidant. Through physical adsorption and pore confinement, the active ingredients are firmly fixed, laying the foundation for controlled release. The solid acid is selected from mild acidic substances such as citric acid, oxalic acid, and tartaric acid, while the solid oxidant uses mild oxidants such as ammonium persulfate, potassium persulfate, and urea peroxide. Together, they dissolve the organic matter and carbonate minerals in the coal seam, opening up pore throats and micro-fractures. The mild reaction characteristics also prevent large-scale damage to the coal structure. The delayed triggering agent is composed of pH-responsive polymers and temperature- and ionic strength-responsive polymers in a specific ratio, forming a double-layer structure with an inner carrier layer and an outer regulating layer. By sensing the pH, temperature, and ionic strength signals deep within the coal seam, it gradually dissolves or decomposes, precisely controlling the timing and rate of active ingredient release. The active ingredients are distributed in a gradient within the carrier pores, avoiding premature mixing and reaction losses. Ultimately, through dual regulation of carrier loading, delayed triggering agent, and synergistic dissolution of active ingredients, the remote targeting and sustained release effect of chemical permeation is achieved, while avoiding direct corrosion of the delivery equipment by traditional liquid acid oxidants throughout the process.

[0007] Preferably, the porous carrier is porous diatomaceous earth with sulfonic acid groups modified on its surface or a modified coal-based carrier; the solid acid includes at least one of citric acid, oxalic acid, and tartaric acid; and the solid oxidant includes at least one of ammonium persulfate, potassium persulfate, and urea peroxide.

[0008] By adopting the above technical solution, the porous carrier is selected from porous diatomaceous earth or modified coal-based carriers with sulfonic acid groups on the surface. Their abundant pores and large specific surface area provide sufficient loading sites for active ingredients. The strong polarity and reactivity of the sulfonic acid groups can form a stable bond with the active ingredients through chemical bonding, significantly improving the loading stability and preventing premature detachment and loss of active ingredients during injection. The solid acid is at least one of citric acid, oxalic acid, and tartaric acid. This type of mild organic solid acid has an acid strength suitable for the dissolution requirements of coal seam minerals. It can react with carbonate minerals to achieve dissolution and pore expansion, without the strong corrosiveness of traditional strong acids. The solid form also facilitates controlled release by binding with the carrier. Multiple acids can be flexibly combined according to the composition of coal seam minerals, with complementary dissociation rates and dissolution characteristics, optimizing the dissolution effect on different minerals. The solid oxidant is at least one of ammonium persulfate, potassium persulfate, and urea peroxide. It has good stability in solid state and is not easily decomposed or ineffective before triggering. After triggering, the active oxygen species released can oxidize and decompose the organic matter in the coal seam, break the blockage of pore throats, and at the same time, it can synergistically improve the dissolution efficiency and pore connectivity with solid acid. The different decomposition temperatures and response characteristics of different oxidants can be adapted to the temperature and pressure environment of coal seams at different depths, thus broadening the application range of the material.

[0009] Preferably, the delayed triggering agent comprises a pH-responsive polymer and a temperature-ionic-strength-responsive polymer, with a dry basis mass ratio of 1:(0.5-3); the pH-responsive polymer is one of dimethylaminoethyl methacrylate-methacrylic acid copolymer, cellulose acetate phthalate, or polyacrylic acid resin; the temperature-ionic-strength-responsive polymer is poly(N-isopropylacrylamide) or a copolymer thereof.

[0010] By adopting the above technical solution, the delayed triggering agent employs a composite design of pH-responsive polymers and temperature- and ionic strength-responsive polymers, combined at a specific dry basis mass ratio to form a dual environmental response mechanism. The ratio can be flexibly adjusted according to differences in environmental parameters at depths of the coal seam, ensuring synergistic matching and avoiding the problems of false triggering or insufficient triggering associated with single-response mechanisms. The pH-responsive polymer is selected from one of the following: dimethylaminoethyl methacrylate-methacrylic acid copolymer, cellulose phthalate acetate, or polyacrylic acid resin. Specific functional groups in its molecular structure can sense changes in the pH value of the coal seam. Upon contact with the pre-activation solution or formation water, it undergoes dissociation, swelling, or dissolution with pH changes, gradually opening the coating channels. Different polymers are adapted to different coal seam pH environments, ensuring precise triggering. The temperature- and ionic strength-responsive polymer is poly(N-isopropylacrylamide) or its copolymers, possessing a clear critical dissolution temperature and ionic strength response characteristics. After entering the coal seam, it senses changes in formation temperature and ionic strength. When the critical conditions are reached, the molecular chain undergoes a phase transition, further regulating the permeability of the coating layer. The copolymer can be copolymerized to optimize critical response parameters, better fitting the environment of coal seams at different depths. The two polymers form a dual guarantee of "pH response triggering + temperature and ion strength response regulation", ensuring that the active ingredients are not released prematurely during injection and pumping, but are released slowly at a controllable rate only in the target area deep in the coal seam, providing core support for targeted permeability enhancement.

[0011] Secondly, this application provides a method for preparing a controlled-release coal seam permeability-enhancing acid oxidant material, employing the following technical solution: A method for preparing a controlled-release coal seam permeability-enhancing acid oxidant material includes the following steps: S1. Carrier pretreatment: The porous carrier is ground and dried to obtain a pretreated carrier; S2. Functional modification of the carrier: The pretreated carrier is reacted with an aqueous solution of sulfonating agent, and after washing and drying, a functionalized porous carrier with sulfonic acid groups modified on its surface is obtained. S3. Gradient loading of active ingredients: Solid acid and solid oxidant are respectively prepared into solutions or dispersions, and loaded onto the functionalized porous support in sequence or in reverse order to obtain loaded particles with a gradient distribution structure of active ingredients. S4, Delayed trigger coating: A pH-responsive polymer layer and a temperature- and ionic strength-responsive polymer layer are sequentially coated on the surface of the supported particles.

[0012] By adopting the above technical solution, the preparation process is optimized stepwise through carrier modification, gradient loading, and double coating, ensuring the material's structural stability and controlled-release permeability enhancement performance. In the carrier pretreatment stage, grinding ensures the porous carrier reaches a suitable particle size, increasing specific surface area and pore exposure. Drying removes surface moisture and impurities, creating clean conditions for effective reaction between the carrier and the sulfonating agent. During carrier functionalization modification, the pretreated carrier reacts fully with the sulfonating agent aqueous solution, and the sulfonic acid groups chemically bond with the hydroxyl groups on the carrier surface to achieve uniform modification. After washing to remove free sulfonating agent and byproducts, and drying and curing, the functionalized porous carrier, due to the strong polarity and reactivity of the sulfonic acid groups, significantly enhances its adsorption and binding capacity for active ingredients. In the active ingredient gradient loading step, the solid acid and solid oxidant are prepared into solutions or dispersions and loaded sequentially or in reverse order, creating a gradient distribution along the carrier pore depth. This avoids premature mixing and reaction losses, ensuring uniform dispersion and firm adsorption of each active ingredient, laying the foundation for orderly and synergistic release. In the delayed trigger coating process, the coating is carried out in the order of pH-responsive polymer layer first, followed by temperature and ion strength-responsive polymer layer. The inner layer forms the first environmental response barrier, and the outer layer is the second regulation layer. The two polymer layers are tightly bonded by spray coating to form a continuous and dense coating structure, which prevents the leakage of active ingredients. At the same time, the release timing and rate of active ingredients are precisely controlled by the sequential response of the two layers, and finally a controlled-release material with "solid load-precise response-controllable release" is constructed.

[0013] Preferably, in step S1, the grinding process reduces the particle size of the porous carrier to 0.1-0.5 mm; the drying temperature is 100-150°C, and the drying time is 2-4 hours.

[0014] By adopting the above technical solution, step S1, carrier pretreatment, lays a solid foundation for subsequent processes through precise control of grinding particle size and drying parameters. Grinding ensures that the porous carrier reaches a suitable particle size, guaranteeing sufficient specific surface area and pore exposure to provide more active sites for the sulfonation reaction. It also avoids the problem of excessively small particle size causing agglomeration and clogging of the drill holes during suspension pumping, or excessively large particle size resulting in low loading efficiency and weak bonding. Simultaneously, it adapts to the pore channel size of the coal seam, ensuring uniform distribution of the material after injection. Drying, using appropriate temperature and time, quickly removes free water from the carrier surface and bound water within the pores, avoiding excessively high temperatures that could damage the porous structure and mechanical stability of the carrier. It effectively removes moisture and residual impurities, reducing interference with the subsequent grafting efficiency of sulfonic acid groups. This ensures the pretreated carrier is in a clean, dry, and structurally stable state, guaranteeing the full development of the sulfonation reaction and uniform modification of the sulfonic acid groups.

[0015] Preferably, in step S2, the concentration of the sulfonating agent aqueous solution is 0.5-1.5 mol / L; the reaction temperature is 60-80℃, and the reaction time is 3-6 h; the drying temperature is 80-120℃; and the sulfonating agent is one of concentrated sulfuric acid, chlorosulfonic acid, or aminosulfonic acid.

[0016] By adopting the above technical solution, the functional modification of the carrier in step S2 achieves uniform and firm grafting of sulfonic acid groups through the selection of specific sulfonating agents and the control of process parameters. The sulfonating agent is selected from concentrated sulfuric acid, chlorosulfonic acid, or aminosulfonic acid. Concentrated sulfuric acid has strong sulfonating activity and can efficiently undergo dehydration sulfonation reaction with the hydroxyl groups of the carrier; chlorosulfonic acid has a fast reaction rate and high efficiency, suitable for carriers with lower reactivity; aminosulfonic acid has a mild and easily controlled reaction, avoiding damage to the porous structure of the carrier due to excessive reaction. The three sulfonating agents are suitable for carriers with different surface properties, ensuring efficient and mild sulfonation reactions. The aqueous solution of the sulfonating agent is used at an appropriate concentration, which provides sufficient sulfonation active sites to ensure the grafting density of sulfonic acid groups and meet the binding requirements of active ingredients, while avoiding localized over-sulfonation that could lead to pore blockage or structural damage to the carrier. Setting the reaction temperature within a suitable range activates the sulfonating agent, accelerates its penetration into the carrier pores, promotes uniform reaction, and avoids slow reaction and incomplete grafting due to excessively low temperatures, or decomposition of the sulfonating agent and decreased thermal stability of the carrier due to excessively high temperatures. Controlling the reaction time within a reasonable range ensures sufficient reaction between the sulfonating agent and the hydroxyl groups on the carrier surface and within the pores, achieving deep grafting of sulfonic acid groups and improving grafting strength. Drying after modification at a suitable temperature thoroughly removes residual sulfonating agent, byproducts, and moisture, preventing impurities from interfering with subsequent active ingredient loading, while also avoiding excessively high temperatures that could damage the grafted sulfonic acid groups. This ensures a clean surface of the functionalized porous carrier rich in active sulfonic acid groups, creating the necessary conditions for forming stable chemical bonds with active ingredients and improving loading strength.

[0017] Preferably, in step S3, the pH value of the solid acid solution is 1-3, and the concentration of the solid oxidant dispersion is 10-30 wt%; the loading process is carried out under vacuum impregnation at 40-60°C and an absolute pressure of 5-20 kPa, with each impregnation lasting 1-3 hours, followed by drying at 50-70°C to remove the solvent; the solvent used to prepare the solution or dispersion is at least one of anhydrous ethanol, acetone, or deionized water.

[0018] By adopting the above technical solution, step S3, gradient loading of active ingredients, achieves orderly and robust loading of active ingredients through solvent selection, solution parameter control, and vacuum impregnation process optimization. At least one of anhydrous ethanol, acetone, or deionized water is selected as the solvent. Deionized water is environmentally friendly and residue-free, suitable for dissolving water-soluble solid acids. Anhydrous ethanol and acetone have stronger solubility for some active ingredients, improving dispersion uniformity and having moderate volatility, facilitating subsequent drying and removal. Multiple solvents can be flexibly combined according to the solubility characteristics of the active ingredients, avoiding crystallization or inactivation of the active ingredients and ensuring the environmental safety of the loading process. The solid acid solution is controlled at an appropriate acidity to ensure sufficient dissociation of the solid acid to form hydrogen ions, which is beneficial for forming electrostatic interactions with the sulfonic acid groups on the carrier surface to improve loading robustness, while maintaining the chemical stability of the solid acid and preventing excessive dissociation and premature inactivation. The solid oxidant dispersion is used at an appropriate concentration to ensure good dispersion flow, facilitating penetration into the deep pores of the carrier, while ensuring sufficient oxidant active ingredients per unit volume to meet the requirements of the permeation enhancement reaction. The loading process employs a vacuum impregnation technique with specific temperature and vacuum levels. The vacuum environment rapidly removes air from the carrier pores, breaking the surface tension at the liquid-solid interface and allowing the solution or dispersion to smoothly penetrate the carrier's micropores and mesopores, improving loading uniformity and depth. The appropriate temperature accelerates the diffusion rate of active ingredient molecules, promoting their interaction with sulfonic acid groups on the carrier surface. This avoids slow penetration and insufficient loading due to excessively low temperatures, or decomposition of active ingredients due to excessively high temperatures. Each impregnation session is controlled within a reasonable range to ensure sufficient adsorption and binding of the active ingredient within the carrier pores, forming a stable loading layer. Sequential or reverse impregnation sequences, combined with drying after each impregnation, effectively prevent premature contact and mixing of the two active ingredients, ensuring the formation of a gradient distribution structure. Drying after impregnation at a suitable temperature quickly removes residual solvent without damaging the chemical structure and stability of the active ingredient. This avoids decomposition of the active ingredient or adverse reactions with the carrier caused by high temperatures, ensuring the active ingredient is firmly fixed within the carrier pores, forming structurally stable loaded particles. This provides a reliable guarantee for subsequent delayed trigger encapsulation and controlled release of the active ingredient.

[0019] Preferably, in step S4, when coating the pH-responsive polymer layer, the coating solution concentration is 3-8 wt%, the spray flow rate is 10-30 mL / min, and the inlet air temperature is 50-65℃; when coating the temperature-ion-strength-responsive polymer layer, the coating solution concentration is 2-6 wt%; the spray pressure during the spray coating process is 0.2-0.4 MPa, and the rotation speed of the fluidized bed is 100-300 r / min.

[0020] By adopting the above technical solution, step S4 achieves orderly coating of the dual-response polymer layer through precise control of spray coating process parameters, constructing a continuous, dense, and responsive coating structure. When coating the pH-responsive polymer layer, the coating solution is used at an appropriate concentration to ensure the film-forming properties of the polymer solution, forming a continuous, non-porous coating layer, while avoiding difficulties in atomization due to excessive concentration or damage to the film layer due to excessively low concentration. The spray flow rate is set within an appropriate range, coordinated with the fluidized bed speed and spray pressure of the material, ensuring that the coating solution uniformly covers the surface of each loaded particle, avoiding localized coating accumulation or incomplete coating. The inlet air temperature is controlled within a suitable range to quickly remove the solvent from the coating solution, promoting rapid polymer film formation, while avoiding excessively high temperatures that could cause thermal denaturation and loss of responsiveness in the pH-responsive polymer, or excessively low temperatures that could cause incomplete solvent evaporation and film adhesion and clumping, thus ensuring the structural integrity and responsive performance of the pH-responsive layer. When coating a temperature- and ion-responsive polymer layer, the coating solution is used at a corresponding concentration to meet the outer coating requirements. This ensures the formation of a controllable membrane of suitable thickness, preventing excessive thickness from hindering environmental signal transmission, while also allowing for close adhesion with the inner pH-responsive polymer layer, forming a seamless composite coating structure. The slightly lower concentration design compared to the inner layer balances the overall thickness and response sensitivity of the dual coating layers, ensuring synergistic effects between the two membranes. During spray coating, a specific pressure spray atomizes the coating solution into fine, uniform droplets. The droplet size matches the particle size of the loaded particles, allowing for uniform adhesion and rapid spread. A fluidized bed with a suitable rotation speed drives the loaded particles to continuously and smoothly tumble, ensuring full contact between all particle surfaces and the atomized droplets. This prevents agglomeration and uneven coating in certain areas. Simultaneously, the slight collisions generated during tumbling promote membrane densification, reducing porosity and ensuring structural stability of the coating layer during injection and pumping. The release channel is only gradually opened under specific environmental signals triggered deep within the coal seam.

[0021] Thirdly, this application provides an application of a controlled-release coal seam permeability-enhancing acid oxidant material, employing the following technical solution: The application of a controlled-release coal seam permeability-enhancing acid oxidant material includes the following steps: P1. Pre-activation environmental conditioning: Pre-activation fluid is injected into the deep part of the target coal seam through drilling; P2. Particle suspension injection: The controlled-release solid acid oxidant material is prepared into a suspension and pumped into the depth of the coal seam; P3. Triggering and sustained-release permeability enhancement: Well shut-in triggers the release of active ingredients from the particles in the formation environment.

[0022] By adopting the above technical solution, this deep coal seam chemical permeation enhancement method is designed with orderly steps of pre-activation conditioning, precise delivery, and targeted slow release to achieve efficient deep coal seam permeation enhancement. In the pre-activation environmental conditioning step, a pre-activation liquid is injected into the deep part of the target coal seam. The pre-activation liquid can be a weakly alkaline electrolyte solution or an aqueous solution containing surfactants. Its core function is to adjust the environmental parameters such as pH value and ionic strength of the target area in advance, providing a precise trigger signal for the dual response mechanism of the delayed triggering agent. At the same time, it wets the coal seam pores, dissolves some of the surface blocking substances, improves the permeation channels, and creates favorable conditions for the uniform diffusion and permeation of the subsequent particle suspension, avoiding material triggering delay or insufficiency due to incompatibility of coal seam environmental parameters. In the particulate suspension injection step, the controlled-release material is mixed with injection water to form a suspension of appropriate concentration. The suspension is then pumped into the deep part of the coal seam at a reasonable discharge rate using a pumping device. The suspension form avoids the problem of easy settling and borehole blockage when solid particles are injected alone. It can carry the material to evenly cover the planned permeability enhancement area. The pumping pressure and discharge rate can be matched with the permeability characteristics of the coal seam to ensure that the material penetrates deep into the micropores and fractures of the coal seam, avoiding uneven permeability enhancement caused by only staying in the shallow part. In the triggering and slow-release permeability enhancement steps, shutting in the well creates a stable and sealed environment in the formation, allowing the loaded particles to remain fully in the target area. Under the combined action of formation water and pre-activation fluid, the pH-responsive polymer layer of the delayed triggering agent senses the pH change and swells or dissolves. The temperature and ion strength responsive polymer layer then adapts to the formation temperature and ion strength to regulate the permeability of the coating layer, promoting the orderly release of active ingredients in a gradient. The solid acid gradually dissolves carbonate minerals, and the solid oxidant oxidizes and decomposes the organic matter blocking the pores. The two work together to gradually expand the pore throats and connect microfractures, achieving long-term permeability enhancement of the deep coal seam without damaging the overall structural stability of the coal body, ultimately achieving the goal of safe, efficient, and durable permeability enhancement.

[0023] Preferably, in step P1, the pre-activation solution is a weakly alkaline electrolyte solution with a pH of 8-10 or an aqueous solution containing 0.01-0.05 mol / L surfactant, and the injection volume is 10-30% of the expected pore volume of the planned permeability enhancement area; the weakly alkaline electrolyte solution is sodium bicarbonate solution, sodium silicate solution, or a mixture of both; the surfactant is sodium dodecylbenzenesulfonate or fatty alcohol polyoxyethylene ether; in step P2, the controlled-release solid acid oxidant material is prepared into a suspension with a mass concentration of 5-15% with the injection water, and pumped through a borehole at a discharge rate of 0.5-2.0 m³ / min.

[0024] By adopting the above technical solution, the pre-activation environment adjustment in step P1, through the selection of pre-activation liquid type and parameter control, lays the foundation for subsequent material triggering and uniform diffusion. Two types of suitable pre-activation liquids are provided: one is a weakly alkaline electrolyte solution, using sodium bicarbonate solution, sodium silicate solution, or a mixture of both. Its pH range precisely matches the pH-responsive polymer sensitivity range in the delayed triggering agent, enabling gentle and efficient triggering of pH-responsive polymer dissociation and swelling, avoiding trigger failure or overreaction due to excessively high or low pH. Simultaneously, the weakly alkaline environment can pre-neutralize local acidic impurities in the coal seam, optimizing the subsequent dissolution reaction environment of the active ingredients. Both solutions possess mild alkalinity and good formation compatibility, do not damage the coal seam structure, and can be mixed to flexibly adjust the alkalinity intensity according to the differences in coal seam pH. Another type is an aqueous solution containing a suitable concentration of surfactant. The surfactant chosen is sodium dodecylbenzenesulfonate or fatty alcohol polyoxyethylene ether. This concentration effectively reduces the liquid-solid interfacial tension within the coal seam pores, breaks the capillary resistance effect of formation water, and simultaneously disperses organic matter and mineral particles on the coal seam surface, clearing micro-permeability channels. Sodium dodecylbenzenesulfonate has strong emulsifying and dispersing capabilities, while fatty alcohol polyoxyethylene ether has mild surface activity and good biodegradability, allowing for flexible selection based on the degree of coal seam pollution and environmental requirements. The pre-activation liquid injection volume is a reasonable proportion of the expected pore volume in the planned permeability enhancement area. This ensures sufficient adjustment of environmental parameters in the target area and wetting of pore channels without encroaching on the subsequent particle suspension's capacity, thus avoiding dilution of the active ingredient concentration. Step P2, particle suspension injection, optimizes the suspension concentration and pumping parameters to ensure efficient and uniform delivery of the material to the target area deep within the coal seam. The controlled-release material and injection water are mixed to prepare a suspension with an appropriate mass concentration. This concentration balances material suspension stability and pumpability, and can be flexibly adjusted according to differences in material particle size and coal seam permeability to adapt to different delivery conditions. The pump discharge rate is set within an appropriate range. A low discharge rate is suitable for dense coal seams with low permeability, avoiding excessive discharge rate that could cause a sudden pressure surge and damage the coal structure. A high discharge rate is suitable for coal seams with relatively high permeability, which can improve material conveying efficiency and shorten operation time. Through discharge rate control, it is possible to ensure that the suspension fully penetrates into the deep micropores and fractures of the coal seam, while avoiding premature settling of particles during transport. This ensures that the material is evenly distributed in the planned permeability enhancement area, providing a guarantee for the uniformity and effectiveness of subsequent slow-release permeability enhancement.

[0025] In summary, this application has the following beneficial effects: 1. This application employs a core-shell structure material formed by loading a porous carrier with a solid acid and a solid oxidant as the core, and coating it with a delayed triggering agent. This material remains inert during injection into the wellbore and pumping, thus avoiding the risk of direct corrosion of the equipment by strong acid. Simultaneously, because the delayed triggering agent only begins to release its internal active ingredients in a controlled manner under the triggering of formation water or specific ions, it achieves remote, slow-release, and targeted chemical permeability enhancement, allowing the permeability enhancement effect to act more persistently deep within the coal seam.

[0026] 2. This application preferably uses mild solid acids such as citric acid and oxalic acid, as well as solid oxidants such as ammonium persulfate, combined with porous diatomaceous earth or modified coal-based supports with sulfonic acid groups on their surface. Because the selected acids and oxidants have relatively mild and controllable reactivity, and the functionalized supports can stably support the load and may have auxiliary ion exchange effects, the overall system is environmentally friendly. It can effectively dissolve organic matter and carbonate minerals without excessively damaging the coal's framework structure, thereby improving permeability.

[0027] 3. The method of this application involves stepwise vacuum impregnation and loading of solid acid and solid oxidant, thereby forming a gradient distribution structure of active ingredients within the carrier. This gradient distribution, combined with sequentially coated pH-responsive and temperature- and ionic strength-responsive layers, enables the sequential or synergistic release of acid and oxidant in time and space. This makes the chemical reaction process more gentle and controllable, facilitating the formation of more uniform and interconnected permeation channels and avoiding excessive local damage to the coal body caused by overly vigorous and concentrated reactions.

[0028] 4. The deep coal seam chemical permeation enhancement method of this application first adjusts the microenvironment of the target area by injecting a pre-activation solution with a specific pH or containing surfactants, and then injects a material suspension. Since the pre-activation step creates optimized initial conditions for the dissolution or response of the subsequent particle-delayed trigger layer, it is possible to more precisely control the release initiation of the material at a predetermined depth, enhancing the controllability and reliability of the entire permeation enhancement operation and ensuring that the slow-release permeation enhancement effect is fully realized in the target area. Attached Figure Description

[0029] Figure 1 This is a flowchart of a method for preparing a controlled-release coal seam permeability-enhancing acid oxidant material provided in this application; Figure 2 This is an application flowchart of a controlled-release coal seam permeability-enhancing acid oxidant material provided in this application. Detailed Implementation

[0030] The present application will be further described in detail below with reference to embodiments and comparative examples. Unless otherwise specified, the experimental methods used below are conventional methods. Unless otherwise specified, the materials, reagents, methods and instruments used are all conventional materials, reagents, methods and instruments in the art, which can be obtained by those skilled in the art through commercial channels or prepared according to literature methods.

[0031] Technical concept: Significant bottlenecks exist in the application of chemical permeability enhancement technologies in deep coal seams. The core issues are high equipment corrosion risk, low efficiency of active ingredients, and poor targeting and sustainability of permeability enhancement. Traditional technologies often involve the direct injection of strong acids or oxidants in liquid form. This direct contact between the liquid active ingredients and the wellbore equipment and delivery pipelines increases maintenance costs and poses safety hazards due to their strong corrosiveness. Furthermore, the lack of effective triggering and controlled-release mechanisms leads to rapid diffusion and loss of the injected active ingredients, making it difficult to accurately reach the target area in the deep coal seam. Pre-mixed active ingredients are also prone to reaction loss, resulting in permeability enhancement concentrated in shallow coal seams, with poor and short-lasting effects in deeper areas. In addition, the lack of targeted functional modification of the carrier results in insufficient load-bearing strength for the active ingredients, further exacerbating premature detachment and failure. These problems collectively restrict the application of chemical permeability enhancement technology in deep coal seam development.

[0032] This technical solution addresses the aforementioned issues by employing a core-shell structure design at the material level, consisting of a porous carrier, active ingredients, and a delayed triggering agent. Mild solid acids and solid oxidants are selected as active ingredients to mitigate the corrosion risk from strong liquid acids. The porous carrier undergoes functionalization with sulfonic acid groups to enhance the loading stability of the active ingredients. Combined with a gradient loading method for the active ingredients, premature mixing and reaction losses are avoided. The triggering mechanism innovatively utilizes a dual-response delayed triggering agent, a composite of pH-responsive polymers and temperature- and ionic strength-responsive polymers. The preparation process employs a step-by-step design involving carrier pretreatment, functionalization modification, gradient loading, and double coating to ensure material structural stability and performance consistency. The accompanying permeation enhancement method, through a series of orderly steps including pre-activation environmental conditioning, precise suspension pumping, and well shut-in slow release, ensures the material efficiently reaches deep into the coal seam and fully exerts its effect, ultimately achieving a safe, corrosion-free, precisely targeted, and long-lasting deep coal seam chemical permeation enhancement goal.

[0033] Preparation Example 1: Preparation method of dimethylaminoethyl methacrylate-methacrylic acid copolymer 15.7 g of dimethylaminoethyl methacrylate and 13.2 g of methacrylic acid were used as comonomers and added to 200 mL of an ethanol-water mixture (80 mL ethanol, 120 mL water, ethanol:water volume ratio 1:1.5). The mixture was stirred with a magnetic stirrer for 30 min to completely dissolve the monomers, resulting in a reaction solution with a monomer concentration of 20 wt%. Then, 0.35 g of azobisisobutyronitrile (AIBN) was added to the reaction solution (1.2% of the total mass of the two monomers), and the mixture was stirred for another 20 min to ensure the initiator was uniformly dispersed in the reaction solution.

[0034] The reaction vessel was placed in a 65°C constant temperature water bath, and nitrogen gas was introduced for inert gas protection at a flow rate of 50 mL / min. Simultaneously, stirring was started at a rate of 80 r / min, and the reaction was carried out at the constant temperature for 7 hours. After the reaction was complete, the water bath was turned off, and the reaction solution was allowed to cool naturally to room temperature.

[0035] The cooled reaction solution was slowly poured into 800 mL of acetone while stirring at a rate of 50 rpm to allow the copolymer to precipitate completely. The precipitate was collected by vacuum filtration using a Buchner funnel, washed three times with 50 mL of acetone, and then repeatedly washed with deionized water until the pH of the washing solution reached 7.0 to remove unreacted monomers and residual initiators.

[0036] The washed product was placed in a vacuum drying oven at 55°C, with the vacuum maintained at -0.09 MPa, and dried to constant weight to obtain dimethylaminoethyl methacrylate-methacrylic acid copolymer. This product has a molecular weight of 35,000 and exhibits good pH response characteristics, making it suitable for direct use in the preparation of delayed triggering agents in controlled-release solid acid oxidant materials.

[0037] Preparation Example 2: Preparation method of cellulose phthalate acetate Take 10g of microcrystalline cellulose and dry it in a 105℃ drying oven for 4 hours to remove moisture. Cool it to room temperature before use. Add the dried microcrystalline cellulose to a 250mL three-necked flask, add 50mL of glacial acetic acid as a solvent, and turn on the magnetic stirrer at a stirring speed of 60r / min to uniformly disperse the microcrystalline cellulose into a suspension.

[0038] Add 30 mL of acetic anhydride to the suspension, then add 5 mL of pyridine as a catalyst, with the dropping rate controlled at 1 mL / min. Keep stirring during the dropping process. After the dropping is completed, place the three-necked flask in a 60℃ constant temperature water bath and stir for 2 hours to complete the acetylation modification.

[0039] Subsequently, 15g of phthalic anhydride was added to the reaction system, and the temperature was further increased to 80℃. The stirring rate was increased to 100r / min, and the reaction was carried out at a constant temperature with stirring for 4 hours to perform the phthalylation reaction. During the reaction, the volatilized solvent was recovered through a reflux condenser to ensure that the reaction proceeded completely.

[0040] After the reaction is complete, turn off the water bath and allow the reaction solution to cool naturally to room temperature. Slowly pour the reaction solution into 500 mL of deionized water while stirring at a rate of 50 rpm to ensure complete precipitation of the product. Collect the precipitate using a Buchner funnel and wash it repeatedly with deionized water until the pH of the washing solution reaches 7.0 to remove unreacted reagents and byproducts.

[0041] The washed product was placed in a vacuum drying oven at 60℃, with the vacuum maintained at -0.09 MPa, and dried to constant weight to obtain cellulose phthalate acetate. This product has an acetyl substitution degree of 0.8 and a phthaloyl substitution degree of 1.2, exhibiting good pH-responsive solubility characteristics. It can gradually dissolve in environments with a pH greater than 6.0 and can be directly used in the preparation of delayed triggering agents in controlled-release solid acid oxidant materials.

[0042] The following are the main raw materials and reagents used in the preparation examples, embodiments, and comparative examples, and their sources and specifications are as follows; unless otherwise specified, all reagents are commercially available analytical grade or higher products: The polyacrylic acid resin was purchased from Shanghai Yuanye Biotechnology Co., Ltd., item number: S30571.

[0043] Poly(N-isopropylacrylamide) was purchased from Shanghai Yuanye Biotechnology Co., Ltd., product number: T25308.

[0044] Sodium dodecylbenzenesulfonate was purchased from Shanghai Yuanye Biotechnology Co., Ltd., product number: S15014.

[0045] The fatty alcohol polyoxyethylene ether was purchased from Shanghai Yuanye Biotechnology Co., Ltd., product number: Y47169.

[0046] Example 1: This example provides a controlled-release coal seam permeability-enhancing acid oxidant material, comprising the following raw materials in parts by weight: 50 parts porous carrier, 10 parts solid acid, 10 parts solid oxidant, and 17 parts delayed triggering agent.

[0047] The porous carrier is porous diatomaceous earth with sulfonic acid groups modified on its surface; the solid acid is citric acid; the solid oxidant is ammonium persulfate; the dry basis mass ratio of the pH-responsive polymer to the temperature-ionic-strength-responsive polymer in the delayed triggering agent is 1:1.5; the pH-responsive polymer is cellulose phthalate acetate prepared by Preparation Example 2; and the temperature-ionic-strength-responsive polymer is poly(N-isopropylacrylamide).

[0048] The preparation method of the above-mentioned controlled-release coal seam permeability-enhancing acid oxidant material includes the following steps: S1. Carrier pretreatment: The porous diatomaceous earth is ground and dried to obtain a pretreated carrier; The grinding process reduces the porous carrier particle size to 0.3 mm; the drying process is carried out at a temperature of 125°C for 3 hours.

[0049] S2. Functional modification of the carrier: The pretreated carrier is reacted with an aqueous solution of sulfonating agent, and after washing and drying, a functionalized porous carrier with sulfonic acid groups modified on its surface is obtained. The concentration of the sulfonating agent aqueous solution is 1.0 mol / L; the reaction temperature is 70℃, the reaction time is 4.5 h; the drying temperature is 100℃; and the sulfonating agent is concentrated sulfuric acid.

[0050] S3. Gradient loading of active ingredients: Citric acid and ammonium persulfate are prepared into solutions or dispersions, and then loaded onto the functionalized porous support in sequence to obtain loaded particles with a gradient distribution structure of active ingredients. The citric acid solution has a pH of 2, and the ammonium persulfate dispersion has a concentration of 20 wt%. The loading process is carried out under vacuum impregnation at 50°C and an absolute pressure of 12.5 kPa for 2 hours each time, followed by drying at 60°C to remove the solvent. The solvent used to prepare the solution or dispersion is deionized water.

[0051] S4, Delayed triggering agent coating: A pH-responsive polymer layer and a temperature- and ionic strength-responsive polymer layer are sequentially coated on the surface of the supported particles; Specifically, when coating the pH-responsive polymer layer, the coating solution concentration is 5.5 wt%, the spray flow rate is 20 mL / min, and the inlet air temperature is 57.5 °C; when coating the temperature-responsive polymer layer, the coating solution concentration is 4 wt%; the spray pressure during the spray coating process is 0.3 MPa, and the rotation speed of the fluidized bed is 200 r / min.

[0052] The application of the above-mentioned controlled-release coal seam permeability-enhancing acid oxidant material includes the following steps: P1. Pre-activation environmental conditioning: Pre-activation fluid is injected into the deep part of the target coal seam through drilling; The pre-activation solution is a sodium bicarbonate solution with a pH of 9, and the injection volume is 20% of the expected pore volume of the planned permeability enhancement area.

[0053] P2. Particle suspension injection: The controlled-release solid acid oxidant material is prepared into a suspension and pumped into the depth of the coal seam; The controlled-release solid acid oxidant material is prepared into a suspension with a mass concentration of 10% by injecting water, and then pumped through a borehole at a discharge rate of 1.25 m³ / min.

[0054] P3. Triggering and sustained-release permeability enhancement: Well shut-in triggers the release of active ingredients from the particles in the formation environment.

[0055] Example 2: This example provides a controlled-release coal seam permeability-enhancing acid oxidant material, comprising the following raw materials in parts by weight: 40 parts porous carrier, 5 parts solid acid, 5 parts solid oxidant, and 10 parts delayed triggering agent.

[0056] Wherein, the porous carrier is a modified coal-based carrier with sulfonic acid groups on its surface; the solid acid is oxalic acid; the solid oxidant is potassium persulfate; the dry basis mass ratio of the pH-responsive polymer to the temperature-ionic strength-responsive polymer in the delayed triggering agent is 1:0.5; the pH-responsive polymer is the dimethylaminoethyl methacrylate-methacrylic acid copolymer prepared by Preparation Example 1; and the temperature-ionic strength-responsive polymer is poly(N-isopropylacrylamide) copolymer.

[0057] The preparation method of the above-mentioned controlled-release coal seam permeability-enhancing acid oxidant material includes the following steps: S1. Carrier pretreatment: The modified coal-based carrier is ground and dried to obtain a pretreated carrier; The grinding process reduces the porous carrier particle size to 0.1 mm; the drying process is carried out at 100°C for 2 hours.

[0058] S2. Functional modification of the carrier: The pretreated carrier is reacted with an aqueous solution of sulfonating agent, and after washing and drying, a functionalized porous carrier with sulfonic acid groups modified on its surface is obtained. The concentration of the sulfonating agent aqueous solution is 0.5 mol / L; the reaction temperature is 60℃ and the reaction time is 3 h; the drying temperature is 80℃; and the sulfonating agent is chlorosulfonic acid.

[0059] S3. Gradient loading of active ingredients: Oxalic acid and potassium persulfate are prepared into solutions or dispersions respectively, and loaded onto the functionalized porous support in reverse order to obtain loaded particles with a gradient distribution structure of active ingredients. The oxalic acid solution has a pH of 1, and the potassium persulfate dispersion has a concentration of 10 wt%. The loading process is carried out under vacuum impregnation at 40°C and an absolute pressure of 5 kPa for 1 hour each time, followed by drying at 50°C to remove the solvent. The solvent used to prepare the solution or dispersion is anhydrous ethanol.

[0060] S4, Delayed triggering agent coating: A pH-responsive polymer layer and a temperature- and ionic strength-responsive polymer layer are sequentially coated on the surface of the supported particles; Specifically, when coating the pH-responsive polymer layer, the coating solution concentration is 3wt%, the spray flow rate is 10mL / min, and the inlet air temperature is 50℃; when coating the temperature-responsive polymer layer, the coating solution concentration is 2wt%; the spray pressure during the spray coating process is 0.2MPa, and the rotation speed of the fluidized bed is 100r / min.

[0061] The application of the above-mentioned controlled-release coal seam permeability-enhancing acid oxidant material includes the following steps: P1. Pre-activation environmental conditioning: Pre-activation fluid is injected into the deep part of the target coal seam through drilling; The pre-activation solution is an aqueous solution containing 0.01 mol / L sodium dodecylbenzenesulfonate, and the injection volume is 10% of the expected pore volume of the planned permeability enhancement area.

[0062] P2. Particle suspension injection: The controlled-release solid acid oxidant material is prepared into a suspension and pumped into the depth of the coal seam; The controlled-release solid acid oxidant material is prepared into a suspension with a mass concentration of 5% by injecting water, and then pumped through a borehole at a discharge rate of 0.5 m³ / min.

[0063] P3. Triggering and sustained-release permeability enhancement: Well shut-in triggers the release of active ingredients from the particles in the formation environment.

[0064] Example 3: This example provides a controlled-release coal seam permeability-enhancing acid oxidant material, comprising the following raw materials in parts by weight: 60 parts porous carrier, 15 parts solid acid, 15 parts solid oxidant, and 25 parts delayed triggering agent.

[0065] The porous carrier is porous diatomaceous earth with sulfonic acid groups modified on its surface; the solid acid is tartaric acid; the solid oxidant is urea peroxide; the dry basis mass ratio of the pH-responsive polymer to the temperature-ionic-strength-responsive polymer in the delayed trigger is 1:3; the pH-responsive polymer is polyacrylic acid resin; and the temperature-ionic-strength-responsive polymer is polyN-isopropylacrylamide.

[0066] The preparation method of the above-mentioned controlled-release coal seam permeability-enhancing acid oxidant material includes the following steps: S1. Carrier pretreatment: The porous diatomaceous earth is ground and dried to obtain a pretreated carrier; The grinding process reduces the porous carrier particle size to 0.5 mm; the drying process is carried out at a temperature of 150°C for 4 hours.

[0067] S2. Functional modification of the carrier: The pretreated carrier is reacted with an aqueous solution of sulfonating agent, and after washing and drying, a functionalized porous carrier with sulfonic acid groups modified on its surface is obtained. The concentration of the sulfonating agent aqueous solution is 1.5 mol / L; the reaction temperature is 80℃, the reaction time is 6 h; the drying temperature is 120℃; and the sulfonating agent is aminosulfonic acid.

[0068] S3. Gradient loading of active ingredients: Tartaric acid and urea peroxide are respectively prepared into solutions or dispersions, and then loaded onto the functionalized porous support in sequence to obtain loaded particles with a gradient distribution structure of active ingredients. The tartaric acid solution has a pH of 3, and the urea peroxide dispersion has a concentration of 30 wt%. The loading process is carried out under vacuum impregnation at 60°C and an absolute pressure of 20 kPa for 3 hours each time, followed by drying at 70°C to remove the solvent. The solvent used to prepare the solution or dispersion is acetone.

[0069] S4, Delayed triggering agent coating: A pH-responsive polymer layer and a temperature- and ionic strength-responsive polymer layer are sequentially coated on the surface of the supported particles; Specifically, when coating the pH-responsive polymer layer, the coating solution concentration is 8 wt%, the spray flow rate is 30 mL / min, and the inlet air temperature is 65 °C; when coating the temperature-responsive polymer layer, the coating solution concentration is 6 wt%; the spray pressure during the spray coating process is 0.4 MPa, and the rotation speed of the fluidized bed is 300 r / min.

[0070] The application of the above-mentioned controlled-release coal seam permeability-enhancing acid oxidant material includes the following steps: P1. Pre-activation environmental conditioning: Pre-activation fluid is injected into the deep part of the target coal seam through drilling; The pre-activation solution is a sodium silicate solution with a pH of 10, and the injection volume is 30% of the expected pore volume of the planned permeability enhancement area.

[0071] P2. Particle suspension injection: The controlled-release solid acid oxidant material is prepared into a suspension and pumped into the depth of the coal seam; The controlled-release solid acid oxidant material is prepared into a suspension with a mass concentration of 15% by injecting water, and then pumped through a borehole at a discharge rate of 2.0 m³ / min.

[0072] P3. Triggering and sustained-release permeability enhancement: Well shut-in triggers the release of active ingredients from the particles in the formation environment.

[0073] Comparative Example 1: The only difference between this comparative example and Example 1 is that in step S4, all delay trigger coating steps are omitted, and the supported particles obtained in step S3 are used directly as the final material.

[0074] Comparative Example 2: The only difference between this comparative example and Example 1 is that in step S3, citric acid and ammonium persulfate are mixed to prepare a single solution, and the functionalized porous carrier is vacuum impregnated and dried in one step to obtain particles with uniformly mixed active ingredients.

[0075] Comparative Example 3: The only difference between this comparative example and Example 1 is that in step S4, the pH-responsive polymer and the temperature-ion strength-responsive polymer are replaced with an equal amount of a single conventional water-soluble slow-release material, polyvinyl alcohol (PVA), for monolayer coating.

[0076] Comparative Example 4: This comparative example does not employ any solid material preparation process. Its technical solution is as follows: Citric acid aqueous solution and ammonium persulfate aqueous solution, with a total equivalent amount of active ingredients as in Example 1, are directly pumped into the coal seam.

[0077] Comparative Example 5: The only difference between this comparative example and Example 1 is that step S2 is omitted, and the pretreated carrier obtained in step S1 is directly used for loading the active ingredient in step S3.

[0078] Experiment 1: Test of controlled release performance of active ingredients in a simulated coal seam environment The reference standard was "Determination of Release Rate of Sustained-Release / Controlled-Release Formulations" (Pharmacopoeia of the People's Republic of China, 2025 Edition, Part IV, General Chapter 0931), adjusted to simulate the deep coal seam environment. The experiment employed a dynamic immersion release method, constructing a constant-temperature, constant-pressure release device simulating the deep coal seam environment. Simulated formation fluid (sodium bicarbonate solution) was added to the device, adjusted to pH 9, with the temperature set at 35°C and the pressure at 10 MPa to match the actual deep coal seam environment. 5g of samples from Examples 1, 2, 3, and Comparative Examples 1 to 5 were weighed, accurate to 0.001g. Each sample was sealed in a breathable bag and then placed in the simulated formation fluid within the release device, ensuring complete immersion. Temperature and pressure were kept constant throughout the experiment. Samples of the released fluid were collected at multiple time points: 1h, 2h, 4h, 8h, 12h, 24h, 48h, 72h, and 96h. Each sample consisted of 10mL, and an equal volume of fresh simulated formation fluid was added simultaneously to maintain system volume stability. The cumulative release of solid acid in the released fluid was determined using acid-base titration, and the cumulative release of solid oxidant was determined using iodometric titration. The cumulative release rate at each time point was calculated based on the measurement results.

[0079] Experiment 2: Test of the permeability enhancement effect of coal seam core samples The reference standard was the relevant provisions on permeability testing in the "Technical Specification for Coalbed Methane Well Enhancement and Stimulation" GB / T39554-2020. The experiment used a self-built coal seam core displacement experimental device. Natural cores with the same lithology as the target coal seam were selected, and each core was processed into standard core samples with a diameter of 25 mm and a length of 50 mm. After vacuum saturation with simulated formation water, the initial permeability of each core was measured and recorded. The samples from Examples 1, 2, 3, and Comparative Examples 1 to 5 were prepared into test systems according to the requirements of the corresponding permeability enhancement methods. The samples from Examples 1, 2, 3, and Comparative Examples 1 to 3 and 5 were prepared as 10% (w / w) suspensions. Comparative Example 4 was prepared by directly preparing a mixture of citric acid aqueous solution and ammonium persulfate aqueous solution with a total equivalent of the active ingredient in Example 1. Each test system was introduced into a different core displacement device. First, the corresponding pre-activation fluid was injected according to the pre-activation environment conditioning requirements of each scheme, with an injection volume of 20% of the core pore volume. After standing for 2 hours, the corresponding test system was pumped in, with the pumping rate controlled at 1.25 m³ / min. After pumping, the well was shut in and allowed to stand for 72 hours to simulate the formation-triggered slow-release process. After standing, the permeability of each core was measured again, and the permeability increase was calculated as: permeability increase = (treated permeability - initial permeability) / initial permeability × 100%.

[0080] Experiment 3: Long-term stability test of anti-reflective effect The reference standard was SY / T6385-2021, "Method for Testing Long-Term Stability of Rock Permeability". Based on the core samples after the permeability enhancement treatment in Experiment 2, the coal seam core displacement experimental device was used to continuously introduce simulated formation water into each core at a rate of 0.5 mL / min, maintaining a constant experimental temperature of 35℃ and a pressure of 10 MPa. The permeability values ​​of each core were measured at 1, 3, 7, 15, and 30 days after the introduction of simulated formation water. The changes in permeability over time were recorded, and the retention rate of permeability at each time point relative to the peak permeability after the permeability enhancement treatment was calculated.

[0081] Table 1 shows the test data of the controlled release performance of active ingredients under simulated coal seam environment.

[0082] Table 1 Sample number 24-hour cumulative release rate of solid acid (%) Cumulative release rate of solid oxidant over 24 hours (%) Cumulative release rate of solid acid over 96 hours (%) Cumulative release rate of solid oxidant over 96 hours (%) Release curve stability Example 1 32.5 30.8 92.3 89.7 5 Example 2 28.3 26.5 88.6 86.2 4 Example 3 35.7 33.2 94.5 91.8 5 Comparative Example 1 85.2 82.6 98.1 96.5 2 Comparative Example 2 68.4 65.9 95.7 93.2 3 Comparative Example 3 52.6 49.8 93.4 90.5 4 Comparative Example 4 98.7 96.3 99.2 97.8 1 Comparative Example 5 72.3 69.5 96.2 94.1 3 Note: Rating is 1-5, with 5 being the best.

[0083] II. The test data of the permeability enhancement effect of coal seam core simulation are shown in Table 2.

[0084] Table 2 Sample number Initial penetration rate (mD) Post-treatment permeability (mD) Penetration rate increase (%) Increase in core porosity (%) Example 1 0.32 3.85 1103.1 8.6 Example 2 0.31 3.24 945.2 7.2 Example 3 0.33 4.12 1148.5 9.1 Comparative Example 1 0.32 2.56 700.0 5.3 Comparative Example 2 0.31 2.28 635.5 4.8 Comparative Example 3 0.32 2.89 803.1 6.1 Comparative Example 4 0.31 1.85 496.8 3.5 Comparative Example 5 0.33 2.16 554.5 4.2 III. The long-term stability test data of the anti-reflective effect are shown in Table 3.

[0085] Table 3 Sample number 1-day penetration retention rate (%) 7-day penetration retention rate (%) 15-day penetration retention rate (%) 30-day penetration retention rate (%) 30-day porosity retention rate (%) Example 1 98.5 92.3 86.7 81.2 83.5 Example 2 97.8 90.5 84.2 78.6 80.8 Example 3 99.1 93.6 88.5 83.4 85.2 Comparative Example 1 95.2 82.4 73.1 65.8 68.3 Comparative Example 2 94.6 79.8 70.5 62.3 65.1 Comparative Example 3 96.3 86.7 79.2 72.5 74.8 Comparative Example 4 92.1 70.3 58.6 49.2 51.6 Comparative Example 5 93.8 76.5 67.8 59.7 62.4 As can be seen from Examples 1-3 and Comparative Example 1, the presence or absence of a delayed-trigger coating layer is a core factor determining product performance. Without this protective layer, the active ingredient is released rapidly and almost completely. While this burst release can produce a certain dissolving effect in a short time, it cannot form a sustained and deep-penetrating chemical permeation-enhancing effect in the coal seam. In stark contrast, the examples with the coating layer exhibit slow and sustained release characteristics. This allows the active ingredient to gradually act on deeper coal seams over time, preventing premature depletion of reaction energy and thus laying the fundamental foundation for achieving a long-lasting and uniform permeation-enhancing effect.

[0086] As can be seen from Examples 1-3 and Comparative Example 2, the distribution of the active ingredient within the carrier has a crucial impact on its release behavior and mode of action. When the acid and oxidant are uniformly mixed and loaded, they are released rapidly and react violently almost synchronously. Although this reaction is intense, it is short-lived and its range of action is concentrated. In contrast, the example using a gradient distribution achieves a staged and orderly release of the acid and oxidant. This design simulates the ideal reaction path of dissolving minerals first and then degrading organic matter, making the chemical reaction milder and more controllable. This not only reduces the risk of damaging the coal structure due to violent reactions but also allows the permeability enhancement to proceed gradually from near to far, significantly improving the uniformity and effectiveness of permeability enhancement.

[0087] As can be seen from Examples 1-3 and Comparative Example 3, the intelligent responsiveness of the coating material is crucial for achieving environment-triggered release. Using a single, conventional slow-release material, the release mechanism mainly relies on the material's dissolution or diffusion, and the release rate is weakly correlated with specific formation environmental conditions, making precise control difficult. However, the example employing a dual mechanism of pH response and temperature-ionic strength response allows the release behavior to intelligently interact with the actual chemical and physical environment deep within the coal seam. This design ensures that the material remains stable before reaching the predetermined environment, and only begins to be released as needed under specific environmental signals, greatly improving the accuracy and reliability of the operation—something conventional slow-release technologies cannot achieve.

[0088] As can be seen from Examples 1-3 and Comparative Example 4, converting liquid strong acid / oxidant into solid particles with a specific structure is a key innovation that fundamentally changes the coal seam chemical permeation enhancement operation mode. While direct injection of liquid reagents results in a direct reaction, its strong corrosiveness, uncontrollable effects, and short effective range cannot be overcome. The solid particle form of this solution first eliminates the direct corrosion risk to wellbore equipment; secondly, through particle transport and subsequent triggering and slow-release mechanisms, chemical energy is delivered to the depths of the coal seam before release, completely changing the limited range of action and realizing a shift from strong point-based stimulation to gradual surface transformation. This represents a fundamental improvement over traditional processes.

[0089] As can be seen from Examples 1-3 and Comparative Example 5, surface functionalization modification of porous supports is not an optional step, but a crucial step in ensuring stable and efficient loading of active ingredients and their synergistic effects. Unmodified supports cannot form a strong and stable bond with active ingredients on their surface properties, easily leading to premature loss of the active ingredient during injection and initial triggering. Supports modified with sulfonic acid groups not only improve the robustness of the loading, ensuring the integrity of the active ingredient before reaching the target location, but the introduced functional groups may also play an additional positive role in the formation environment, such as regulating the local microenvironment or adsorbing harmful ions. This creates a beneficial synergy with the sustained-release and permeation-enhancing effect of the active ingredient, jointly ensuring the stability and durability of the final permeation-enhancing effect.

[0090] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A controlled-release coal seam permeability-enhancing acid oxidant material, characterized in that: It includes the following components in parts by weight: 40-60 parts porous carrier, 5-15 parts solid acid, 5-15 parts solid oxidant, and 10-25 parts delayed triggering agent.

2. The controlled-release coal seam permeability-enhancing acid oxidant material according to claim 1, characterized in that: The porous carrier is porous diatomaceous earth with sulfonic acid groups on its surface or a modified coal-based carrier; the solid acid includes at least one of citric acid, oxalic acid, and tartaric acid; the solid oxidant includes at least one of ammonium persulfate, potassium persulfate, and urea peroxide.

3. The controlled-release coal seam permeability-enhancing acid oxidant material according to claim 1, characterized in that: The delayed triggering agent comprises a pH-responsive polymer and a temperature-ionic-strength-responsive polymer, with a dry basis mass ratio of 1:(0.5-3); the pH-responsive polymer is one of dimethylaminoethyl methacrylate-methacrylic acid copolymer, cellulose acetate phthalate, or polyacrylic acid resin; the temperature-ionic-strength-responsive polymer is poly(N-isopropylacrylamide) or a copolymer thereof.

4. A method for preparing a controlled-release coal seam permeability-enhancing acid oxidant material, characterized in that, The controlled-release coal seam permeability-enhancing acid oxidant material according to any one of claims 1-4 comprises the following steps: S1. Carrier pretreatment: The porous carrier is ground and dried to obtain a pretreated carrier; S2. Functional modification of the carrier: The pretreated carrier is reacted with an aqueous solution of sulfonating agent, and after washing and drying, a functionalized porous carrier with sulfonic acid groups modified on its surface is obtained. S3. Gradient loading of active ingredients: Solid acid and solid oxidant are respectively prepared into solutions or dispersions, and loaded onto the functionalized porous support in sequence or in reverse order to obtain loaded particles with a gradient distribution structure of active ingredients. S4, Delayed trigger coating: A pH-responsive polymer layer and a temperature- and ionic strength-responsive polymer layer are sequentially coated on the surface of the supported particles.

5. The preparation method of a controlled-release coal seam permeability-enhancing acid oxidant material according to claim 4, characterized in that: In step S1, the grinding process reduces the particle size of the porous carrier to 0.1-0.5 mm; the drying temperature is 100-150°C, and the drying time is 2-4 hours.

6. The preparation method of a controlled-release coal seam permeability-enhancing acid oxidant material according to claim 4, characterized in that: In step S2, the concentration of the sulfonating agent aqueous solution is 0.5-1.5 mol / L; the reaction temperature is 60-80℃, and the reaction time is 3-6 h; the drying temperature is 80-120℃; and the sulfonating agent is one of concentrated sulfuric acid, chlorosulfonic acid, or aminosulfonic acid.

7. The preparation method of a controlled-release coal seam permeability-enhancing acid oxidant material according to claim 4, characterized in that: In step S3, the pH value of the solid acid solution is 1-3, and the concentration of the solid oxidant dispersion is 10-30 wt%. The loading process is carried out under vacuum impregnation at 40-60℃ and an absolute pressure of 5-20 kPa, with each impregnation lasting 1-3 hours, followed by drying at 50-70℃ to remove the solvent. The solvent used to prepare the solution or dispersion is at least one of anhydrous ethanol, acetone, or deionized water.

8. The preparation method of a controlled-release coal seam permeability-enhancing acid oxidant material according to claim 4, characterized in that: In step S4, when coating the pH-responsive polymer layer, the coating solution concentration is 3-8 wt%, the spray flow rate is 10-30 mL / min, and the inlet air temperature is 50-65℃; when coating the temperature-ion-strength-responsive polymer layer, the coating solution concentration is 2-6 wt%; the spray pressure during the spray coating process is 0.2-0.4 MPa, and the rotation speed of the fluidized bed is 100-300 r / min.

9. The application of a controlled-release coal seam permeability-enhancing acid oxidant material, characterized in that, Using the controlled-release solid acid oxidant material as described in any one of claims 1-3 includes the following steps: P1. Pre-activation environmental conditioning: Pre-activation fluid is injected into the deep part of the target coal seam through drilling; P2. Particle suspension injection: The controlled-release solid acid oxidant material is prepared into a suspension and pumped into the depth of the coal seam; P3. Triggering and sustained-release permeability enhancement: Well shut-in triggers the release of active ingredients from the particles in the formation environment.

10. The application of the controlled-release coal seam permeability-enhancing acid oxidant material according to claim 9, characterized in that: In step P1, the pre-activation solution is a weakly alkaline electrolyte solution with a pH of 8-10 or an aqueous solution containing 0.01-0.05 mol / L surfactant, and the injection volume is 10-30% of the expected pore volume of the planned permeability enhancement area; the weakly alkaline electrolyte solution is sodium bicarbonate solution, sodium silicate solution, or a mixture of both; the surfactant is sodium dodecylbenzenesulfonate or fatty alcohol polyoxyethylene ether; in step P2, the controlled-release solid acid oxidant material is prepared into a suspension with a mass concentration of 5-15% with the injection water, and pumped through a borehole at a discharge rate of 0.5-2.0 m³ / min.

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