Multi-field coupling simulation method for hydraulic fracturing enhanced gas extraction in low-permeability coal seam roof

Abstract

The application provides a low-permeability coal seam roof hydraulic fracturing enhanced gas extraction multi-field coupling simulation method, and relates to the technical field of numerical simulation of coal mine gas enhanced extraction. The method is realized based on a multi-physical field simulation software. Firstly, a geometric model of the roof hydraulic fracturing enhanced gas extraction of the coal mining face is constructed, and the heterogeneity of the coal and rock layer is set. Then, related physical and mechanical parameters and physical variables in the simulation process of the hydraulic fracturing enhanced gas extraction are set, the function of the water pressure change with time in the hydraulic fracturing process is determined, and the related physical property parameters of the water and gas temperature are determined. Then, a multi-physical field coupling model of the low-permeability coal seam roof hydraulic fracturing enhanced gas extraction is established. Then, the fluid migration parameters in the multi-field coupling model are input, and the boundary conditions in the process of the hydraulic fracturing enhanced gas extraction are applied. Finally, the numerical simulation of the hydraulic fracturing enhanced gas extraction of the high-gas low-permeability coal seam is realized based on the multi-field coupling model after the grid division.

Description

Technical Field

[0001] This invention relates to the field of numerical simulation technology for enhanced gas extraction in coal mines, and in particular to a multi-field coupled simulation method for enhanced gas extraction in low-permeability coal seam roof hydraulic fracturing. Background Technology

[0002] To improve coal seam permeability, hydraulic fracturing is widely used as an important enhanced extraction technology. It induces fracture propagation in the coal seam through high-pressure water injection, thereby significantly increasing permeability and improving gas extraction efficiency. However, in soft, low-permeability coal seams, due to the loose coal structure, poor permeability, and complex gas occurrence, traditional hydraulic fracturing technology often fails to achieve ideal results due to problems such as fracture closure and water-locking effects. Roof hydraulic fracturing technology uses high-pressure water to fracture the rock mass above the coal seam, inducing damage to its internal structure and causing a redistribution of the original rock stress field, thus reducing the working face support pressure. Simultaneously, the roof fracture network extends and connects towards the coal seam, forming new gas flow paths and achieving a synergistic effect of stress release and permeability improvement.

[0003] Hydraulic fracturing of the roof has demonstrated good production enhancement effects in practical engineering. However, due to the complex rock fracture mechanism, seepage-induced fracture propagation, gas-water two-phase flow, gas adsorption-desorption, and thermal effects involved, numerical simulation has become a key tool for mechanism research and engineering optimization. However, traditional simulation methods mostly use simplified models, neglecting the porous characteristics of the coal seam and the multi-physics coupling effects of gas adsorption, desorption, diffusion, and seepage processes, making it difficult to accurately predict gas migration patterns and extraction effects after hydraulic fracturing. Therefore, it is urgent to establish a high-precision numerical simulation method with multi-physics coupling applicable to the hydraulic fracturing process of high-gas, low-permeability coal seams, providing reliable technical support for optimizing fracturing parameter design and predicting extraction effects. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to address the shortcomings of the prior art by providing a multi-field coupled simulation method for enhanced gas extraction by hydraulic fracturing of the roof of low-permeability coal seams, thereby realizing multi-field coupled numerical simulation of enhanced gas extraction by hydraulic fracturing of the roof of low-permeability coal seams.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0006] On the one hand, this invention provides a multi-field coupled simulation method for enhanced gas extraction in low-permeability coal seam roof hydraulic fracturing, implemented based on multiphysics simulation software, including the following steps:

[0007] Construct a geometric model for enhanced gas extraction via hydraulic fracturing of the roof of the longwall mining face;

[0008] Set the heterogeneity of coal and rock strata occurrence;

[0009] Set the relevant physical and mechanical parameters and physical variables in the simulation process of hydraulic fracturing enhanced gas extraction, and determine the water pressure change function with time and the relevant physical property parameters of water and gas temperature during the hydraulic fracturing process;

[0010] A multi-physics coupling model for enhanced gas extraction by hydraulic fracturing of the roof of a low-permeability coal seam was established. The multi-physics coupling model includes the stress field equation, the water and gas seepage field equation, the gas diffusion field equation, the temperature field equation, and the coal and rock mass damage field equation.

[0011] Input the fluid transport parameters in the multi-field coupled model of hydraulic fracturing enhanced gas extraction in low-permeability coal seam roof, and apply boundary conditions of stress, water, gas and temperature during the hydraulic fracturing enhanced gas extraction process. The borehole boundary water pressure is applied through the water pressure change function over time.

[0012] Mesh generation for a multi-field coupled model of hydraulic fracturing-enhanced gas extraction;

[0013] Numerical simulation of enhanced gas extraction by hydraulic fracturing in high-gas, low-permeability coal seams was achieved using a multi-field coupled model based on mesh generation.

[0014] Furthermore, the method creates a random function rn1(x,y,z) that satisfies a normal distribution and has an average value of 1 to realize the heterogeneity of the coal seam and the roof and floor, where x,y,z represent directional parameters; the elastic modulus, porosity, tensile strength, compressive strength, and cohesion of the coal and rock strata are all multiplied by the random function rn1(x,y,z) to represent the heterogeneity of the coal seam and the roof and floor.

[0015] Furthermore, the stress field equation is shown in the following formula:

[0016] (1);

[0017] in, u Indicates displacement. for u The tensor form, where the first subscript indicates the variable. u of i Directional component, the second subscript indicates the direction component. u i beg j The directional partial derivative, the third subscript indicates the direction of the derivative. beg j directional partial derivative; It is in tensor form, where the first subscript indicates the variable. u of j Directional component, the second subscript indicates the direction component. beg j The directional partial derivative, the third subscript indicates the direction of the derivative. beg i directional partial derivative; G It is the shear modulus of the coal mass; Poisson's ratio of the coal and rock mass; α m The Biot coefficient is the porosity coefficient. The coefficient of thermal expansion of the coal and rock mass; K Bulk modulus of coal and rock mass; The Biot coefficient for the crack; For the matrix gas pressure at i Component of direction; For the fracture fluid pressure at i Component of direction; Strain caused by gas adsorption / desorption i Component of direction; For the change in temperature i Component of direction; The volume forces of the coal and rock mass;

[0018] The equations for the water and gas seepage field are shown in the following formula:

[0019] (2);

[0020] In the formula, M fracture Q represents the mass of fluid in a unit volume of coal fractures. fracture It is the mass source or sink of the fluid; F fracture It represents the seepage flow rate of fluid in the fracture; t is time; v, Both represent the integration region, where v is the unit volume of coal-rock fracture; Γ is the surface boundary of the coal-rock fracture.

[0021] The gas diffusion field equation is shown in the following formula:

[0022] (3);

[0023] In the formula, M matrix M represents the mass of gas in the coal matrix. g p is the molar mass of gas; R is the molar constant of gas; fg The pressure of the gas in the fissure; τ is the matrix gas pressure; τ is the gas desorption time; T is the coal seam temperature;

[0024] The temperature field equation is shown in the following formula:

[0025] (4);

[0026] In the formula, M energy F is the energy density within coal fractures. energy For heat flux; Qenergy A source or sink of heat;

[0027] The coal and rock mass damage field equation is shown in formula (5), and the coal and rock mass damage is dynamically updated through state variables;

[0028] (5);

[0029] In the formula, F1 is the maximum tensile stress criterion, F2 is the Mohr-Coulomb criterion; σ1 is the maximum principal stress of the coal and rock mass; f t0 σ3 is the uniaxial tensile strength; σ3 is the minimum principal stress of the coal and rock mass; θ is the internal friction angle of the coal; f c0 It represents the uniaxial compressive strength.

[0030] Furthermore, the specific method for numerical simulation of enhanced gas extraction through hydraulic fracturing in high-gas, low-permeability coal seams based on a multi-field coupled model after mesh generation is as follows:

[0031] The influence of gas on hydraulic fracturing is not considered, that is, the gas seepage field equation and diffusion field equation in the multi-field coupling model are not considered. The numerical simulation of hydraulic fracturing is carried out.

[0032] The elastic modulus, permeability, water pressure, and temperature of the coal and rock strata after hydraulic fracturing were obtained as initial values ​​for gas extraction simulation.

[0033] By modifying the boundary conditions for water and temperature in the water and gas seepage field equations and temperature field equations, numerical simulation of enhanced gas extraction through hydraulic fracturing in high-gas, low-permeability coal seams can be achieved.

[0034] Secondly, this application proposes an electronic device, comprising: one or more processors, and a memory for storing instructions, which, when executed by the one or more processors, cause the one or more processors to execute the multi-field coupling simulation method for enhanced gas extraction in low-permeability coal seam roof hydraulic fracturing.

[0035] Thirdly, this application proposes a computer-readable storage medium storing executable instructions that, when executed, cause a processor to perform the multi-field coupling simulation method for enhanced gas extraction using hydraulic fracturing of the roof of a low-permeability coal seam.

[0036] Fourthly, this application proposes a computer program product, including a computer program or instructions, which, when executed by a processor, implements the aforementioned multi-field coupling simulation method for hydraulic fracturing enhanced gas extraction in low-permeability coal seam roofs.

[0037] The beneficial effects of adopting the above technical solution are as follows: The multi-field coupled simulation method for enhanced gas drainage in low-permeability coal seam roof hydraulic fracturing provided by this invention, based on the COMSOL Multiphysics platform, establishes a multi-field coupled model covering stress, seepage, diffusion, and heat transfer, which realistically reflects the response behavior during enhanced gas drainage in high-gas, low-permeability coal seams through hydraulic fracturing; the method can adjust the model parameters according to different coal seam conditions, and has good adaptability and scalability; by optimizing the drainage scheme, the gas drainage efficiency is improved, the gas pressure is reduced, thereby improving the safety and economic benefits of coal mine operations. Attached Figure Description

[0038] Figure 1 This is a flowchart of a multi-field coupled simulation method for enhanced gas extraction in low-permeability coal seam roof hydraulic fracturing provided in Embodiment 1 of the present invention;

[0039] Figure 2 The geometric model for enhanced gas extraction by hydraulic fracturing of the roof of the longwall mining face is provided as an example of one implementation of the present invention.

[0040] Figure 3 The fracture propagation pattern under different fracturing times is provided in Embodiment 1 of the present invention;

[0041] Figure 4 The ratio of permeability before and after fracturing near the contact between the coal seam and the rock strata, as provided in Embodiment 1 of the present invention;

[0042] Figure 5 This is a graph showing the change in gas pressure at different times after fracturing, as provided in Embodiment 1 of the present invention.

[0043] In the diagram: 1. Roof; 2. Coal seam; 3. Floor; 4. Transverse section; 5. Longitudinal section; 6. High-level borehole; 7. Low-level borehole. Detailed Implementation

[0044] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0045] Example 1:

[0046] This embodiment takes a high-gas, low-permeability coal seam as an example, and uses the multi-field coupling simulation method of the low-permeability coal seam roof hydraulic fracturing enhanced gas extraction to numerically simulate the hydraulic fracturing enhanced gas extraction of the coal seam.

[0047] In this embodiment, the multi-field coupled simulation method for enhanced gas extraction via hydraulic fracturing of the roof of a low-permeability coal seam is implemented using COMSOL Multiphysics software, such as... Figure 1 As shown, it includes the following steps:

[0048] Step 1: Construct a geometric model of hydraulic fracturing-enhanced gas extraction on the roof of the longwall face in the geometry module of COMSOL Multiphysics software, such as... Figure 2 As shown, the geometric model includes a roof 1, a coal seam 2, and a floor 3 arranged in sequence, as well as a transverse section 4, a longitudinal section 5, a high-level borehole 6, and a low-level borehole 7 that run through the entire model.

[0049] Step 2: Set the heterogeneity of the coal seam and roof and floor; use COMSOL Multiphysics' global definition → function → random function → normal distribution to create a random function rn1(x,y,z) with an average value of 1 to realize the heterogeneity of the coal seam and roof and floor, where x,y,z represent direction parameters;

[0050] Step 3: In COMSOL Multiphysics software, set the relevant physical and mechanical parameters and physical variables in the simulation process of hydraulic fracturing enhanced gas extraction, and determine the water pressure change function with time and the relevant physical property parameters of water and gas temperature during the hydraulic fracturing process;

[0051] Step 3.1: In the COMSOL Multiphysics software component → Definition → Variable, input the relevant physical and mechanical parameters of the coal seam and roof and floor. The elastic modulus, porosity, tensile strength, compressive strength and cohesion of the coal seam and roof and floor are multiplied by the random function rn1(x,y,z) to represent the heterogeneous characteristics of the coal seam and roof and floor.

[0052] Step 3.2: Based on the water pressure change curve over time during the hydraulic fracturing process in the coal mine, establish the water pressure change function pw(t) over time in the COMSOL Multiphysics software component → Definition → Function → Interpolation Function;

[0053] Step 3.3: Use interpolation functions to define the temperature-related physical properties of water and gas, including thermal conductivity, coefficient of thermal expansion, constant pressure heat capacity, density, dynamic viscosity and specific heat rate;

[0054] Step 4: Establish a multi-physics coupling model for hydraulic fracturing-enhanced gas extraction in the roof of low-permeability coal seams; input the control equations for hydraulic fracturing-enhanced gas extraction into COMSOL Multiphysics to construct the multi-physics coupling model for hydraulic fracturing-enhanced gas extraction. The control equations include stress field equations, water and gas seepage field equations, gas diffusion field equations, temperature field equations, and coal and rock mass damage field equations. The constructed multi-physics coupling model is a stress-seepage-temperature-damage coupling model.

[0055] Step 4.1: Use the solid mechanics module of COMSOL Multiphysics to apply the equivalent force field equations;

[0056] (1);

[0057] in, u Indicates displacement. for u The tensor form, where the first subscript indicates the variable. u of i Directional component, the second subscript indicates the direction component. u i beg j The directional partial derivative, the third subscript indicates the direction of the derivative. beg j directional partial derivative; It is in tensor form, where the first subscript indicates the variable. u of j Directional component, the second subscript indicates the direction component. beg j The directional partial derivative, the third subscript indicates the direction of the derivative. beg i directional partial derivative; G It is the shear modulus of the coal mass; Poisson's ratio of the coal and rock mass; α m The Biot coefficient is the porosity coefficient. The coefficient of thermal expansion of the coal and rock mass; K Bulk modulus of coal and rock mass; The Biot coefficient for the crack; For the matrix gas pressure at i Component of direction; For the fracture fluid pressure at i Component of direction; Strain caused by gas adsorption / desorption i Component of direction; For the change in temperature i Component of direction; The volume force of the coal and rock mass is GPa;

[0058] Step 4.2: Define the equations for the water and gas seepage field using the Darcy's Law module in COMSOL Multiphysics;

[0059] (2);

[0060] In the formula, M fracture The mass of fluid per unit volume of coal fracture, kg / m³ 3 Q fracture It is the mass source or sink of the fluid, kg / (s·m 3 );F fractureIt is the seepage flow rate of fluid in the fracture, kg / (s·m 2 ); t is time; v, Both represent the integration region, where v is the unit volume of coal-rock fracture (the volume domain of coal-rock fracture), which is mathematically a three-dimensional spatial integration domain, corresponding to the spatial volume occupied by fractures in the coal-rock mass; Γ is the surface boundary of coal-rock fracture (the boundary domain of coal-rock fracture), which is mathematically a two-dimensional surface domain, corresponding to the interface between coal-rock fracture and the surrounding medium (such as coal-rock matrix or other fractures).

[0061] Step 4.3: Define the gas diffusion field equation using the PDE (Partial Differential Equation) module in COMSOL Multiphysics;

[0062] (3);

[0063] In the formula, M matrix M represents the mass of gas in the coal matrix. g R is the molar mass of gas, g / mol; R is the molar constant of gas, J / (mol·K); p fg The pressure of the gas in the fissure is MPa; τ is the matrix gas pressure; τ is the gas desorption time, d; T is the coal seam temperature, K.

[0064] Step 4.4: Define the temperature field equation using the porous media heat transfer module in COMSOL Multiphysics;

[0065] (4);

[0066] In the formula, M energy Energy density within coal fractures, J / m 3 ;F energy For heat flux, J / (s,m) 2 );Q energy For heat sources or sinks, J / (s,m 3 ).

[0067] Step 4.5: Define the coal and rock mass damage field equation in the COMSOL Multiphysics variable table;

[0068] (5);

[0069] In the formula, F1 is the maximum tensile stress criterion, F2 is the Mohr-Coulomb criterion; σ1 is the maximum principal stress of the coal and rock mass, Pa, f t0 σ3 is the uniaxial tensile strength, Pa; σ3 is the minimum principal stress of the coal and rock mass, Pa; θ is the internal friction angle of the coal; fc0 , where is the uniaxial compressive strength, Pa.

[0070] Step 4.5: Add state variables in the COMSOL Multiphysics component → Definition to dynamically update the coal and rock mass damage;

[0071] Step 5: Input the fluid transport parameters such as the molar mass of gas, slip factor, and molar gas constant of gas in the multi-field coupling model of hydraulic fracturing enhanced gas extraction in low-permeability coal seam roof, and apply the boundary conditions of stress, water, gas, and temperature during the hydraulic fracturing enhanced gas extraction process. The borehole boundary water pressure is applied through the water pressure change function pw(t) over time.

[0072] Step 6: Mesh generation for the multi-field coupled model of hydraulic fracturing enhanced gas extraction; in this embodiment, the Delaunay triangulation algorithm is selected for mesh generation.

[0073] Step 7: In the Study module of COMSOL Multiphysics software, add the first study (sol1), and disable the gas seepage field equation and diffusion field equation in the model configuration options of the modified study step, and perform hydraulic fracturing numerical simulation.

[0074] Step 8: Use the withsol("sol1", required parameters) command to retrieve the elastic modulus, permeability, water pressure and temperature of the coal and rock strata after hydraulic fracturing as the initial values ​​for gas extraction simulation.

[0075] Step 9: Add a second study (sol2) in the study module, modify the boundary conditions of water and temperature in the water seepage module and the porous medium heat transfer module, and realize the numerical simulation of hydraulic fracturing to enhance gas extraction in high-gas, low-permeability coal seams.

[0076] In this embodiment, the fracture propagation pattern under different hydraulic fracturing times is as follows: Figure 3 As shown, the fractures propagate along the direction of maximum principal stress; the ratio of permeability before and after fracturing near the contact between the coal seam and the rock strata is as follows. Figure 4 As shown, the permeability at the site of damage is significantly increased; the changes in gas pressure at different extraction times after fracturing are shown in the figure. Figure 5 As shown, the gas pressure in the coal seam drops rapidly.

[0077] Example 2:

[0078] This embodiment proposes an electronic device, including: one or more processors, and a memory, wherein the memory is used to store instructions, and when the instructions are executed by the one or more processors, the one or more processors execute the multi-field coupling simulation method for enhanced gas extraction by hydraulic fracturing of the roof of a low-permeability coal seam.

[0079] The electronic device can be a mobile phone, computer, or tablet computer, etc., and includes a memory and a processor. The memory stores a computer program, which, when executed by the processor, implements the multi-field coupling simulation method for enhanced gas extraction in low-permeability coal seam roof hydraulic fracturing as described in the embodiments. It is understood that the electronic device may also include input / output (I / O) interfaces and communication components.

[0080] The processor is used to execute all or part of the steps in the multi-field coupled simulation method for enhanced gas extraction under hydraulic fracturing of the roof of a low-permeability coal seam, as described in the above embodiments. The memory is used to store various types of data, which may include, for example, instructions for any application or method in the electronic device, as well as application-related data.

[0081] The processor can be implemented as an Application Specific Integrated Circuit (ASIC), Digital Signal Processor (DSP), Programmable Logic Device (PLD), Field Programmable Gate Array (FPGA), controller, microcontroller, microprocessor, or other electronic components, and is used to execute the multi-field coupling simulation method for enhanced gas extraction under hydraulic fracturing of low-permeability coal seam roof described in the above embodiments.

[0082] Example 3:

[0083] This embodiment proposes a computer-readable storage medium that stores executable instructions. When these instructions are executed, if they are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium.

[0084] The computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the multi-field coupling simulation method for enhanced gas extraction by hydraulic fracturing of the roof of low-permeability coal seams as described in the various embodiments of this application.

[0085] The aforementioned storage media include: flash memory, hard disks, multimedia cards, card-type memory (e.g., SD (Secure Digital Memory Card) or DX (Memory Data Register, MDR) memory), random access memory (RAM), static random-access memory (SRAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), programmable read-only memory (PROM), magnetic storage, disks, optical discs, servers, APP (Application) app stores, and other media capable of storing program verification codes. These media store computer programs, which, when executed by a processor, can implement the various steps of the aforementioned multi-field coupled simulation method for enhanced gas extraction using hydraulic fracturing of the roof of low-permeability coal seams.

[0086] Example 4:

[0087] This embodiment proposes a computer program product, including a computer program or instructions, which, when executed by a processor, implements the multi-field coupling simulation method for enhanced gas extraction using hydraulic fracturing of the roof of a low-permeability coal seam.

[0088] Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or part of the technical solution, can be embodied in the form of a computer program product.

[0089] The various embodiments in this application are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0090] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope defined by the present invention.

Claims

1. A multi-field coupled simulation method for enhanced gas extraction in low-permeability coal seam roof hydraulic fracturing, implemented based on multiphysics simulation software, characterized in that... Includes the following steps: Construct a geometric model for enhanced gas extraction via hydraulic fracturing of the roof of the longwall mining face; Set the heterogeneity of coal and rock strata occurrence; Set the relevant physical and mechanical parameters and physical variables in the simulation process of hydraulic fracturing enhanced gas extraction, and determine the water pressure change function with time and the relevant physical property parameters of water and gas temperature during the hydraulic fracturing process; A multi-physics coupling model for enhanced gas extraction by hydraulic fracturing of the roof of a low-permeability coal seam was established. The multi-physics coupling model includes the stress field equation, the water and gas seepage field equation, the gas diffusion field equation, the temperature field equation, and the coal and rock mass damage field equation. The stress field equation is shown in the following formula: (1)； in, u Indicates displacement. u i,jj for u The tensor form, where the first subscript indicates the variable. u of i Directional component, the second subscript indicates the direction component. u i beg j The directional partial derivative, the third subscript indicates the direction of the derivative. u i,j beg j directional partial derivative; u j,ji It is in tensor form, where the first subscript indicates the variable. u of j Directional component, the second subscript indicates the direction component. u j beg j The directional partial derivative, the third subscript indicates the direction of the derivative. u j,j beg i directional partial derivative; G It is the shear modulus of the coal mass; Poisson's ratio of the coal and rock mass; The Biot coefficient is the porosity coefficient. The coefficient of thermal expansion of the coal and rock mass; K Bulk modulus of coal and rock mass; The Biot coefficient for the crack; For the matrix gas pressure at i Component of direction; For the fracture fluid pressure at i Component of direction; Strain caused by gas adsorption / desorption i Component of direction; For the change in temperature i Component of direction; F i The volume forces of the coal and rock mass; The equations for the water and gas seepage field are shown in the following formula: (2)； In the formula, M fracture Q represents the mass of fluid in a unit volume of coal fractures. fracture It is the mass source or sink of the fluid; F fracture It represents the seepage flow rate of fluid in the fracture; t is time; v, Both represent the integration region, where v is the unit volume of coal-rock fracture; Γ is the surface boundary of the coal-rock fracture. The gas diffusion field equation is shown in the following formula: (3)； In the formula, M matrix M represents the mass of gas in the coal matrix. g p is the molar mass of gas; R is the molar constant of gas; fg The pressure of the gas in the fissure; τ is the matrix gas pressure; τ is the gas desorption time; T is the coal seam temperature; The temperature field equation is shown in the following formula: (4)； In the formula, M energy F is the energy density within coal fractures. energy For heat flux; Q energy A source or sink of heat; The coal and rock mass damage field equation is shown in formula (5), and the coal and rock mass damage is dynamically updated through state variables; (5)； In the formula, F1 is the maximum tensile stress criterion, F2 is the Mohr-Coulomb criterion; σ1 is the maximum principal stress of the coal and rock mass; f t0 σ3 is the uniaxial tensile strength; σ3 is the minimum principal stress of the coal and rock mass; θ is the internal friction angle of the coal; f c0 Uniaxial compressive strength; Input the fluid transport parameters in the multi-field coupled model of hydraulic fracturing enhanced gas extraction in low-permeability coal seam roof, and apply boundary conditions of stress, water, gas and temperature during the hydraulic fracturing enhanced gas extraction process. The borehole boundary water pressure is applied through the water pressure change function over time. Mesh generation for a multi-field coupled model of hydraulic fracturing-enhanced gas extraction; Numerical simulation of enhanced gas extraction by hydraulic fracturing in high-gas, low-permeability coal seams was achieved using a multi-field coupled model based on mesh generation.

2. The multi-field coupled simulation method for enhanced gas extraction by hydraulic fracturing of the roof of a low-permeability coal seam according to claim 1, characterized in that, The method creates a random function rn1(x,y,z) that satisfies a normal distribution and has an average value of 1 to realize the heterogeneity of the coal seam and the roof and floor, where x,y,z represent directional parameters; the elastic modulus, porosity, tensile strength, compressive strength, and cohesion of the coal and rock strata are all multiplied by the random function rn1(x,y,z) to represent the heterogeneity of the coal seam and the roof and floor.

3. The multi-field coupled simulation method for enhanced gas extraction by hydraulic fracturing of the roof of a low-permeability coal seam according to claim 2, characterized in that, The specific method for numerical simulation of enhanced gas extraction through hydraulic fracturing in high-gas, low-permeability coal seams based on a multi-field coupled model after mesh generation is as follows: The influence of gas on hydraulic fracturing is not considered, that is, the gas seepage field equation and diffusion field equation in the multi-field coupling model are not considered. The numerical simulation of hydraulic fracturing is carried out. The elastic modulus, permeability, water pressure, and temperature of the coal and rock strata after hydraulic fracturing were obtained as initial values ​​for gas extraction simulation. By modifying the boundary conditions for water and temperature in the water and gas seepage field equations and temperature field equations, numerical simulation of enhanced gas extraction through hydraulic fracturing in high-gas, low-permeability coal seams can be achieved.

4. An electronic device for executing the multi-field coupled simulation method for enhanced gas extraction in low-permeability coal seam roof hydraulic fracturing as described in any one of claims 1-3, characterized in that, include: One or more processors, and a memory for storing instructions that, when executed by the one or more processors, cause the one or more processors to perform the multi-field coupled simulation method for enhanced gas extraction by hydraulic fracturing of the roof of a low-permeability coal seam.

5. A computer-readable storage medium storing executable instructions for performing the multi-field coupled simulation method for enhanced gas extraction in low-permeability coal seam roof hydraulic fracturing as described in any one of claims 1-3, characterized in that... When the instruction is executed, it causes the processor to perform the multi-field coupling simulation method for enhanced gas extraction by hydraulic fracturing of the roof of a low-permeability coal seam.

6. A computer program product for executing the multi-field coupled simulation method for enhanced gas extraction in low-permeability coal seam roof hydraulic fracturing as described in any one of claims 1-3, characterized in that, This includes a computer program or instructions that, when executed by a processor, implement the multi-field coupled simulation method for enhanced gas extraction using hydraulic fracturing of the roof of a low-permeability coal seam.

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