Method and device for predicting fractures in coal seam roof hydraulic fracturing

Abstract

The present application proposes a method and device for predicting coal seam roof fracturing cracks. The method includes: obtaining observation data of the coal seam, and constructing a physical simulation model of the coal seam based on the observation data; performing adaptive meshing on the physical simulation model, and performing simulation prediction of coal seam roof fracturing cracks on the physical simulation model based on the meshing results; and determining prediction information of roof fracturing cracks based on the simulation prediction results. Therefore, by adaptively meshing the physical simulation model, the present solution can make the meshing results meet both the engineering scale of the model and the refinement of the calculation, ensuring that the grid size at the crack tip position is fine, ensuring high calculation accuracy of the crack tip expansion process, and ensuring that the number of grids in the entire domain is not too large, promoting fast and high-precision calculations, and improving calculation efficiency.

Description

Technical Field

[0001] The present application relates to the field of coal mining technology, and in particular to a method and device for predicting coal seam roof fracturing cracks. Background Art

[0002] Hydraulic fracturing is a key technology that injects high-pressure fracturing fluid into underground formations to create artificial fractures, thereby enhancing the recovery of oil, gas, coalbed methane, or geothermal resources. Numerical simulation, a key tool in hydraulic fracturing research, plays a crucial role in selecting fracturing layers, optimizing fracturing parameters, and pre-evaluating fracturing effectiveness before hydraulic fracturing. By simulating the formation and propagation of fractures, numerical simulation can predict fracture morphology, length, width, and their interaction with the natural fracture network, providing a scientific basis for optimizing fracturing design. Summary of the Invention

[0003] The purpose of this application is to solve one of the technical problems in the related art at least to a certain extent.

[0004] To this end, the first purpose of this application is to propose a prediction method for coal seam roof fracturing cracks to achieve adaptive grid division of the physical simulation model, ensure high calculation accuracy of the crack tip expansion process, and ensure that the number of grids in the entire domain will not be too large, thereby promoting fast and high-precision calculations and improving calculation efficiency.

[0005] The second purpose of this application is to provide a device for predicting coal seam roof fracturing cracks.

[0006] To achieve the above-mentioned purpose, the first embodiment of the present application proposes a method for predicting coal seam roof pressure fracture cracks, including: obtaining observation data of the coal seam, and constructing a physical simulation model of the coal seam based on the observation data; adaptively meshing the physical simulation model, and performing simulation prediction of coal seam roof pressure fracture cracks on the physical simulation model based on the meshing results; and determining prediction information of the roof pressure fracture cracks based on the simulation prediction results.

[0007] To achieve the above-mentioned purpose, the second embodiment of the present application proposes a prediction device for coal seam roof fracturing cracks, including: a construction module for obtaining observation data of the coal seam and constructing a physical simulation model of the coal seam based on the observation data; a simulation module for adaptively gridding the physical simulation model and performing simulation prediction of coal seam roof fracturing cracks on the physical simulation model based on the grid division results; a determination module for determining the prediction information of the roof fracturing cracks based on the simulation prediction results.

[0008] The present application provides a method and device for predicting coal seam roof pressure fracture cracks. The method and device construct a physical simulation model of the coal seam based on the observation data of the coal seam, and adaptively mesh the physical simulation model to simulate and predict the coal seam roof pressure fracture cracks based on the meshing results. Thus, the prediction information of the roof pressure fracture cracks can be determined based on the simulation prediction results. Thus, by adaptively meshing the physical simulation model, the meshing results can simultaneously meet the engineering scale of the model and the calculation refinement, ensuring that the grid size at the crack tip position is fine, and the uncalculated part still uses a relatively large grid size, which not only ensures high calculation accuracy of the crack tip expansion process, but also ensures that the number of grids in the entire domain will not be too large, promotes fast and high-precision calculations, and improves calculation efficiency.

[0009] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0011] Figure 1 A schematic flow chart of a method for predicting coal seam roof fracturing cracks provided in an embodiment of the present application;

[0012] Figure 2 A schematic diagram of the grid division provided in an embodiment of the present application;

[0013] Figure 3 A schematic flow chart of another method for predicting coal seam roof hydraulic fracturing cracks provided in an embodiment of the present application;

[0014] Figure 4 A schematic flow chart of another method for predicting coal seam roof hydraulic fracturing cracks provided in an embodiment of the present application;

[0015] Figure 5 A schematic diagram of the bidirectional display coupling provided in an embodiment of the present application;

[0016] Figure 6 A schematic diagram of a process for predicting hydraulic fractures provided in an embodiment of the present application;

[0017] Figure 7 A schematic diagram of the structure of a device for predicting coal seam roof fracturing cracks provided in an embodiment of the present application. DETAILED DESCRIPTION

[0018] The following describes in detail embodiments of the present application, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present application, and should not be construed as limiting the present application.

[0019] The following describes the method and device for predicting coal seam roof fracturing cracks according to an embodiment of the present application with reference to the accompanying drawings.

[0020] Figure 1 This is a flow chart of a method for predicting coal seam roof fracturing cracks provided in an embodiment of the present application, such as Figure 1 As shown, the method for predicting coal seam roof fracturing cracks in the embodiment of the present application includes but is not limited to the following steps:

[0021] S101, obtaining observation data of the coal seam, and constructing a physical simulation model of the coal seam based on the observation data.

[0022] It should be noted that the execution subject of the coal seam roof pressure fracture prediction method provided in the embodiment of the present application is an electronic device, which can be a terminal device. Optionally, the terminal device can be a mobile electronic device or a non-mobile electronic device. For example, the mobile electronic device can be a mobile phone, tablet computer, laptop computer, PDA, in-vehicle electronic device, wearable device, ultra-mobile personal computer (UMPC), netbook or personal digital assistant (PDA), etc., and the non-mobile electronic device can be a personal computer (PC), television, etc. The embodiment of the present application does not specifically limit this.

[0023] In some embodiments, physical properties of the coal seam and core samples may be obtained and used as observation data of the coal seam.

[0024] In some embodiments, physical properties of coal seams are measured using various physical methods, including conductivity, resistivity, acoustic wave velocity, density, and natural gamma rays. The physical properties of coal seams can provide indirect information about their lithology. For example, resistivity changes can be used to infer the oil and water content of coal seams, while acoustic wave transit time can be used to assess the porosity and permeability of coal seams.

[0025] In some embodiments, core samples are obtained from the coal seam by drilling equipment. The core samples can directly reflect the lithology, structure and structural characteristics of the coal seam.

[0026] In some embodiments, a fluid-solid coupling model of the coal seam may be constructed based on the observation data, and the physical properties of the coal seam may be combined with the fluid-solid coupling model to obtain a physical simulation model of the coal seam.

[0027] Among them, a fluid-solid coupling model can be constructed based on the solid mechanics equations and fluid dynamics equations, and the fracture mechanical behavior can also be combined to enable the physical simulation model of the coal seam to consider the crack initiation criteria, that is, the fracture mechanics theory and expansion path.

[0028] S102, performing adaptive meshing on the physical simulation model, and performing simulation prediction of coal seam roof fracturing cracks on the physical simulation model based on the meshing result.

[0029] In some embodiments, by performing adaptive meshing on the physical simulation model, dynamic changes of the mesh can be achieved, and the meshing result can simultaneously meet the engineering scale of the model and the mesh refinement.

[0030] In some embodiments, a preliminary grid division may be performed based on the physical simulation model, and multiple preliminary grid divisions within a set range around the injection point of the fracturing cluster may be obtained. The multiple preliminary grid divisions may be refined to obtain a grid density within the set range around the injection point of the fracturing cluster that is greater than the grid density of the remaining part of the physical simulation model, as a grid division result.

[0031] For example, Figure 2 The schematic diagram of mesh division is shown. Taking the mesh division result in the upper left corner as an example, point A is the injection point of the fracturing cluster, and the density of the mesh within a certain range around point A is greater than that of the rest of the mesh.

[0032] In some embodiments, by injecting fracturing fluid into the fracturing cluster injection point, the fracturing cracks are expanded according to the time step until they expand to the boundary of the grid with a high mesh density in the mesh division result, and the mesh within a set range around the boundary is continuously refined until the boundary of the grid with a high mesh density reaches the boundary of the physical simulation model and stops expanding.

[0033] Optionally, the hydraulic fracture expands according to a time step, and in response to the expansion of the hydraulic fracture reaching a set time length, the expansion is stopped.

[0034] S103: Determine prediction information of roof fracturing cracks based on the simulation prediction results.

[0035] In some embodiments, fracture parameters of the fracture, such as fracture edge coordinates, fracture width distribution, and fluid and solid field sets, can be obtained when the fracture stops expanding, and the fracture parameters can be used as simulation prediction results. Further, prediction information for the roof fracture can be determined based on the simulation prediction results.

[0036] In some embodiments, the fracture morphology of the hydraulic fracture may be determined based on fracture parameters, such as fracture length, fracture width, and shape, and the fracture morphology of the hydraulic fracture may be used as prediction information for the roof hydraulic fracture.

[0037] In some embodiments, a pressure variation curve of the fracturing fluid injected at the fracturing cluster injection point may also be obtained, and the pressure variation curve may be used as prediction information of the roof fracturing cracks.

[0038] In some embodiments, the pressure variation curve may be correlated with the fracture morphology of the fracture to determine the fracture morphology of the fracture corresponding to the fracture fluids of different pressures.

[0039] In some embodiments, when the hydraulic fractures extend to the boundaries of the grid, fracture parameters of the hydraulic fractures may be acquired to obtain multiple sets of different fracture parameters, and the multiple sets of different fracture parameters may be used as prediction information of the roof hydraulic fractures.

[0040] In the prediction method for coal seam roof pressure fracture cracks provided in the embodiment of the present application, a physical simulation model of the coal seam is constructed based on the observation data of the coal seam, and the physical simulation model is adaptively meshed, so as to simulate and predict the coal seam roof pressure fracture cracks on the physical simulation model based on the meshing results, so that the prediction information of the roof pressure fracture cracks can be determined based on the simulation prediction results. Therefore, by adaptively meshing the physical simulation model, the meshing results can simultaneously meet the engineering scale of the model and the calculation refinement, ensuring that the grid size at the crack tip position is fine, and the uncalculated part still uses a relatively large grid size, which not only ensures high calculation accuracy of the crack tip expansion process, but also ensures that the number of grids in the entire domain will not be too large, promotes fast and high-precision calculation, and improves calculation efficiency.

[0041] Figure 3 This is a flow chart of a method for predicting coal seam roof fracturing cracks provided in an embodiment of the present application, such as Figure 3 As shown, the method for predicting coal seam roof fracturing cracks in the embodiment of the present application includes but is not limited to the following steps:

[0042] S301, obtaining observation data of the coal seam, and constructing a physical simulation model of the coal seam based on the observation data.

[0043] In the embodiment of the present application, the implementation method of step S301 can be implemented by any method in the various embodiments of the present application, which is not limited here and will not be repeated.

[0044] S302 , adaptively meshing the physical simulation model, and injecting fracturing fluid into the fracturing cluster injection points based on the meshing result, so that the fracturing cracks expand according to the time step.

[0045] In some embodiments, the physical simulation model may be preliminarily meshed based on the model structure of the physical simulation model to obtain an initial meshing result, and then the mesh in the initial meshing result may be refined to obtain a meshing result.

[0046] In some embodiments, the fracturing cluster injection point of the physical simulation model is determined, and the fracturing cluster injection point is determined in a third grid within a set range in the initial grid division result, wherein the fracturing cluster injection point is the initial point for generating the fracturing crack.

[0047] For example, the four grids around the injection point of the fracturing cluster can be used as the third grid, and the third grid can be refined to obtain a first grid with a higher grid density than the third grid. Furthermore, a grid division result can be generated based on the first grid and the initial grid division result.

[0048] Optionally, a grid division result may be obtained by replacing the third grid in the initial division result with the first grid.

[0049] In some embodiments, a fracturing cluster injection point is determined and a fracturing fluid is injected into the fracturing cluster injection point to generate a fracturing crack. Furthermore, a time step is determined so that the fracturing crack expands toward the boundary of the physical simulation model within the time step.

[0050] In some embodiments, the time step may be dynamically adjusted according to the crack expansion rate and the pressure change of the fracturing fluid.

[0051] In some embodiments, the initial time step is determined by obtaining the injection rate of the fracturing fluid and the initial expansion velocity of the fracturing crack in the i-th time step, and based on the injection rate and the initial expansion velocity.

[0052] Furthermore, the changes in the fracturing fluid pressure and the expansion rate of the cracks are monitored to obtain the rate of change of the fracturing fluid pressure and the expansion rate of the fracturing cracks in the i+1th time step, and then the initial time step can be adjusted based on the rate of change and expansion rate of the fracturing fluid pressure to obtain the time step.

[0053] In some embodiments, the initial time step may be adjusted according to a threshold value by obtaining a change rate threshold corresponding to the change rate of the fracturing fluid pressure and a speed threshold corresponding to the expansion speed.

[0054] In response to the change rate being less than or equal to the change rate threshold and the expansion speed being less than or equal to the speed threshold, the initial time step is increased to obtain the time step; otherwise, the initial time step is decreased to obtain the time step.

[0055] S303: Determine an initial boundary corresponding to the first grid in the grid division result.

[0056] S304 : In response to the hydraulic fracture extending to the initial boundary, determining a second grid within a set range adjacent to the first grid in the boundary direction of the physical simulation model.

[0057] In some embodiments, during the fracturing crack propagation process, an initial boundary corresponding to a first grid in the grid division result is determined, where the first grid refers to a grid having a grid density greater than a density threshold. Alternatively, the grid density can be determined based on the grid size, with smaller grid sizes corresponding to greater grid density. In other words, a grid having a grid size less than the size threshold can be used as the first grid.

[0058] In some embodiments, the boundary of the first grid is determined as the initial boundary, and it is determined whether the fracturing crack has extended to the initial boundary. When the fracture has extended to the initial boundary, the second grid within a set range adjacent to the first grid is further refined.

[0059] In some embodiments, by determining the expansion path of the hydraulic fracture, wherein the hydraulic fracture expands based on the expansion path, it can be determined whether the expansion path reaches the initial boundary to determine whether the hydraulic fracture expands to the initial boundary.

[0060] In some embodiments, the propagation path of the fracture may be determined based on the time step.

[0061] Optionally, a nonlinear ordinary differential equation may be used to determine the expansion path of the fracturing crack, and the differential equation is assumed to be: y′(t)=f(t,y), y(t0)=y0.

[0062] At a certain moment t n We can solve the next moment t n+1 =t n +Δt value y n+1 , the formula is:

[0063] y n+1 =y n +Δt·k2(1)

[0064] Where Δt is the time step; k1 is the initial slope estimate, k1 = f(t n ,y n ); k2 is the correction slope calculated using k1, k2 = f(t n +Δt,y n +Δt·k1).

[0065] In some embodiments, by determining (t n ,y n) and use k1 to calculate the predicted point y n +Δt·k1; and recalculate the slope k2 at the prediction point, and then substitute k2 into formula (1) to obtain the value y at the next moment n+1 , so that we can base on y n+1 Generates an extension path.

[0066] In some embodiments, when the expansion path is obtained, it can be determined whether the fracturing crack has expanded to the initial boundary based on the expansion path. Whether the expansion path has reached the initial boundary can be determined based on the coordinate values ​​of the expansion path.

[0067] S305: Refine the second grid to obtain an updated grid division result.

[0068] In some embodiments, when it is determined that the fracturing crack has extended to the initial boundary, a second grid within a set range adjacent to the first grid in the boundary direction of the physical simulation model is determined, and the second grid is refined, and the refined second grid is used as the first grid, and the refined second grid is used to update the grid division result to obtain an updated grid division result, thereby realizing adaptive adjustment of the grid division result.

[0069] S306 , continue to inject fracturing fluid into the fracturing cluster injection point to expand and refine the mesh toward the boundary of the physical simulation model based on the updated mesh division result until the fracturing cracks extend to the boundary of the physical simulation model, or the fracturing cracks extend for a set time and then stop extending.

[0070] In some embodiments, after the grid division result is adaptively adjusted, the fracturing fluid is continuously injected into the fracturing cluster injection point to allow the fracturing crack to continue to expand toward the boundary of the physical simulation model. When the fracturing crack once again expands to the initial boundary corresponding to the first grid, the above-mentioned step of refining the grid is continued to be executed to expand the refined grid toward the boundary of the physical simulation model, and the fracturing fluid is continuously injected to allow the fracturing crack to continue to expand until the fracturing crack expands to the boundary of the physical simulation model, or the expansion time of the fracturing crack reaches the set time and stops expanding. Figure 2 As shown in the schematic diagram of grid division, whenever the fracturing crack expands to the corresponding initial boundary of the first grid, the second grid within the set range adjacent to the first grid in the boundary direction of the physical simulation model is refined.

[0071] Example description:

[0072] a. Determine the data set Γ = {Node, x, y, z} corresponding to the meshing result, where Node represents the node number and (x, y, z) is the three-dimensional coordinate of the node;

[0073] b. When the fracturing crack extends to the initial boundary of the first grid in the grid division result, the grid is further refined toward the boundary of the physical simulation model to update the grid division result, obtaining an updated data set Γˊ={Nodeˊ,xˊ,yˊ,zˊ};

[0074] c. Continue to expand the fracture based on the updated data set Γˊ until the fracture expands to the boundary of the refined grid corresponding to Γˊ, and repeat steps ac until the fracture expands to the boundary of the physical simulation model or the fracture expansion time reaches the set time and stops expanding.

[0075] S307: Determine prediction information of roof fracturing cracks based on the simulation prediction results.

[0076] In some embodiments, when the hydraulic fracture expands to the initial boundary, fracture parameters of the hydraulic fracture, such as fracture edge coordinates, fracture width distribution, and fluid and solid field sets, can be obtained and used as simulation prediction results. Further, prediction information for the roof hydraulic fracture can be determined based on the simulation prediction results.

[0077] In some embodiments, the fracture morphology of the hydraulic fracture may be determined based on fracture parameters, such as fracture length, fracture width, and shape, and the fracture morphology of the hydraulic fracture may be used as prediction information for the roof hydraulic fracture.

[0078] Optionally, the fracture morphology when the hydraulic fracture stops expanding can be obtained, that is, the fracture parameters when the hydraulic fracture stops expanding can be obtained from the simulation prediction results, and the corresponding fracture morphology can be determined according to the fracture parameters.

[0079] Furthermore, since the pressure of the injected fracturing fluid changes during the expansion of the fracture, the pressure change data of the fracturing fluid can be obtained to obtain a fracturing fluid pressure change curve based on the pressure change data. The fracture morphology and change curve can then be output as prediction information.

[0080] In the prediction method of the coal seam roof fracturing crack provided by the embodiment of the present application, by injecting fracturing fluid into the fracturing cluster injection point, so that the fracturing crack is expanded according to the time step, and when the fracturing crack expands to the initial boundary, the second grid is refined to obtain the updated grid division result, and then the fracturing fluid is continued to be injected into the fracturing cluster injection point, so as to expand and refine the grid toward the boundary of the physical simulation model based on the updated grid division result, until the fracturing crack expands to the boundary of the physical simulation model, or the expansion time of the fracturing crack reaches the set time length and stops expanding. Thus, it is possible to realize adaptive grid division of the physical simulation model, so that the grid division result can simultaneously meet the engineering scale and calculation refinement of the model. Optimizing the time step during the calculation process can improve the efficiency of the calculation convergence and avoid the non-convergence of the calculation due to the fixed step size.

[0081] Figure 4 This is a flow chart of a method for predicting coal seam roof fracturing cracks provided in an embodiment of the present application, such as Figure 4 As shown, the method for predicting coal seam roof fracturing cracks in the embodiment of the present application includes but is not limited to the following steps:

[0082] S401 obtains observation data of the coal seam.

[0083] In the embodiment of the present application, the implementation method of step S401 can be implemented by any method in the various embodiments of the present application, which is not limited here and will not be repeated.

[0084] S402, determining the mechanical properties of the coal seam based on the observation data.

[0085] In some embodiments, the mechanical properties of the coal seam can be analyzed based on the observed data to determine the mechanical properties of the coal seam. The lithologic structure of the coal seam can also be determined based on the observed data. To simplify the physical simulation model, coal seam segments with similar mechanical properties and lithologic structures can be merged to obtain lithologic sublayers.

[0086] In some embodiments, by performing mechanical property tests on the observed data, the elastic modulus E, Poisson's ratio υ, and tensile fracture energy η can be obtained. Ⅰ and shear fracture energy η Ⅱ , as the mechanical properties of coal seams.

[0087] In some embodiments, the ground stress state of the lithologic layer can also be calculated as the mechanical property of the coal seam. The ground stress state includes the stress state of the overlying rock layer of each lithologic layer σ v , maximum horizontal principal stress state σ H The ground stress state σ h .

[0088] Alternatively, the formula for calculating the ground stress state is as follows:

[0089]

[0090] Among them, Δσ v is the pressure gradient, ε H , ε h is the maximum and minimum horizontal principal stress direction strain, P p is the formation pore pressure, α is the coefficient, and h is the vertical depth of the formation.

[0091] Among them, the expansion direction of the fracturing crack can be determined according to the ground stress state.

[0092] Alternatively, the minimum stress may be determined from the ground stress state based on the maximum principal stress criterion, and the crack propagation direction is perpendicular to the direction of the minimum stress.

[0093] Based on the above embodiment, the fracture type of a hydraulic fracture can be determined based on mechanical properties. The tensile fracture energy and shear fracture energy can be determined based on the mechanical properties. During the simulation, the fracturing fluid pressure is obtained as the front pressure of the hydraulic fracture. Furthermore, the fracture type of the hydraulic fracture can be determined based on the tensile fracture energy, shear fracture energy, and front pressure.

[0094] For example, let the leading edge pressure be P p , the tensile fracture energy is η Ⅰ , the shear fracture energy is η Ⅱ , when P p <η Ⅰ <η Ⅱ When η Ⅰ <P p <η Ⅱ When η Ⅰ <η Ⅱ <P p When , shear fracture occurs at the crack front.

[0095] S403: Based on the observation data, a fluid-solid coupling model of the coal seam is established.

[0096] In some embodiments, a fluid-solid coupling model of a coal seam is established by determining solid mechanics equations and fluid mechanics equations and substituting observed data into the method.

[0097] It is understandable that the roof coal seam is shallowly buried, the vertical principal stress is small, and the horizontal principal stress is the main controlling factor. There is a natural fracture network, and the coupling effect with the hydraulic fracture is significant. In other words, the fluid field and the solid field adopt a two-way display coupling method, that is, the fluid field and the solid field act in a two-way manner. The fluid pressure in the fracture and the pore fluid pressure in the matrix solved in the fluid field affect the deformation and fracture of the solid field, and the spatial changes caused by the deformation and fracture of the solid field affect the fluid pressure in the fracture and the pore fluid pressure in the matrix solved in the fluid field. Figure 5 The schematic diagram of the bidirectional display coupling effect is shown.

[0098] Alternatively, the mass transport of the coal seam can be calculated to achieve solid mechanical balance, as shown in the following formula:

[0099]

[0100] Where σ is the stress tensor, ρ is the rock density, and g is the acceleration due to gravity.

[0101] Alternatively, the saturation changes with the seepage behavior. The saturation of the fluid can be calculated to describe the seepage behavior of the fluid in the fractures and pores. The calculation formula is as follows:

[0102]

[0103] Where q is the flow rate, k is the permeability, μ is the fluid viscosity, and P is the pressure.

[0104] S404: Add the mechanical characteristics to the fluid-solid coupling model to obtain a physical simulation model.

[0105] In some embodiments, a physical simulation model may be obtained by combining the determined mechanical properties with a fluid-structure coupling model.

[0106] In some embodiments, before obtaining the physical simulation model, boundary conditions of the physical simulation model may be set so that the physical simulation model can accurately reflect physical reality and ensure the accuracy of the simulation results.

[0107] Optionally, you can set solid field boundary conditions. Use the outer boundary of the physical simulation model as the solid field boundary and set the solid long boundary as a fixed boundary to ensure that the model does not experience boundary instability.

[0108] Optionally, a geostress field boundary condition can be set. A three-dimensional geostress boundary condition is applied to the solid field boundary, where the three-dimensional geostress can be calculated according to formula (2). The stress equilibrium after the geostress field is applied to the model is calculated to ensure that stress is accurately applied to each model node.

[0109] Optionally, you can set fluid field boundary conditions. These consist of two parts: the first is the fluid field boundary conditions at the fracturing cluster injection point, including injection rate and injection volume; the second is the pore pressure, which can be set for different lithologic strata.

[0110] S405 , adaptively meshing the physical simulation model, and performing simulation prediction of coal seam roof fracturing cracks on the physical simulation model based on the meshing result.

[0111] In the embodiment of the present application, the implementation method of step S405 can be implemented by any method in the various embodiments of the present application, which is not limited here and will not be repeated.

[0112] S406: Determine prediction information of roof fracturing cracks based on the simulation prediction results.

[0113] In the embodiment of the present application, the implementation method of step S406 can be implemented by any method in the various embodiments of the present application, which is not limited here and will not be repeated.

[0114] In the method for predicting hydraulic fractures in a coal seam roof provided in an embodiment of the present application, observational data of the coal seam is obtained, and the mechanical properties and fluid-solid coupling model of the coal seam are determined based on the observational data. A physical simulation model is then constructed based on the mechanical properties and the fluid-solid coupling model. This physical simulation model can thus combine the mechanical properties of the coal seam with the fluid-solid coupling effect to more accurately simulate the coal seam during the hydraulic fracture process, thereby improving the accuracy of hydraulic fracture prediction.

[0115] Figure 6 The figure shows a schematic diagram of the process of predicting fracturing cracks. By acquiring coal seam observation data, a physical simulation model of the coal seam is established based on the observation data. The stress balance calculation can be performed according to the above formula (2), and the three ground stresses obtained are used to initialize the stress state. Furthermore, the boundary conditions of the model are determined, and the fluid saturation is calculated based on the above formula (4), and the mass migration is calculated based on the above formula (3). The fluid field and solid field are updated to obtain the physical simulation model.

[0116] After obtaining the physical simulation model, the physical simulation model is divided into an adaptive grid to obtain a grid division result, and a fracturing fluid is injected into the fracturing cluster injection point to generate a fracturing crack, and in the fracturing crack expansion process, it is judged whether the fracturing crack expands to the initial boundary corresponding to the first grid in the grid division result, and when the initial boundary is reached, it is judged whether the crack expands to the boundary of the model, and when it expands to the model boundary, the crack morphology and the pressure change curve of the fracturing fluid are determined and output as prediction information. If the crack does not expand to the model boundary, the above-mentioned expansion step is repeated to continue to judge whether the crack expands to the initial boundary corresponding to the first grid in the grid division result, if it does not expand to the initial boundary, it is judged whether the crack expansion time reaches a set value, and when it reaches the set value, the expansion is stopped, and the prediction information is obtained and output. If the crack expansion time does not reach the set value, the time step of the expansion can be increased, and the expansion step is continued until the crack expands to the model boundary, or the expansion time reaches the set value, and then the prediction information is determined and output.

[0117] Corresponding to the prediction methods for coal seam roof pressure fracturing cracks proposed in the above-mentioned embodiments, an embodiment of the present application further proposes a prediction device for coal seam roof pressure fracturing cracks. Since the prediction device for coal seam roof pressure fracturing cracks proposed in the embodiment of the present application corresponds to the prediction methods for coal seam roof pressure fracturing cracks proposed in the above-mentioned embodiments, the implementation method of the above-mentioned method for predicting coal seam roof pressure fracturing cracks is also applicable to the prediction device for coal seam roof pressure fracturing cracks proposed in the embodiment of the present application, and will not be described in detail in the following embodiments.

[0118] In order to implement the above embodiment, the present application also proposes a device for predicting coal seam roof fracturing cracks.

[0119] Figure 7 A schematic structural diagram of a device for predicting coal seam roof fracturing cracks provided in an embodiment of the present application.

[0120] like Figure 7 As shown, the coal seam roof pressure fracture prediction device 700 includes:

[0121] A construction module 701 is used to obtain observation data of the coal seam and construct a physical simulation model of the coal seam based on the observation data;

[0122] The simulation module 702 is used to perform adaptive meshing on the physical simulation model and simulate and predict the fractures of the coal seam roof based on the meshing result.

[0123] The determination module 703 is used to determine the prediction information of the roof fracturing cracks according to the simulation prediction results.

[0124] In a possible implementation of an embodiment of the present application, the simulation module 702 is also used to: inject fracturing fluid into the fracturing cluster injection point based on the grid division result, so that the fracturing crack expands according to the time step; determine the initial boundary corresponding to the first grid in the grid division result; in response to the fracturing crack expanding to the initial boundary, determine a second grid within a set range adjacent to the first grid in the boundary direction of the physical simulation model; refine the second grid to obtain an updated grid division result; continue to inject fracturing fluid into the fracturing cluster injection point to expand and refine the grid toward the boundary of the physical simulation model based on the updated grid division result until the fracturing crack expands to the boundary of the physical simulation model, or the expansion time of the fracturing crack reaches the set time and stops expanding.

[0125] In a possible implementation of an embodiment of the present application, the simulation module 702 is further used to: perform preliminary grid division on the physical simulation model based on the model structure of the physical simulation model to obtain an initial grid division result; determine the fracturing cluster injection point of the physical simulation model, and determine a third grid within the set range of the fracturing cluster injection point in the initial grid division result, where the fracturing cluster injection point is the initial point for generating fracturing cracks; refine the third grid to obtain a first grid with a grid density greater than that of the third grid; and generate a grid division result based on the first grid and the initial grid division result.

[0126] In a possible implementation of the embodiment of the present application, the simulation module 702 is further used to: determine an expansion path of the fracturing crack based on a time step, wherein the fracturing crack expands based on the expansion path; and determine whether the fracturing crack expands to the initial boundary based on the expansion path.

[0127] In a possible implementation of an embodiment of the present application, the simulation module 702 is further used to: obtain the injection rate of the fracturing fluid in the i-th time step and the initial expansion speed of the fracturing crack; determine the initial time step based on the injection rate and the initial expansion speed; obtain the rate of change of the fracturing fluid pressure in the i+1-th time step, and the expansion speed of the fracturing crack; and adjust the initial time step based on the rate of change of the fracturing fluid pressure and the expansion speed to obtain the time step.

[0128] In a possible implementation of an embodiment of the present application, the simulation module 702 is further used to: obtain a change rate threshold corresponding to the change rate of the fracturing fluid pressure, and a speed threshold corresponding to the expansion speed; in response to the change rate being less than or equal to the change rate threshold, and the expansion speed being less than or equal to the speed threshold, increase the initial time step to obtain a time step; otherwise, decrease the initial time step to obtain a time step.

[0129] In a possible implementation of an embodiment of the present application, construction module 701 is also used to: determine the mechanical properties of the coal seam based on the observation data; establish a fluid-solid coupling model of the coal seam based on the observation data; and add the mechanical properties to the fluid-solid coupling model to obtain a physical simulation model.

[0130] In a possible implementation of the embodiment of the present application, the determination module 703 is further used to: obtain the crack morphology when the fracturing crack stops expanding; obtain the change curve of the fracturing fluid pressure; and output the crack morphology and the change curve as prediction information.

[0131] In a possible implementation of an embodiment of the present application, the device further includes: determining tensile fracture energy and shear fracture energy based on mechanical properties; obtaining the fracturing fluid pressure as the front pressure of the fracturing crack; and determining the fracture type of the fracturing crack based on the tensile fracture energy, shear fracture energy and front pressure.

[0132] In the prediction device for coal seam roof pressure fracture cracks provided in the embodiment of the present application, a physical simulation model of the coal seam is constructed based on the observation data of the coal seam, and the physical simulation model is adaptively meshed to simulate and predict the coal seam roof pressure fracture cracks based on the meshing results. Thus, the prediction information of the roof pressure fracture cracks can be determined based on the simulation prediction results. Thus, by adaptively meshing the physical simulation model, the meshing results can simultaneously meet the engineering scale of the model and the calculation refinement, ensuring that the grid size at the crack tip position is fine, and the uncalculated part still uses a relatively large grid size, which not only ensures high calculation accuracy of the crack tip expansion process, but also ensures that the number of grids in the entire domain is not too large, promotes fast and high-precision calculations, and improves calculation efficiency.

[0133] It should be noted that the above explanation of the embodiment of the method for predicting the pressure-fracture cracks in the coal seam roof is also applicable to the device for predicting the pressure-fracture cracks in the coal seam roof of this embodiment, and will not be repeated here.

[0134] The collection, storage, use, processing, transmission, provision and application of user personal information involved in this application are in compliance with relevant laws and regulations and do not violate public order and good morals.

[0135] It is important to note that personal information collected from users should be used for legitimate and reasonable purposes and should not be shared or sold beyond these legitimate uses. Furthermore, such collection / sharing should be conducted only after receiving the user's informed consent, including but not limited to notifying the user to read the user agreement / user notice and sign an agreement / authorization that includes the relevant user information before using the feature. Furthermore, any necessary steps must be taken to safeguard and secure access to such personal information and ensure that others with access to personal information comply with its privacy policy and procedures.

[0136] This application contemplates providing implementation options for users to selectively block the use or access of personal information data. Specifically, this application contemplates providing hardware and / or software to prevent or block access to such personal information data. Risks can be minimized by limiting data collection and deleting data once it is no longer needed. Furthermore, where applicable, such personal information can be de-identified to protect user privacy.

[0137] In the descriptions of the foregoing embodiments, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, unless they are mutually inconsistent.

[0138] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of such features. Throughout the description of this application, "plurality" means at least two, for example, two, three, etc., unless otherwise specifically defined.

[0139] Any process or method description in a flowchart or otherwise described herein may be understood to represent a module, segment or portion of code comprising one or more executable instructions for implementing the steps of a custom logical function or process, and the scope of the preferred embodiments of the present application includes alternative implementations in which functions may be performed out of the order shown or discussed, including performing functions in a substantially simultaneous manner or in the reverse order depending on the functions involved, which should be understood by those skilled in the art to which the embodiments of the present application belong.

[0140] The logic and / or steps represented in the flowcharts or otherwise described herein, for example, can be considered as a sequenced list of executable instructions for implementing the logical functions, and can be embodied in any computer-readable medium for use by, or in conjunction with, an instruction execution system, apparatus, or device (e.g., a computer-based system, a system including a processor, or other system that can fetch and execute instructions from an instruction execution system, apparatus, or device). For purposes of this specification, a "computer-readable medium" can be any device that can contain, store, communicate, propagate, or transport a program for use by, or in conjunction with, an instruction execution system, apparatus, or device. More specific examples (a non-exhaustive list) of computer-readable media include the following: an electrical connection with one or more wires (electronic devices), a portable computer disk cartridge (magnetic device), random access memory (RAM), read-only memory (ROM), erasable and programmable read-only memory (EPROM or flash memory), fiber optic devices, and a portable compact disc read-only memory (CDROM). Furthermore, the computer-readable medium may even be paper or other suitable medium on which the program is printed, since the program may be obtained electronically, for example, by optically scanning the paper or other medium and then editing, interpreting or processing it in another suitable manner if necessary, and then storing it in a computer memory.

[0141] It should be understood that various parts of the present application can be implemented using hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented using software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented using hardware, as in another embodiment, any one of the following technologies known in the art or a combination thereof can be used to implement: a discrete logic circuit having a logic gate circuit for implementing a logic function on a data signal, an application-specific integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.

[0142] Those skilled in the art will understand that all or part of the steps in the method of the above embodiment can be completed by instructing related hardware through a program, and the program can be stored in a computer-readable storage medium. When the program is executed, it includes one or a combination of the steps of the method embodiment.

[0143] In addition, the functional units in the various embodiments of the present application may be integrated into a processing module, or each unit may exist physically separately, or two or more units may be integrated into a module. The above-mentioned integrated module may be implemented in the form of hardware or in the form of a software functional module. If the integrated module is implemented in the form of a software functional module and sold or used as an independent product, it may also be stored in a computer-readable storage medium.

[0144] The storage medium mentioned above may be a read-only memory, a magnetic disk, or an optical disk, etc. Although the embodiments of the present application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present application. Persons skilled in the art may make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present application.

Claims

1. A method for predicting coal seam roof fractures, characterized in that: The method comprises: Acquiring observation data of a coal seam, and constructing a physical simulation model of the coal seam based on the observation data; Adaptively meshing the physical simulation model, and performing simulation prediction of coal seam roof fracturing cracks on the physical simulation model based on the meshing result; Determine the prediction information of roof fracturing cracks based on the simulation prediction results; The method of performing simulation prediction of coal seam roof fracturing cracks on the physical simulation model based on the grid division result includes: Based on the grid division result, injecting fracturing fluid into the fracturing cluster injection point to expand the fracturing crack according to the time step; Determining an initial boundary corresponding to a first grid in the grid division result; In response to the fracturing crack extending to the initial boundary, determining a second grid within a set range adjacent to the first grid in a boundary direction of the physical simulation model; Refining the second grid to obtain an updated grid division result; Continue to inject fracturing fluid into the fracturing cluster injection point to expand and refine the grid toward the boundary of the physical simulation model based on the updated grid division result until the fracturing crack expands to the boundary of the physical simulation model, or the expansion time of the fracturing crack reaches a set time and stops expanding; The process of determining the time step includes: Obtaining the injection rate of the fracturing fluid in the i-th time step and the initial expansion speed of the fracturing crack; determining an initial time step based on the injection rate and the initial expansion velocity; Obtaining the rate of change of the fracturing fluid pressure and the expansion speed of the fracturing crack in the (i+1)th time step; Adjusting the initial time step to obtain the time step based on the rate of change of the fracturing fluid pressure and the expansion speed; The obtaining of observation data of the coal seam and constructing a physical simulation model of the coal seam based on the observation data includes: determining mechanical properties of the coal seam based on the observation data; Based on the observation data, a fluid-solid coupling model of the coal seam is established; Adding the mechanical characteristics to the fluid-solid coupling model to obtain the physical simulation model; The method further comprises: Based on the mechanical properties, determining the tensile fracture energy and the shear fracture energy; Obtaining the fracturing fluid pressure as the front pressure of the fracturing crack; The fracture type of the hydraulic fracture is determined based on the tensile fracture energy, the shear fracture energy, and the front pressure.

2. The method according to claim 1, characterized in that The adaptive meshing of the physical simulation model comprises: Based on the model structure of the physical simulation model, the physical simulation model is preliminarily meshed to obtain an initial meshing result; Determining a fracturing cluster injection point of the physical simulation model, and determining a third grid within a set range of the initial grid division result for the fracturing cluster injection point, wherein the fracturing cluster injection point is the initial point for generating a fracturing crack; Refining the third grid to obtain the first grid having a higher grid density than the third grid; The grid division result is generated based on the first grid and the initial grid division result.

3. The method according to claim 1, characterized in that The method further comprises: determining a propagation path of the hydraulic fracture based on the time step, wherein the hydraulic fracture propagates based on the propagation path; Based on the expansion path, it is determined whether the hydraulic fracture has expanded to the initial boundary.

4. The method according to claim 1, wherein The adjusting the initial time step to obtain the time step based on the rate of change of the fracturing fluid pressure and the expansion speed includes: Obtaining a change rate threshold corresponding to the change rate of the fracturing fluid pressure and a speed threshold corresponding to the expansion speed; In response to the change rate being less than or equal to the change rate threshold and the expansion speed being less than or equal to the speed threshold, the initial time step is increased to obtain the time step; otherwise, the initial time step is decreased to obtain the time step.

5. The method according to claim 1, characterized in that Determining prediction information of roof fracturing cracks based on the simulation prediction results includes: Obtaining the fracture morphology when the hydraulic fracture stops expanding; Obtaining a change curve of the fracturing fluid pressure; The crack morphology and the change curve are output as the prediction information.

6. A device for predicting fractures in coal seam roof, characterized in that: The device comprises: A construction module, configured to obtain observation data of a coal seam and construct a physical simulation model of the coal seam based on the observation data; A simulation module, configured to adaptively mesh the physical simulation model and simulate and predict the fractures of the coal seam roof based on the meshing result; A determination module, used to determine prediction information of roof fracturing cracks based on simulation prediction results; Wherein, the simulation module is further used for: Based on the grid division result, injecting fracturing fluid into the fracturing cluster injection point to expand the fracturing crack according to the time step; Determining an initial boundary corresponding to a first grid in the grid division result; In response to the fracturing crack extending to the initial boundary, determining a second grid within a set range adjacent to the first grid in a boundary direction of the physical simulation model; Refining the second grid to obtain an updated grid division result; Continue to inject fracturing fluid into the fracturing cluster injection point to expand and refine the grid toward the boundary of the physical simulation model based on the updated grid division result until the fracturing crack expands to the boundary of the physical simulation model, or the expansion time of the fracturing crack reaches a set time and stops expanding; The simulation module is further used for: Obtaining the injection rate of the fracturing fluid in the i-th time step and the initial expansion speed of the fracturing crack; determining an initial time step based on the injection rate and the initial expansion velocity; Obtaining the rate of change of the fracturing fluid pressure and the expansion speed of the fracturing crack in the (i+1)th time step; Adjusting the initial time step to obtain the time step based on the rate of change of the fracturing fluid pressure and the expansion speed; The building block is further configured to: determining mechanical properties of the coal seam based on the observation data; Based on the observation data, a fluid-solid coupling model of the coal seam is established; Adding the mechanical characteristics to the fluid-solid coupling model to obtain the physical simulation model; The device further comprises: Based on the mechanical properties, determining the tensile fracture energy and the shear fracture energy; Obtaining the fracturing fluid pressure as the front pressure of the fracturing crack; The fracture type of the hydraulic fracture is determined based on the tensile fracture energy, the shear fracture energy, and the front pressure.

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