Prediction method and device for coal seam roof fracturing crack

Abstract

The invention provides a coal seam roof fracturing crack prediction method and device. The method comprises the following steps: acquiring observation data of a coal seam, and constructing a physical simulation model of the coal seam based on the observation data; carrying out self-adaptive grid division on the physical simulation model, and carrying out simulation prediction on the coal seam roof fracturing crack on the physical simulation model based on a grid division result; and according to a simulation prediction result, determining prediction information of the roof fracturing crack. Therefore, according to the scheme, self-adaptive mesh generation is carried out on the physical simulation model, the mesh generation result can meet the engineering scale and calculation refinement of the model at the same time, it is guaranteed that the size of the mesh located at the seam tip position is fine, it is guaranteed that the calculation precision of the seam tip crack expansion process is high, and it is also guaranteed that the number of global meshes is not too large; and rapid and high-precision calculation is promoted, and the calculation efficiency is improved.

Description

Technical Field

[0001] This application relates to the technical field of coal mining, and particularly to a method and device for predicting fractures in coal seam roof strata. Background Art

[0002] Hydraulic fracturing technology is a key technology for improving the recovery rate of oil and gas, coalbed methane, or geothermal resources by injecting high-pressure fracturing fluid into underground formations to generate artificial fractures. As an important means for studying hydraulic fracturing, numerical simulation technology is a key technology for such aspects as fracture layer selection, fracturing parameter optimization, and pre-evaluation of fracturing effects before carrying out hydraulic fracturing transformation on formations. By simulating the generation and propagation process of fractures, numerical simulation technology can predict fracture morphology, length, width, and the interaction between fractures and natural fracture networks, providing a scientific basis for optimizing fracturing design. Summary of the Invention

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

[0004] To this end, the first objective of this application is to propose a method for predicting fractures in coal seam roof strata, so as to achieve adaptive mesh generation for the physical simulation model, ensuring high calculation accuracy in the process of crack tip fracture propagation, and also ensuring that the total number of meshes in the entire domain is not too large, promoting fast and high-precision calculations, and improving the calculation efficiency.

[0005] The second objective of this application is to propose a device for predicting fractures in coal seam roof strata.

[0006] To achieve the above objective, an embodiment of the first aspect of this application proposes a method for predicting fractures in coal seam roof strata, including: obtaining observation data of a coal seam, and constructing a physical simulation model of the coal seam based on the observation data; performing adaptive mesh generation on the physical simulation model, and performing simulation prediction of fractures in the coal seam roof strata on the physical simulation model based on the mesh generation result; and determining prediction information of the roof fracturing fractures according to the simulation prediction result.

[0007] To achieve the above objective, an embodiment of the second aspect of this application proposes a device for predicting fractures in coal seam roof strata, including: 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 perform adaptive mesh generation on the physical simulation model, and perform simulation prediction of fractures in the coal seam roof strata on the physical simulation model based on the mesh generation result; and a determination module, configured to determine prediction information of the roof fracturing fractures according to the simulation prediction result.

[0008] The prediction method and device for coal seam roof fracturing cracks provided by this application construct a physical simulation model of the coal seam based on the observed data of the coal seam, and perform adaptive mesh division on the physical simulation model, so as to perform simulation prediction of coal seam roof fracturing cracks based on the mesh division result, and thus the prediction information of the roof fracturing cracks can be determined according to the simulation prediction result. Therefore, through the adaptive mesh division of the physical simulation model, the mesh division result can simultaneously meet the engineering scale and calculation refinement of the model, ensure that the mesh size at the crack tip position is fine, and the relatively large-sized meshes are still used for the uncalculated part, which not only ensures high calculation accuracy in the process of crack tip crack propagation, but also ensures that the total number of meshes in the whole domain will not be too large, promotes fast and high-precision calculation, and improves the calculation efficiency.

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

[0010] The above-mentioned and / or additional aspects and advantages of this application will become apparent and easy to understand from the following description of the embodiments in conjunction with the drawings, where:

[0011] Figure 1 is a schematic flowchart of a prediction method for coal seam roof fracturing cracks provided by an embodiment of this application;

[0012] Figure 2 is a schematic diagram of mesh division provided by an embodiment of this application;

[0013] Figure 3 is a schematic flowchart of another prediction method for coal seam roof fracturing cracks provided by an embodiment of this application;

[0014] Figure 4 is a schematic flowchart of another prediction method for coal seam roof fracturing cracks provided by an embodiment of this application;

[0015] Figure 5 is a schematic diagram of the bidirectional display coupling effect provided by an embodiment of this application;

[0016] Figure 6 is a schematic flowchart of the process for predicting fracturing cracks provided by an embodiment of this application;

[0017] Figure 7 is a schematic structural diagram of a prediction device for coal seam roof fracturing cracks provided by an embodiment of this application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0018] Embodiments of the present application will be described in detail below. Examples of the embodiments are shown in the accompanying drawings, where the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the accompanying drawings are exemplary and are intended to explain the present application, and should not be construed as a limitation of the present application.

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

[0020] Figure 1 is a flowchart of a method for predicting fracturing cracks in a coal seam roof according to an embodiment of the present application. As Figure 1 shown, the method for predicting fracturing cracks in a coal seam roof according to an embodiment of the present application includes, but is not limited to, the following steps:

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

[0022] It should be noted that the execution subject of the method for predicting fracturing cracks in a coal seam roof provided by the embodiments of the present application is an electronic device, and the electronic device may be a terminal device. Optionally, the terminal device may be a mobile electronic device or a non-mobile electronic device. Exemplarily, the mobile electronic device may be a mobile phone, a tablet computer, a laptop computer, a handheld computer, a vehicle-mounted electronic device, a wearable device, an ultra-mobile personal computer (UMPC), a netbook, or a personal digital assistant (PDA), etc., and the non-mobile electronic device may be a personal computer (PC), a television, etc. The embodiments of the present application do not make specific limitations.

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

[0024] In some embodiments, the physical properties of the coal seam are measured by different physical methods, and the physical properties include conductivity, resistivity, acoustic velocity, density, natural gamma ray, etc. The physical properties of the coal seam can provide indirect information about the lithology of the coal seam. For example, the oil content and water content of the coal seam can be inferred from the change in resistivity; the porosity and permeability of the coal seam can be evaluated by the acoustic travel time.

[0025] In some embodiments, core samples in the coal seam are drilled by a drilling device, and the core samples can directly reflect the lithology, structure, and tectonic characteristics of the coal seam.

[0026] In some embodiments, a fluid-solid coupling model of a coal seam can be constructed based on observed data, and by combining the physical properties of the coal seam with the fluid-solid coupling model, a physical simulation model of the coal seam can be obtained.

[0027] Among them, a fluid-solid coupling model can be constructed based on solid mechanics equations and fluid dynamics equations, and the mechanical behavior of fractures can also be combined, so that the physical simulation model of the coal seam takes into account the fracture initiation criterion of fractures, that is, fracture mechanics theory and propagation path.

[0028] S102. Perform adaptive mesh division on the physical simulation model, and based on the mesh division result, perform simulation prediction of the fracturing cracks in the roof of the coal seam for the physical simulation model.

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

[0030] In some embodiments, the mesh can be initially divided according to the physical simulation model, and multiple initially divided meshes within a set range around the injection point of the fracturing cluster are obtained, and the multiple initially divided meshes are refined, so that the mesh density within the set range around the injection point of the fracturing cluster is greater than that of the remaining part of the physical simulation model, as the mesh division result.

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

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

[0033] Optionally, the fracturing cracks expand according to the time step, and when the set duration is reached in response to the expansion of the fracturing cracks, the expansion stops.

[0034] S103. Determine the prediction information of the roof fracturing cracks according to the simulation prediction result.

[0035] In some embodiments, the crack parameters of the fracturing cracks, such as crack edge coordinates, crack width distribution, fluid field and solid field set, can be obtained when the fracturing cracks stop expanding, and the crack parameters are used as the simulation prediction result. Further, the prediction information of the roof fracturing cracks can be determined according to the simulation prediction result.

[0036] In some embodiments, the fracture pattern of the fracturing fracture, such as the fracture length, fracture width, and shape, can be determined according to the fracture parameters, and the fracture pattern of the fracturing fracture can be used as the prediction information of the roof fracturing fracture.

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

[0038] In some embodiments, the pressure change curve can be associated with the fracture pattern of the fracturing fracture to determine the fracture pattern of the fracturing fracture corresponding to the fracturing fluid at different pressures.

[0039] In some embodiments, when the fracturing fracture extends to the boundary of the grid, the fracture parameters of the fracturing fracture can also be obtained to obtain multiple groups of different fracture parameters, and the multiple groups of different fracture parameters can be used as the prediction information of the roof fracturing fracture.

[0040] In the prediction method of the coal seam roof fracturing fracture provided by the embodiments of the present application, a physical simulation model of the coal seam is constructed according to the observation data of the coal seam, and adaptive mesh division is performed on the physical simulation model, so as to perform simulation prediction of the coal seam roof fracturing fracture based on the mesh division result. Thus, according to the simulation prediction result, the prediction information of the roof fracturing fracture can be determined. Therefore, through the adaptive mesh division of the physical simulation model, the mesh division result can simultaneously meet the engineering scale and calculation refinement of the model, ensure that the mesh size at the crack tip position is fine, and the relatively large-sized mesh is still used for the uncalculated part, which not only ensures high calculation accuracy in the process of crack tip fracture propagation, but also ensures that the total number of global meshes will not be too large, promotes fast and high-precision calculation, and improves the calculation efficiency.

[0041] Figure 3 is a flowchart of a prediction method for a coal seam roof fracturing fracture provided by an embodiment of the present application. As Figure 3 shown, the prediction method of the coal seam roof fracturing fracture in the embodiment of the present application includes but is not limited to the following steps:

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

[0043] In the embodiment of the present application, the implementation manner of step S301 can be implemented by any one of the embodiments of the present application, and no limitation is made here and will not be elaborated.

[0044] S302, perform adaptive mesh division on the physical simulation model, and based on the mesh division result, inject fracturing fluid into the fracturing cluster injection point to make the fracturing fracture expand according to the time step.

[0045] In some embodiments, based on the model structure of the physical simulation model, an initial mesh division of the physical simulation model can be performed to obtain an initial mesh division result. Furthermore, the meshes in the initial mesh division result can be refined to obtain a mesh division result.

[0046] In some embodiments, by determining the fracturing cluster injection points of the physical simulation model and determining the third meshes within a set range in the initial mesh division result, where the fracturing cluster injection points are the initial points for generating fracturing cracks.

[0047] For example, 4 meshes around the fracturing cluster injection points can be used as the third meshes. Furthermore, the third meshes can be refined to obtain first meshes with a greater mesh density than the third meshes. Further, based on the first meshes and the initial mesh division result, a mesh division result can be generated.

[0048] Optionally, by replacing the third meshes in the initial division result with the first meshes, a mesh division result can be obtained.

[0049] In some embodiments, by determining the fracturing cluster injection points and injecting fracturing fluid into the fracturing cluster injection points to generate fracturing cracks. Further, a time step is determined such that the fracturing cracks expand towards the boundary of the physical simulation model within the time step.

[0050] In some embodiments, the time step can be dynamically adjusted according to the propagation speed of the cracks and the pressure change of the fracturing fluid.

[0051] In some embodiments, by obtaining the injection rate of the fracturing fluid within the i-th time step and the initial propagation speed of the fracturing cracks, and based on the injection rate and the initial propagation speed, an initial time step is determined.

[0052] Further, monitor the pressure change of the fracturing fluid and the propagation speed of the cracks to obtain the rate of change of the pressure of the fracturing fluid within the (i + 1)-th time step, and the propagation speed of the fracturing cracks. Furthermore, based on the rate of change of the pressure of the fracturing fluid and the propagation speed, the initial time step can be adjusted to obtain the time step.

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

[0054] Wherein, in response to the rate of change being less than or equal to the threshold of the rate of change, and the propagation speed being less than or equal to the threshold of the speed, 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 the initial boundary corresponding to the first grid in the grid division result.

[0056] S304. In response to the fracturing crack extending to the initial boundary, determine the 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, determine the initial boundary corresponding to the first grid in the grid division result, where the first grid refers to the grid with a grid density greater than the density threshold. Optionally, the grid density can be determined according to the grid size. The smaller the grid size, the greater the corresponding grid density. That is, the grid with a grid size smaller than the size threshold can be used as the first grid.

[0058] In some embodiments, determine the boundary of the first grid as the initial boundary, and determine whether the fracturing crack extends to the initial boundary. When it extends to the initial boundary, continue to refine the second grid within a set range adjacent to the first grid.

[0059] In some embodiments, by determining the propagation path of the fracturing crack, where the fracturing crack propagates based on the propagation path, it can be further determined whether the propagation path reaches the initial boundary to determine whether the fracturing crack extends to the initial boundary.

[0060] In some embodiments, the propagation path of the fracturing crack can be determined based on the time step.

[0061] Optionally, a nonlinear ordinary differential equation can be used to determine the propagation path of the fracturing crack. Let the differential equation be: y′(t) = f(t, y), y(t0) = y0.

[0062] At a certain moment t n the value of the next moment t n+1 = t n + Δt, y n+1 can be solved, and its formula is:

[0063] y n+1 = y n + Δt·k2(1)

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

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

[0066] In some embodiments, when the extended path is obtained, it is possible to determine whether the fracturing crack has extended to the initial boundary based on the extended path. It is possible to determine whether the extended path reaches the initial boundary according to the coordinate values of the extended 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, by determining the second grid within a set range adjacent to the first grid in the boundary direction of the physical simulation model, refining the second grid, using the refined second grid as the first grid, and using the refined second grid to update the grid division result to obtain an updated grid division result, the adaptive adjustment of the grid division result is realized.

[0069] S306, continue to inject fracturing fluid into the fracturing cluster injection point to expand and refine the grid towards the boundary of the physical simulation model based on the updated grid division result until the fracturing crack extends to the boundary of the physical simulation model or the extension duration of the fracturing crack reaches the set duration and stops extending.

[0070] In some embodiments, after the grid division result is adaptively adjusted, continue to inject fracturing fluid into the fracturing cluster injection point to make the fracturing crack continue to extend towards the boundary of the physical simulation model. When the fracturing crack extends to the initial boundary corresponding to the first grid again, continue to execute the above steps of refining the grid to realize the expansion and refinement of the grid towards the boundary of the physical simulation model, and continue to inject fracturing fluid to make the fracturing crack continue to extend until the fracturing crack extends to the boundary of the physical simulation model or the extension duration of the fracturing crack reaches the set duration and stops extending. As Figure 2 shown in the schematic diagram of grid division, whenever the fracturing crack extends to the initial boundary corresponding to the first grid, refine the second grid within a set range adjacent to the first grid in the boundary direction of the physical simulation model.

[0071] Exemplary illustration:

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

[0073] b. When the fracturing crack extends to the initial boundary of the first grid in the mesh division result, continue to refine the mesh towards the boundary of the physical simulation model to update the mesh division result, obtaining the updated dataset Γˊ = {Nodeˊ, xˊ, yˊ, zˊ};

[0074] c. Based on the updated dataset Γˊ, continue the extension of the fracturing crack until the crack extends to the boundary of the refined mesh corresponding to Γˊ, and repeat steps a - c until the fracturing crack extends to the boundary of the physical simulation model, or the extension duration of the fracturing crack reaches the set duration and stops extending.

[0075] S307. Determine the prediction information of the roof fracturing crack according to the simulation prediction result.

[0076] In some embodiments, when the fracturing crack extends to the initial boundary, the crack parameters of the fracturing crack can be obtained, such as the crack edge coordinates, the seam width distribution, the fluid field and the solid field set, and the crack parameters can be used as the simulation prediction result. Further, the prediction information of the roof fracturing crack can be determined according to the simulation prediction result.

[0077] In some embodiments, the crack shape of the fracturing crack, such as the crack length, the seam width, and the shape, can be determined according to the crack parameters, and the crack shape of the fracturing crack can be used as the prediction information of the roof fracturing crack.

[0078] Optionally, the crack shape when the fracturing crack stops extending can be obtained, that is, the crack parameters when the fracturing crack stops extending are obtained from the simulation prediction result, and the corresponding crack shape is determined according to the crack parameters.

[0079] Furthermore, since the pressure of the fracturing fluid injected during the extension of the fracturing crack changes, by obtaining the pressure change data of the fracturing fluid, the change curve of the fracturing fluid pressure can be obtained according to the pressure change data. Furthermore, the crack shape and the change curve can be output as prediction information.

[0080] In the prediction method of coal seam roof fracturing cracks provided by the embodiments of the present application, fracturing fluid is injected into the fracturing cluster injection point to cause the fracturing cracks to expand according to the time step. When the fracturing cracks expand to the initial boundary, the second grid is refined to obtain an updated grid division result. Then, fracturing fluid is continuously injected into the fracturing cluster injection point to expand and refine the grid based on the updated grid division result to the boundary of the physical simulation model until the fracturing cracks expand to the boundary of the physical simulation model or the expansion duration of the fracturing cracks reaches the set duration and stops expanding. Thus, adaptive grid division of the physical simulation model can be realized, and 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 calculation convergence and avoid non-convergence caused by a fixed step size.

[0081] Figure 4 is a flowchart of a prediction method for coal seam roof fracturing cracks provided by the embodiments of the present application. As Figure 4 shown, the prediction method for coal seam roof fracturing cracks in the embodiments of the present application includes but is not limited to the following steps:

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

[0083] In the embodiments of the present application, the implementation manner of step S401 can be implemented by any one of the embodiments of the present application, and no limitation is made here and will not be elaborated further.

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

[0085] In some embodiments, the mechanical properties of the coal seam can be analyzed based on the observation data to determine the mechanical properties of the coal seam. The lithological structure of the coal seam can also be determined according to the observation data. In order to simplify the physical simulation model, coal seam segments with similar mechanical properties and lithological structures can be merged to obtain small lithological layers.

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

[0087] In some embodiments, the in-situ stress state of the small lithological layer can also be calculated as the mechanical property of the coal seam. Among them, the in-situ stress state includes the overlying rock stress state σ v of each small lithological layer, the maximum horizontal principal stress state σ H and the minimum horizontal principal stress in-situ stress state σ h .

[0088] Optionally, the formula for calculating the in-situ stress state is as follows:

[0089]

[0090] where Δσ v is the pressure gradient, ε H , ε h are the strains in the directions of the maximum and minimum horizontal principal stresses, P p is the formation pore pressure, α is a coefficient, and h is the formation vertical depth.

[0091] Among them, the propagation direction of the fracturing crack can be judged according to the in-situ stress state.

[0092] Optionally, based on the maximum principal stress criterion, the minimum stress can be determined from the in-situ stress state, and the crack propagation direction is perpendicular to the direction of the minimum stress.

[0093] Based on the above embodiments, the fracture type of the fracturing crack can be determined according to the mechanical properties. The tensile fracture energy and shear fracture energy can be determined based on the mechanical properties, and during the simulation process, the fracturing fluid pressure is obtained as the front-edge pressure of the fracturing crack. Furthermore, based on the tensile fracture energy, shear fracture energy, and front-edge pressure, the fracture type of the fracturing crack can be determined.

[0094] Exemplarily, let the front-edge pressure be P p , the tensile fracture energy be η Ⅰ , the shear fracture energy be η Ⅱ . When P p < η Ⅰ < η Ⅱ , since the front-edge pressure does not reach the energy required for fracture at the crack front, the crack front does not propagate; when η Ⅰ < P p < η Ⅱ , tensile fracture occurs at the crack front; when η Ⅰ < η Ⅱ < P p , shear fracture occurs at the crack front.

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

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

[0097] It is understandable that the roof coal seam has a shallow burial depth, with a relatively small vertical principal stress and the horizontal principal stress being the main controlling factor. There is a natural fracture network, and the coupling effect with hydraulic fractures is significant. That is to say, the fluid field and the solid field adopt a two-way explicit coupling method, namely, the fluid field and the solid field act on each other bidirectionally. 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 in turn affect the fluid pressure in the fracture and the pore fluid pressure in the matrix solved in the fluid field. As Figure 5 shown in the schematic diagram of the two-way explicit coupling effect.

[0098] Optionally, the solid mechanics equilibrium can be achieved by calculating the mass migration of the coal seam, and the calculation formula is as follows:

[0099]

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

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

[0102]

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

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

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

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

[0107] Optionally, the boundary conditions of the solid field can be set. Taking the outer boundary of the physical simulation model as the boundary of the solid field, the long boundary of the solid is set as a fixed boundary to ensure that the model does not show boundary instability.

[0108] Optionally, the boundary conditions of the in-situ stress field can be set. A triaxial in-situ stress boundary condition is applied on the boundary of the solid field, where the triaxial in-situ stress can be calculated according to formula (2). By calculating the stress balance after applying the in-situ stress field to the model, it is ensured that the stress is accurately applied to each model node.

[0109] Optionally, fluid field boundary conditions can be set. The fluid field boundary conditions include two parts. The first is the fluid field boundary conditions at the injection points of the fracturing clusters, including the injection rate and injection volume. The second part is the pore pressure, and the pore pressures of different lithologic sub-layers can be set.

[0110] S405. Perform adaptive mesh division on the physical simulation model, and based on the mesh division results, perform simulation prediction of the fracturing cracks in the coal seam roof of the physical simulation model.

[0111] In the embodiments of the present application, the implementation manner of step S405 can be implemented by any one of the embodiments of the present application respectively. No limitation is made here and it will not be elaborated further.

[0112] S406. Determine the prediction information of the roof fracturing cracks according to the simulation prediction results.

[0113] In the embodiments of the present application, the implementation manner of step S406 can be implemented by any one of the embodiments of the present application respectively. No limitation is made here and it will not be elaborated further.

[0114] In the prediction method of the fracturing cracks in the coal seam roof provided by the embodiments of the present application, by obtaining the observation data of the coal seam and determining the mechanical properties and fluid-solid coupling model of the coal seam according to the observation data, a physical simulation model of the coal seam is constructed based on the mechanical properties and fluid-solid coupling model. Thus, the physical simulation model can combine the mechanical properties of the coal seam and the fluid-solid coupling effect, so as to more accurately simulate the coal seam during the fracturing process and improve the accuracy of predicting the fracturing cracks.

[0115] Figure 6 The flowchart of predicting the fracturing cracks is shown. By obtaining the coal seam observation data, a physical simulation model of the coal seam is established according to the observation data. The stress balance calculation can be performed according to the above formula (2), and the three in-situ stresses obtained are used to initialize the stress state. Further, the boundary conditions of the model are determined, and the fluid saturation is calculated based on the above formula (4), and the mass transfer is calculated based on the above formula (3) to update the fluid field and the solid field to obtain the physical simulation model.

[0116] After obtaining the physical simulation model, perform adaptive mesh division on the physical simulation model to obtain the mesh division result, and inject fracturing fluid into the fracturing cluster injection points to generate fracturing cracks. During the propagation process of the fracturing cracks, determine whether the fracturing cracks extend to the initial boundary corresponding to the first grid in the mesh division result. When reaching the initial boundary, determine whether the cracks extend to the boundary of the model. When extending to the model boundary, determine the crack morphology and the pressure change curve of the fracturing fluid, and output them as prediction information. If the cracks do not extend to the model boundary, repeat the above extension steps to continue to determine whether the cracks extend to the initial boundary corresponding to the first grid in the mesh division result. If not extending to the initial boundary, determine whether the crack extension duration reaches the set value. When reaching the set value, stop the extension and obtain the prediction information for output. If the crack extension duration does not reach the set value, the time step of the extension can be increased, and the extension steps are continued until the cracks extend to the model boundary or the extension duration reaches the set value, and then the prediction information is determined and output.

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

[0118] To implement the above embodiments, the present application also proposes a prediction device for fracturing cracks in the coal seam roof.

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

[0120] As Figure 7 shown, the prediction device 700 for fracturing cracks in the coal seam roof includes:

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

[0122] A simulation module 702, configured to perform adaptive mesh division on the physical simulation model and perform simulation prediction of fracturing cracks in the coal seam roof based on the mesh division result;

[0123] A determination module 703, configured to determine the prediction information of the roof fracturing cracks according to the simulation prediction result.

[0124] In a possible implementation manner of the embodiment of the present application, the simulation module 702 is further configured to: based on the mesh division result, inject fracturing fluid into the fracturing cluster injection points so that the fracturing cracks expand according to the time step; determine the initial boundary corresponding to the first mesh in the mesh division result; in response to the fracturing cracks expanding to the initial boundary, determine the second meshes within a set range adjacent to the first mesh in the boundary direction of the physical simulation model; perform refinement processing on the second meshes to obtain an updated mesh division result; continue to inject fracturing fluid into the fracturing cluster injection points to expand and refine the meshes towards the boundary of the physical simulation model based on the updated mesh division result until the fracturing cracks expand to the boundary of the physical simulation model or the expansion duration of the fracturing cracks reaches the set duration and stops expanding.

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

[0126] In a possible implementation manner of the embodiment of the present application, the simulation module 702 is further configured to: based on the time step, determine the expansion path of the fracturing cracks, where the fracturing cracks expand based on the expansion path; based on the expansion path, determine whether the fracturing cracks have expanded to the initial boundary.

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

[0128] In a possible implementation manner of the embodiment of the present application, the simulation module 702 is further configured to: obtain the change rate threshold corresponding to the change rate of the fracturing fluid pressure and the 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, perform an increasing process on the initial time step to obtain the time step, otherwise, perform a decreasing process on the initial time step to obtain the time step.

[0129] In a possible implementation manner of the embodiment of the present application, the construction module 701 is further configured 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 manner of the embodiment of the present application, the determination module 703 is further configured to: obtain the fracture morphology when the hydraulic fracture stops expanding; obtain the change curve of the hydraulic fracturing fluid pressure; and output the fracture morphology and the change curve as prediction information.

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

[0132] In the prediction device for the roof hydraulic fractures of the coal seam provided by the embodiment of the present application, a physical simulation model of the coal seam is constructed according to the observation data of the coal seam, and adaptive mesh division is performed on the physical simulation model, so as to perform simulation prediction of the roof hydraulic fractures of the coal seam based on the mesh division result, and thus the prediction information of the roof hydraulic fractures can be determined according to the simulation prediction result. Therefore, through the adaptive mesh division of the physical simulation model, the mesh division result can simultaneously meet the engineering scale and calculation refinement of the model, ensure that the mesh size at the crack tip position is fine, and the relatively larger mesh is still used for the uncalculated part, which not only ensures high calculation accuracy in the process of crack tip crack expansion, but also ensures that the total number of global meshes will not be too large, promotes fast and high-precision calculation, and improves the calculation efficiency.

[0133] It should be noted that the foregoing explanation of the embodiment of the prediction method for the roof hydraulic fractures of the coal seam is also applicable to the prediction device for the roof hydraulic fractures of the coal seam in this embodiment, and will not be repeated here.

[0134] The collection, storage, use, processing, transmission, provision, and application, etc., of the user's personal information involved in the present application all comply with the provisions of relevant laws and regulations and do not violate public order and good customs.

[0135] It should be noted that personal information from users should be collected for legal and reasonable purposes and should not be shared or sold outside of these legal uses. In addition, such collection / sharing should be carried out after obtaining the informed consent of the user, including but not limited to notifying the user to read the user agreement / user notice and signing an agreement / authorization including authorizing relevant user information before the user uses this function. In addition, any necessary steps should be taken to defend and protect access to such personal information data and ensure that others with access to the personal information data comply with their privacy policies and procedures.

[0136] This application is expected to provide an implementation scheme for users to selectively prevent the use or access of personal information data. That is, this application is expected to provide hardware and / or software to prevent or block access to such personal information data. Once the personal information data is no longer needed, the risk can be minimized by restricting data collection and deleting the data. In addition, when applicable, personal identifiers are removed from such personal information to protect the privacy of users.

[0137] In the description of the foregoing embodiments, the descriptions referring to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples", etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of this application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0138] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one of the features. In the description of this application, "a plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0139] Any process or method description shown in the flowchart or described in other ways herein can be understood to represent a module, segment, or part of code including one or more executable instructions for implementing a customized logic function or process, and the scope of the preferred implementation of this application includes additional implementations, where the functions can be executed in a substantially simultaneous manner or in the reverse order according to the functions involved, rather than in the order shown or discussed, which should be understood by those skilled in the art to which the embodiments of this application belong.

[0140] The logic and / or steps represented in the flowchart or otherwise described herein can, for example, be considered as a definable sequence list of executable instructions for implementing logical functions, which can be specifically implemented in any computer-readable medium for use by an instruction execution system, apparatus, or device (such as a computer-based system, a system including a processor, or other systems that can fetch and execute instructions from the instruction execution system, apparatus, or device), or used in conjunction with these instruction execution systems, apparatuses, or devices. For the 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 (non-exhaustive list) of computer-readable media include the following: electrical connection parts with one or more wirings (electronic devices), portable computer disk cartridges (magnetic devices), random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fiber devices, and portable compact disc read-only memory (CDROM). Additionally, the computer-readable medium can even be paper or other suitable media on which the program can be printed, because the program can be obtained electronically, for example, by optically scanning the paper or other media, followed by editing, interpretation, or other appropriate processing if necessary, and then stored in a computer memory.

[0141] It should be understood that various parts of the present application can be implemented using hardware, software, firmware, or combinations thereof. In the above-described 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 or a combination of the following techniques well known in the art can be used: discrete logic circuits having logic gate circuits for implementing logical functions on data signals, application-specific integrated circuits having appropriate combinational logic gate circuits, programmable gate arrays (PGAs), field-programmable gate arrays (FPGAs), etc.

[0142] Those of ordinary skill in the art of this technology can understand that all or part of the steps carried by the methods of the above embodiments can be completed by instructing relevant 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 embodiments.

[0143] In addition, each functional unit in various embodiments of the present application may be integrated into one processing module, or each unit may exist physically alone, or two or more units may be integrated into one module. The above-mentioned integrated module may be implemented in the form of hardware or in the form of a software functional module. When 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 above-mentioned storage medium may be a read-only memory, a magnetic disk or an optical disc, etc. Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present application. Those of ordinary skill in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present application.

Claims

1. A method for predicting fractures in coal seam roof, 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 based on the meshing result, performing simulation prediction of coal seam roof fracturing cracks on the physical simulation model; According to the simulation prediction results, the prediction information of the roof fracturing cracks is determined.

2. The method according to claim 1, characterized in that 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 so that the fracturing cracks are extended according to the time step; Determine an initial boundary corresponding to the 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.

3. The method according to claim 2, 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 initially meshed to obtain an initial meshing result; Determine a fracturing cluster injection point of the physical simulation model, and determine 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 an 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 mesh division result is generated based on the first mesh and the initial mesh division result.

4. The method according to claim 2, 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.

5. The method according to claim 2, characterized in that: 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+1th time step; The time step is obtained by adjusting the initial time step based on the rate of change of the fracturing fluid pressure and the expansion speed.

6. The method according to claim 5, characterized in that The adjusting the initial time step to obtain the time step based on the change rate 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.

7. The method according to claim 1, characterized in that The step of obtaining observation data of the coal seam and constructing a physical simulation model of the coal seam based on the observation data includes: Determining the mechanical properties of the coal seam based on the observed data; Based on the observation data, a fluid-solid coupling model of the coal seam is established; The mechanical characteristics are added to the fluid-solid coupling model to obtain the physical simulation model.

8. The method according to claim 5, characterized in that Determining prediction information of roof fracturing cracks according to 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.

9. The method according to claim 7, characterized in that: The method further comprises: Based on the mechanical properties, determining the tensile fracture energy and the shear fracture energy; Acquiring the fracturing fluid pressure as the front edge 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.

10. A device for predicting fractures in coal seam roof, characterized in that: The device comprises: A construction module, used for acquiring observation data of a coal seam and constructing a physical simulation model of the coal seam based on the observation data; A simulation module, used for 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; The determination module is used to determine the prediction information of the roof fracturing cracks according to the simulation prediction results.

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