A dynamic-static coupling simulation method for hydraulic-detonation combined fracturing reconstruction

Abstract

The present invention belongs to the fields of oil and gas development and energy utilization, and specifically relates to a dynamic-static coupling simulation method for hydraulic-detonation combined fracturing transformation, aiming to solve the problem of poor transformation effect in the prior art when fracturing and transforming deep-ultra-deep reservoirs. This method includes: constructing a dynamic-static coupling numerical calculation model for hydraulic-detonation fracturing transformation; through a discontinuous calculation method, simulating the propagation process of the main hydraulic fracture under static conditions, and ending the static simulation after reaching the preset main fracture length; keeping the model stress and the geometric shape of the main fracture unchanged, loading detonation shock waves in the preset detonation area, converting the static boundary conditions into dynamic boundary conditions, and simulating the propagation process of the detonation fracture network under dynamic conditions. After reaching the preset simulation time, the dynamic simulation ends, and the spatial configuration of the fracture network is output. The present invention improves the fracturing transformation effect of deep-ultra-deep reservoirs through dynamic-static coupling simulation calculation of hydraulic-detonation fracturing.

Description

Technical Field

[0001] The present invention belongs to the fields of oil and gas development and energy utilization, and particularly relates to a dynamic and static coupling simulation method and system for hydraulic-detonation combined fracturing transformation. Background Technique

[0002] Unconventional energy reservoirs (such as shale oil and gas, tight oil and gas, etc.) have relatively low permeability of the reservoir rock itself. Therefore, artificial fracturing transformation technology must be used to create fractures in the reservoir and form a dense seepage network in order to achieve the effective development of oil and gas resources. Hydraulic fracturing technology is the most commonly used means for reservoir fracturing transformation. Past applications and research have shown that hydraulic fracturing can effectively fracture shale oil and gas reservoirs and greatly improve the permeability of the reservoir. Therefore, hydraulic fracturing technology has promoted the application and rapid development of unconventional energy such as shale oil and gas.

[0003] In recent years, due to the gradual depletion of the remaining shallow oil and gas resources, it is no longer sufficient to support the rapid development of the social economy. The newly added oil and gas reserves mainly come from unconventional oil and gas reservoirs deeper than 4,500 meters. Due to the relatively large in-situ stress in deep and ultra-deep reservoirs, the reservoirs are more compact, the rock brittleness is low, and the pressability is poor, so higher requirements are imposed on reservoir fracturing transformation. The exploration and development of deep shale oil and gas reservoirs have shown that it is difficult to form a dense artificial fracture network like that in shallow reservoirs by applying traditional hydraulic fracturing technology to transform deep reservoirs. The reservoir transformation range is limited, main fractures and branch fractures are difficult to form, or the fractures are easy to close after formation, and the transformation effect is poor. Therefore, to achieve the effective development of deep and ultra-deep oil and gas resources, it is necessary to upgrade the traditional hydraulic fracturing technology system. Among them, on the basis of hydraulic fracturing, using the chemical reaction of liquid explosives to generate detonation shock waves inside the fractures, thereby fracturing the reservoir, is a very promising fracturing transformation technology for deep and ultra-deep reservoirs. The hydraulic-detonation combined fracturing transformation method utilizes the advantage of hydraulic fracturing in creating main fractures, and uses static water pressure to promote the formation of a macroscopically wide and dominant seepage channel inside the reservoir; it utilizes the advantage of detonation fracturing in creating a complex small-scale complex fracture network, and uses the high-pressure dynamic detonation shock wave to force the rock to fragment around the main fracture, ultimately forming a high-permeability fracture network in which the main fracture and the complex branch fracture network around the main fracture are connected in series. Therefore, due to the unique concept of dynamic and static reservoir transformation, the hydraulic-detonation combined fracturing transformation method may become a key technical means for the transformation of the reservoir transformation technology system.

[0004] At present, there is no available numerical simulation software for the combined hydraulic-detonation fracturing transformation in the world, which severely restricts the further application of this technology. Traditional hydraulic fracturing simulation methods and software (such as MEYER, GOHFER, etc.) are aimed at the problem of main fracture propagation under static water pressure conditions and cannot be directly applied to the simulation of dynamic detonation fracturing transformation. In addition, the combined hydraulic-detonation fracturing transformation is a continuous physical process, and its geometric model, fracture morphology, boundary conditions, etc. need to be transferred between the static analysis of hydraulic fracturing and the dynamic analysis of detonation fracturing. Therefore, if different simulation methods are selected to simulate hydraulic fracturing and detonation fracturing respectively and then information is transferred, it will cause unnecessary operations and may bring errors and seriously affect the calculation efficiency. However, it is difficult to consider the static fracture formation of hydraulic fracturing and the dynamic fracture formation of detonation fracturing within the framework of a unified calculation method, and it is also difficult to achieve dynamic-static coupling simulation for a unified numerical model. At present, there is no mature solution. Therefore, if a dynamic-static coupling simulation method for the combined hydraulic-detonation fracturing transformation can be proposed, it will greatly promote the application of this technology.

[0005] Based on this, the present invention proposes a dynamic-static coupling simulation method for the combined hydraulic-detonation fracturing transformation. Summary of the Invention

[0006] In order to solve the above problems in the prior art, that is, when fracturing and transforming deep and ultra-deep reservoirs in the prior art, the reservoir transformation range is effective, it is difficult to form main fractures and branch fractures, or the fractures are easy to close after formation, the transformation effect is poor, and the effective development of oil and gas resources in deep and ultra-deep reservoirs cannot be achieved. In the first aspect of the present invention, a dynamic-static coupling simulation method for the combined hydraulic-detonation fracturing transformation is proposed, which is used to simulate the expansion process of the fracture network in deep oil and gas reservoirs under the combined action of hydraulic fracturing and detonation fracturing, and obtain the expansion form of the fracture network; the method includes:

[0007] According to the three-dimensional transformation method of deep oil and gas reservoirs, a target simulation area is selected; the target simulation area is divided into grids, and then a dynamic-static coupling numerical calculation model for hydraulic-detonation fracturing transformation is constructed; the three-dimensional transformation method includes segmented perforation and segmented fracturing transformation;

[0008] Combined with the dynamic-static coupling numerical calculation model for hydraulic-detonation fracturing transformation, through a discontinuous calculation method, the overall stress balance of grid units under the initial in-situ stress conditions is completed, and the fluid injection rate is set to simulate the expansion process of the main fracture of hydraulic fracturing under static conditions. After reaching the preset main fracture length, the static simulation ends;

[0009] Keep the model stress and the geometry of the main cracks unchanged. Load the detonation shock wave in the preset detonation area to convert the static boundary conditions into dynamic boundary conditions, and simulate the expansion process of the detonation-induced fracture network under dynamic conditions. After reaching the preset simulation time, the dynamic simulation ends, and the spatial configuration of the fracture network in the deep oil and gas reservoir, that is, the expansion form of the detonation-induced fracture network, is output.

[0010] In some preferred embodiments, a dynamic-static coupling numerical calculation model for hydraulic-detonation fracturing transformation is constructed, and the method is as follows:

[0011] According to the three-dimensional transformation method of the deep oil and gas reservoir, select a single-side area of a single perforation cluster in the deep oil and gas reservoir as the target simulation area;

[0012] Determine the length and width of the target simulation area according to the fracturing transformation range in terms of the fracturing stage spacing and length, and then perform grid division on the target simulation area;

[0013] Combined with the target simulation area after grid division, define the dynamic-static coupling boundary and the geometric symmetry boundary, set the position of the fluid injection point, the boundary stress, the maximum principal stress, and the minimum principal stress. Finally, generate a dynamic-static coupling numerical calculation model for hydraulic-detonation fracturing transformation; wherein, the position of the fluid injection point is set at the midpoint of the geometric symmetry boundary.

[0014] In some preferred embodiments, the method for defining the dynamic-static coupling boundary and the geometric symmetry boundary is as follows: Define the left boundary, right boundary, and upper boundary of the numerical calculation model as the dynamic-static coupling boundary, and the lower boundary as the geometric symmetry boundary; the dynamic-static coupling boundary is converted between dynamic and static according to the calculation type during the numerical calculation process.

[0015] In some preferred embodiments, the numerical simulation calculation method for the expansion process of the main cracks in hydraulic fracturing under static conditions is as follows:

[0016] If the main crack in hydraulic fracturing is a tensile crack, calculate the flow velocity along the crack direction based on the viscosity of the fluid, the aperture of the crack, the pressure of the fluid in the crack, and the length coordinate along the crack direction;

[0017] Adopt the maximum tensile stress criterion to judge the crack criticality, and obtain the normal stress between elements, that is, the normal stress between elements at the crack tip;

[0018] Convert the conditions of the dynamic-static coupling boundary into fixed boundary conditions to obtain the displacements at the nodes on the boundary;

[0019] Calculate the fluid pressure based on the flow velocity along the crack direction; combine the fluid pressure, the normal stress between elements at the crack tip, and the displacements at the nodes on the boundary to construct a linear solution system of equations under static conditions of hydraulic fracturing KD=F, the static expansion form of the hydraulic fracture network is obtained by solving, that is, the geometric form of the main fracture; among them, K represents the stiffness matrix, D represents the displacement vector to be solved, F represents the total load vector on the element.

[0020] In some preferred embodiments, the simulation calculation method for the expansion process of the detonation fracture network under dynamic conditions is as follows:

[0021] According to the Mohr-Coulomb strength criterion, based on the cohesive strength of the rock under static conditions and the cohesive strength of the rock under the loading condition of the detonation shock wave load, the dynamic growth factor of the rock strength under high strain rate conditions is calculated;

[0022] According to the change of the cohesive strength and friction angle under high strain rate, combined with the dynamic growth factor of the rock strength under the high strain rate condition and the normal stress between the elements, the tangential stress between the elements is calculated;

[0023] Convert the conditions of the dynamic-static coupling boundary into a transmission boundary, simulate the transmission phenomenon of the shock wave at the boundary, and obtain the stiffness matrix correction amount of the elements on the transmission boundary;

[0024] Based on the stiffness matrix correction amount, the stiffness matrix of the corresponding element is corrected; combined with the corrected stiffness matrix of the element, the loads on the boundary and inside of the element, and the tangential stress between the elements, a linear solution equation set under the dynamic detonation shock wave condition is constructed, and then the dynamic expansion form of the hydraulic fracture network is obtained by solving.

[0025] In some preferred embodiments, the method for calculating the tangential stress between elements is as follows:

[0026] ;

[0027] ;

[0028] Among them, σ τ is the tangential stress between elements, DIF is the dynamic growth factor of the rock strength under high strain rate conditions, C n0 is the cohesive strength of the rock under static conditions, obtained through a shear test, C n is the cohesive strength of the rock under the loading condition of the detonation shock wave load, obtained by impact testing of a rock specimen in a uniaxial state through a split Hopkinson pressure bar test, is the internal friction angle, σ n is the normal stress between elements.

[0029] In some preferred embodiments, the method for obtaining the angle of the actual propagation direction of the cracks formed by rock fracture under detonation load is as follows:

[0030] ;

[0031] ;

[0032] Wherein, represents the circumferential stress at the crack tip, represents the angle of the actual propagation direction of the crack, represents the angle.

[0033] In some preferred embodiments, the calculation method for the stiffness matrix correction of the elements on the transmission boundary is as follows:

[0034] ;

[0035] Wherein, ΔK i is the stiffness matrix correction of element , p is the stiffness of the damper set at the transmission boundary, T i is the displacement transformation matrix of the discontinuous calculation method, F is the direction cosine matrix.

[0036] In some preferred embodiments, the linear solution equations under the condition of dynamic detonation shock wave are as follows:

[0037] ;

[0038] Wherein, M represents the mass matrix of the element, μ is the damping matrix, is the acceleration vector, is the velocity vector

[0039] In the second aspect of the present invention, a dynamic-static coupling simulation system for hydraulic-detonation combined fracturing reconstruction is proposed, which is used to simulate the propagation process of the fracture network in deep oil and gas reservoirs under the combined action of hydraulic fracturing and detonation fracturing, and obtain the propagation morphology of the fracture network; the system includes;

[0040] A model construction module, configured to select a target simulation area according to the three-dimensional reconstruction method of the deep oil and gas reservoir; perform network division on the target simulation area, and then construct a dynamic-static coupling numerical calculation model for hydraulic-detonation fracturing reconstruction; the three-dimensional reconstruction method includes segmented perforation and segmented fracturing reconstruction;

[0041] A static simulation module, configured to combine with the dynamic-static coupling numerical calculation model for hydraulic-detonation fracturing reconstruction, complete the overall stress balance of grid cells under initial in-situ stress conditions through a discontinuous calculation method, set the fluid injection rate, simulate the propagation process of the main fracture in hydraulic fracturing under static conditions, and end the static simulation after reaching the preset main fracture length;

[0042] A dynamic simulation module, configured to keep the model stress and the geometric shape of the main fracture unchanged, load detonation shock waves in the preset detonation area, convert the static boundary conditions into dynamic boundary conditions, simulate the propagation process of the detonation fracture network under dynamic conditions, end the dynamic simulation after reaching the preset simulation time, and output the fracture network spatial configuration of the deep oil and gas reservoir, that is, the expansion form of the fracture network.

[0043] Advantages of the present invention:

[0044] The present invention realizes the dynamic-static coupling simulation calculation of hydraulic-detonation fracturing under one calculation model, one set of grid cells, and one set of calculation frameworks (that is, taking advantage of the superiority of hydraulic fracturing in creating main fractures, promoting the formation of macroscopically wide and dominant seepage channels inside the reservoir through static water pressure; taking advantage of the superiority of detonation fracturing in creating complex small-scale complex fracture networks, forcing the rock to fragment around the main fracture through high-pressure dynamic detonation shock waves, and finally forming a high-permeability fracture network in which the main fracture and the complex branch fracture networks around the main fracture are connected in series). The whole process simulation of hydraulic-detonation combined fracturing reconstruction can be realized without additional technical means, improving the effect of fracturing reconstruction of deep-ultra-deep reservoirs, enhancing the calculation efficiency, and realizing the effective development of oil and gas resources in deep-ultra-deep reservoirs. Description of the drawings

[0045] By reading the detailed description of the non-limiting embodiments with reference to the following drawings, other features, purposes, and advantages of the present application will become more obvious.

[0046] Figure 1 is a schematic flow chart of the dynamic-static coupling simulation method for hydraulic-detonation combined fracturing reconstruction according to an embodiment of the present invention;

[0047] Figure 2 is a schematic diagram of the dynamic-static coupling numerical calculation model for hydraulic-detonation fracturing reconstruction of deep oil and gas reservoirs according to an embodiment of the present invention;

[0048] Figure 3 is a schematic diagram of the process of obtaining the angle of the actual propagation direction of the fracture in rock fracture under detonation load according to an embodiment of the present invention. Detailed implementation manners

[0049] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0050] The present application will be further described in detail below with reference to the accompanying drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the relevant invention and are not intended to limit the invention. Additionally, it should be noted that for ease of description, only parts related to the relevant invention are shown in the drawings.

[0051] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments may be combined with each other.

[0052] A dynamic-static coupling simulation method for hydraulic-detonation combined fracturing reconstruction in the first embodiment of the present invention is used to simulate the expansion process of the fracture network in deep oil and gas reservoirs under the combined action of hydraulic fracturing and detonation fracturing, and obtain the expansion form of the fracture network; as Figure 1 shown, the method includes:

[0053] According to the three-dimensional reconstruction method of deep oil and gas reservoirs, a target simulation area is selected; the target simulation area is divided into grids, and then a dynamic-static coupling numerical calculation model for hydraulic-detonation fracturing reconstruction is constructed; the three-dimensional reconstruction method includes segmented perforation and segmented fracturing reconstruction.

[0054] Combined with the dynamic-static coupling numerical calculation model for hydraulic-detonation fracturing reconstruction, through a discontinuous calculation method, the overall stress balance of grid cells under the initial in-situ stress conditions is completed, and the fluid injection rate is set to simulate the expansion process of the main hydraulic fracture under static conditions. After reaching the preset main fracture length, the static simulation ends;

[0055] Keeping the model stress and the geometry of the main fracture unchanged, detonation shock waves are loaded in the preset detonation area, and the static boundary conditions are transformed into dynamic boundary conditions to simulate the expansion process of the detonation fracture network under dynamic conditions. After reaching the preset simulation time, the dynamic simulation ends, and the fracture network spatial configuration of the deep oil and gas reservoir, that is, the expansion form of the fracture network, is output.

[0056] To more clearly illustrate the dynamic-static coupling simulation method for hydraulic-detonation combined fracturing reconstruction of the present invention, each step in an embodiment of the method of the present invention will be described in detail below with reference to the accompanying drawings.

[0057] The present invention provides a dynamic-static coupling discontinuous numerical simulation method, which can realize the whole-process simulation of hydraulic-detonation combined fracturing reconstruction without additional technical means, and is intended for the optimal design of reservoir reconstruction to promote the improvement of oil and gas recovery rate. The method includes the following steps:

[0058] According to the three-dimensional reconstruction method of deep oil and gas reservoirs, select the target simulation area; conduct mesh division on the target simulation area, and then construct a dynamic-static coupling numerical calculation model for hydraulic-detonation fracturing reconstruction; the three-dimensional reconstruction method includes staged perforation and staged fracturing reconstruction.

[0059] When using horizontal wells for fracturing reconstruction and development of deep oil and gas reservoirs, staged perforation and staged fracturing reconstruction are generally adopted to conduct three-dimensional reconstruction of the reservoir. From the perspective of the spatial geometric relationship between the horizontal well and the perforation, each perforation fracturing section can be considered similar, and its upper and lower parts can be considered symmetric.

[0060] In this embodiment, when conducting numerical simulation calculation on the reservoir reconstruction problem, select the unilateral area of a single perforation cluster for simulation. The specific simulation process is as follows:

[0061] First, determine the length L , width W of the target simulation area according to the fracturing reconstruction range in terms of the fracturing section spacing and length. Use quadrilateral meshes to conduct mesh division on the target calculation area, and the mesh size is dL ; then, define the left, right, and upper boundaries of the numerical calculation model as dynamic-static coupling boundaries, which can be dynamically and statically converted according to the type of calculation in the numerical calculation. The lower boundary is a geometric symmetry boundary; secondly, set the fluid injection point at the midpoint of the lower boundary of the model; after that, set the boundary stress (in-situ stress) of the model, the maximum principal stress σ 1 and the minimum principal stress σ 3; finally, generate a dynamic-static coupling numerical calculation model for hydraulic-detonation fracturing reconstruction of deep oil and gas reservoirs. Assume that the length of the dynamic-static coupling numerical calculation model for hydraulic-detonation fracturing reconstruction of deep oil and gas reservoirs is 100 m, the width is 200 m, and the mesh size is 4 m, then the generated dynamic-static coupling numerical calculation model for hydraulic-detonation fracturing reconstruction of deep oil and gas reservoirs is as Figure 2 shown.

[0062] Combined with the dynamic-static coupling numerical calculation model for hydraulic-detonation fracturing reconstruction, through the discontinuous calculation method, complete the overall stress balance of the grid elements under the initial in-situ stress conditions, and set the fluid injection rate to simulate the propagation process of the main hydraulic fracture under static conditions. After reaching the preset main fracture length, the static simulation ends;

[0063] Among them, the method for obtaining the overall stress balance is as follows: First, set the stress loads on the model boundary according to the in-situ stress conditions of the formation, that is, the minimum principal stress and the maximum principal stress, and apply them to the boundary conditions of the model. The model is used as an internal load added to the inside of the element. Second, adopt fixed boundary conditions and set the outer boundary of the model as fixed boundary conditions, where no displacement can occur. Then, form the overall stiffness matrix and the load matrix, solve to obtain the displacements of each element in the model under the initial stress load, and perform multiple iterations until the displacement converges, that is, the overall stress balance of the grid element is achieved. Clear the element displacements, use the stress as the initial condition, and save the results.

[0064] In this embodiment, based on the established dynamic and static coupling numerical calculation model for hydraulic-detonation fracturing transformation, combined with the discontinuous calculation framework (the discontinuous method is a numerical calculation method different from traditional continuous methods (such as finite element method, finite difference method, finite volume method, etc.). It can conveniently simulate the separation, slip, etc. between elements, realize the simulation of crack propagation, and can achieve seamless conversion between dynamic and static states), the numerical simulation calculation of the hydraulic fracturing crack propagation process under static conditions is realized. Specifically as follows:

[0065] In the present invention, it is assumed that the main hydraulic fracturing crack is a tensile crack, and its internal flow process satisfies:

[0066] (1)

[0067] Among them, q is the flow velocity along the crack direction, μ is the viscosity of the fluid, ω is the crack aperture, p is the pressure of the fluid in the crack, l is the length coordinate along the crack direction.

[0068] The crack critical discrimination adopts the maximum tensile stress criterion, that is, when the normal stress between elements at the crack tip reaches the tensile stress strength of the rock, the crack propagates:

[0069] (2)

[0070] Among them, σ n is the normal stress between elements at the crack tip, that is, the normal stress between elements, T 0 is the tensile stress strength of the rock.

[0071] For the dynamic and static coupling boundary conditions in the dynamic and static coupling numerical calculation model for deep hydrocarbon reservoir hydraulic-detonation fracturing transformation, they are transformed into fixed boundary conditions during the static calculation of hydraulic fracturing, that is,

[0072] (3)

[0073] wherein, u i represents the displacement at the nodes on the boundary, i represents the coordinates, and in the two-dimensional case i the number is 2.

[0074] Under the static condition of hydraulic fracturing, ignoring the effects of inertia and viscous damping, a linear solution equation set is established to obtain the static expansion form of the fracture network, that is, the geometric form of the main fractures. The linear solution equation set under the static condition of hydraulic fracturing is as follows:

[0075] KD=F (4)

[0076] wherein, K represents the stiffness matrix, which is the overall stiffness matrix here and is related to the elastic parameters of the rock, displacement boundary conditions, etc.; D represents the displacement vector to be solved; F represents the overall load vector borne by the element.

[0077] Keeping the model stress and the geometric form of the main fractures unchanged, detonation shock waves are loaded in the preset detonation area to convert the static boundary conditions into dynamic boundary conditions, and the expansion process of the detonation fracture network under dynamic conditions is simulated. After reaching the preset simulation time, the dynamic simulation ends, and the fracture network spatial configuration of the deep oil and gas reservoir is output, that is, the expansion form of the fracture network.

[0078] In this embodiment, based on the constructed dynamic-static coupling numerical calculation model of hydraulic-detonation fracturing transformation, the numerical simulation calculation of the expansion process of the detonation fracture network under dynamic conditions is realized based on the discontinuous calculation framework, specifically as follows:

[0079] Under high strain rate conditions, rock fracture is a high-speed fracture behavior within a short time and is correlated with time and strain rate. In this technical solution, under the discontinuous calculation framework, a strain rate-related Mohr-Coulomb strength criterion is additionally introduced to describe the fracture behavior of the rock, and the dynamic growth factor is defined:

[0080] (5)

[0081] wherein, DIF is the dynamic growth factor of the rock strength under high strain rate conditions; C n0 is the cohesive strength of the rock under static conditions and is obtained through shear tests; C nThe cohesive strength of rock under the loading condition of detonation shock wave can be obtained by conducting impact tests on rock specimens in uniaxial state through the split Hopkinson pressure bar test. Using the defined dynamic increase factor DIF, considering that the cohesive strength is enhanced under high strain rate and the friction angle remains basically unchanged, the Mohr-Coulomb criterion is modified.

[0082] (6)

[0083] Among them, σ τ is the tangential stress between elements, C n0 is the cohesive strength of rock under static condition, is the internal friction angle; σ n is the normal stress between elements. Using the above formula, a strength criterion considering strain rate correlation can be obtained, and only the cohesive force needs to be modified in the calculation program, which is convenient for calculation.

[0084] Based on the modified criterion of Mohr-Coulomb, the discrimination of rock fracture under detonation load can be realized. However, the crack propagation trajectory cannot be accurately discriminated. When using the discontinuous method to simulate the crack propagation under detonation load, it is necessary to divide the model into grid elements. The traditional method generally believes that cracks will occur as long as the fracture criterion is satisfied between elements. However, due to the inability to reflect the singularity of the stress at the crack tip, the simulation accuracy of the crack trajectory is not high.

[0085] The present invention proposes a high-precision discrimination method for the crack propagation trajectory under detonation load. First, a coordinate system is established at the crack tip element, and the circumferential stress σ θθ at the crack tip is obtained according to the element stress distribution. θ The distribution with the angle θ 0 satisfies:

[0086] (7)

[0087] (8)

[0088] According to the above formula, the actual crack propagation direction θ 0 can be determined, and the propagation path can be determined. Then, the elements at the crack tip are optimized and divided. According to θ the 0 direction, the elements on the propagation trajectory Ω are divided into two, becoming Ω 1 and Ω 2, so that the crack can pass through the element ( Figure 3 ). The above method avoids high-resolution grid meshing and can greatly improve the calculation accuracy and efficiency of the trajectories of a large number of crack propagations under detonation load.

[0089] For the dynamic-static coupling boundary conditions in the numerical calculation model of hydraulic-detonation fracturing for deep oil and gas reservoirs, they are transformed into transmission boundaries during the dynamic calculation of detonation fracturing to simulate the transmission phenomenon of shock waves at the boundaries and prevent shock wave reflection. When an element is located on the transmission boundary, its element stiffness matrix is modified as follows:

[0090] (9)

[0091] Wherein, ΔK i is the correction amount of the stiffness matrix of the element , p is the stiffness of the damper set at the transmission boundary, T i is the displacement transformation matrix of the discontinuous calculation method, F is the direction cosine matrix. The stiffness matrix of the corresponding element is corrected based on the correction amount of the stiffness matrix.

[0092] Under the condition of dynamic detonation shock waves, the influence of inertia and the transient process related to time must be considered, a linear solution equation set is formed and solved, and then the dynamic expansion form of the fracture network is obtained. The linear solution equation set under the condition of dynamic detonation shock waves is shown as follows:

[0093] (10)

[0094] Wherein, M represents the mass matrix of the element, μ is the damping matrix, is the acceleration vector, is the velocity vector, K represents the stiffness matrix, which is the stiffness matrix of the element here.

[0095] In summary, the present invention can achieve the dynamic and static coupling simulation calculation of hydraulic-detonation fracturing under the establishment of a calculation model, a set of grid units, and a set of calculation frameworks. That is, first, a numerical calculation model for the dynamic and static coupling of hydraulic-detonation fracturing transformation is constructed. Then, in a discontinuous calculation system, first, the overall stress balance of the grid units under the initial in-situ stress conditions is completed. Second, the fluid injection rate is set to simulate the propagation process of the main hydraulic fracture under static conditions. After reaching the preset main fracture length, the static simulation ends. After that, keeping the model stress, the geometric shape of the main fracture, etc. unchanged, detonation shock waves are loaded in the preset detonation area to convert the static boundary conditions into dynamic boundary conditions, and the time step is set to dt to simulate the detonation fracturing process. Finally, after reaching the preset simulation time, the simulation ends, and the spatial configuration of the fracture network is output, realizing the full-process simulation of the hydraulic-detonation combined fracturing transformation without additional technical means, facilitating the optimization design of fracturing parameters and the characterization of the fracture network morphology, thereby improving the reservoir transformation effect and oil and gas recovery rate.

[0096] A dynamic and static coupling simulation system for hydraulic-detonation combined fracturing transformation according to the second embodiment of the present invention is used to simulate the expansion process of the fracture network in deep oil and gas reservoirs under the combined action of hydraulic fracturing-detonation fracturing, and obtain the expansion morphology of the fracture network; as Figure 2 shown, the system includes:

[0097] A model construction module configured to select a target simulation area according to the three-dimensional transformation method of the deep oil and gas reservoir; perform network division on the target simulation area, and then construct a numerical calculation model for the dynamic and static coupling of hydraulic-detonation fracturing transformation; the three-dimensional transformation method includes staged perforation and staged fracturing transformation;

[0098] A static simulation module configured to combine the numerical calculation model for the dynamic and static coupling of hydraulic-detonation fracturing transformation, and complete the overall stress balance of the grid units under the initial in-situ stress conditions through a discontinuous calculation method, and set the fluid injection rate to simulate the propagation process of the main hydraulic fracture under static conditions. After reaching the preset main fracture length, the static simulation ends;

[0099] A dynamic simulation module configured to keep the model stress and the geometric shape of the main fracture unchanged, load detonation shock waves in the preset detonation area, convert the static boundary conditions into dynamic boundary conditions, and simulate the expansion process of the detonation fracture network under dynamic conditions. After reaching the preset simulation time, the dynamic simulation ends, and the spatial configuration of the fracture network of the deep oil and gas reservoir is output, that is, the expansion morphology of the fracture network.

[0100] It should be noted that the dynamic-static coupling simulation system for hydraulic-detonation combined fracturing transformation provided in the above embodiments is only illustrated by dividing the above functional modules. In actual applications, the above functions can be allocated to different functional modules according to needs, that is, the modules or steps in the embodiments of the present invention can be further decomposed or combined. For example, the modules in the above embodiments can be combined into one module or further split into multiple sub-modules to complete all or part of the functions described above. The names of the modules and steps involved in the embodiments of the present invention are only used to distinguish each module or step and are not regarded as an improper limitation of the present invention.

[0101] An electronic device according to a third embodiment of the present invention includes: at least one processor; and a memory communicatively connected to at least one of the processors; wherein the memory stores instructions executable by the processor, and the instructions are used to be executed by the processor to implement the above-mentioned dynamic-static coupling simulation method for hydraulic-detonation combined fracturing transformation.

[0102] A computer-readable storage medium according to a fourth embodiment of the present invention stores computer instructions, and the computer instructions are used to be executed by a computer to implement the above-mentioned dynamic-static coupling simulation method for hydraulic-detonation combined fracturing transformation.

[0103] Those skilled in the art can clearly understand that for the convenience and brevity of description, the specific working processes and related descriptions of the above-described electronic device and computer-readable storage medium can refer to the corresponding processes in the foregoing method examples and will not be repeated here.

[0104] Those skilled in the art should be able to realize that the modules and method steps of each example described in combination with the embodiments disclosed herein can be implemented by electronic hardware, computer software, or a combination of the two. The programs corresponding to the software modules and method steps can be placed in a random access memory (RAM), memory, read-only memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disk, removable disk, CD-ROM, or any other form of storage medium well-known in the art. To clearly illustrate the interchangeability of electronic hardware and software, the composition and steps of each example have been generally described according to functions in the above description. Whether these functions are executed in the form of electronic hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered to exceed the scope of the present invention.

[0105] Terms such as "first" and "second" are used to distinguish similar objects rather than to describe or represent a specific order or sequence.

[0106] The term "comprising" or any other similar term is intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus / device that comprises a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to those processes, methods, articles, or apparatus / devices.

[0107] So far, the technical solution of the present invention has been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it is easy for those skilled in the art to understand that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will fall within the protection scope of the present invention.

Claims

1. A dynamic and static coupling simulation method for hydraulic-detonation combined fracturing reconstruction, used to simulate the expansion process of the fracture network of deep oil and gas reservoirs under the combined action of hydraulic fracturing-detonation fracturing, and obtain the expansion form of the fracture network; characterized in that, The method includes: According to the three-dimensional transformation method of deep oil and gas reservoirs, a target simulation area is selected; the target simulation area is network-divided, and then a dynamic-static coupling numerical calculation model of hydraulic-detonation fracturing transformation is constructed; the three-dimensional transformation method includes segmented perforation and segmented fracturing transformation; Combined with the dynamic-static coupling numerical calculation model of hydraulic-detonation fracturing, the overall stress balance of the grid unit under the initial ground stress condition is completed through a discontinuous calculation method, and the fluid injection rate is set to simulate the expansion process of the main hydraulic fracturing crack under static conditions. After the preset main crack length is reached, the static simulation ends; Keeping the model stress and the main fracture geometry unchanged, loading the detonation shock wave in the preset detonation area, converting the static boundary conditions into dynamic boundary conditions, simulating the expansion process of the detonation fracture network under dynamic conditions, and ending the dynamic simulation after reaching the preset simulation time, outputting the fracture network spatial configuration of the deep oil and gas reservoir, that is, the expansion form of the fracture network; The simulation calculation method for the expansion process of the detonation pressure crack network under dynamic conditions is: According to the Mohr-Coulomb strength criterion, based on the cohesive strength of rock under static conditions and the cohesive strength of rock under detonation shock wave loading conditions, the dynamic growth factor of rock strength under high strain rate conditions is calculated; According to the changes of cohesion strength and friction angle under high strain rate, combined with the dynamic growth factor of rock strength under the high strain rate condition and the normal stress between units, the tangential stress between units is calculated; The conditions of the dynamic-static coupling boundary are converted into the transmission boundary, the transmission phenomenon of the shock wave at the boundary is simulated, and the stiffness matrix correction of the unit on the transmission boundary is obtained; The stiffness matrix of the corresponding unit is corrected based on the stiffness matrix correction amount; combining the stiffness matrix of the corrected unit, the load on the unit boundary and inside, and the tangential stress between the units, a linear solution equation group under dynamic detonation shock wave conditions is constructed, and then the dynamic expansion form of the fracture network is solved.

2. The dynamic-static coupling simulation method of hydraulic-detonation combined fracturing reconstruction according to claim 1 is characterized in that: The dynamic and static coupling numerical calculation model of hydraulic-detonation fracturing transformation is constructed by: According to the three-dimensional transformation method of the deep oil and gas reservoir, a single side area of ​​a single perforation cluster of the deep oil and gas reservoir is selected as a target simulation area; According to the fracturing reconstruction range in terms of the fracturing stage spacing and length, the length and width of the target simulation area are determined, and then the target simulation area is gridded; Combined with the target simulation area after grid division, the dynamic-static coupling boundary and the geometric symmetry boundary are defined, the fluid injection point position, boundary stress, maximum principal stress and minimum principal stress are set, and finally, the dynamic-static coupling numerical calculation model of hydraulic-detonation fracturing transformation is generated; wherein, the fluid injection point position is set at the midpoint of the geometric symmetry boundary.

3. The dynamic-static coupling simulation method of hydraulic-detonation combined fracturing reconstruction according to claim 2 is characterized in that: Define dynamic-static coupling boundaries and geometric symmetry boundaries as follows: The left boundary, the right boundary and the upper boundary of the numerical calculation model are defined as dynamic-static coupling boundaries, and the lower boundary is a geometric symmetry boundary; the dynamic-static coupling boundaries are converted into dynamic-static according to the calculation type during the numerical calculation process.

4. The dynamic-static coupling simulation method of hydraulic-detonation combined fracturing reconstruction according to claim 3 is characterized in that: The numerical simulation calculation method for the expansion process of the main fracture of hydraulic fracturing under static conditions is: If the main hydraulic fracturing crack is a tensile crack, the flow velocity along the crack direction is calculated based on the viscosity of the fluid, the opening of the crack, the pressure of the fluid in the crack, and the length coordinate along the crack direction; The maximum tensile stress criterion is used to determine the crack criticality and obtain the normal stress between units, that is, the normal stress between units at the crack tip; Convert the dynamic-static coupling boundary conditions into fixed boundary conditions to obtain the displacements of the nodes on the boundary; The fluid pressure is calculated based on the flow velocity along the fracture direction; a linear solution equation group under the static condition of hydraulic fracturing is constructed by combining the fluid pressure, the normal stress between the units at the fracture tip, and the displacement at the node on the boundary. KD= F , the static expansion form of the hydraulic fracture network, i.e. the main fracture geometry, is obtained by solving ; K represents the stiffness matrix, D represents the displacement vector to be determined, F Represents the overall load vector acting on the element.

5. The method for dynamic-static coupling simulation of hydraulic-detonation combined fracturing reconstruction according to claim 4 is characterized in that: The tangential stress between elements is calculated as follows: ； ； in, σ τ is the tangential stress between units, DIF is the dynamic growth factor of rock strength under high strain rate conditions, C n0 is the cohesive strength of rock under static conditions, obtained through shear test, C n The cohesive strength of rock under detonation shock wave loading conditions is obtained by impact testing rock specimens in uniaxial state using a split Hopkinson pressure bar test. is the internal friction angle, σ n is the normal stress between elements.

6. The method for dynamic-static coupling simulation of hydraulic-detonation combined fracturing reconstruction according to claim 5, characterized in that: The actual extension direction angle of the cracks in rock fracture under detonation load is obtained as follows: ； ； in, represents the hoop stress at the crack tip, The angle that indicates the actual crack expansion direction, Indicates an angle.

7. The method for dynamic-static coupling simulation of hydraulic-detonation combined fracturing reconstruction according to claim 5, characterized in that: The stiffness matrix correction of the unit on the transmission boundary is calculated as follows: ； in, ΔK i For unit The stiffness matrix correction of p is the stiffness of the damper set at the transmission boundary, T i is the displacement transformation matrix of the discontinuous calculation method, F is the direction cosine matrix.

8. The method for dynamic-static coupling simulation of hydraulic-detonation combined fracturing reconstruction according to claim 7, characterized in that: The linear solution equation group under the dynamic detonation shock wave condition is: ； in, M represents the mass matrix of the element, μ is the damping matrix, is the acceleration vector, is the velocity vector.

9. A dynamic and static coupling simulation system for hydraulic-detonation combined fracturing reformation, used to simulate the expansion process of the fracture network of deep oil and gas reservoirs under the combined action of hydraulic fracturing-detonation fracturing, and obtain the expansion form of the fracture network; characterized in that, The system includes: The model building module is configured to select a target simulation area according to a three-dimensional transformation method of a deep oil and gas reservoir; divide the target simulation area into a network, and then build a dynamic and static coupling numerical calculation model of hydraulic-detonation fracturing transformation; the three-dimensional transformation method includes segmented perforation and segmented fracturing transformation; The static simulation module is configured to combine the dynamic-static coupling numerical calculation model of hydraulic-detonation fracturing transformation, complete the overall stress balance of the grid unit under the initial ground stress condition through a discontinuous calculation method, and set the fluid injection rate to simulate the expansion process of the main hydraulic fracturing crack under static conditions. After reaching the preset main crack length, the static simulation ends; A dynamic simulation module is configured to keep the model stress and the main fracture geometry unchanged, load the detonation shock wave in the preset detonation area, convert the static boundary conditions into dynamic boundary conditions, simulate the expansion process of the detonation fracture network under dynamic conditions, and after reaching the preset simulation time, the dynamic simulation ends and outputs the fracture network spatial configuration of the deep oil and gas reservoir, that is, the expansion form of the fracture network; The simulation calculation method for the expansion process of the detonation pressure crack network under dynamic conditions is: According to the Mohr-Coulomb strength criterion, based on the cohesive strength of rock under static conditions and the cohesive strength of rock under detonation shock wave loading conditions, the dynamic growth factor of rock strength under high strain rate conditions is calculated; According to the changes of cohesion strength and friction angle under high strain rate, combined with the dynamic growth factor of rock strength under the high strain rate condition and the normal stress between units, the tangential stress between units is calculated; The conditions of the dynamic-static coupling boundary are converted into the transmission boundary, the transmission phenomenon of the shock wave at the boundary is simulated, and the stiffness matrix correction of the unit on the transmission boundary is obtained; The stiffness matrix of the corresponding unit is corrected based on the stiffness matrix correction amount; combining the stiffness matrix of the corrected unit, the load on the unit boundary and inside, and the tangential stress between the units, a linear solution equation group under dynamic detonation shock wave conditions is constructed, and then the dynamic expansion form of the fracture network is solved.

Images