Shale reservoir multi-scale fracture prediction method

Abstract

The invention provides a shale reservoir multi-scale fracture prediction method, and belongs to the field of shale oil and gas geology, and the method comprises the steps: obtaining the development characteristics of different-scale fractures of a target stratum and the basic rock mechanical parameters of a sample rock under different temperature and pressure conditions; determining a stress evolution threshold value of crack growth in the sample rock through a discrete element numerical simulation technology; establishing a temperature and pressure damage constitutive model of the sample rock based on the basic rock mechanical parameters; based on the temperature and pressure damage constitutive model, a fine geomechanical model is established in combination with fracture development characteristics; according to the stress evolution threshold values corresponding to the fractures of different scales under the fine geomechanical model, the strain coefficient of the rock in the target stratum is determined, the fracture prediction model of the target stratum is constructed according to the strain coefficient, and then the fracture prediction result of the target stratum is obtained. Therefore, complex geological conditions in the target stratum are fully considered, the effect of the temperature on the rock in the target stratum is increased, and the accuracy and reliability of crack prediction are improved.

Description

Technical Field

[0001] The present invention belongs to the field of shale oil and gas geology, and particularly relates to a multi-scale fracture prediction method for shale reservoirs. Background Art

[0002] The accurate prediction of reservoir fractures is crucial for the analysis of oil and gas migration, the design of wellbore trajectories, the optimization of fracturing schemes, etc. At present, shallow shale resources have been effectively developed, and the focus of exploration and development is gradually shifting to deeper layers.

[0003] With the increase of burial depth, the formation conditions become more complex, and more factors need to be considered for the prediction of reservoir fractures. The current research on reservoir fracture evaluation and prediction mainly focuses on two aspects: the first is to carry out prediction work based on seismic wave characteristics and kinematic characteristics, but it has strong multi-solution problems, the resolution and continuation ability of each prediction method are limited, and it can only predict the current stress field and cannot predict the fracture distribution of the paleo-stress field; the second aspect is to predict fractures based on numerical simulation of tectonic stress fields. This method mainly inversely predicts the current stress state by comprehensively using geological models, mechanical models, and mathematical models to invert the multi-stage paleo-tectonic stress fields, and finally determines the specific fracture development situation based on the fracture criterion. However, the existing technologies in the above two aspects do not consider the influence of high temperature on fracture formation, resulting in inaccurate prediction results of deep shale reservoir fractures.

[0004] Therefore, in the prior art, the influence of temperature on shale reservoirs has not been considered in the work of fracture prediction, resulting in large errors in the prediction of reservoir fractures. Summary of the Invention

[0005] In order to solve the problem of inaccurate prediction results of shale reservoir fractures caused by the action of temperature, the present invention provides a multi-scale fracture prediction method, device, equipment, and medium for shale reservoirs.

[0006] To achieve the above object, the present invention provides the following technical solutions: First, a multi-scale fracture prediction method for shale reservoirs is provided. The method includes: Obtaining the development characteristics of fractures of different scales in the target formation and the basic rock mechanical parameters of sample rocks under different temperature and pressure conditions; Determining the stress evolution threshold for fracture growth in sample rocks through discrete element numerical simulation technology; Based on the basic rock mechanical parameters, establishing a temperature-pressure damage constitutive model of sample rocks under the simultaneous action of temperature and pressure; Based on the temperature-pressure damage constitutive model, establishing a fine geomechanical model in combination with fracture development characteristics; Determine the strain coefficient of the rock in the target formation through the stress evolution thresholds corresponding to fractures of different scales under the refined geomechanical model, construct a fracture prediction model for the target formation through the strain coefficient, and obtain the fracture prediction result of the target formation through the fracture prediction model.

[0007] Optionally, the temperature-pressure damage constitutive model is: ; Where: is the elastic modulus of the rock at room temperature; is the elastic modulus of the rock at different real-time temperatures; is the total thermo-mechanical coupling damage variable; is the peak strain, is the peak stress, is the elastic modulus, is the Poisson's ratio; is the circumferential stress, is the axial strain, and m is the Weibull statistical distribution parameter.

[0008] Optionally, establishing a refined geomechanical model based on the temperature-pressure damage constitutive model and combining the fracture development characteristics includes: Establish a structural model of the target formation by integrating seismic, drilling, logging, and stratification conditions of the target formation; Restore the formation conditions according to the structural model and the temperature-pressure damage constitutive model, and establish a refined geomechanical model of the target formation by integrating rock mechanics, fracture development characteristics, and fracture distribution information.

[0009] Optionally, determining the stress evolution threshold for fracture growth in sample rock through the discrete element numerical simulation technology includes: Divide the fractures by scale to obtain fractures of different scales; Simulate the states of fractures of different scales in the sample rock at different pressurization stages through the discrete element numerical simulation technology to determine the stress evolution threshold for fracture growth.

[0010] Optionally, the calculation formula of the fracture prediction model is: ; Where, is the volumetric density of fractures in the representative elementary volume; J is the energy required to generate a unit area of fractures, i.e., the fracture surface energy; is the total strain energy density; is the elastic strain energy density that must be overcome to generate fractures; is the strain energy density of the newly added fracture surface area; is the surface area of the newly added fracture; a and b are strain coefficients; the calculation formula of the total strain energy density is: Among them, is the total strain energy density; E is the elastic modulus; is the Poisson's ratio; , , are the maximum principal stress, the intermediate principal stress, and the minimum principal stress, respectively.

[0011] Secondly, a multi-scale fracture prediction device for shale reservoirs is provided. The device includes: An acquisition module for acquiring the development characteristics of fractures at different scales in the target formation and the basic rock mechanics parameters of sample rocks under different temperature and pressure conditions; A determination module for determining the stress evolution threshold of fracture growth in the sample rock by using the discrete element numerical simulation technique; A construction module for establishing a temperature-pressure damage constitutive model of the sample rock under the simultaneous action of temperature and pressure based on the basic rock mechanics parameters; and establishing a fine geomechanics model by combining the fracture development characteristics based on the temperature-pressure damage constitutive model; A prediction module for determining the strain coefficient of the rock in the target formation through the stress evolution threshold corresponding to fractures at different scales under the fine geomechanics model, constructing a fracture prediction model of the target formation through the strain coefficient, and obtaining the fracture prediction result of the target formation through the fracture prediction model.

[0012] In addition, a computer-readable storage medium is provided. The storage medium stores a computer program, and when the computer program is executed by a processor, the above-mentioned multi-scale fracture prediction method for shale reservoirs is implemented.

[0013] Finally, a computer device is provided, including a memory, a processor, and a computer program stored on the memory and executable on the processor. When the processor executes the program, the above-mentioned multi-scale fracture prediction method for shale reservoirs is implemented.

[0014] The multi-scale fracture prediction method for shale reservoirs provided by the present invention has the following beneficial effects: Using the above method, first, the fracture data of the area to be predicted was collected, and the basic rock mechanical parameters of the sample rock under different conditions were obtained, providing a basis for subsequent modeling. Secondly, the stress evolution threshold for fracture growth was determined through numerical simulation, and the strain coefficient of the rock in the target formation was obtained based on the stress evolution thresholds corresponding to fractures of different scales, providing key parameters for constructing the fracture prediction model. Then, by constructing a temperature-pressure damage constitutive model, the influence mechanism of temperature and pressure on rock damage was clarified, providing theoretical support for simulating and predicting the behavior of rocks in complex environments. Based on the temperature-pressure damage constitutive model, a refined geomechanical model was established by combining rock mechanics and fracture development characteristics, comprehensively considering the mechanical properties of the rock, fracture development characteristics, and the influence of temperature and pressure, and being able to more accurately describe the mechanical behavior and deformation process of the rock, providing a powerful tool for subsequent fracture prediction and formation stability analysis. Finally, a fracture prediction model for the target formation was constructed through the strain coefficient, fully considering the complex geological conditions in the target formation, increasing the effect of temperature on the rock in the target formation, and being beneficial to improving the accuracy and reliability of fracture prediction. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the embodiments of the present invention and their design schemes, the accompanying drawings required for the embodiments will be briefly introduced below. The accompanying drawings in the following description are only partial embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0016] Figure 1 It is a schematic flow chart of a multi-scale fracture prediction method for shale reservoirs according to an exemplary embodiment of the present invention.

[0017] Figure 2 It is a schematic flow chart of another multi-scale fracture prediction method for shale reservoirs according to an exemplary embodiment of the present invention.

[0018] Figure 3 It is a schematic diagram of a particle cluster according to an exemplary embodiment of the present invention.

[0019] Figure 4 It is a schematic diagram of the number of fractures at different stages of fractures of different scales according to an exemplary embodiment of the present invention.

[0020] Figure 5 It is a stress nephogram according to an exemplary embodiment of the present invention; wherein, a is the distribution range of the maximum principal stress, b is the distribution range of the intermediate principal stress, and c is the distribution range of the minimum principal stress.

[0021] Figure 6 It is a block diagram of a multi-scale fracture prediction device for shale reservoirs according to an exemplary embodiment of the present invention. Detailed implementation manners

[0022] In order to enable those skilled in the art to better understand the technical solution of the present invention and be able to implement it, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0023] In order to solve the above problems, the present invention provides a multi-scale fracture prediction method for shale reservoirs considering temperature effects, as Figure 1 shown, including the following steps: 1) Analyze and statistically analyze the development characteristics of shale fractures at different scales in the study area by means of outcrop observation, downhole core observation, imaging logging, microscopic thin section analysis, scanning electron microscopy, etc.; 2) Conduct real-time high-temperature triaxial rock mechanics experiments to analyze the influence of real-time high-temperature conditions on rock mechanical properties and its internal mechanism; 3) Establish a thermal-mechanical coupling numerical model to explore the fracture formation law at different loading stages and conduct quantitative evaluation; 4) Based on the Weibull distribution and damage mechanics theory, establish a damage model of rock under the coupling action of temperature and pressure; 5) Use the established temperature-pressure damage constitutive model to restore the formation conditions of tectonic movements, and establish a fine geological mechanics model of the study area by integrating one-dimensional geological mechanics information of single wells, rock mechanics and fracture distribution information, etc.; 6) With the help of discrete element technology, determine the development thresholds of fractures at different scales according to the dynamic evolution law of fracture formation under in-situ conditions (stress and temperature); 7) Combine the stress threshold with the energy evolution during the rock pressurization process to establish the relationship between stress, strain and fracture density of underground rock mass under complex stress conditions, and complete the prediction of fractures at different scales in the work area. The present invention can more accurately predict the distribution law of multi-scale fractures in deep shale gas reservoirs in wells, and provide a basis for well placement, well trajectory design and fracturing scheme optimization, etc.

[0024] The technical solutions provided by the embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0025] First, the present invention provides a multi-scale fracture prediction method for shale reservoirs, specifically as Figure 2 shown, including the following steps: S201. Obtain the development characteristics of fractures at different scales in the target formation and the basic rock mechanical parameters of sample rocks under different temperature and pressure conditions.

[0026] In this step, the development characteristics of shale fractures at different scales in the study area can be observed and statistically analyzed by means of outcrop observation, downhole core observation, imaging logging, microscopic thin section analysis, scanning electron microscopy, etc.

[0027] Specifically, the development characteristics of shale fractures at different scales in the study area can be observed and statistically analyzed by means of outcrop observation, downhole core observation, imaging logging, microscopic thin section analysis, scanning electron microscopy, etc. Then, real-time high-temperature triaxial rock mechanics experiments are carried out. During the experiment, an ultrasonic system and a strain observation system are used to record the acoustic wave changes and deformation characteristics during the failure process, and to analyze the influence of real-time high-temperature conditions on the mechanical properties of rocks and its internal mechanism.

[0028] Exemplarily, fracture information at different scales in the study work area can be collected, including outcrop scale, core scale (core observation and imaging logging interpretation), and microscopic scale (including scanning electron microscopy and microscopic thin sections, etc.), to achieve the characterization of fractures at different scales, including attitude information, filling degree, fracture density and other information. The main controlling factors for fracture development can be obtained through the analysis of fracture development information. Then, for the target horizon samples taken on-site, standard plug samples (25 mm in diameter and 50 mm in height) are made. According to the temperature and pressure ranges experienced during the paleotectonic movement period in the work area, the experimental conditions are set, and real-time high-temperature triaxial rock mechanics experiments are carried out. During the experiment, an ultrasonic system and a strain observation system are used to record the acoustic wave changes and deformation characteristics during the failure process, and to analyze the influence of real-time high-temperature conditions on the mechanical properties of rocks and its internal mechanism. Through this experiment, basic rock mechanical parameters such as the compressive strength, elastic modulus, and Poisson's ratio of rocks under different temperature and pressure conditions can be obtained.

[0029] S202. Determine the stress evolution threshold for crack growth in the sample rock through discrete element numerical simulation technology.

[0030] In this step, the fractures can be classified by scale to obtain fractures at different scales. Based on discrete element numerical simulation technology, numerical simulation of the sample rock is carried out to obtain the states of fractures at different scales in the sample rock at different pressurization stages; then, through the states of fractures at different scales in different pressurization stages, the stress evolution threshold for crack growth in the sample rock is determined.

[0031] Specifically, a two-dimensional particle flow code is used to establish a thermo-mechanical coupling model based on a smooth joint model and a thermal contact model, to carry out simulation studies on the change in the number of cracks and the crack evolution process of shale specimens at different temperatures, to explore the law of crack formation at different loading stages and to conduct quantitative evaluation.

[0032] Exemplarily, first, rock mineral component determination and QEMSCAN mineral composition analysis are carried out for the sample rock. Based on the determination results, a thermo-mechanical coupling model based on a smooth joint model and a thermal contact model is established in combination with a two-dimensional particle flow code. Secondly, the same temperature and pressure conditions as those in the physical experiment are applied to the established numerical specimen to study the microscopic mechanism under the macroscopic rock fracture appearance, mainly referring to the analysis of information such as the number, attitude, and scale of cracks in the numerical specimen at different loading stages.

[0033] For example, with the help of discrete element numerical simulation technology, the development thresholds of fractures at different scales can be determined according to the dynamic evolution law of fracture formation under in-situ conditions (simulated target formation conditions). Since there are scale differences between fractures formed by the breakage of force bonds (abbreviated as "grain fractures") and core macroscopic fractures (abbreviated as "core fractures"), for the convenience of further analysis, the concept of "grain cluster" is introduced here, that is, the area where grain fractures are formed and connected to each other is regarded as the same cluster of grains (core fractures). The specific "grain cluster" is as follows Figure 3 shown. At the same time, the actual fracture is equivalent to an ellipse, the major axis of the ellipse is equivalent to the fracture length L, and the minor axis is equivalent to the fracture aperture W. According to the fracture length L, the fractures at the grain cluster scale can be classified. Among them, micro-fractures L < 2 mm, small-scale fractures 2 mm < L < 5 mm, medium-scale fractures 5 mm < L < 10 mm, and large-scale fractures L > 10 mm. By statistically analyzing the growth of fractures at different scales in different stages of rock pressurization, the stress evolution thresholds for the growth of fractures at different scales can be obtained. It can be seen from Figure 4 that fractures mainly develop after 0.85 and macroscopic fractures are formed at the peak strength. Therefore, 0.85 and can be defined as the evolution thresholds for the growth of micro-fractures and the formation of macroscopic fractures respectively, where is the peak stress.

[0034] Furthermore, the mechanical behavior of sample rocks under different temperature and pressure conditions can also be simulated by discrete element numerical simulation, and the simulation results can be compared with the experimental results to verify the accuracy and reliability of the discrete element numerical simulation results.

[0035] S203. Based on these basic rock mechanics parameters, a temperature-pressure damage constitutive model of sample rocks under the simultaneous action of temperature and pressure is established.

[0036] In this step, considering the interaction between temperature and load, then the model parameter m is determined according to the peak point method, and a temperature-pressure damage constitutive model of sample rocks under the combined action of rock temperature and pressure is established.

[0037] Provide a data basis for the establishment of a three-dimensional fine geomechanics model.

[0038] Among them, the temperature-pressure damage constitutive model is: ; where: is the elastic modulus of the rock at normal temperature; is the elastic modulus of the rock at different real-time temperatures; is the total thermo-mechanical coupling damage variable; is the peak strain, is the peak stress, is the elastic modulus, is the Poisson's ratio; is the circumferential stress, is the axial strain, and m is the Weibull statistical distribution parameter.

[0039] S204. Based on this temperature-pressure damage constitutive model, a fine geomechanical model is established by combining the fracture development characteristics.

[0040] In this step, based on this temperature-pressure damage constitutive model, a fine geomechanical model is established by combining the relevant theoretical knowledge of rock mechanics and the fracture development characteristics. Specifically, a structural model of the target formation can be established based on the well-seismic fusion technology method, integrating the basic information such as seismic, drilling, logging, and stratification; then, according to this structural model and the temperature-pressure damage constitutive model, the formation conditions are restored, and simulations are carried out by integrating one-dimensional geomechanical information of single wells, rock mechanics, and fracture distribution information, etc., to establish a fine geomechanical model. In addition, as Figure 5 shown, the geomechanical results show that the maximum principal stress in the study area is concentrated between 107 - 125 MPa, the minimum principal stress is concentrated between 49.5 - 98.0 MPa, and the intermediate principal stress is distributed between 64.7 - 104 MPa.

[0041] S205. Based on this fine geomechanical model, the strain coefficient of the rock in the target formation is determined, and then the fracture prediction result is obtained according to the strain coefficient.

[0042] Specifically, the stress evolution thresholds corresponding to fractures of different scales under this fine geomechanical model are determined to obtain the strain coefficient of the rock in the target formation. A fracture prediction model of the target formation is constructed through this strain coefficient, and the fracture prediction result of the target formation is obtained through this fracture prediction model.

[0043] In this step, through a fine geomechanical model that comprehensively considers the temperature effect, the energy evolution of the rock during the pressurization process is analyzed, and the strain coefficient can be obtained, thereby establishing a fracture volume density calculation model of different scales and predicting the distribution characteristics of fractures of different scales in the work area.

[0044] Here, based on the energy evolution of the rock during the pressurization process, the relationship between stress, strain, and the fracture density of the underground rock mass under complex stress states is established. A parallelepiped unit with side lengths L 1 、L 2 、L 3 is selected. It is stipulated that compression is positive and tension is negative, and . Then, this hexahedron unit will generate fractures under the action of stress, and the normal of the fracture plane is located in the - principal plane, and the main direction of the fracture makes an angle of with the maximum principal stress. is the angle of internal friction.

[0045] The calculation formula for the elastic strain energy density is as follows: ; In the formula: is the total strain energy density, J / m 3 ; E is the elastic modulus, Pa; is the Poisson's ratio; , , are the maximum principal stress, intermediate principal stress, and minimum principal stress, respectively, Pa.

[0046] Then the calculation formula for the crack volume density is: ; In the formula: is the volume density of cracks in the representative elementary volume, m 2 / m 3 ; J is the energy required to generate cracks per unit area, that is, the crack surface energy, J / m 2 ; is the total strain energy density, J / m 3 ; is the elastic strain energy density that must be overcome to generate cracks, J / m 3 ; is the strain energy density of the newly added crack surface area, J / m 3 ; is the surface area of the newly added crack, m 2 ; a and b are strain coefficients.

[0047] Using the above method, first, the crack data of the area to be predicted were collected, and the basic rock mechanical parameters of the sample rocks under different conditions were obtained, providing a basis for subsequent modeling. Second, the stress evolution threshold for crack growth was determined through numerical simulation, and the strain coefficients of the rocks in the target formation were obtained based on the stress evolution thresholds corresponding to cracks of different scales, providing key parameters for constructing the crack prediction model. Then, by constructing a temperature-pressure damage constitutive model, the influence mechanism of temperature and pressure on rock damage was clarified, providing theoretical support for simulating and predicting the behavior of rocks in complex environments. Based on the temperature-pressure damage constitutive model, a fine geomechanics model was established by combining rock mechanics and crack development characteristics, comprehensively considering the mechanical properties of rocks, crack development characteristics, and the influence of temperature and pressure, which can more accurately describe the mechanical behavior and deformation process of rocks, providing a powerful tool for subsequent crack prediction and formation stability analysis. Finally, a crack prediction model for the target formation was constructed through strain coefficients, fully considering the complex geological conditions in the target formation, increasing the effect of temperature on rocks in the target formation, and being conducive to improving the accuracy and reliability of crack prediction.

[0048] Secondly, the present invention also provides a multi-scale fracture prediction device for shale reservoirs, as Figure 6 shown, including: An acquisition module 601, configured to acquire the development characteristics of fractures of different scales in the target formation and the basic rock mechanical parameters of the sample rock under different temperature and pressure conditions.

[0049] A determination module 602, configured to determine the stress evolution threshold for fracture growth in the sample rock through discrete element numerical simulation technology.

[0050] A construction module 603, configured to establish a temperature-pressure damage constitutive model of the sample rock under the simultaneous action of temperature and pressure based on the basic rock mechanical parameters; and establish a fine geomechanical model in combination with the fracture development characteristics based on the temperature-pressure damage constitutive model.

[0051] A prediction module 604, configured to determine the strain coefficient of the rock in the target formation through the stress evolution thresholds corresponding to fractures of different scales under the fine geomechanical model, construct a fracture prediction model for the target formation through the strain coefficient, and obtain the fracture prediction result of the target formation through the fracture prediction model.

[0052] Using the above device, first, the fracture data of the area to be predicted is collected, and the basic rock mechanical parameters of the sample rock under different conditions are obtained, providing a basis for subsequent modeling. Secondly, the stress evolution threshold for fracture growth is determined through numerical simulation, and the strain coefficient of the rock in the target formation is obtained according to the stress evolution thresholds corresponding to fractures of different scales, providing key parameters for constructing the fracture prediction model. Then, by establishing a temperature-pressure damage constitutive model, the influence mechanism of temperature and pressure on rock damage is clarified, providing theoretical support for simulating and predicting the behavior of rocks in complex environments. Based on the temperature-pressure damage constitutive model, a fine geomechanical model is established in combination with rock mechanics and fracture development characteristics, comprehensively considering the mechanical properties of rocks, fracture development characteristics, and the influence of temperature and pressure, and can more accurately describe the mechanical behavior and deformation process of rocks, providing a powerful tool for subsequent fracture prediction and formation stability analysis. Finally, a fracture prediction model for the target formation is constructed through the strain coefficient, fully considering the complex geological conditions in the target formation, increasing the effect of temperature on rocks in the target formation, and being conducive to improving the accuracy and reliability of fracture prediction.

[0053] The present invention also provides a computer-readable storage medium storing a computer program, and the computer program can be used to execute the steps of Figure 1 a multi-scale fracture prediction method for shale reservoirs provided above.

[0054] The present invention also provides a computer device. At the hardware level, the computer device includes a processor, an internal bus, a network interface, a memory, and a non-volatile memory. Of course, it may also include other hardware required for other services. The processor reads the corresponding computer program from the non-volatile memory into the memory and then runs it to implement the above Figure 1 steps of a multi-scale fracture prediction method for shale reservoirs provided.

[0055] Those skilled in the art should understand that the embodiments of the present invention can be provided as a method, a system, or a computer program product. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present invention can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk memory, CD-ROM, optical memory, etc.) containing computer-usable program code.

[0056] The present invention is described with reference to the flowcharts and / or block diagrams of methods, apparatuses (systems), and computer program products according to embodiments of the present invention. It should be understood that each flow and / or block in the flowcharts and / or block diagrams can be implemented by computer program instructions, and the combination of the flows and / or blocks in the flowcharts and / or block diagrams can also be implemented. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing devices generate a device for implementing the functions specified in Figure 1 one or more flows and / or blocks Figure 1 one or more blocks.

[0057] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer-readable memory generate a manufactured article including an instruction device, and the instruction device implements the functions specified in Figure 1 one or more flows and / or blocks Figure 1 one or more blocks.

[0058] These computer program instructions can also be loaded onto a computer or other programmable data processing device, so that a series of operation steps are executed on the computer or other programmable device to generate a computer-implemented process, and thus the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in Figure 1 one or more flows and / or blocks Figure 1 one or more blocks.

[0059] It should be noted that the above-described specific embodiments can enable those skilled in the art to more comprehensively understand the present invention-creation, but do not limit the present invention-creation in any way. Therefore, although this specification has described the present invention-creation in detail, those skilled in the art should understand that modifications or equivalent replacements can still be made to the present invention-creation; and all technical solutions and improvements that do not depart from the spirit and scope of the present invention-creation are covered by the protection scope of the patent for the present invention-creation. Any reference signs in the claims should not be construed as limiting the claimed invention.

Claims

1. A multi-scale fracture prediction method for shale reservoirs, characterized in that: The method comprises: Obtain the development characteristics of fractures of different scales in the target formation and the basic rock mechanics parameters of the sample rock under different temperature and pressure conditions; Through discrete element numerical simulation technology, the stress evolution threshold of crack growth in the sample rock is determined; Based on the basic rock mechanics parameters, a temperature-pressure damage constitutive model of the sample rock under the simultaneous action of temperature and pressure is established; Based on the temperature-pressure damage constitutive model, a fine geomechanical model is established in combination with the crack development characteristics; The strain coefficient of the rock in the target formation is determined by the stress evolution thresholds corresponding to fractures of different scales under the fine geomechanical model, a fracture prediction model of the target formation is constructed by the strain coefficient, and the fracture prediction results of the target formation are obtained by the fracture prediction model.

2. A shale reservoir multi-scale fracture prediction method according to claim 1, characterized in that: The temperature-pressure damage constitutive model is: ； in: is the elastic modulus of rock at room temperature; is the elastic modulus of rock at different real-time temperatures; is the total thermal-mechanical coupling damage variable; is the peak strain, is the peak stress, is the elastic modulus, is Poisson's ratio; is the circumferential stress, is the axial strain, and m is the Weibull statistical distribution parameter.

3. A shale reservoir multi-scale fracture prediction method according to claim 2, characterized in that: Based on the temperature-pressure damage constitutive model, a fine geomechanical model is established in combination with the crack development characteristics, including: Establish a structural model of the target stratum based on the seismic, drilling, logging and stratification conditions of the target stratum; The formation conditions are restored according to the structural model and the temperature-pressure damage constitutive model, and a fine geomechanical model of the target formation is established by integrating rock mechanics, fracture development characteristics and fault distribution information.

4. The method for predicting multi-scale fractures in shale reservoirs according to claim 1, characterized in that: Determining the stress evolution threshold of crack growth in the sample rock by discrete element numerical simulation technology includes: Divide the cracks into different scales to obtain cracks of different scales; The discrete element numerical simulation technology is used to simulate the state of cracks of different scales in the sample rock at different pressurization stages to determine the stress evolution threshold of crack growth.

5. The method for predicting multi-scale fractures in shale reservoirs according to claim 1, characterized in that: The calculation formula of the crack prediction model is: ； in, is the volume density of cracks in the unit body; J is the energy required to produce cracks per unit area, that is, the crack surface energy; is the total strain energy density; The density of elastic strain energy that must be overcome to produce a crack; is the strain energy density of the newly added crack surface area; is the surface area of ​​the newly added cracks; a and b are strain coefficients; the calculation formula for the total strain energy density is: in, is the total strain energy density; E is the elastic modulus; is Poisson's ratio; , , are the maximum principal stress, the intermediate principal stress and the minimum principal stress respectively.

6. A shale reservoir multi-scale fracture prediction device, characterized in that: The device comprises: An acquisition module is used to obtain the development characteristics of fractures of different scales in the target formation and the basic rock mechanical parameters of the sample rock under different temperature and pressure conditions; A determination module, for determining a stress evolution threshold of crack growth in a sample rock by using a discrete element numerical simulation technique; A construction module is used to establish a temperature-pressure damage constitutive model of the sample rock under the simultaneous action of temperature and pressure based on the basic rock mechanics parameters; based on the temperature-pressure damage constitutive model, a fine geomechanical model is established in combination with the crack development characteristics; The prediction module is used to determine the strain coefficient of the rock in the target formation through the stress evolution threshold corresponding to the fractures of different scales under the fine geomechanical model, to construct a fracture prediction model of the target formation through the strain coefficient, and to obtain the fracture prediction result of the target formation through the fracture prediction model.

7. A computer-readable storage medium, characterized in that: The storage medium stores a computer program, and when the computer program is executed by a processor, the method according to any one of claims 1 to 5 is implemented.

8. A computer device, characterized in that: The method comprises a memory, a processor and a computer program stored in the memory and executable on the processor, wherein the processor implements the method according to any one of claims 1 to 5 when executing the program.

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