Method for evaluating safe distance from fault during hydraulic fracturing process based on in-situ stress

Abstract

The present application relates to a method for avoiding fault safety distance in hydraulic fracturing process based on ground stress evaluation. The moment magnitude of earthquake caused by fault activity is calculated by seismic moment. The fault is characterized in a three-dimensional geomechanical model by three-dimensional elements through the fault surface. Firstly, a single fault element is taken to analyze the magnitude of moment magnitude caused by the destruction of the single fault element, and then the total moment magnitude caused by the destruction of the single fault element is analyzed according to the overall fault destruction. The shear strain at the fault surface is calculated. The destruction of the single fault element is calculated. The magnitude of the seismic moment caused by the destruction of the single fault element is calculated. The seismic moment of all destroyed fault elements is summed to obtain the total seismic moment. The magnitude of the moment magnitude caused by the fault activation under different working conditions is obtained. Based on the three-dimensional geomechanical technology, the fault displacement and the response calculation process of the moment magnitude are quantified. The fault activation risk level is evaluated by the response of the moment magnitude, and then the safety avoidance distance of the hydraulic fracturing well position is quantified.

Description

Technical Field

[0001] This invention relates to the field of shale gas extraction, and more specifically, to a method for assessing the safe distance to avoid faults during hydraulic fracturing based on three-dimensional geomechanical evaluation. Background Technology

[0002] Shale gas is a vast unconventional oil and gas resource. Due to the inherent tightness of shale, hydraulic fracturing has become an effective technology for shale gas extraction. Hydraulic fracturing involves injecting large amounts of fracturing fluid under high pressure to break up tight shale. The potential environmental impact of this process (such as fracturing-induced earthquakes) has attracted widespread attention, especially in the Sichuan Basin of my country, where shale gas development is frequently accompanied by local earthquakes. To ensure safer and more rational shale gas extraction, optimize hydraulic fracturing operations and well location deployment, and reduce the environmental impact of the hydraulic fracturing process, there is an urgent need to develop a quantitative assessment method for the fault activation risk and safe avoidance distance during hydraulic fracturing.

[0003] Patent CN112302601A provides a method and device for evaluating fault activation control based on a geomechanical model. This design can effectively characterize fault activation, control fault activation in drilling operations, and reduce the probability of casing deformation in shale gas horizontal wells during construction, making fracturing operations safer and more reasonable. However, this design is designed to overcome well casing deformation problems and cannot quantitatively assess the correlation between the magnitude of fault activation displacement and the magnitude of potential induced earthquakes. Consequently, it cannot provide technical reference for the safe fault avoidance distance of shale gas hydraulic fracturing wells.

[0004] Patent CN112925015A proposes a method for early warning of casing deformation by utilizing the b-value variation characteristics of hydraulic fracturing microseismic data. However, this method is mostly based on the inversion of microseismic data to obtain whether the fault is activated or not, but it does not have a calculation method to quantify the scale of fault activation.

[0005] It can be seen that existing technologies are limited to assessing whether faults are activated and the impact of activation on the deformation of the casing around the well. They fail to quantify the fault shear displacement caused by pore pressure rise and stress diffusion during hydraulic fracturing, as well as the moment and seismic response induced by fault activation. Therefore, they cannot provide a design method for safe avoidance distances for hydraulic fracturing well locations in shale gas reservoirs. Summary of the Invention

[0006] To address the aforementioned problems, the purpose of this invention is to provide a method for assessing fault activation risk and safe avoidance distance based on three-dimensional geomechanical technology. This method includes: acquiring well logging data, core data, seismic inversion data, formation model, fault and natural fracture system, hydraulic fracturing operation data, and drilling logs for the study block.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] Methods for assessing safe distances to avoid faults during hydraulic fracturing include:

[0009] The moment magnitude of earthquakes generated after fault activity is obtained through seismic moment calculation;

[0010] The characterization of faults in a three-dimensional geomechanical model is achieved by representing the three-dimensional units through which fault planes pass. First, a single fault unit is taken and the magnitude of the moment magnitude generated after the failure of the single fault unit is analyzed. Then, the total moment magnitude generated is explained based on the overall fault failure situation.

[0011] Calculate the shear strain at the fracture surface;

[0012] Calculate the failure status of a single fault unit;

[0013] Calculate the magnitude of the seismic moment generated after the failure of a single fault element;

[0014] By summing the seismic moments of all damaged fault elements, the total seismic moment is obtained, which in turn yields the moment magnitude generated after fault activation under different working conditions:

[0015] In conjunction with measures to prevent and control earthquake risks induced by hydraulic fracturing, and to further enhance the safety level of earthquake risk prevention and control, if the total moment magnitude is greater than or equal to 2, fracturing operations shall be stopped. If the moment magnitude is assessed and it is determined that the fault has been activated and has a tendency to cause further damage, the distance between the corresponding well and the fault shall be the minimum safe avoidance distance.

[0016] Seismic moment is a physical quantity that measures the magnitude of an earthquake, defined as the product of the area of ​​the earthquake fault, the average slip of the fault, and the shear modulus of the medium near the fault plane.

[0017] Calculate the shear strain at the fracture surface:

[0018]

[0019] In the formula,

[0020] ε fault Shear strain at the fracture surface;

[0021] d represents the average slip of the fault;

[0022] l is the length in the sliding direction.

[0023] The failure status of a single fault unit is approximately represented by equations (3), (4), and (5):

[0024]

[0025]

[0026]

[0027] In the formula,

[0028] A represents the area of ​​the fracture region of the fault unit;

[0029] 'a' represents the side length of the fault unit on the horizontal plane.

[0030] h is the vertical height;

[0031] γ is the angle between the fault plane and the horizontal plane;

[0032] G equiv The shear modulus of the rock near the fault;

[0033] E equiv The equivalent Young's modulus of the element traversed by the fault;

[0034] μ fault The friction coefficient of the fault filling material;

[0035] l is the length in the sliding direction.

[0036] Calculate the magnitude of the seismic moment generated after the failure of a single fault element:

[0037]

[0038] In the formula,

[0039] M 0_element This represents the seismic moment after the failure of a single fault element.

[0040] Summing the seismic moments of all damaged fault elements using equation (6) yields the total seismic moment ΣM. 0_element , will ΣM 0_element Substituting into equation (2), we can obtain the magnitude of the moment magnitude generated after fault activation under different working conditions:

[0041]

[0042] Where: M w_all The total moment magnitude is the magnitude generated by fault activation slip.

[0043] E equiv The calculation method adopts the equivalent stiffness theory. Under the same stress state, the deformation of a discontinuous element is the sum of the deformation of a complete rock element and the deformation of the material within the fault (see appendix). Figure 4 The relevant equivalent deformation relationship is as follows:

[0044]

[0045] In the formula,

[0046] σ represents stress;

[0047] E equiv The equivalent Young's modulus of the element traversed by the fault;

[0048] E intact Young's modulus for a complete rock unit;

[0049] E fault This is the Young's modulus of the fault material.

[0050] The Young's modulus E of the interrupted layer in equation (8) is... fault Converted to fault normal stiffness K n Equation (8) can be expressed as follows:

[0051]

[0052] In the formula,

[0053] K n For fault normal stiffness;

[0054] S represents the fault spacing.

[0055] The calculation of fault moment magnitude using three-dimensional shear strain includes: calculating the fault slip displacement using three-dimensional shear strain, calculating the seismic moment using the fault area and slip displacement, and then converting this into the induced moment magnitude.

[0056] The calculation of safe avoidance distance includes: comparing the calculated moment magnitude induced by hydraulic fracturing with that of a magnitude 2 earthquake. If the magnitude is below 2, the current well location distance from the fault is reasonable; if the moment magnitude is greater than 2, it is necessary to increase the distance between the well location and the fault, or optimize the hydraulic fracturing construction pressure.

[0057] The present invention has the following advantages due to the adoption of the above technical solutions:

[0058] The method for assessing fault activation risk and safe avoidance distance based on three-dimensional geomechanical technology provided by this invention can effectively quantify the fault activation risk level of the research area, provide a design basis for optimizing the minimum safe distance of hydraulic fracturing, reduce the impact of hydraulic fracturing process on the surrounding environment of shale gas extraction, and make hydraulic fracturing construction and well location deployment safer and more reasonable.

[0059] Based on the actual heterogeneous and anisotropic strata characteristics, the dynamic quantification of three-dimensional geostress levels is used to measure the changes in fault shear displacement during hydraulic fracturing and obtain the cumulative deformation of fault zone displacement.

[0060] We provide a set of calculation processes for quantifying fault displacement and seismic moment-magnitude response based on three-dimensional geomechanical technology. By assessing the fault activation risk level through moment-magnitude response, we can then quantify the safe avoidance distance for hydraulic fracturing well locations. Attached Figure Description

[0061] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts. In the drawings:

[0062] Figure 1 This is a schematic diagram of a three-dimensional geomechanical technique for assessing fault activation risk levels in shale gas reservoirs based on anisotropy.

[0063] Figure 2 This is a schematic diagram of the calculation process for fault activation risk level and moment magnitude;

[0064] Figure 3A This is a schematic diagram of a fault unit subjected to shear forces.

[0065] Figure 3B This is a simplified schematic diagram of the slip displacement of a fault unit;

[0066] Figure 4 This is a planar schematic diagram of a fault unit;

[0067] Figure 5 This is a schematic diagram of the three-dimensional shear strain energy equivalent moment magnitude method;

[0068] Figure 6 This is a schematic diagram of the technical process for safely avoiding faults in hydraulic fracturing well locations;

[0069] Figure 7 This is a schematic diagram for calculating the stress disturbance range during hydraulic fracturing. Detailed Implementation

[0070] Exemplary embodiments of the invention will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the invention are shown in the drawings, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the invention and to fully convey the scope of the invention to those skilled in the art.

[0071] The overall technical solution for the evaluation method is attached. Figure 1 As shown, the implementation content of each sub-process module is as follows:

[0072] I. Block Logging Data Module: This module analyzes the P-wave, S-wave, rock density, gamma, resistivity, and Elan data of individual wells within the block to provide effective interpretive data for calculating the mechanical parameters of individual wells.

[0073] II. Anisotropic Single-Well Geomechanical Module: Based on well logging data, the elastic parameters, strength parameters, and triaxial stress parameters of a single well are calculated. Core data serves as the verification basis for the calculated parameters. The data obtained from the core test include: Young's modulus, Poisson's ratio, uniaxial compressive strength, tensile strength, and internal friction angle.

[0074] III. Three-Dimensional Geological Model Module: Seismic inversion results provide information on tectonic layers within the region, clarifying the fault system and the distribution of natural fractures. The geological model provides stratigraphic information for each tectonic layer and the characteristics of the three-dimensional properties between layers.

[0075] IV. Fault and Fracture Model Module: Fault and fracture modeling depicts a multi-scale natural fracture system and the corresponding mechanical parameters of each level of natural fracture, which is used to finely characterize the geostress field of the study block.

[0076] V. Spatial Distribution of 3D Geomechanical Parameters: Combining seismic inversion results, geological models, and one-dimensional geomechanical models, the distribution of 3D geomechanical parameter attribute volumes is obtained based on spatial interpolation (seismic volume constraints). The geomechanical parameter attribute volumes mainly include: 3D acoustic volume, 3D rock density field, 3D elastic parameters (Young's modulus, Poisson's ratio), and 3D strength parameters (uniaxial compressive strength, tensile strength, internal friction angle). The main functions of seismic volume constraints are: (a) controlling the inter-well interpolation trend; (b) characterizing parameter abrupt changes at faults and natural fracture discontinuities.

[0077] VI. Three-dimensional pore pressure field module: Based on the three-dimensional acoustic wave spatial distribution and rock three-dimensional density volume data, the three-dimensional pore pressure field is calculated and obtained;

[0078] VII. Three-dimensional finite element simulation module: By coupling the three-dimensional pore pressure field and the three-dimensional geomechanical parameter property volume, the three-dimensional geostress field is obtained based on the three-dimensional finite element calculation.

[0079] 8. Dynamically Coupled Hydraulic Fracturing Module: By embedding hydraulic fracturing construction data, the module quantifies the three-dimensional geostress field disturbance caused by reservoir pore pressure rise and stress diffusion during the hydraulic fracturing process.

[0080] IX. Calculation of three-dimensional shear strain in the block: Based on the three-dimensional dynamic stress field calculated by the hydraulic fracturing module, the spatial distribution of three-dimensional shear strain of the shale in the research block is calculated based on the stress-strain relationship;

[0081] 10. Statistical analysis of shear displacement in fault fracture zones: Based on three-dimensional shear strain and considering the unit size of the fault region, calculate the shear displacement near the fault.

[0082] XI. Moment-magnitude energy equivalence method: used to calculate the correspondence between cumulative fault displacement and induced earthquake magnitude;

[0083] 12. Fault Activation Risk Level Module: Used to assess the magnitude of fault activation risk based on earthquake magnitude;

[0084] Thirteen, Fault Safety Avoidance Distance Module: When the fault activation risk level exceeds the threshold allowed by hydraulic fracturing, the distance between the well location and the fault is dynamically adjusted, and the fault activation risk level is recalculated iteratively. The minimum value of the fault safety avoidance distance can be obtained when the threshold condition is met.

[0085] Appendix Figure 2 The diagram shows the calculation process for determining fault activation risk level and safe fault avoidance distance based on three-dimensional geomechanical technology. The specific implementation steps are as follows:

[0086] Step 1: The moment magnitude of an earthquake generated after fault activity can be calculated from the seismic moment. The seismic moment is a physical quantity defining the magnitude of an earthquake, defined as the product of the fault area, the average slip of the fault, and the shear modulus of the medium near the fault plane. Its calculation expression is shown in equation (1). Furthermore, the moment magnitude can be calculated using equation (2).

[0087] M0=AGd (1)

[0088]

[0089] In the formula: M0 is the seismic moment; A is the area of ​​the fault fracture zone, in meters. 2 G is the shear modulus of the medium near the fault plane, in Pa; d is the average slip of the fault, in m; M w It is a moment magnitude earthquake.

[0090] Step 2: In the three-dimensional geomechanical model, the fault is characterized by three-dimensional units through which the fault plane passes. Therefore, we can first take a single fault unit, analyze the magnitude of the moment magnitude generated after the unit is destroyed, and then explain the total moment magnitude generated based on the overall fault failure.

[0091] As shown in Figure (3), the fault element under shear conditions is analyzed by taking the force F acting on the left and right surfaces. Wherein:

[0092] a. The side length of each fault unit on the horizontal plane is 'a', and the vertical height is 'h'.

[0093] b. The angle between the fault plane and the horizontal plane, i.e., the dip angle is γ;

[0094] c. The fault plane has an angle γ with the horizontal plane in the rock mass unit and a side length of l.

[0095] Step 3: Calculate the shear strain at the fracture surface.

[0096] Step 4: Fault condition of a single fault unit, including the area A of the fractured region of the fault unit and the shear modulus of the rock near the fault.

[0097] G equiv The length l in the sliding direction can be approximated by equations (3), (4), and (5):

[0098]

[0099]

[0100]

[0101] In the formula: E equiv This is the equivalent Young's modulus of the element traversed by the fault.

[0102] Step 5: Substituting equations (3) to (5) into equation (1) yields the magnitude of the seismic moment generated after the failure of a single fault element:

[0103]

[0104] Where: M 0_element This represents the seismic moment after the failure of a single fault element.

[0105] Step 6: Summate the seismic moments of all damaged fault elements according to equation (6) to obtain the total seismic moment ΣM. 0_element , will ΣM 0_element Substituting into equation (2), we can obtain the magnitude of the moment magnitude generated after fault activation under different working conditions:

[0106]

[0107] Where: M w_all The total moment magnitude is the magnitude generated by fault activation slip.

[0108] Step 7: Combining hydraulic fracturing-induced earthquake risk prevention and control measures, and to further improve the safety level of induced earthquake risk prevention and control, the total moment magnitude M w_all If the magnitude is greater than or equal to 2, the fracturing operation is stopped. The fault is considered to have been activated and has a tendency to cause further damage based on the magnitude of the moment and seismic intensity. The distance between the production well and the fault at this time is the minimum safe avoidance distance.

[0109] Step 2: Solving for the geometric parameters of the fault unit is shown in Figure 3. Based on the size of the three-dimensional finite element mesh, the geometric dimensions of each unit are known. Then, the area A cut by the three-dimensional rock block is calculated according to the fault's attitude (strike, dip, dip angle).

[0110] In step 4, E equivThe calculation method employs the equivalent stiffness theory. Under the same stress state, the deformation of a discontinuous element is the sum of the deformation of a complete rock element and the deformation of the material within the fault (see appendix). Figure 4 The relevant equivalent deformation relationship is as follows:

[0111]

[0112] In the formula: σ is the stress; E equiv E represents the equivalent Young's modulus of the element traversed by the fault; intact E represents the Young's modulus of a complete rock unit. fault This is the Young's modulus of the fault material.

[0113] The Young's modulus E of the interrupted layer in equation (8) is... fault Converted to fault normal stiffness K n Equation (8) can be expressed as follows:

[0114]

[0115] In the formula: K n is the fault normal stiffness; S is the fault spacing.

[0116] The principle of three-dimensional shear strain calculation for fault moment and magnitude in steps 4 and 5 is attached. Figure 5 As shown, the fault slip displacement is calculated using three-dimensional shear strain, and the seismic moment is calculated by combining the fault area and slip volume, which in turn is converted into the induced moment magnitude.

[0117] The principle behind calculating the safe avoidance distance in step 7 is as follows: Figure 6 As shown, the calculated moment magnitude induced by hydraulic fracturing is compared with that of a magnitude 2 earthquake. If the magnitude is below 2, the distance between the current well location and the fault is reasonable. If the moment magnitude is greater than 2, it is necessary to increase the distance between the well location and the fault, or optimize the hydraulic fracturing construction pressure.

[0118] Appendix Figure 6 The input parameters mainly consist of the results of dynamic coupling calculations between three-dimensional geomechanics and hydraulic fracturing, including three-dimensional shear strain. The calculation process for this part is as follows:

[0119] (1) Based on well logging data, calculate the perimeter elastic parameters, strength parameters and triaxial stress parameters of a single well. Core data is used as the verification basis for the calculated parameters. The data obtained from the core test include: Young's modulus, Poisson's ratio, uniaxial compressive strength, tensile strength and internal friction angle.

[0120] (2) Based on the three-dimensional geological model and the three-dimensional property distribution characteristics between layers, the fault and fracture modeling depicts the multi-scale natural fracture system and the corresponding mechanical parameters of each level of natural fracture.

[0121] (3) Combining seismic inversion results, geological models, and one-dimensional geomechanical models, the three-dimensional geomechanical parameter attribute volume distribution is obtained based on spatial interpolation (seismic volume constraint);

[0122] (4) Based on the three-dimensional acoustic wave spatial distribution and the three-dimensional density volume data of rock, the three-dimensional pore pressure field is calculated and obtained;

[0123] (5) By coupling the three-dimensional pore pressure field and the three-dimensional geomechanical parameter property volume, the three-dimensional geostress field is obtained based on the three-dimensional finite element calculation.

[0124] (6) By embedding hydraulic fracturing construction data, the three-dimensional geostress field disturbance caused by reservoir pore pressure rise and stress diffusion during hydraulic fracturing is quantified. The range of hydraulic fracturing stress disturbance is shown in the attached figure. Figure 7 As shown;

[0125] (7) Based on the three-dimensional dynamic stress field calculated by the hydraulic fracturing module, the spatial distribution of three-dimensional shear strain of the shale in the research block was calculated based on the stress-strain relationship;

[0126] (8) Based on the three-dimensional shear strain and considering the unit size of the fault region, calculate the shear displacement near the fault.

[0127] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for assessing the safe distance to avoid faults during hydraulic fracturing based on in-situ stress, characterized in that, include: The moment magnitude of earthquakes generated after fault activity is obtained through seismic moment calculation; The characterization of faults in a three-dimensional geomechanical model is achieved by representing the three-dimensional units through which fault planes pass. First, a single fault unit is taken and the magnitude of the moment magnitude generated after the failure of the single fault unit is analyzed. Then, the total moment magnitude generated is explained based on the overall fault failure situation. Calculate the shear strain at the fracture surface; Calculate the failure status of a single fault unit; Calculate the magnitude of the seismic moment generated after the failure of a single fault element; By summing the seismic moments of all damaged fault elements, the total seismic moment is obtained, which in turn yields the moment magnitude generated after fault activation under different working conditions: In conjunction with measures to prevent and control earthquake risks induced by hydraulic fracturing, and to further enhance the safety level of earthquake risk prevention and control, if the total moment magnitude is greater than or equal to 2, fracturing operations shall be stopped. If the moment magnitude is assessed and it is determined that the fault has been activated and has a tendency to cause further damage, the distance between the corresponding well and the fault shall be the minimum safe avoidance distance.

2. The method for assessing the safe distance to avoid faults during hydraulic fracturing based on in-situ stress according to claim 1, characterized in that, The earthquake moment is a physical quantity used to measure the magnitude of an earthquake, defined as the product of the area of ​​the earthquake fault, the average slip of the fault, and the shear modulus of the medium near the fault plane. The calculation expression is shown in equation (1), and the moment magnitude can be calculated using equation (2): （1） （2） In the formula, It is the seismic moment; The area of ​​the fault fracture region; The shear modulus of the medium near the fault plane; This represents the average slip of the fault. It is a moment magnitude earthquake.

3. The method for assessing the safe distance to avoid faults during hydraulic fracturing based on in-situ stress according to claim 1, characterized in that, The shear strain at the fracture surface is calculated using the following formula: In the formula, ε fault Shear strain at the fracture surface; This represents the average slip of the fault. l is the length in the sliding direction.

4. The method for assessing the safe distance to avoid faults during hydraulic fracturing based on in-situ stress according to claim 3, characterized in that, The failure status of a single fault unit is approximately represented by equations (3), (4), and (5): (3) (4) (5) In the formula, A The area of ​​the fractured region of the fault unit; a This represents the side length of the fault unit on the horizontal plane. h Vertical height; The angle between the fault plane and the horizontal plane; G equiv The shear modulus of the rock near the fault; The equivalent Young's modulus of the element traversed by the fault; μ fault The friction coefficient of the fault filling material; l is the length in the sliding direction.

5. The method for assessing the safe distance to avoid faults during hydraulic fracturing based on in-situ stress according to claim 4, characterized in that, The magnitude of the seismic moment generated after the failure of a single fault element is calculated according to equation (6): (6) In the formula, This represents the seismic moment after the failure of a single fault element.

6. The method for assessing the safe distance to avoid faults during hydraulic fracturing based on in-situ stress according to claim 5, characterized in that, Summing the seismic moments of all damaged fault elements using equation (6) yields the total seismic moment. ,Will Substituting into equation (2), we can obtain the magnitude of the moment magnitude generated after fault activation under different working conditions: (7) In the formula: The total moment magnitude is the magnitude generated by fault activation slip.

7. The method for assessing the safe distance to avoid faults during hydraulic fracturing based on in-situ stress according to claim 5, characterized in that, The calculation method adopts the equivalent stiffness theory. Under the same stress state, the deformation of the discontinuous element is the sum of the deformation of the intact rock element and the deformation of the material within the fault (Figure 4). The relevant equivalent deformation relationship is as follows: (8) In the formula, For stress; The equivalent Young's modulus of the element traversed by the fault; Young's modulus for a complete rock unit; This is the Young's modulus of the fault material.

8. The method for assessing the safe distance to avoid faults during hydraulic fracturing based on in-situ stress according to claim 7, characterized in that, The Young's modulus of the interrupted layer in equation (8) Converted to fault normal stiffness Equation (8) can be expressed as follows: （9） In the formula, For fault normal stiffness; This represents the fault spacing.

9. The method for assessing the safe distance to avoid faults during hydraulic fracturing based on in-situ stress according to claim 1, characterized in that, The calculation of fault moment magnitude using three-dimensional shear strain includes: calculating the fault slip displacement using three-dimensional shear strain, calculating the seismic moment using the fault area and slip displacement, and then converting this into the induced moment magnitude.

10. The method for assessing the safe distance to avoid faults during hydraulic fracturing based on in-situ stress according to claim 1, characterized in that, The calculation of safe avoidance distance includes: comparing the calculated moment magnitude induced by hydraulic fracturing with that of a magnitude 2 earthquake. If the magnitude is below 2, the current well location distance from the fault is reasonable; if the moment magnitude is greater than 2, it is necessary to increase the distance between the well location and the fault, or optimize the hydraulic fracturing construction pressure.

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