A method for analyzing crack activity

Abstract

The present invention provides a fracture activity analysis method applicable to the field of oil and gas geology. Collect data on the main oil and gas layer sections of n wells in the study area, observe their core cracks and collect experimental samples, and calculate the degree of fracture filling; carry out differential strain stress test, triaxial rock mechanics experiment and friction sliding experiment, obtain the maximum principal stress, intermediate principal stress, minimum principal stress, static elastic modulus, static Poisson's ratio and friction coefficient of the experimental samples; calculate the dynamic elastic modulus and dynamic Poisson's ratio by logging, and establish the relationship between dynamic and static rock mechanics parameters; interpret the fracture occurrence, well wall collapse and drilling-induced fractures, determine the current dominant direction of ground stress, and calculate the fracture density; construct a three-dimensional geological model and geomechanics model of the main oil and gas layer sections in the study area, divide the unit grid, and perform fracture geological modeling; calculate the sliding tolerance of each fracture, and quantitatively analyze the fracture activity based on it. This method takes into account comprehensive factors, has strong operability, and has high credibility of results.

Description

Technical Field

[0001] The invention relates to a fracture activity analysis method, which is particularly applicable to the field of oil and gas geology. Background Art

[0002] Fracture systems developed within oil and gas reservoirs not only serve as important reservoir spaces for oil and gas but also as primary migration pathways, effectively influencing both oil and gas enrichment and seepage. Fracture zones within reservoirs are often "sweet spots" for oil and gas exploration and development. Therefore, studying the distribution patterns and activity of fractures is crucial for efficient oil and gas exploration and development.

[0003] Previous studies have mostly focused on fault activity evaluation, with few patented technologies targeting fracture activity. The invention patent, with authorization announcement number CN111025391B, proposes a quantitative evaluation method for fault activity, including the following steps: performing seismic inversion on the study area, selecting interpretation points within the fault, interpretation points on the downthrown plate, and interpretation points on the upthrown plate, calculating the peak frequency attributes corresponding to each interpretation point, plotting a peak frequency attribute plane diagram, selecting downthrown plate study points and upthrown plate study points, and performing anomaly assessments on the downthrown plate study points and upthrown plate study points along the sand body distribution direction. If anomalies exist at the downthrown plate study point or / and the upthrown plate study point, a new study point is replaced and anomaly assessments are performed on the new study point until no anomalies are found at the study point. The difference in the peak frequency attributes between the current downthrown plate study point and the upthrown plate study point is used to describe the activity frequency of the corresponding part of the fault, thereby obtaining the fault activity evaluation result. The invention patent with application publication number CN114545499A proposes a method, device and medium for predicting the relative activity of a fault under the Anderson stress state, obtaining the Anderson stress state, cohesion, internal friction angle and friction coefficient of the fault to be detected; determining the relative differential stress corresponding to the fault to be detected based on a preset relationship between the Anderson stress state and the relative differential stress; determining the first horizontal principal stress and the second horizontal principal stress based on the preset principal stress value, the relative differential stress corresponding to the fault to be detected, the Anderson stress state, cohesion and internal friction angle of the fault to be detected; establishing a Mohr space corresponding to the fault to be detected based on the Anderson stress state, preset principal stress value, first horizontal principal stress and second horizontal principal stress of the fault to be detected; drawing a fault shear activity line based on the cohesion and friction coefficient; projecting the attitude to be detected onto the Mohr space to obtain the attitude projection point; and determining the relative activity of the fault to be detected based on the fault shear activity line and the attitude projection point. The invention patent with application publication number CN107844614A proposes a method and device for predicting the potential mechanical activity of a fault. The method includes the following steps: obtaining a three-dimensional stress field and a three-dimensional spatial data model of the fault, the three-dimensional stress field and the three-dimensional spatial data model having the same three-dimensional coordinate system, obtaining the current stress field parameters of each point on the fault plane based on the three-dimensional stress field, obtaining the strike information of each point on the fault plane based on the three-dimensional spatial data model, and determining the potential activity index of each point on the fault plane based on the three-dimensional coordinates, current stress field parameters and strike information of each point on the fault plane. The potential activity index is used to quantitatively represent the potential mechanical activity of each point on the fault plane.

[0004] Regarding the prediction and evaluation of fracture activity, Jiang Tongwen et al. (2021) published a paper in China Petroleum Exploration proposing a fracture activity prediction technique. This technique defines the ratio of shear stress to normal stress on the fracture surface as an indicator of fracture surface activity, a key index reflecting fracture permeability and fluid flow. This method does not consider the effects of rock cohesion and friction coefficient on fracture activity. Summary of the Invention

[0005] To address the problems existing in the prior art, the present invention provides a fracture activity analysis method with simple operating steps and high reliability. The core of the method is to consider the rock cohesion and internal friction coefficient, quantitatively analyze the ratio of the shear stress on the fracture surface under the current ground stress to the theoretical shear stress for shear sliding, and analyze the fracture activity based on this.

[0006] To achieve the above objectives, a fracture activity analysis method was proposed. The imaging logging data, conventional logging curves, pore pressure data and seismic data of the main oil and gas layer sections of n wells in the study area were collected. The core fractures in each well were observed on site and experimental samples at different depths of the main oil and gas layer sections were collected to observe whether the fractures were filled and to calculate the degree of fracture filling, thereby constraining the cohesion. The differential strain in situ stress test was performed on the collected experimental samples to obtain the maximum principal stress, intermediate principal stress and minimum principal stress of the experimental samples collected at different depths in all the wells. The static elastic modulus and static Poisson's ratio of each test sample were obtained through triaxial rock mechanics experiments, and the friction sliding test was used to obtain the static elastic modulus and static Poisson's ratio of each test sample. Friction coefficient; use logging data to calculate the dynamic elastic modulus and dynamic Poisson's ratio of the drilling rock where the sample is located, and establish the relationship between dynamic and static rock mechanics parameters; interpret fracture occurrence, wellbore collapse and drilling-induced fractures, determine the current dominant direction of ground stress, and calculate fracture density; by constructing a three-dimensional geological model of the main oil and gas layer sections in the study area and a geomechanical model of the main oil and gas layer sections in the study area covering n wells, divide the unit grid in the model, and perform numerical simulation of the current ground stress field and fracture geological modeling; calculate the shear stress and normal stress on each fracture surface, combine the cohesion and friction coefficient, define and calculate the sliding tolerance, and use this as an indicator parameter of fracture activity to quantitatively analyze fracture activity.

[0007] The specific steps are as follows:

[0008] Step 1: Collect imaging logging data, conventional logging curves, pore pressure data and seismic data of the main oil and gas layers of n wells drilled in the study area;

[0009] Step 2: Observe the core cracks of the main oil and gas layer sections of the n wells in step 1, including the cracks developed in the oil and gas layer sections, calculate the filling degree of the cracks in each well, collect core test samples at different depths of the main oil and gas layer sections of each well, and record the sampling depths of all test samples. Prepare the core test samples into plunger test samples with a diameter of 20 mm and a height of 40 mm, plunger test samples with a diameter of 25 mm and a height of 50 mm, and fan-shaped test samples with a radius of 50 mm and a height of 50 mm and a central angle of 90°, and process the end faces of the samples using a grinder or a lathe to keep them parallel;

[0010] Step 3: Cut the plunger test sample with a diameter of 20 mm and a height of 40 mm prepared in step 2 along a 35° angle with the axial direction to serve as the sliding surrounding rock block. Then, conduct a friction sliding test. During the test, apply the pore pressure collected in step 1 to obtain the friction coefficient of the plunger test sample:

[0011]

[0012] Where: μ is the friction coefficient, τ is the shear stress, σ ne represents the effective normal stress, P o is the pore pressure;

[0013] Step 4: Using the plunger test sample with a diameter of 25 mm and a height of 50 mm prepared in step 2, conduct triaxial rock mechanics experiments to obtain the static elastic modulus and static Poisson's ratio of the rock:

[0014]

[0015]

[0016] Where: E s The rock elastic modulus obtained from the experimental test, namely the rock static elastic modulus, μ s The rock Poisson's ratio obtained from the experimental test, that is, the rock static Poisson's ratio, (S1-S3) (50) 50% of the maximum principal stress difference of the specimen, ε h(50) Indicates (S1-S3) (50) The corresponding axial compressive strain, ε d(50) (S1-S3) (50) The corresponding circumferential compressive strain;

[0017] Step 5: Using the sector-shaped experimental sample with a radius of 50 mm, a height of 50 mm, and a central angle of 90° prepared in Step 2, a differential strain in-situ stress test is performed to obtain the current in-situ stress of the core experimental sample: maximum principal stress, intermediate principal stress, and minimum principal stress;

[0018] Step 6: Calculate the rock dynamic elastic modulus and dynamic Poisson's ratio using the conventional logging curves collected in step 1:

[0019]

[0020]

[0021]

[0022] Where: μ d is the dynamic Poisson's ratio of rock, G is the shear modulus, E d is the dynamic elastic modulus of rock, ρ brepresents the formation volume density, Δt s is the formation shear wave time difference, Δt p is the formation longitudinal wave time difference.

[0023] Step 7: Use the linear fitting method to establish the relationship between the static rock mechanical parameters obtained in step 4 and the dynamic rock mechanical parameters obtained in step 6. Based on the relationship, the dynamic elastic modulus and dynamic Poisson's ratio obtained by logging curve calculation are converted into static elastic modulus and static Poisson's ratio, thus achieving the continuity of static rock mechanical parameters throughout the entire well section:

[0024]

[0025] Where: a, b, c, d are fitting coefficients.

[0026] Step 8: Using the imaging logging data collected in step 1, interpret the fractures, wellbore collapse and drilling-induced fractures, pick up the fracture occurrence parameters, wellbore collapse azimuth and drilling-induced fracture azimuth, calculate the density of the fractures, and record the wellbore collapse azimuth ±90° as α j , the drilling-induced fracture orientation is recorded as α k , change α j and α k By converting all ±180° values into the range of [0, 180°), the dominant direction of the current ground stress near the wellbore is determined based on the relationship between wellbore collapse, drilling-induced fractures and current ground stress, and its azimuth is expressed as:

[0027]

[0028] Where p and q represent the number of wellbore collapse and drilling-induced fractures, respectively.

[0029] Step 9: Use the seismic data collected in step 1 to establish a three-dimensional geometric model of the main oil and gas layer sections in the study area, divide the unit grid, and use the spatial interpolation method to interpolate the rock mechanical parameters of the different drilling full-well sections obtained in step 7 into the three-dimensional grid using the Gaussian sequential method to achieve three-dimensional geological model construction. Combined with the current ground stress magnitude obtained in step 5 and the current ground stress direction obtained in step 8, a three-dimensional geomechanical model of the main oil and gas layer sections in the study area is constructed. Finite element numerical simulation technology is used to find out the maximum principal stress, intermediate principal stress, and minimum principal stress of each unit grid in the three-dimensional geomechanical model of the main oil and gas layer sections;

[0030] Step 10: Under the constraints of fracture occurrence and density in step 8, a stochastic fracture modeling method is used based on discrete fracture patterns to construct a fracture model, and the fracture development distribution and occurrence characteristics of the main oil and gas-bearing layers in the study area are quantitatively characterized by the model;

[0031] Step 11: interpolate the pore pressure of the main oil and gas layer sections of the n wells in the study area obtained in step 1 to the main oil and gas layer grid divided in step 9. Combined with the fracture model obtained in step 10, the current dominant orientation of the ground stress obtained in step 8, and the maximum principal stress, intermediate principal stress, and minimum principal stress of each unit grid obtained in step 9, calculate the shear stress τ and effective normal stress σ on each fracture surface in the fracture model in step 10. ne , the formula is as follows:

[0032] τ=F 11 F 12 σ1+F 12 F 22 σ2+F 13 F 23 σ3

[0033]

[0034] Among them: F xy are direction cosines:

[0035]

[0036] Where: σ1, σ2 and σ3 are the maximum principal stress, intermediate principal stress and minimum principal stress respectively, γ represents the angle between the normal line of the crack surface and the minimum principal stress, ω is the angle between the projection of the crack direction in the σ1-σ2 plane and the maximum principal stress, τ is the shear stress, σ ne is the effective normal stress, P o is the pore pressure;

[0037] Step 12: Using the fracture filling degree of the main oil and gas layer segments of the n wells in the study area obtained in Step 2, the fracture cohesion C is defined. When the fractures are fully filled, the fracture cohesion C is defined as 15 MPa; when the fractures are partially filled, the fracture cohesion C is defined as 8 MPa; when the fractures are not filled, the fracture cohesion C is defined as 1 MPa. The fracture cohesion C is then interpolated into the unit grid of the main oil and gas layer segment divided in Step 9.

[0038] In step 13, the rock friction coefficient of the main oil and gas layer sections of the n wells in the study area obtained in step 3 is interpolated into the unit grid divided in step 9. The shear stress and effective normal stress obtained in step 11 and the cohesion obtained in step 12 are combined to calculate the sliding tolerance value of each fracture in the fracture model constructed in step 10. The high or low value quantitatively represents the strength of the fracture activity. The sliding tolerance is calculated using the following formula:

[0039]

[0040] Where: T is the crack sliding tolerance, μ is the friction coefficient, C is the cohesion, τ is the shear stress on the crack surface, σ ne is the effective normal stress on the crack surface.

[0041] Furthermore, the conventional well logging curve in step 1 reports at least gamma, density and acoustic travel time.

[0042] Furthermore, the degree of crack filling in step 2 is divided into three types: fully filled, partially filled, and unfilled.

[0043] Furthermore, in step 8, the crack density is calculated in the form of line density, that is, the number of cracks per unit length.

[0044] Furthermore, the crack sliding tolerance value calculated in step 13 is between 0 and 1, and a larger value indicates a stronger crack activity.

[0045] Beneficial effects:

[0046] This method collects imaging logging data, conventional logging curves, pore pressure data and seismic data from the main oil and gas strata of n wells in the study area, observes the core fractures, collects experimental samples, and calculates the degree of fracture filling; conducts differential strain in situ stress testing, triaxial rock mechanics experiments and friction sliding experiments to obtain the maximum principal stress, intermediate principal stress, minimum principal stress, elastic modulus, Poisson's ratio and friction coefficient of the experimental samples; calculates the dynamic elastic modulus and Poisson's ratio through logging, and establishes the relationship between dynamic and static rock mechanics parameters; interprets the fracture occurrence, wellbore collapse and drilling-induced fractures, determines the current dominant in situ stress orientation, and calculates the fracture density; constructs a three-dimensional geological model and geomechanical model of the main oil and gas strata in the study area, divides the unit grid, and performs fracture geological modeling; calculates the sliding tolerance of each fracture, and uses it to quantitatively analyze the fracture activity.

[0047] The method of the present invention fully considers the influence of rock cohesion and friction coefficient on fracture activity, quantitatively analyzes the ratio of the shear stress on the fracture surface under the current ground stress to the theoretical shear stress for shear sliding, and analyzes the fracture activity based on this. The method takes into account comprehensive factors, has strong operability, simple operation steps, and highly reliable results. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 The figure is a flow chart of a method for analyzing crack activity according to the present invention. DETAILED DESCRIPTION

[0049] The embodiments of the present invention are further described below with reference to the accompanying drawings:

[0050] like Figure 1As shown, a fracture activity analysis method of the present invention collects imaging logging data, conventional logging curves, pore pressure data and seismic data of the main oil and gas layer sections of n wells in the study area, observes the core cracks in each well on site and collects experimental samples at different depths of the main oil and gas layer sections to observe whether the cracks are filled and calculate the degree of crack filling, thereby constraining the cohesion; differential strain in situ stress tests are performed on the collected experimental samples to obtain the maximum principal stress, intermediate principal stress and minimum principal stress of the experimental samples collected at different depths in all the wells; static elastic modulus and static Poisson's ratio of each test sample are obtained through triaxial rock mechanics experiments; friction and sliding tests are performed to obtain friction coefficient. friction coefficient; use logging data to calculate the dynamic elastic modulus and dynamic Poisson's ratio of the drilling rock where the sample is located, and establish the relationship between dynamic and static rock mechanics parameters; interpret fracture occurrence, wellbore collapse and drilling-induced fractures, determine the current dominant direction of ground stress, and calculate fracture density; by constructing a three-dimensional geological model of the main oil and gas layer sections in the study area and a geomechanical model of the main oil and gas layer sections in the study area covering n wells, divide the unit grid in the model, and perform numerical simulation of the current ground stress field and fracture geological modeling; calculate the shear stress and normal stress on each fracture surface, combine the cohesion and friction coefficient, define and calculate the sliding tolerance, and use this as an indicator parameter of fracture activity to quantitatively analyze fracture activity.

[0051] Specifically:

[0052] Step 1: Collect imaging logging data, conventional logging curves, pore pressure data and seismic data of the main oil and gas layers of n wells drilled in the study area; conventional logging curves should at least report gamma, density and acoustic travel time;

[0053] Step 2: Observe the core fractures of the main oil and gas layer sections of the n wells in step 1, including the fractures developed in the oil and gas layer sections, and calculate the filling degree of the fractures in each well. The fracture filling degree is divided into three types: fully filled, partially filled, and unfilled.

[0054] Core test samples were collected from different depths of the main oil and gas formations in each well, and the sampling depths of all test samples were recorded. The core test samples were prepared into plunger test samples with a diameter of 20 mm and a height of 40 mm, plunger test samples with a diameter of 25 mm and a height of 50 mm, and fan-shaped test samples with a radius of 50 mm and a height of 50 mm and a central angle of 90°. The sample end faces were machined using a grinder or lathe to keep them parallel.

[0055] Step 3: Cut the plunger test sample with a diameter of 20 mm and a height of 40 mm prepared in step 2 along a 35° angle with the axial direction to serve as the sliding surrounding rock block. Then, conduct a friction sliding test. During the test, apply the pore pressure collected in step 1 to obtain the friction coefficient of the plunger test sample:

[0056]

[0057] Where: μ is the friction coefficient, τ is the shear stress, σ ne represents the effective normal stress, P o is the pore pressure;

[0058] Step 4: Using the plunger test sample with a diameter of 25 mm and a height of 50 mm prepared in step 2, conduct triaxial rock mechanics experiments to obtain the static elastic modulus and static Poisson's ratio of the rock:

[0059]

[0060]

[0061] Where: E s The rock elastic modulus obtained from the experimental test, namely the rock static elastic modulus, μ s The rock Poisson's ratio obtained from the experimental test, that is, the rock static Poisson's ratio, (S1-S3) (50) 50% of the maximum principal stress difference of the specimen, ε h(50) Indicates (S1-S3) (50) The corresponding axial compressive strain, ε d(50) (S1-S3) (50) The corresponding circumferential compressive strain;

[0062] Step 5: Using the sector-shaped experimental sample with a radius of 50 mm, a height of 50 mm, and a central angle of 90° prepared in Step 2, a differential strain in-situ stress test is performed to obtain the current in-situ stress of the core experimental sample: maximum principal stress, intermediate principal stress, and minimum principal stress;

[0063] Step 6: Calculate the rock dynamic elastic modulus and dynamic Poisson's ratio using the conventional logging curves collected in step 1:

[0064]

[0065]

[0066]

[0067] Where: μ d is the dynamic Poisson's ratio of rock, G is the shear modulus, E d is the dynamic elastic modulus of rock, ρ b represents the formation volume density, Δt s is the formation shear wave time difference, Δt p is the formation longitudinal wave time difference.

[0068] Step 7: Use the linear fitting method to establish the relationship between the static rock mechanical parameters obtained in step 4 and the dynamic rock mechanical parameters obtained in step 6. Based on the relationship, the dynamic elastic modulus and dynamic Poisson's ratio obtained by logging curve calculation are converted into static elastic modulus and static Poisson's ratio, thus achieving the continuity of static rock mechanical parameters throughout the entire well section:

[0069]

[0070] Where: a, b, c, d are fitting coefficients.

[0071] Step 8: Using the imaging logging data collected in step 1, interpret the fractures, wellbore collapse and drilling-induced fractures, pick up the fracture occurrence parameters, wellbore collapse azimuth and drilling-induced fracture azimuth, and calculate the fracture density. The fracture density is expressed as line density, that is, the number of fractures per unit length; the wellbore collapse azimuth ±90° is recorded as α j , the drilling-induced fracture orientation is recorded as α k , change α j and α k By converting all ±180° values into the range of [0, 180°), the dominant direction of the current ground stress near the wellbore is determined based on the relationship between wellbore collapse, drilling-induced fractures and current ground stress, and its azimuth is expressed as:

[0072]

[0073] Where p and q represent the number of wellbore collapse and drilling-induced fractures, respectively.

[0074] Step 9: Use the seismic data collected in step 1 to establish a three-dimensional geometric model of the main oil and gas layer sections in the study area, divide the unit grid, and use the spatial interpolation method to interpolate the rock mechanical parameters of the different drilling full-well sections obtained in step 7 into the three-dimensional grid using the Gaussian sequential method to achieve three-dimensional geological model construction. Combined with the current ground stress magnitude obtained in step 5 and the current ground stress direction obtained in step 8, a three-dimensional geomechanical model of the main oil and gas layer sections in the study area is constructed. Finite element numerical simulation technology is used to find out the maximum principal stress, intermediate principal stress, and minimum principal stress of each unit grid in the three-dimensional geomechanical model of the main oil and gas layer sections;

[0075] Step 10: Under the constraints of fracture occurrence and density in step 8, a stochastic fracture modeling method is used based on discrete fracture patterns to construct a fracture model, and the fracture development distribution and occurrence characteristics of the main oil and gas-bearing layers in the study area are quantitatively characterized by the model;

[0076] Step 11: interpolate the pore pressure of the main oil and gas layer sections of the n wells in the study area obtained in step 1 to the main oil and gas layer grid divided in step 9. Combined with the fracture model obtained in step 10, the current dominant orientation of the ground stress obtained in step 8, and the maximum principal stress, intermediate principal stress, and minimum principal stress of each unit grid obtained in step 9, calculate the shear stress τ and effective normal stress σ on each fracture surface in the fracture model in step 10. ne , the formula is as follows:

[0077] τ=F 11 F 12 σ1+F 12 F 22 σ2+F 13 F 23 σ3

[0078]

[0079] Among them: F xy are direction cosines:

[0080]

[0081] Where: σ1, σ2 and σ3 are the maximum principal stress, intermediate principal stress and minimum principal stress respectively, γ represents the angle between the normal line of the crack surface and the minimum principal stress, ω is the angle between the projection of the crack direction in the σ1-σ2 plane and the maximum principal stress, τ is the shear stress, σ ne is the effective normal stress, P o is the pore pressure;

[0082] Step 12: Using the fracture filling degree of the main oil and gas layer segments of the n wells in the study area obtained in Step 2, the fracture cohesion C is defined. When the fractures are fully filled, the fracture cohesion C is defined as 15 MPa; when the fractures are partially filled, the fracture cohesion C is defined as 8 MPa; when the fractures are not filled, the fracture cohesion C is defined as 1 MPa. The fracture cohesion C is then interpolated into the unit grid of the main oil and gas layer segment divided in Step 9.

[0083] In step 13, the rock friction coefficient of the main oil and gas layer sections of the n wells in the study area obtained in step 3 is interpolated into the unit grid divided in step 9. The shear stress and effective normal stress obtained in step 11 and the cohesion obtained in step 12 are combined to calculate the sliding tolerance value of each crack in the fracture model constructed in step 10. The fracture sliding tolerance value ranges from 0 to 1. The larger the value, the stronger the fracture activity. The fracture activity is quantitatively represented by the high or low fracture sliding tolerance value. The sliding tolerance is calculated using the following formula:

[0084]

[0085] Where: T is the crack sliding tolerance, μ is the friction coefficient, C is the cohesion, τ is the shear stress on the crack surface, σ ne is the effective normal stress on the crack surface.

Claims

1. A method for analyzing crack activity, characterized by: The imaging logging data, conventional logging curves, pore pressure data, and seismic data volumes were collected from the main oil and gas formations of n wells in the study area. The core fractures in each well were observed on-site, and experimental samples were collected at different depths in the main oil and gas formations to observe whether the fractures were filled. The degree of fracture filling was calculated and used to constrain the cohesion. Differential strain in situ stress tests were performed on the collected experimental samples to obtain the maximum principal stress, intermediate principal stress, and minimum principal stress of the experimental samples collected at different depths in all wells. The static elastic modulus and static Poisson's ratio of each test sample were obtained through triaxial rock mechanics experiments, and the friction coefficient was obtained through friction-sliding experiments. The dynamic elastic modulus and dynamic Poisson's ratio of the rock in the well where the sample was located were calculated using the logging data, and the relationship between dynamic and static rock mechanics parameters was established. Interpret fracture occurrence, wellbore collapse, and drilling-induced fractures to determine the dominant orientation of current geostress and calculate fracture density. Construct a three-dimensional geological model of the main oil and gas strata in the study area and a geomechanical model of the main oil and gas strata in the study area covering n wells. Divide the model into unit grids to perform numerical simulations of the current geostress field and fracture geological modeling. Calculate the shear stress and effective normal stress on each fracture surface in the fracture model. Use the obtained fracture filling degree of the main oil and gas strata in the n wells in the study area to define fracture cohesion. Define fracture cohesion C=15MPa for fully filled fractures, C=8MPa for partially filled fractures, and C=1MPa for unfilled fractures. Interpolate this value to the divided unit grids of the main oil and gas strata. The rock friction coefficients of the main oil and gas layers of the n wells in the study area were interpolated into the divided unit grids. The shear stress, effective normal stress, and cohesion obtained were combined to calculate the sliding tolerance of each fracture in the constructed fracture model. The high or low value quantitatively represents the strength of the fracture activity. The sliding tolerance was calculated using the following formula: ； Where: T is the crack sliding tolerance, μ is the friction coefficient, C is the cohesion, τ is the shear stress on the crack surface, σ ne is the effective normal stress on the crack surface.

2. A crack activity analysis method according to claim 1, characterized in that: The steps include: Step 1: Collect imaging logging data, conventional logging curves, pore pressure data and seismic data of the main oil and gas layers of n wells drilled in the study area; Step 2: Observe the core cracks of the main oil and gas layer sections of the n wells in step 1, including the cracks developed in the oil and gas layer sections, calculate the filling degree of the cracks in each well, collect core test samples at different depths of the main oil and gas layer sections of each well, and record the sampling depths of all test samples. Prepare the core test samples into plunger test samples with a diameter of 20 mm and a height of 40 mm, plunger test samples with a diameter of 25 mm and a height of 50 mm, and fan-shaped test samples with a radius of 50 mm and a height of 50 mm and a central angle of 90°, and process the end faces of the samples using a grinder or a lathe to keep them parallel; Step 3: Cut the plunger test sample with a diameter of 20 mm and a height of 40 mm prepared in step 2 along a 35° angle with the axial direction to serve as the sliding surrounding rock block. Then, conduct a friction sliding test. During the test, apply the pore pressure collected in step 1 to obtain the friction coefficient of the plunger test sample: ； Where: μ is the friction coefficient, τ is the shear stress, σ ne represents the effective normal stress, P o is the pore pressure; Step 4: Using the plunger test sample with a diameter of 25 mm and a height of 50 mm prepared in step 2, conduct triaxial rock mechanics experiments to obtain the static elastic modulus and static Poisson's ratio of the rock: ； ； Where: E s The rock elastic modulus obtained from the experimental test, namely the rock static elastic modulus, μ s The rock Poisson's ratio obtained from the experimental test, that is, the rock static Poisson's ratio, (S1-S3) (50) 50% of the maximum principal stress difference of the specimen, ε h(50) Indicates (S1-S3) (50) The corresponding axial compressive strain, ε d(50) (S1-S3) (50) The corresponding circumferential compressive strain; Step 5: Using the sector-shaped experimental sample with a radius of 50 mm, a height of 50 mm, and a central angle of 90° prepared in Step 2, a differential strain in-situ stress test is performed to obtain the current in-situ stress of the core experimental sample: maximum principal stress, intermediate principal stress, and minimum principal stress; Step 6: Calculate the rock dynamic elastic modulus and dynamic Poisson's ratio using the conventional logging curves collected in step 1: ； ； ； Where: µ d is the dynamic Poisson's ratio of rock, G is the shear modulus, E d is the dynamic elastic modulus of rock, ρ b represents the formation volume density, Δt s is the formation shear wave time difference, Δt p is the formation P-wave time difference; Step 7: Use the linear fitting method to establish the relationship between the static rock mechanical parameters obtained in step 4 and the dynamic rock mechanical parameters obtained in step 6. Based on the relationship, the dynamic elastic modulus and dynamic Poisson's ratio obtained by logging curve calculation are converted into static elastic modulus and static Poisson's ratio, thus achieving the continuity of static rock mechanical parameters throughout the entire well section: ； Where: a, b, c, d are fitting coefficients; Step 8: Using the imaging logging data collected in step 1, interpret the fractures, wellbore collapse and drilling-induced fractures, pick up the fracture occurrence parameters, wellbore collapse azimuth and drilling-induced fracture azimuth, calculate the density of the fractures, and record the wellbore collapse azimuth ±90° as α j , the drilling-induced fracture orientation is recorded as α k , change α j and α k By converting all ±180° values into the range of [0, 180°), the dominant direction of the current ground stress near the wellbore is determined based on the relationship between wellbore collapse, drilling-induced fractures and current ground stress, and its azimuth is expressed as: ； Where: p and q represent the number of wellbore collapse and drilling-induced fractures, respectively; Step 9: Use the seismic data collected in step 1 to establish a three-dimensional geometric model of the main oil and gas layer sections in the study area, divide the unit grid, and use the spatial interpolation method to interpolate the rock mechanical parameters of the different drilling full-well sections obtained in step 7 into the three-dimensional grid using the Gaussian sequential method to achieve three-dimensional geological model construction. Combined with the current ground stress magnitude obtained in step 5 and the current ground stress direction obtained in step 8, a three-dimensional geomechanical model of the main oil and gas layer sections in the study area is constructed. Finite element numerical simulation technology is used to find out the maximum principal stress, intermediate principal stress, and minimum principal stress of each unit grid in the three-dimensional geomechanical model of the main oil and gas layer sections; Step 10: Under the constraints of fracture occurrence and density in step 8, a stochastic fracture modeling method is used based on discrete fracture patterns to construct a fracture model, and the fracture development distribution and occurrence characteristics of the main oil and gas-bearing layers in the study area are quantitatively characterized by the model; Step 11: interpolate the pore pressure of the main oil and gas layer sections of the n wells in the study area obtained in step 1 to the main oil and gas layer grid divided in step 9. Combined with the fracture model obtained in step 10, the current dominant orientation of the ground stress obtained in step 8, and the maximum principal stress, intermediate principal stress, and minimum principal stress of each unit grid obtained in step 9, calculate the shear stress on each fracture surface in the fracture model in step 10. and effective normal stress , the formula is as follows: ； ； Among them: F xy are direction cosines: ； Where: σ1, σ2 and σ3 are the maximum principal stress, intermediate principal stress and minimum principal stress respectively, γ represents the angle between the normal line of the crack surface and the minimum principal stress, ω is the angle between the projection of the crack direction in the σ1-σ2 plane and the maximum principal stress, τ is the shear stress, σ ne is the effective normal stress, P o is the pore pressure; Step 12: Define the fracture cohesion C using the fracture filling degree of the main oil and gas layer segments of the n wells in the study area obtained in Step 2. When the fractures are fully filled, the fracture cohesion C is defined as 15 MPa; when the fractures are partially filled, the fracture cohesion C is defined as 8 MPa; when the fractures are not filled, the fracture cohesion C is defined as 1 MPa. Interpolate the result into the unit grid of the main oil and gas layer segment divided in Step 9. In step 13, the rock friction coefficient of the main oil and gas layer sections of the n wells in the study area obtained in step 3 is interpolated into the unit grid divided in step 9. The shear stress and effective normal stress obtained in step 11 and the cohesion obtained in step 12 are combined to calculate the sliding tolerance value of each fracture in the fracture model constructed in step 10. The high or low value quantitatively represents the strength of the fracture activity. The sliding tolerance is calculated using the following formula: ； Where: T is the crack sliding tolerance, μ is the friction coefficient, C is the cohesion, τ is the shear stress on the crack surface, σ ne is the effective normal stress on the crack surface.

3. A crack activity analysis method according to claim 2, characterized in that: The conventional logging curve in step 1 includes at least gamma, density and acoustic time difference.

4. A crack activity analysis method according to claim 2, characterized in that: In step 2, the degree of crack filling is divided into three types: fully filled, partially filled, and unfilled.

5. A crack activity analysis method according to claim 2, characterized in that: In step 8, the crack density is expressed in the form of line density, that is, the number of cracks per unit length.

6. A crack activity analysis method according to claim 2, characterized in that: The crack sliding tolerance value calculated in step 13 is between 0 and 1, and a larger value indicates a stronger crack activity.

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