Fault slip analysis method based on coupling pore medium elastic mechanics

Abstract

The invention discloses a fault slip analysis method based on coupling pore medium elastic mechanics. The fault slip analysis method comprises the steps that needed geological data are collected and preprocessed; the required geological data comprises stratigraphic structure, rock physical properties and pore pressure change information; the method comprises the following steps: establishing a mathematical model based on a Biot pore elasticity theory, carrying out mathematical analysis solution on a Biot equation by utilizing Hankel transformation, and describing underground fluid flow and influence of the underground fluid flow on mechanical properties of surrounding rocks; coupling analysis between the pore pressure and the rock elastic stress is achieved, and solving is conducted through Hankel transformation; the mathematical model is verified through specific cases, the effectiveness of the mathematical model under different geological conditions is ensured, and model parameters are adjusted according to actual conditions to optimize the performance of the mathematical model; a Monte-Carlo random process algorithm is adopted to predict and analyze the uncertainty in the geological process, and a potential fault slippage area is identified. The mechanism of the underground physical process can be deeply reflected.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of geological engineering and resource exploitation, and particularly relates to a fault slip analysis method based on coupled poroelasticity. BACKGROUND

[0002] In the field of geological engineering and resource exploitation, assessing and predicting fault slip risk is a key step to ensure the safety of mining activities and environmental protection. Traditional risk prediction methods and software mainly rely on the direct change of pore pressure and the reduction of effective stress to assess fault slip risk, but fail to fully consider the influence of coupled stress field conduction. SUMMARY

[0003] In view of this, the present application provides a fault slip analysis method based on coupled poroelasticity.

[0004] The present application discloses a fault slip analysis method based on coupled poroelasticity, which comprises the following steps:

[0005] Step 1: Collect the required geological data and preprocess it; the required geological data includes stratigraphic structure, rock physical properties and pore pressure change information;

[0006] Step 2: Based on the Biot poroelasticity theory, a mathematical model is established, and the Biot equation is mathematically analyzed and solved by using Hankel transform to describe the underground fluid flow and its influence on the mechanical properties of the surrounding rock;

[0007] Step 3: Realize the coupling analysis between pore pressure and rock elastic stress and solve it by Hankel transform;

[0008] Step 4: Verify the mathematical model in step 2 through specific cases to ensure its effectiveness under different geological conditions, and adjust the model parameters according to the actual situation to optimize its performance;

[0009] Step 5: Use Monte-Carlo random process algorithm to predict and analyze the uncertainty in the geological process and identify the potential fault slip area.

[0010] Further, in step 2, a mathematical model is established based on Biot poroelasticity theory, which considers the problem of injecting fluid into a horizontal permeable layer with a thickness of 2h, which is bounded on both sides by semi-infinite impermeable formations, the injection segment penetrates the thickness of the permeable layer, and exchanges fluid with the surrounding rock at a constant volume rate Q, which is uniformly distributed over the thickness of the reservoir, all layers are homogeneous and isotropic, and have the same elastic properties, i.e., the same shear modulus G and Poisson's ratio; the permeable layer is also characterized by additional poroelastic parameters, and the layers are bonded, i.e., the displacement at the interface is continuous; the origin of time t = 0 is chosen to coincide with the moment when fluid exchange begins, and at t = 0, all pre-existing hydraulic and solid mechanics fields are assumed to be in equilibrium; a cylindrical coordinate system (r, θ, z) is defined with its origin at the point of coordinates 0 and the z-axis pointing upward, perpendicular to the layer plane; in this cylindrical coordinate system, the uniform source density σ along the well corresponds to QH(t)δ(r) / (8πh), where H(t) and δ(r) represent the Heaviside step function and the Dirac delta function, respectively; the fluid-structure interaction response is governed by the Biot equation; where h is the formation thickness direction coordinate, r is the normal coordinate in the cylindrical coordinate system, and θ is the tangential coordinate in the cylindrical coordinate system.

[0011] Further, the Biot equation is mathematically solved using Hankel transform, including:

[0012] If the displacement field u is irrotational, i.e., then the coupled equation can be simplified; by applying Hankel transform, the Biot equation is converted from real space to frequency space, and the partial differential equation is simplified to an ordinary differential equation for ease of solution; in the conversion process, the original Biot partial differential equation is converted into a set of algebraic equations related to the Hankel transform parameters and simplified, and the analytical or numerical solution in the original physical space is obtained through inverse Hankel transform, which is used to understand and predict fluid-structure coupling in porous media.

[0013] Further, the flow of underground fluid and its effect on the mechanical properties of the surrounding rock involve complex coupling effects, which are described by the Biot equation in the theories of porous media, poroelasticity, and fluid dynamics:

[0014] The flow of underground fluid is mainly affected by factors such as porosity, permeability, and the viscosity of the fluid; the movement of underground fluid under the action of pressure gradient is described by Darcy's law, which flows from high-pressure areas to low-pressure areas, and the movement of underground fluid directly affects the pressure distribution in the porous medium, and further affects the migration and distribution of fluid in the formation;

[0015] Rock mechanical properties include elastic modulus, shear modulus, and Poisson's ratio, which describe the deformation and fracture characteristics of rocks under external forces, determining the response of rocks to stress changes, including compression, expansion, and shear deformation of rocks; changes in fluid pressure can change the stress state in rocks, thereby affecting the mechanical behavior and structural stability of rocks;

[0016] There is a complex coupling relationship between underground fluid flow and the mechanical properties of surrounding rocks, which is reflected in the following aspects: feedback between pore pressure change, rock deformation and flow, crack formation and expansion, and pore elasticity effect.

[0017] Further, the change in pore pressure: the movement of fluid leads to a change in pore pressure, which directly affects the effective stress of the rock, and the change in effective stress can cause the rock to compress or expand, affecting its permeability and porosity; feedback between rock deformation and flow: rock deformation changes the pore structure, which in turn affects the flow characteristics of the fluid; crack formation and expansion: an increase in fluid pressure can sometimes cause the stress inside the rock to exceed its strength limit, leading to the formation and expansion of cracks; pore elasticity effect: the pore elasticity theory considers the coupling between fluid flow in porous media and solid skeleton deformation; changes in fluid pressure will cause deformation of the solid skeleton, which in turn affects the pore space and fluid flow.

[0018] Further, step 3 includes:

[0019] (1) Define the problem and establish the model:

[0020] 1) Clearly define the physical background and objectives of the problem, including the geological conditions considered, the type of fluid, and the characteristics of the rock;

[0021] 2) Establish a mathematical model to describe the coupling between pore pressure and rock elastic stress;

[0022] (2) Apply Hankel transform:

[0023] Choose a type of Hankel transform that is suitable for the symmetry of the problem;

[0024] Convert the partial differential equations corresponding to the Biot coupled equations into ordinary differential equations in the frequency domain through Hankel transform; involves converting spatial variables to frequency space variables;

[0025] (3) Solve the equations in the frequency domain:

[0026] 1) Solve the ordinary differential equation;

[0027] 2) For non-homogeneous equations, specific integration techniques or numerical methods may be needed to find the solution;

[0028] (4) Apply the inverse Hankel transform:

[0029] Convert the solution in the frequency domain back to real space through the inverse Hankel transform;

[0030] (5) Analysis and verification results:

[0031] 1) Analyze the obtained pore pressure and rock elastic stress distribution results, and check their physical reasonableness;

[0032] 2) Comparison with experimental data or field observation data may be needed to verify the accuracy and reliability of the model;

[0033] (6) Parameter sensitivity analysis and further research:

[0034] 1) Perform parameter sensitivity analysis to understand the impact of changes in different rock physical parameters on pore pressure and elastic stress distribution;

[0035] 2) Further optimization and research as needed to improve the model or explore different geological conditions and fluid dynamic conditions.

[0036] Further, step 4 comprises:

[0037] Select representative shale gas blocks, collect observed data of fault slip events and rock mechanics parameters of shale layers, and input them into the mathematical model in step 2 for analysis. Based on the mathematical model, calculate the pore pressure change, rock stress distribution and their evolution over time during shale gas exploitation, and compare the calculated pore pressure change, rock stress distribution and their evolution over time with the observed data of fault slip events to check whether the mathematical model can accurately reflect the actual observed data. Use the data predicted by the mathematical model to analyze how cracks expand or generate new cracks as the pressure changes during shale gas exploitation, and compare the crack distribution, direction and density predicted by the mathematical model with geological survey and microseismic monitoring data to verify whether the model can accurately predict the complex nature of crack development.

[0038] Further, step 5 comprises:

[0039] Monte-Carlo model setup and parameterization: Clearly represent the fault area and its surrounding rock properties in the Monte-Carlo model, including the location, strike and dip angle of the fault; parameterize key factors affecting fault stability; key factors include pore pressure, rock mechanical properties and friction coefficient on the fault plane;

[0040] Monte-Carlo simulation: Numerical simulation is performed on each set of parameter generated by Monte-Carlo method, calculating the change of pore pressure and its influence on the stress state of surrounding rock during the change of pore pressure, and focusing on the fault area in the simulation results, evaluating the reduction of effective normal stress caused by pressure change and its influence on fault slip stability;

[0041] Assessing fault slip potential: Assessing the ratio of shear stress to normal stress on the fault plane to determine the potential of fault slip; analyzing the stress changes of the fault area under different simulation scenarios to identify the fault areas that are more prone to slip under the influence of pressure change;

[0042] Statistical analysis and probability assessment: Statistical analysis of all simulation results to assess the probability of fault slip under different conditions and identify high-probability slip areas; considering the uncertainty of model parameters, the uncertainty of prediction is quantified by calculating the results of Monte-Carlo model output; the results include confidence intervals;

[0043] Sensitivity analysis: Sensitivity analysis to understand the parameters that have the greatest impact on the prediction of fault slip potential, to identify the key factors that affect fault stability;

[0044] Result interpretation and risk assessment: Comprehensive simulation results and risk analysis to form a comprehensive assessment of potential fault slip areas, and map the fault slip area to provide a risk view; according to the probability of fault slip, the potential risks are sorted and classified.

[0045] Further, after step 5, it further includes: assessing the geological risks caused by each factor, including changes in pore pressure; the assessment of geological risks caused by each factor includes the following steps:

[0046] (1) Preliminary geological survey:

[0047] Data collection: Collect relevant data on geology, geophysics, hydrogeology and engineering geology, including rock types, stratigraphic structure, fault distribution and historical instability events; Geological model construction: Based on the collected data, construct a geological model to analyze the areas that may be affected by changes in pore pressure;

[0048] (2) Rock mechanics and fluid dynamics analysis:

[0049] Rock mechanics parameter evaluation: Determine the mechanical properties of rock, including elastic modulus, Poisson's ratio and shear strength; Fluid pressure analysis: Analyze the migration path of fluid in rock during the change of pore pressure, the change of pressure and its influence on the surrounding rock;

[0050] (3) Application of numerical simulation:

[0051] Coupled simulation: using numerical simulation software, combined with rock mechanics and fluid dynamics theory, to conduct coupled simulation to predict the influence of fluid injection on rock stress state; fault slip and fracture propagation analysis: simulate the response of faults and fractures under injection activities, and evaluate the possibility of slip and new fracture formation;

[0052] (4) Geological risk assessment:

[0053] Identify sensitive areas: based on simulation results, identify high-risk areas where fault slip or fracture propagation is likely to occur; evaluate surface impacts: consider the potential impacts of underground activities on surface stability, groundwater systems, and ecological environment;

[0054] (5) Uncertainty and sensitivity analysis:

[0055] Uncertainty analysis: assess the impact of Monte-Carlo model parameter uncertainty on risk assessment results; sensitivity analysis: determine the parameters that have the greatest impact on risk assessment results for risk management; analyze the geological risks caused by fracturing or wastewater injection.

[0056] Further, it also includes result presentation and interpretation: display the calculation results and provide interpretation and analysis report to facilitate user understanding and application; the calculation results include stress distribution map and risk area identification.

[0057] The present invention has the following advantages:

[0058] 1. Based on Biot poroelasticity theory, the method of coupling stress field conduction and pore pressure is adopted, and the calculation program developed by high-level programming language effectively handles complex geological data and mathematical operations, improving the accuracy and efficiency of geological risk assessment, and having significant advantages in predicting the fault slip potential caused by poroelastic stress.

[0059] 2. Improve the accuracy of prediction: by considering the direct effect of pore pressure and the complex interaction between pore pressure and rock elastic stress, it can more accurately predict the coupled stress changes of underground medium and the Coulomb stress increment on the fault surface induced by pore pressure changes. This method can accurately simulate and predict the impact of underground fluid activity on fault stability, and has significant advantages in assessing the risk of geological body instability in non-directly affected areas.

[0060] 3. Improve the speed and efficiency of data processing: the calculation program developed by Mathematica and Matlab programming language can efficiently handle large amounts of geological data and complex mathematical operations, not only reducing the time required for risk assessment, but also improving the efficiency of the entire assessment process.

[0061] 4. Expanded applicability of the prediction model: The successful application of the invention is not limited to specific geological conditions or specific mining activities, but can be widely applied to various geological environments and different types of underground operations. This greatly expands the applicability of the prediction model, making it capable of meeting the needs of a wider range of geological engineering and resource exploitation.

[0062] 5. Enhanced ability of geological risk management: The invention provides strong support for geological risk management by providing more accurate and reliable risk assessment results of geological body instability, enabling decision-makers to make risk management and response strategies based on more reliable data, thereby effectively reducing the risk and impact of geological disasters.

[0063] 6. Promote environmental protection and sustainable development: The invention helps to prevent possible environmental pollution and geological disasters by accurately predicting and assessing geological risks caused by underground activities, supporting environmental protection and sustainable exploitation of resources.

[0064] 7. By adopting a model that combines coupled stress field conduction and pore pressure, the invention uses mathematical transformation to achieve accurate analytical solution of complex Biot equations, which can deeply reflect the mechanism of underground physical processes and is leading in the field of fault slip risk prediction. Compared with traditional methods that mainly rely on pore pressure changes for prediction, the invention considers the interaction of fluid dynamics and solid mechanics, providing a deeper understanding and analysis of the impact of underground fluid activity on fault stability, and can more accurately simulate and predict the impact of underground fluid activity on fault stability, with significant advantages in the risk assessment of geological body instability in non-directly affected areas. In summary, the invention aims to provide a more efficient and accurate method for risk assessment of geological body instability, providing strong technical support for the prevention and management of geological disasters.

[0065] 8. The invention develops a new risk assessment model by introducing the concept of coupled stress field conduction, providing a more comprehensive and accurate method for fault slip risk prediction. Its core advantage lies in its ability to consider the impact of coupled stress field on fault stability, thereby effectively predicting the risk of geological body instability in the direct pore pressure rise area and the area far from the intervention area, significantly improving the accuracy and reliability of the prediction.

[0066] 9. The method's deep understanding and analysis of complex geological phenomena not only enhances its application value in the field of geological engineering and resource exploitation, but also has important significance for the safe exploitation of underground resources and environmental protection, providing a powerful new tool for risk assessment and management of geological body instability, and helping to promote the development of resource exploitation activities towards a safer and more sustainable direction. BRIEF DESCRIPTION OF DRAWINGS

[0067] The accompanying drawings are only some of the embodiments of the present application, and other embodiments can be obtained by those skilled in the art according to the drawings.

[0068] Figure 1 A fault stress state diagram (Simpson coefficient diagram) of a certain block of an embodiment of the present application;

[0069] Figure 2 A relative position diagram of a fault and a fractured well of a certain block of an embodiment of the present application;

[0070] Figure 3 A coupling stress increment-time relationship diagram on a certain fault of an embodiment of the present application;

[0071] Figure 4 A coupling stress influence range distribution diagram (8 million cubic meters of injection volume) of an embodiment of the present application;

[0072] Figure 5 An influence diagram of coupling stress generated by fracturing on a certain fault of an embodiment of the present application;

[0073] Figure 6 A flowchart of a fault slip analysis method based on coupling poroelasticity of an embodiment of the present application. DETAILED DESCRIPTION

[0074] The present application will be further described in conjunction with the drawings and embodiments, and the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those skilled in the art shall fall within the scope of protection of the embodiments of the present application.

[0075] Reference Figure 6 , the present application provides an embodiment of a fault slip analysis method based on coupling poroelasticity, which comprises the following steps:

[0076] Step 1: Data collection and pretreatment: collect the required geological data and pretreat it; the required geological data includes formation structure, rock physical properties and pore pressure change information.

[0077] Step 2: Establish a mathematical model: establish a mathematical model based on Biot poroelasticity theory, use Hankel transform to solve the Biot equation, and describe the migration of underground fluid and its influence on the mechanical properties of surrounding rocks.

[0078] Based on the Biot poroelasticity theory, a mathematical model is established: The problem considered is that of a vertical source segment injecting fluid into a horizontal permeable layer of thickness 2h bounded on both sides by semi-infinite impermeable strata. The injection segment penetrates the thickness of the permeable layer and exchanges fluid with the surrounding rock at a constant volumetric rate Q, which is uniformly distributed over the thickness of the reservoir layer. All layers are homogeneous and isotropic and have identical elastic properties, i.e. the same shear modulus G and Poisson's ratio. However, the permeable layer is also characterized by additional poroelastic parameters. There is perfect bonding between the layers. That is, the displacement is continuous at the interfaces. The origin of time, t = 0, is chosen to coincide with the instant at which the fluid exchange begins. At that time point, all pre-existing fields (hydrodynamic and solid mechanics) are assumed to be in equilibrium. A cylindrical coordinate system (r, θ, z) is defined with its origin at the middle of the source segment and the z-axis pointing upward, normal to the layer plane. In this coordinate system, the uniform source density σ along the well corresponds to QH(t)δ(r) / (8πh), where H(θ) and δ(θ) denote the Heaviside step function and the Dirac delta function, respectively. The fluid-structure interaction response is governed by the equations of the poroelasticity theory, which was originally introduced by Biot. This theory combines the classical theory of elasticity and the theory of compressible fluid flow in porous media by introducing a coupling between the hydrodynamic and mechanical fields in the constitutive equations of the fluid-saturated porous solid.

[0079] Mathematical analytical solution of the Biot equations using Hankel transform: If the displacement field u is irrotational (i.e. if ), then the coupled equations can be significantly simplified. In the particular problem considered, the irrotationality of the displacement is a consequence of the sufficient combination of three conditions: the infinite extent of the domain, the homogeneity of its elastic properties, and the purely hydrodynamic nature of the boundary conditions at the interfaces between the well and the permeable layer and the impermeable layers. To prove the irrotationality of the displacement, an equivalent problem is considered in which the original poroelastic properties of the permeable layer have been extended to the entire domain, while an "internal" no-flow condition has been imposed at the original interfaces. These hydrodynamic interface conditions ensure that the pore pressure remains constant in the adjacent layers, so the hydro-mechanical response of the equivalent problem is identical to that of the original problem.

[0080] The irrotationality of the displacement can then be obtained, in principle, by superimposing the full-space poroelastic fluid source and dipole singular solutions and noting the irrotational nature of these singularities. In practice, the fluid exchange between the well and the reservoir can be modeled by integrating the continuous full-space source / sink singularities over a segment extending through the thickness of the original permeable layer, enforcing the zero flux conditions on the top and bottom faces by convolving the instantaneous fluid dipoles in time and space on both interfaces.

[0081] Mathematical solution of Biot's equations using Hankel transform is an effective method for analyzing the coupled fluid motion and solid deformation in porous elastic media. First, by applying Hankel transform, Biot's equations are converted from real space to frequency space, simplifying partial differential equations into ordinary differential equations for easier solution. Hankel transform is particularly suitable for axisymmetric problems where displacement and pressure fields depend on radial distance and time. During the conversion, the original Biot partial differential equations are transformed into a set of algebraic equations related to the Hankel transform parameter. These equations can then be solved through standard mathematical techniques, such as further simplification using Laplace transform and application of inverse transform to obtain solutions in real space. This approach allows us to study the dynamic response of porous elastic media caused by fluid injection or extraction in detail, including changes in pressure distribution and displacement field. Finally, through inverse Hankel transform, analytical or numerical solutions in the original physical space can be obtained, providing a powerful tool for understanding and predicting fluid-solid coupling behavior in porous media.

[0082] Mathematical solution of Biot's equations using Hankel transform. Subsurface fluid migration and its impact on surrounding rock mechanical properties: Subsurface fluid flow and its impact on surrounding rock mechanical properties involve complex coupling effects, which are described by the aforementioned Biot's equations in porous media theory, poroelasticity theory, and fluid dynamics:

[0083] Subsurface fluid flow: Subsurface fluid flow is mainly influenced by factors such as porosity (the proportion of pore space), permeability (the ability of rock to allow fluid to pass through), and fluid viscosity. Fluid flows from areas of high pressure to low pressure under the action of pressure gradient. This flow can be described by Darcy's Law, which defines the relationship between fluid flow rate and pressure gradient. The movement of subsurface fluids directly affects the pressure distribution in porous media, which in turn affects the migration and distribution of fluids in the formation.

[0084] Rock mechanical properties: Rock mechanical properties, including elastic modulus, shear modulus, and Poisson's ratio, describe the deformation and fracture characteristics of rock under external forces. These properties determine the response of rock to stress changes, including compression, expansion, and shear deformation of rock. Changes in fluid pressure can change the stress state in rock, affecting the mechanical behavior and structural stability of rock.

[0085] Coupling effects: There is a complex coupling relationship between subsurface fluid flow and surrounding rock mechanical properties. This mainly manifests in the following aspects:

[0086] (1) Pore pressure changes: The movement of fluids leads to changes in pore pressure, which directly affect the effective stress of the rock. Changes in effective stress can cause the rock to compress or expand, affecting its permeability and porosity.

[0087] (2) Feedback between rock deformation and flow: Deformation of the rock (such as due to compression or expansion) changes the pore structure, which in turn affects the flow characteristics of the fluids. For example, compression of the rock can decrease porosity and permeability, slowing down fluid flow.

[0088] (3) Formation and propagation of fractures: Increases in fluid pressure can sometimes cause stresses within the rock to exceed its strength limits, leading to the formation and propagation of fractures. The development of fractures not only changes the structure and mechanical properties of the rock but also provides new pathways for fluids, greatly affecting the migration patterns of fluids.

[0089] (4) Poro-elastic effects: Poro-elastic theory considers the coupling between fluid flow in porous media and deformation of the solid skeleton. Changes in fluid pressure cause deformation of the solid skeleton, which in turn affects the pore space and fluid flow.

[0090] Step 3: Implement the coupling analysis between pore pressure and rock elastic stress and solve it through Hankel transform. Specifically, it is divided into the following steps:

[0091] (1) Define the problem and establish the model

[0092] 1) Clearly define the physical background and objectives of the problem, including the geological conditions considered, the type of fluid, the characteristics of the rock, etc.

[0093] 2) Establish a mathematical model to describe the coupling relationship between pore pressure and rock elastic stress. Typically involves Biot's equation in poro-elastic theory, which describes the coupling behavior of fluid flow and solid skeleton deformation in porous media.

[0094] (2) Apply Hankel transform

[0095] 1) Choose the type of Hankel transform (0th order or 1st order) suitable for the symmetry of the problem. For axisymmetric problems, the 0th order Hankel transform is usually more suitable.

[0096] 2) Convert the partial differential equations (PDEs) corresponding to the Biot coupling equations into ordinary differential equations (ODEs) in the frequency domain through Hankel transform. This step involves converting spatial variables (such as radial distance) to frequency space variables.

[0097] (3) Solve the equations in the frequency domain

[0098] 1) Ordinary differential equations. In the frequency domain, the coupled equations become relatively simple forms, which can be solved using standard mathematical methods.

[0099] 2) For non-homogeneous equations, specific integration techniques or numerical methods may be needed to find the solution.

[0100] (4) Apply inverse Hankel transform

[0101] Convert the solution in the frequency domain back to real space through the inverse Hankel transform. This step is complex and may require the use of numerical methods to estimate the inverse transform, especially for non-analytical solutions.

[0102] (5) Analysis and verification of results

[0103] 1) Analyze the obtained pore pressure and rock elastic stress distribution results, and check their physical reasonableness.

[0104] 2) May need to compare with experimental data or field observation data to verify the accuracy and reliability of the model.

[0105] (6) Parameter sensitivity analysis and further research

[0106] 1) Perform parameter sensitivity analysis to understand the impact of changes in different rock physical parameters (such as permeability, elastic modulus, etc.) on pore pressure and elastic stress distribution.

[0107] 2) Further optimization and research as needed to improve the model or explore different geological conditions and fluid dynamic conditions.

[0108] Step4: Model verification and adjustment: Verify the model through specific cases to ensure its effectiveness under different geological conditions, and adjust the model parameters according to the actual situation to optimize its performance.

[0109] Verify the pore pressure and rock elastic stress coupling model solved by Hankel transform, especially in the stress conduction mechanism caused by shale gas exploitation, which can follow the following steps to ensure the accuracy and practicality of the model:

[0110] (1) Select specific cases

[0111] 1) Select a representative shale gas block: Select a shale gas exploitation block as the research object, which should have detailed geological, geophysical and exploitation history data.

[0112] 2) Collect observation data of regional geological events: including ground subsidence, instability events, fracture distribution, etc., as verification points for model prediction.

[0113] 3) Organize detailed geological data: Collect information about the rock mechanics parameters of the shale formation (e.g., elastic modulus, Poisson's ratio, permeability), pore structure, fracture system, etc.

[0114] (2) Model application and analysis

[0115] 1) Apply the coupled pore pressure and rock elastic stress model: Use the model obtained from Step above by Hankel transform, input the specific case's geological and physical parameters for analysis.

[0116] 2) Perform simulation predictions: Based on the model, calculate the pore pressure changes, rock stress distribution, and their evolution over time during shale gas extraction.

[0117] (3) Validate the model

[0118] 1) Validate the coupled stress conduction mechanism:

[0119] Compare with observed data: Compare the simulation results with observed data of geological instability events, such as ground subsidence, location and intensity of instability events, etc.

[0120] Evaluate the model's predictive ability: Especially for the prediction of fracture propagation, rock displacement, and stress concentration areas, check if the model accurately reflects the observed phenomena.

[0121] 2) Validate the model's predicted stress conduction mechanism:

[0122] Analyze fracture propagation and new fracture generation: Use the model's predicted data to analyze how fractures propagate or generate new fractures as pressure changes during shale gas extraction.

[0123] Compare with geological data: Compare the model's predicted fracture distribution, direction, and density with geological survey and microseismic monitoring data to verify whether the model can accurately predict the complex nature of fracture development.

[0124] (4) Further research and optimization

[0125] 1) Identify the limitations of the model: Through the above validation steps, identify where the model deviates from actual observations, and analyze possible reasons.

[0126] 2) Model optimization: Adjust and optimize the model based on the validation results, which may include improving the description of the coupling mechanism, adjusting parameters, or introducing new influencing factors.

[0127] 3) Case studies: Select more shale gas extraction blocks with different geological characteristics for case studies to further validate and refine the model.

[0128] In this way, the coupling model can be systematically verified and refined, ensuring its accuracy and reliability in practical applications, providing a scientific basis for risk assessment and management in shale gas exploitation.

[0129] Step 5: Risk Assessment Analysis: Using the Monte-Carlo random process algorithm, the uncertainty in the geological process is predicted and analyzed, identifying potential fault slip areas, and assessing the geological risks caused by changes in pore pressure.

[0130] The Monte-Carlo random process algorithm is used to predict and analyze the uncertainty in the geological process, involving the introduction of randomness in the simulation, particularly for potential fault slip areas caused by changes in pore pressure, to assess geological risks. The specific steps for implementing the Monte-Carlo method are as follows:

[0131] (1) Define the problem and determine the input parameters

[0132] 1) Problem definition: Clearly define the type of risk that needs to be assessed in the geological process, for example, assess the impact of hydraulic fracturing activities on the stability of surrounding rock layers.

[0133] 2) Parameter selection: Identify key parameters that affect the geological process, such as rock elastic modulus, Poisson's ratio, permeability, initial pore pressure, fluid injection rate, etc.

[0134] (2) Probability distribution of parameters

[0135] Distribution assignment: Assign an appropriate probability distribution to each key parameter, which reflects the uncertainty of the parameter. For example, the rock elastic modulus may follow a normal distribution, while the fluid injection rate may follow a uniform distribution.

[0136] (3) Build Monte-Carlo model

[0137] 1) Random sampling: Use the Monte-Carlo method to randomly sample samples from the probability distribution of each parameter, which can be achieved through Monte-Carlo sampling techniques such as simple random sampling, Latin hypercube sampling, etc.

[0138] 2) Model running: For each randomly sampled parameter combination, run the geological process model. This may involve complex numerical simulation, such as coupling analysis of pore pressure and rock stress.

[0139] (4) Risk assessment

[0140] 1) Output analysis: Collect the results of all simulation runs and analyze the output data, such as fault slip probability, fracture development pattern, etc.

[0141] 2) Statistical Analysis: Use statistical analysis methods (e.g., calculating the mean, variance, confidence intervals of output variables) to comprehensively evaluate the results and identify potential high-risk areas.

[0142] (5) Uncertainty and Sensitivity Analysis

[0143] 1) Uncertainty Analysis: Assess the uncertainty of the model output by observing the impact of different parameter variations on the final results.

[0144] 2) Sensitivity Analysis: Determine which parameters have the greatest impact on the model output to better understand the sensitive factors of the geological risk assessment.

[0145] Through the above prediction analysis, especially the application of Monte-Carlo random process algorithm, potential fault slip areas in geological processes, especially in pore pressure change activities, can be effectively identified. The specific steps and methods are as follows:

[0146] (1) Model Setting and Parameterization

[0147] 1) Clearly represent the fault area and its surrounding rock properties in the model, including basic geological information such as fault location, strike, dip angle, etc.

[0148] 2) Parameterize key factors affecting fault stability, such as pore pressure, rock mechanical properties (elastic modulus, Poisson's ratio), friction coefficient on the fault surface, etc.

[0149] (2) Apply Monte-Carlo Simulation

[0150] 1) For each set of parameters generated by the Monte-Carlo method, perform numerical simulation to calculate the change in pore pressure during the pore pressure change process and its impact on the stress state of the surrounding rock.

[0151] 2) Pay special attention to the fault area in the simulation results, evaluate the reduction of effective normal stress (effective vertical stress minus pore pressure) caused by pressure change, and its impact on fault slip stability.

[0152] (3) Evaluate Fault Slip Potential

[0153] 1) Use empirical criteria such as Byerlee's law or more complex friction laws to evaluate the ratio of shear stress to normal stress on the fault surface to determine the potential for fault slip.

[0154] 2) Analyze stress changes in the fault area under different simulation scenarios to identify fault areas that are more prone to slip under the influence of pressure changes.

[0155] (4) Statistical Analysis and Probability Assessment

[0156] 1) Statistical analysis of all simulation results to assess the probability of fault slip under different conditions and identify high-probability slip areas.

[0157] 2) Consideration of model parameter uncertainty by calculating statistical indicators such as confidence intervals of model outputs to quantify the uncertainty of the prediction.

[0158] (5) Sensitivity analysis

[0159] Sensitivity analysis is conducted to understand which parameters have the greatest impact on the prediction of fault slip potential, helping to identify the most critical factors affecting fault stability, such as increases in pore pressure or changes in rock mechanical properties.

[0160] (6) Result interpretation and risk assessment

[0161] 1) Combine simulation results and risk analysis to form a comprehensive assessment of potential fault slip areas. Map these areas to provide an intuitive risk view.

[0162] 2) Sort and classify potential risks according to the probability of fault slip.

[0163] Through this process, the risk of fault slip caused by activities such as changes in pore pressure can be effectively identified and evaluated, providing scientific basis for geological disaster prevention and environmental protection. This analysis also helps to develop safer operation plans and risk mitigation strategies, reducing potential threats to the environment and public safety.

[0164] Evaluating geological risks caused by activities such as changes in pore pressure involves considering a variety of factors, including rock mechanics, groundwater flow, the complexity of geological structures, and the potential impact of these activities on the surrounding environment and the stability of the strata. The specific steps are as follows:

[0165] (1) Preliminary geological survey

[0166] 1) Data collection: Collect detailed geological, geophysical, hydrogeological and engineering geological data, including rock types, stratum structure, fault distribution, historical instability events and other information.

[0167] 2) Geological model construction: Based on the above data, construct a detailed geological model to analyze the areas that may be affected by changes in pore pressure activities.

[0168] (2) Rock mechanics and fluid dynamics analysis

[0169] 1) Rock mechanics parameter evaluation: Determine the mechanical properties of rock, such as elastic modulus, Poisson's ratio, shear strength, etc., which are crucial for evaluating rock layer response.

[0170] 2) Fluid pressure analysis: Analyzing the migration path of fluids in the rock formation, pressure changes, and their impact on surrounding rocks during changes in pore pressure.

[0171] (3) Application of numerical simulation

[0172] 1) Coupled simulation: Using numerical simulation software, combining rock mechanics and fluid dynamics theory, to conduct coupled simulation and predict the impact of fluid injection on rock stress state.

[0173] 2) Fault slip and fracture propagation analysis: Simulate the response of faults and fractures under injection activities, and evaluate the possibility of slip and new fracture formation.

[0174] (4) Geological risk assessment

[0175] 1) Identify sensitive areas: Based on simulation results, identify high-risk areas such as locations prone to fault slip or fracture propagation.

[0176] 2) Evaluate surface impacts: Consider the potential impacts of underground activities on surface stability, groundwater systems, and ecological environment.

[0177] (5) Uncertainty and sensitivity analysis

[0178] 1) Uncertainty analysis: Through methods such as Monte-Carlo simulation, evaluate the impact of model parameter uncertainty on risk assessment results.

[0179] 2) Sensitivity analysis: Determine the parameters that have the greatest impact on risk assessment results to facilitate more accurate risk management.

[0180] Geological risks caused by activities such as fracturing or wastewater injection, protect the environment and public safety, while achieving effective resource development.

[0181] Step 6: Result presentation and interpretation: Intuitively display the calculation results such as stress distribution map and risk area identification, and provide detailed interpretation and analysis report, to facilitate user understanding and application.

[0182] The present application successfully solves the key technical problems faced by the geological engineering field for many years, that is, how to accurately predict the long-distance geological body instability risk caused by underground fluid activity and the time-related geological body instability risk. By introducing the coupled stress field concept and mathematical analytical solution method, the limitations of existing prediction methods in dealing with geological body instability prediction are effectively solved, the prediction accuracy is significantly improved, and the application range of the prediction model is expanded. Compared with existing technologies (such as coupled finite element numerical simulation), the present application has higher prediction accuracy, faster data processing speed and wider model applicability in terms of main technical indicators. The improvement of these comprehensive performances not only reflects the innovation of the theoretical method, but also reflects the ability to solve key problems in practical applications: through efficient data processing and analysis capabilities, the accuracy and reliability of geological risk assessment are greatly improved, and the speed and efficiency of the assessment are improved, which has a significant advantage in predicting geological body instability far from the fracturing area, and has a wide application prospect in the fields of geological engineering, resource exploitation, environmental monitoring, disaster prevention and environmental protection.

[0183] Figure 1 A fault stress state diagram (Simpson coefficient diagram) of a certain block of an embodiment of the present application; Figure 2 A relative position diagram of a fault and a fracturing well of a certain block of an embodiment of the present application; Figure 3 A coupled stress increment and time relationship diagram of a certain fault of an embodiment of the present application; Figure 4 A coupled stress influence range distribution diagram (8 million cubic meters of injection volume) of an embodiment of the present application; Figure 5 An impact diagram of the coupled stress generated by fracturing on a certain fault of an embodiment of the present application.

[0184] It is to be understood that the above embodiments are only used to illustrate the technical solutions of the present application but not to limit it. Although the present application has been described in detail with reference to the above embodiments, the ordinary skilled in the art can still modify or equivalently replace the specific implementation of the present application without departing from the spirit and scope of the present application, and any modification or equivalent replacement should be covered in the protection scope of the claims of the present application.

Claims

1. A fault slip analysis method based on coupled poroelasticity mechanics, characterized by, Comprise: Step 1: Collect and preprocess the required geological data, including stratigraphic structure, rock physical properties, and pore pressure variation information; Step 2: Based on Biot poroelasticity theory, establish a mathematical model, and use Hankel transform to analytically solve Biot equations to describe the flow of underground fluids and their impact on the mechanical properties of surrounding rocks; Step 3: Implement coupling analysis between pore pressure and rock elastic stress and solve it using Hankel transform; Step 4: Verify the mathematical model in Step 2 through specific cases to ensure its effectiveness under different geological conditions, and adjust model parameters according to actual conditions to optimize its performance; Step 5: Use Monte-Carlo random process algorithm to predict and analyze the uncertainty in the geological process and identify potential fault slip areas.

2. The method of claim 1, wherein, In Step 2, based on Biot poroelasticity theory, a mathematical model is established. The problem considered is that a vertical source segment injects fluid into a horizontal permeable layer with a thickness of 2h, bounded on both sides by semi-infinite impermeable layers. The injection segment penetrates the thickness of the permeable layer and exchanges fluid with the surrounding rock at a constant volume rate Q, which is uniformly distributed over the thickness of the reservoir. All layers are homogeneous and isotropic, with the same elastic properties, i.e., the same shear modulus G and Poisson's ratio. The permeable layer is also characterized by additional poroelastic parameters, and the layers are bonded, i.e., the displacement at the interface is continuous. The origin of time t=0 is chosen to coincide with the start of fluid exchange, and at t=0, all pre-existing hydrodynamic and solid mechanical fields are assumed to be in equilibrium. A cylindrical coordinate system (r, θ, z) is defined with its origin at the coordinate 0 and the z-axis pointing upwards, perpendicular to the layer plane. In this cylindrical coordinate system, the uniform source density σ along the well corresponds to QH(t)δ(r) / (8πh), where H(t) and δ(r) represent the Heaviside step function and Dirac delta function, respectively. The fluid-structure interaction response is governed by the Biot equation, where h is the stratigraphic thickness coordinate, r is the normal coordinate in the cylindrical coordinate system, and θ is the tangential coordinate in the cylindrical coordinate system.

3. The method of claim 2, wherein, Mathematical analytical solution of Biot equations using Hankel transform includes: If the displacement field u is irrotational, i.e. The coupling equations can be simplified; by applying Hankel transform, the Biot equations are converted from real space to frequency space, the partial differential equations are simplified to ordinary differential equations for ease of solution; in the conversion process, the original Biot partial differential equations are converted into a set of algebraic equations related to the Hankel transform parameters and simplified, and the analytical or numerical solutions in the original physical space are obtained by inverse Hankel transform, for understanding and predicting the fluid-structure coupling in porous media.

4. The method of claim 3, wherein, The flow of underground fluids and their impact on the mechanical properties of surrounding rocks involve complex coupling effects, which are described by Biot equations in the theories of porous media, poroelasticity, and fluid dynamics: The flow of underground fluids is mainly influenced by porosity, permeability, and the viscosity of the fluid. The Darcy's law describes the flow of fluid from high-pressure areas to low-pressure areas under the action of pressure gradients. The movement of underground fluids directly affects the pressure distribution in the porous medium, which in turn affects the migration and distribution of fluids in the formation; Rock mechanical properties include elastic modulus, shear modulus, and Poisson's ratio, which describe the deformation and fracture characteristics of rocks under external forces, determining the response of rocks to stress changes, including compression, expansion, and shear deformation; changes in fluid pressure can alter the stress state in the rock, affecting its mechanical behavior and structural stability; There is a complex coupling relationship between underground fluid flow and the mechanical properties of surrounding rocks, which is reflected in the following aspects: pore pressure changes, feedback between rock deformation and flow, crack formation and propagation, and pore elasticity effects.

5. The method of claim 4, wherein, Pore pressure changes: the movement of fluids leads to changes in pore pressure, which directly affects the effective stress of the rock, and changes in effective stress can cause the rock to compress or expand, affecting its permeability and porosity; feedback between rock deformation and flow: rock deformation changes the pore structure, which in turn affects the flow characteristics of the fluid; crack formation and propagation: an increase in fluid pressure can sometimes cause the stress within the rock to exceed its strength limit, leading to the formation and propagation of cracks; pore elasticity effects: the pore elasticity theory considers the coupling between fluid flow in porous media and deformation of the solid skeleton; changes in fluid pressure will cause deformation of the solid skeleton, which in turn affects the pore space and fluid flow.

6. The method of claim 1, wherein, Step 3 includes: (1) Define the problem and establish the model: 1) Clearly define the physical background and objectives of the problem, including the geological conditions considered, fluid types, and rock characteristics; 2) Establish a mathematical model to describe the coupling between pore pressure and rock elastic stress; (2) Apply Hankel transform: Choose a type of Hankel transform that is suitable for the symmetry of the problem; Convert the partial differential equations corresponding to the Biot coupled equations into ordinary differential equations in the frequency domain through Hankel transform; involves converting spatial variables to frequency space variables; (3) Solve the equations in the frequency domain: 1) Solve the ordinary differential equations; 2) For non-homogeneous equations, integral or numerical methods may be needed to find the solution; (4) Apply inverse Hankel transform: Convert the solution in the frequency domain back to real space through inverse Hankel transform; (5) Analyze and verify the results: 1) Analyze the obtained pore pressure and rock elastic stress distribution results, and check their physical reasonableness; 2) May need to compare with experimental data or field observation data to verify the accuracy and reliability of the model; (6) Parameter sensitivity analysis and further research: 1) Perform parameter sensitivity analysis to understand the influence of changes in different rock physical parameters on pore pressure and elastic stress distribution; 2) Further optimization and research as needed to improve the model or explore different geological conditions and fluid dynamic conditions.

7. The method of claim 1, wherein, Step 4 includes: Selecting a representative shale gas block, collecting the observed data of fault slip events and the rock mechanics parameters of shale layer and inputting them into the mathematical model in step 2 for analysis, calculating the pore pressure change, rock stress distribution and their evolution with time in the shale gas exploitation process based on the mathematical model, comparing the calculated pore pressure change, rock stress distribution and their evolution with time with the observed data of fault slip events to check whether the mathematical model can accurately reflect the actually observed data; using the data predicted by the mathematical model to analyze how the cracks expand or generate new cracks with the pressure change in the shale gas exploitation process, comparing the crack distribution, direction and density predicted by the mathematical model with the geological survey and microseismic monitoring data to verify whether the model can accurately predict the complex nature of crack development.

8. The method of claim 1, wherein, Step 5 comprises: Monte-Carlo model setting and parameterization: explicitly representing the fault area and the rock properties around it in the Monte-Carlo model, including the location, strike and dip angle of the fault; parameterizing the key factors affecting the stability of the fault; the key factors include pore pressure, rock mechanics properties and friction coefficient on the fault surface; Applying Monte-Carlo simulation: performing numerical simulation on each set of parameter collection generated by the Monte-Carlo method, calculating the change of pore pressure and its influence on the stress state of the surrounding rock during the change of pore pressure, and focusing on the fault area in the simulation results to evaluate the reduction of effective normal stress caused by pressure change and its influence on fault slip stability; Assessing fault slip potential: evaluating the ratio of shear stress to normal stress on the fault surface to determine the potential of fault slip; analyzing the stress change of the fault area under different simulation scenarios to identify the fault area that is more prone to slip under the influence of pressure change; Statistical analysis and probability evaluation: statistically analyzing all simulation results to evaluate the probability of fault slip under different conditions and identify high-probability slip areas; considering the uncertainty of model parameters, quantifying the uncertainty of prediction by calculating the results output by the Monte-Carlo model; the results include confidence intervals; Sensitivity analysis: understanding the parameters that have the greatest impact on the prediction of fault slip potential through sensitivity analysis to identify the key factors that affect fault stability; Result interpretation and risk assessment: forming a comprehensive assessment of potential fault slip areas by integrating simulation results and risk analysis, and mapping the fault slip area to provide a risk view; according to the probability of fault slip and the severity of the ground displacement it may cause, ranking and classifying potential risks.

9. The method of claim 1, wherein, After step 5, it further comprises: evaluating the geological risks caused by each factor, including pore pressure change; the evaluation of the geological risks caused by each factor comprises the following steps: (1) Pre-geological survey: Data collection: Collect relevant data on geology, geophysics, hydrogeology, and engineering geology, including rock types, stratigraphic structure, fault distribution, and historical instability events; Geological model construction: Based on the collected data, construct a geological model to analyze the areas that may be affected by changes in pore pressure activity; (2) Rock mechanics and fluid dynamics analysis: Rock mechanics parameter evaluation: Determine the mechanical properties of the rock, including elastic modulus, Poisson's ratio, and shear strength; Fluid pressure analysis: Analyze the migration path of fluids in the rock formation, pressure changes, and their impact on surrounding rocks during changes in pore pressure; (3) Application of numerical simulation: Coupled simulation: Use numerical simulation software to combine rock mechanics and fluid dynamics theories to perform coupled simulation to predict the impact of fluid injection on rock stress state; Fault slip and fracture propagation analysis: Simulate the response of faults and fractures under injection activities to assess the possibility of slip and new fracture formation; (4) Geological risk assessment: Identify sensitive areas: Based on simulation results, identify high-risk areas where fault slip or fracture propagation is likely to occur; Evaluate surface impact: Consider the possible impact of underground activities on surface stability, groundwater systems, and ecological environment; (5) Uncertainty and sensitivity analysis: Uncertainty analysis: Evaluate the impact of Monte-Carlo model parameter uncertainty on risk assessment results; Sensitivity analysis: Determine the parameters that have the greatest impact on risk assessment results for risk management; Analyze the geological risks caused by fracturing or wastewater injection.

10. The method of claim 1, wherein, Also includes result presentation and interpretation: Display the calculation results and provide interpretation and analysis reports for users to understand and apply; Calculation results include stress distribution maps and risk area identification.

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