Method, system, and apparatus for evaluating wellbore cement sheath under seismic fault slip conditions

Abstract

The application provides an evaluation method, system and equipment for a wellbore cement sheath under seismic fault slip conditions, comprising: obtaining wellbore structure parameters, material mechanics parameters, well completion working condition parameters and strength parameters of the cement sheath of a target wellbore; obtaining a seismic moment magnitude and a fault stress drop of a region where the target wellbore is located to calculate a fault slip amount; establishing a three-dimensional coupling model according to the wellbore structure parameters and the material mechanics parameters, the three-dimensional coupling model comprising a virtual casing, a virtual cement sheath and a virtual formation block; based on the fault slip amount, a hydrostatic column pressure applied to an inner wall of the virtual casing and an in-situ ground stress field applied to an outermost boundary of the three-dimensional coupling model, calculating radial stress distribution and circumferential stress distribution of the virtual cement sheath by using a finite element algorithm; and obtaining an evaluation result of the cement sheath according to the radial stress distribution, the circumferential stress distribution and the strength parameters. The application realizes standardized evaluation of the wellbore cement sheath under seismic fault slip conditions.

Description

Technical Field

[0001] This invention relates to the field of oil and gas drilling engineering technology, specifically to a method, system, and equipment for evaluating wellbore cement sheaths under seismic fault slip conditions. Background Technology

[0002] In deepwater oil and gas field development, the wellbore cement sheath plays a crucial role in sealing interlayers, preventing fluid channeling, and supporting the casing. Its integrity directly impacts the long-term safety and operational reliability of oil and gas wells. Deepwater environments are characterized by high hydrostatic pressure, low temperatures, and frequent shallow geological hazards. In particular, earthquakes can induce submarine fault slippage, causing relative displacement of the surrounding formations and introducing significant shear stress and additional bending effects into the cement sheath. This can lead to damage modes such as hydraulic fracturing, tensile cracking, or interface debonding. Failure to identify and repair such damage in a timely manner can result in annular pressure, gas channeling, and even well control risks. Therefore, establishing a quantitative method for evaluating the integrity of the wellbore cement sheath under seismic fault slippage is of great significance for the safe and efficient development of deepwater oil and gas.

[0003] Currently, research on wellbore cement sheath integrity mainly focuses on evaluating cement sheath bonding quality, the impact of temperature and pressure cycling on cement sheath performance, and failure caused by natural gas hydrate decomposition. In engineering evaluation practice, some methods use empirical formulas or two-dimensional plane strain models to simplify the analysis of the wellbore structure, while others use finite element numerical simulation to solve for the stress distribution of the casing-cement sheath-formation system. For example, existing technologies attempt to estimate formation displacement based on seismic parameters and use finite element software (such as ABAQUS) to build two-dimensional or three-dimensional models of the wellbore structure to analyze the stress response of the cement sheath under different loads. These methods provide technical support for wellbore integrity assessment to a certain extent.

[0004] However, existing technologies still have the following shortcomings: First, they lack a quantitative conversion link from seismic moment magnitude and fault stress drop to wellbore shear displacement, making it difficult to engineer seismic parameters into boundary conditions of the finite element model, resulting in a lack of uniformity and comparability in evaluations under different magnitude conditions. Second, the two-dimensional simplified model cannot fully consider the nonlinear behavior of interface contact in the casing-cement sheath-formation system (such as tangential slip and normal separation), and it is also difficult to accurately capture the spatial distribution of stress along the well axis and local stress concentration, thus affecting the accuracy of predicting the location of cement sheath failure. Third, existing evaluation methods often use the amplitude of stress or displacement as a qualitative judgment basis, lacking quantitative failure criteria that combine experimental parameters such as cement strength parameters, making it difficult to achieve quantitative evaluation of the integrity of the wellbore cement sheath under seismic fault slip. Summary of the Invention

[0005] In view of this, it is necessary to provide a method, system and equipment for evaluating wellbore cement sheath under seismic fault slip conditions, so as to solve the technical problem that the existing technology cannot comprehensively consider seismic fault slip, well completion conditions and cement sheath material strength parameters to quantitatively evaluate the integrity of wellbore cement sheath.

[0006] To address the aforementioned technical problems, in a first aspect, the present invention provides a method for evaluating wellbore cement sheaths under seismic fault slip conditions, comprising: The wellbore structural parameters, material mechanical parameters, completion condition parameters, and cement sheath strength parameters of the target wellbore are obtained. The target wellbore includes a casing, a cement sheath surrounding the casing, and formation blocks surrounding the cement sheath. The completion condition parameters include hydrostatic pressure and in-situ stress field. Obtain the seismic moment magnitude and fault stress drop of the area where the target well is located, and calculate the fault slip. A three-dimensional coupled model is established based on the wellbore structural parameters and the material mechanical parameters; the three-dimensional coupled model includes virtual casing, virtual cement sheath and virtual formation block corresponding to the casing, cement sheath and formation block of the target wellbore; Based on the fault slip, the hydrostatic pressure applied to the inner wall of the virtual casing, and the in-situ stress field applied to the outermost boundary of the three-dimensional coupled model, the radial stress distribution and circumferential stress distribution of the virtual cement ring are calculated using the finite element algorithm. Based on the radial stress distribution, the circumferential stress distribution, and the strength parameters, the evaluation results of the cement sheath of the target wellbore under earthquake-induced fault slip are obtained.

[0007] In one possible implementation, the calculation of fault slip includes: The fault radius is calculated based on the earthquake moment magnitude and the fault stress drop. The fault slip is calculated based on the fault radius, the fault stress drop, and the formation shear modulus of the area where the target well is located, which is obtained in advance.

[0008] In one possible implementation, establishing a three-dimensional coupled model based on the wellbore structural parameters and the material mechanical parameters includes: Based on the wellbore structural parameters, the virtual formation block is established using a three-dimensional block structure, and the virtual casing and the virtual cement sheath are established using a coaxial concentric cylindrical structure. Based on the material mechanics parameters, a linear elastic constitutive model is assigned to the virtual casing, and an elastoplastic constitutive model based on the Mohr-Coulomb strength criterion is assigned to the virtual cement sheath and the virtual formation block to obtain the initial model; An interface contact relationship is established between the virtual casing and the virtual cement sheath, and between the virtual formation block and the virtual cement sheath in the initial model. The interface friction coefficient between the virtual casing and the virtual cement sheath is set to be less than that between the virtual formation block and the virtual cement sheath, thereby establishing the three-dimensional coupled model. The tangential behavior of the interface contact is simulated using the Coulomb friction model, and the normal behavior of the interface contact is simulated using the hard contact model.

[0009] In one possible implementation, the calculation of the radial and circumferential stress distributions of the virtual cement sheath using a finite element method, based on the fault slip, the hydrostatic pressure applied to the inner wall of the virtual casing, and the in-situ stress field applied to the outermost boundary of the three-dimensional coupled model, includes: Based on the fault slip, a shear displacement boundary condition is applied to the boundary of the virtual stratum block; the shear displacement boundary condition includes applying a pre-set fully constrained boundary condition at one end of the virtual stratum block and applying a shear displacement component corresponding to the fault slip at the other end of the virtual stratum block. The hydrostatic pressure is applied to the inner wall of the virtual sleeve, and the in-situ stress field is applied to the outermost boundary of the three-dimensional coupled model. The radial stress distribution and circumferential stress distribution of the virtual cement ring in the three-dimensional coupled model are extracted by solving the problem using the finite element method.

[0010] In one possible implementation, obtaining the evaluation result of the cement sheath of the target wellbore under earthquake-induced fault slip based on the radial stress distribution, the circumferential stress distribution, and the strength parameters includes: The radial stress distribution is compared with the compressive strength in the strength parameters to obtain a first comparison result; A second comparison result is obtained by comparing the circumferential stress distribution with the tensile strength in the strength parameters. Monitor the first interface contact pressure between the dummy casing and the dummy cement sheath, and the second interface contact pressure between the dummy formation block and the dummy cement sheath; The evaluation result is obtained based on the first comparison result, the second comparison result, the first interface contact pressure, and the second interface contact pressure.

[0011] In one possible implementation, obtaining the evaluation result based on the first comparison result, the second comparison result, the first interface contact pressure, and the second interface contact pressure includes: If the first comparison result indicates that the radial stress is greater than or equal to the compressive strength, it is determined that the evaluation result includes the cement sheath of the target wellbore having a risk of fracturing at the corresponding location; If the second comparison result indicates that the circumferential stress is greater than or equal to the tensile strength, it is determined that the evaluation result includes the risk of tensile cracking of the cement sheath at the corresponding location in the target wellbore; If the first interface contact pressure drops to zero and a relative displacement occurs between the dummy casing and the dummy cement sheath, the evaluation result is determined to include the risk of interface debonding between the cement sheath and the casing of the target wellbore. If the second interface contact pressure drops to zero and a relative displacement occurs between the virtual formation block and the virtual cement sheath, the evaluation result is determined to include the risk of interface debonding between the cement sheath and the formation block in the target wellbore.

[0012] In one possible implementation, after calculating the radial and circumferential stress distributions of the dummy cement ring, the process includes: Based on the radial stress distribution and the circumferential stress distribution, stress concentration areas along the axial direction of the target wellbore are identified; The axial length of the stress concentration region is determined, and the identified stress concentration region and its axial length are added to the evaluation results as potential failure zones.

[0013] One possible implementation also includes: By adjusting at least one parameter in the three-dimensional coupled model, such as the elastic modulus of the cement sheath, the fault dip angle, the seismic moment magnitude, or the interface friction coefficient, multiple new evaluation results can be obtained. Based on multiple evaluation results, key parameters leading to the destruction of the cement sheath in the target wellbore were identified.

[0014] Secondly, the present invention also provides an evaluation system for wellbore cement sheath under seismic fault slip conditions, comprising: The parameter acquisition module is used to acquire the wellbore structural parameters, material mechanical parameters, completion condition parameters, and cement sheath strength parameters of the target wellbore. The target wellbore includes a casing, a cement sheath surrounding the casing, and formation blocks surrounding the cement sheath. The completion condition parameters include hydrostatic pressure and in-situ stress field. The data acquisition module is used to acquire the seismic moment magnitude and fault stress drop of the area where the target well is located, and to calculate the fault slip. The model creation module is used to establish a three-dimensional coupled model based on the wellbore structural parameters and the material mechanical parameters; the three-dimensional coupled model includes virtual casing, virtual cement sheath and virtual formation block corresponding to the casing, cement sheath and formation block of the target wellbore; The calculation module is used to calculate the radial and circumferential stress distributions of the virtual cement ring based on the fault slip, the hydrostatic pressure applied to the inner wall of the virtual casing, and the in-situ stress field applied to the outermost boundary of the three-dimensional coupled model, using the finite element algorithm. The evaluation module is used to obtain the evaluation results of the cement sheath of the target wellbore under earthquake-induced fault slip based on the radial stress distribution, the circumferential stress distribution, and the strength parameters.

[0015] Thirdly, the present invention also provides an electronic device, including a memory and a processor, wherein, The memory is used to store programs; The processor, coupled to the memory, is used to execute the program stored in the memory to implement the steps in the evaluation method of wellbore cement sheath under seismic fault slip conditions as described in any of the above implementations.

[0016] The beneficial effects of this invention are as follows: Firstly, by acquiring the seismic moment magnitude and fault stress drop, and quantitatively converting them into fault slip, this invention achieves a direct mapping between seismic energy release and shear displacement load on the wellbore. This allows seismic action to be input into the finite element model with clear displacement boundary conditions, avoiding the arbitrariness of traditional methods that rely solely on empirical estimation, and significantly improving the comparability and scientific rigor of evaluation results under different magnitude conditions. Furthermore, the established three-dimensional coupled model includes virtual casing, virtual cement sheath, and virtual formation blocks corresponding to the target wellbore entity. This model can realistically reflect the coaxial and concentric structural characteristics between the casing, cement sheath, and formation. Combined with the application of three types of loads—fault slip displacement, hydrostatic pressure, and in-situ stress field—the stress state of the cement sheath more closely resembles the actual service conditions in deep-water environments, thereby improving the fidelity of the numerical simulation. Furthermore, the radial and circumferential stress distributions of the virtual cement sheath were calculated using the finite element method, providing an accurate numerical description of the mechanical behavior of the cement sheath. Based on the comparative analysis of these stress distributions and the compressive and tensile strength parameters of the cement sheath, it is possible to quantitatively identify whether the cement sheath has experienced phenomena such as compression fracturing or tensile fracturing, and to clarify the location and extent of failure, thereby improving the accuracy of cement sheath evaluation, enhancing the reliability of cementing design optimization and adjustment, and strengthening the safety risk management level of deepwater oil and gas wells. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A schematic flowchart of an embodiment of the method for evaluating wellbore cement sheath under seismic fault slip conditions provided by the present invention; Figure 2 A schematic diagram of an embodiment of the three-dimensional coupled model of the present invention, including a virtual casing, a virtual cement sheath, and a virtual formation block; Figure 3 For the present invention Figure 1 A schematic diagram of an embodiment of S102; Figure 4 For the present invention Figure 1 A schematic diagram of an embodiment of S103; Figure 5 A schematic diagram of an embodiment of mesh generation for a three-dimensional coupled model provided by the present invention; Figure 6 For the present invention Figure 1 A schematic diagram of an embodiment of S104; Figure 7 A schematic diagram of an embodiment of the model boundary conditions and shear displacement loading provided by the present invention; Figure 8 For the present invention Figure 1 A schematic diagram of an embodiment of S105; Figure 9 A schematic flowchart of another embodiment of the method for evaluating wellbore cement sheath under seismic fault slip conditions provided by the present invention; Figure 10 A schematic flowchart of another embodiment of the method for evaluating wellbore cement sheath under seismic fault slip conditions provided by the present invention; Figure 11 A schematic diagram of an embodiment of the wellbore cement sheath evaluation system under seismic fault slip conditions provided by the present invention; Figure 12 A schematic diagram of an embodiment of the electronic device provided by the present invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0020] In the description of the embodiments of the present invention, unless otherwise stated, "multiple" means two or more. "And / or" describes the relationship between related objects, indicating that there can be three relationships. For example, A and / or B can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone.

[0021] The terms "first," "second," etc., used in the embodiments of this invention are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a technical feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature.

[0022] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0023] This invention provides a method, system, and equipment for evaluating wellbore cement sheaths under seismic fault slip conditions, which will be described below.

[0024] Figure 1 This is a schematic flowchart of an embodiment of the method for evaluating wellbore cement sheath under seismic fault slip conditions provided by the present invention, as shown below. Figure 1 As shown, the evaluation methods for wellbore cement sheaths under seismic fault slip conditions include: S101. Obtain the wellbore structural parameters, material mechanical parameters, completion condition parameters, and cement sheath strength parameters of the target wellbore. The target wellbore includes a casing, a cement sheath surrounding the casing, and formation blocks surrounding the cement sheath. The completion condition parameters include hydrostatic pressure and in-situ stress field.

[0025] It should be noted that the target wellbore comprises, from the inside out, the casing, the cement sheath, and the formation blocks, i.e., the cement sheath surrounds the casing, and the formation blocks surround the cement sheath. Wellbore structural parameters include geometric parameters such as the casing outer diameter, casing wall thickness, cement sheath outer diameter, cement sheath thickness, and wellbore dimensions. These parameters determine the radial dimensions and relative positions of the components of the target wellbore. Material mechanics parameters encompass the physical and mechanical properties of the casing, cement sheath, and formation materials, including strength parameters such as elastic modulus and Poisson's ratio. Currently, if an elastoplastic constitutive model is used, strength indices such as internal friction angle and cohesion must also be included. These parameters can be obtained through field design data, wellbore structural design documents, or core mechanics experiments. Completion condition parameters include hydrostatic pressure and in-situ stress field, both of which together constitute the basic load environment during the wellbore's service life. Among these, the hydrostatic pressure refers to the pressure generated by the static fluid column inside the casing after well completion, and its magnitude depends on the completion fluid density and wellbore depth; the in-situ stress field refers to the naturally existing triaxial principal stress state in the formation, including the vertical principal stress, the maximum horizontal principal stress, and the minimum horizontal principal stress. These two types of parameters together constitute the basic load environment during the wellbore's service life. The strength parameters of the cement sheath refer to the compressive strength and tensile strength determined through laboratory mechanical testing or field cement slurry system performance evaluation experiments. These two strength values ​​will serve as the benchmark for subsequent determination of whether the cement sheath has experienced compressive or tensile fracturing failure.

[0026] S102. Obtain the seismic moment magnitude and fault stress drop of the area where the target well is located, and calculate the fault slip.

[0027] It should be noted that the seismic activity parameters of the area where the target wellbore is located are obtained, specifically including the moment magnitude scale and fault stress drop. The moment magnitude scale is a standard measure of the energy released by an earthquake, reflecting its intensity. Fault stress drop characterizes the magnitude of stress release on the fault plane during an earthquake and is a key parameter describing the dynamic characteristics of an earthquake. Based on the aforementioned moment magnitude and fault stress drop, and utilizing the basic principles of the disk fault model in seismology, a quantitative relationship between fault geometry and slip is established, thereby calculating the fault slip. Fault slip represents the relative displacement distance between the two sides of the fault along the fault plane under seismic action, used to quantitatively characterize the intensity of the seismic slip effect on the wellbore structure.

[0028] S103. Establish a three-dimensional coupled model based on the wellbore structural parameters and the material mechanical parameters; the three-dimensional coupled model includes virtual casing, virtual cement sheath and virtual formation block corresponding to the casing, cement sheath and formation block of the target wellbore.

[0029] It should be noted that, based on the obtained structural parameters and material mechanics parameters of the target wellbore, a three-dimensional coupled model is constructed in the finite element analysis software. For example... Figure 2 As shown, this 3D coupled model is not the physical entity of the target wellbore, but consists of three virtual components that correspond one-to-one with the physical components: a virtual casing, a virtual cement sheath, and a virtual formation block. Specifically, the virtual casing corresponds to the physical casing of the target wellbore, the virtual cement sheath corresponds to the cement sheath of the target wellbore, and the virtual formation block corresponds to the formation block surrounding the target wellbore. The three virtual components are assembled according to the geometric positional relationship of the actual wellbore; that is, the virtual cement sheath is located outside the virtual casing, and the virtual formation block is located outside the virtual cement sheath, forming a coaxial and concentric structure. In this way, the geometric dimensions (derived from wellbore structural parameters) and material mechanical properties (derived from material mechanical parameters) of the target wellbore are assigned to the corresponding virtual components, thereby establishing a 3D coupled model that reflects the actual structural characteristics and mechanical behavior of the wellbore.

[0030] S104. Based on the fault slip, the hydrostatic pressure applied to the inner wall of the virtual casing, and the in-situ stress field applied to the outermost boundary of the three-dimensional coupled model, the radial stress distribution and circumferential stress distribution of the virtual cement ring are calculated using the finite element algorithm.

[0031] It should be noted that, based on the calculated fault slip, and combined with the hydrostatic pressure and in-situ stress field in the well completion parameters, the finite element method (FEM) is used to numerically solve the three-dimensional coupled model, thereby obtaining the radial and circumferential stress distributions of the virtual cement sheath. Specifically, the fault slip represents the relative displacement of the two fault blocks along the fault plane under seismic loading, which is applied as a displacement boundary condition to the virtual formation block boundary in the model to simulate the shearing effect of fault displacement on the wellbore structure. Hydrostatic pressure is applied to the inner wall of the virtual casing to simulate the continuous support of the fluid inside the wellbore on the casing, and the in-situ stress field is applied to the outermost boundary of the three-dimensional coupled model to reflect the original triaxial stress environment of the formation where the wellbore is located. Under the combined action of the above three types of loads, the finite element method is used to solve the three-dimensional coupled model, calculating the radial stress (normal stress perpendicular to the wellbore axis) and circumferential stress (tangential normal stress around the wellbore axis) at each node of the virtual cement sheath.

[0032] S105. Based on the radial stress distribution, the circumferential stress distribution, and the strength parameters, the evaluation results of the cement sheath of the target wellbore under earthquake-induced fault slip are obtained.

[0033] It should be noted that: based on the radial and circumferential stress distribution of the virtual cement sheath, and combined with the strength parameters such as compressive strength and tensile strength of the cement sheath obtained through prior experimental measurements, the integrity of the cement sheath of the target wellbore under seismic fault slip conditions is comprehensively evaluated to determine whether the cement sheath has experienced compressive fracturing, tensile fracturing, or interface debonding, and to determine the location and extent of the failure.

[0034] In summary, the evaluation method for wellbore cement sheath under seismic fault slip conditions provided in this embodiment of the invention first obtains the seismic moment magnitude and fault stress drop, and quantitatively converts them into fault slip, realizing a direct mapping between seismic energy release and shear displacement load on the wellbore. This allows the seismic action to be input into the finite element model with clear displacement boundary conditions, avoiding the arbitrariness of relying solely on empirical estimation in traditional methods, and significantly improving the comparability and scientific validity of evaluation results under different magnitude conditions. Furthermore, the established three-dimensional coupled model includes virtual casing, virtual cement sheath, and virtual formation blocks corresponding to the target wellbore entity, which can realistically reflect the coaxial and concentric structural characteristics between casing, cement sheath, and formation. Combined with the joint application of three types of loads—fault slip displacement, hydrostatic pressure, and in-situ stress field—the stress state of the cement sheath is closer to the actual service conditions in deep water environments, thereby improving the fidelity of the numerical simulation. Furthermore, the radial and circumferential stress distributions of the virtual cement sheath were calculated using the finite element method, providing an accurate numerical description of the mechanical behavior of the cement sheath. Based on the comparative analysis of these stress distributions and the compressive and tensile strength parameters of the cement sheath, it is possible to quantitatively identify whether the cement sheath has experienced phenomena such as compression fracturing or tensile fracturing, and to clarify the location and extent of failure, thereby improving the accuracy of cement sheath evaluation, enhancing the reliability of cementing design optimization and adjustment, and strengthening the safety risk management level of deepwater oil and gas wells.

[0035] In some embodiments of the present invention, such as Figure 3 As shown, step S102 includes: S301. The fault radius is calculated based on the earthquake moment magnitude and the fault stress drop.

[0036] It should be noted that the calculation of fault slip is based on the Brune model of disk faults in seismology, obtaining the seismic moment and magnitude of the area where the target well is located. Moment Magnitude and fault stress drop ( After StressDrop, the seismic moment in the disk fault model ( ) and earthquake moment magnitude Fault stress drop Theoretical relationship, calculate equivalent fault radius As shown below: ; Assuming that the earthquake moment magnitude is taken from the regional seismic activity statistics... Fault stress drop Substituting into the above formula, the fault radius is calculated. The fault radius characterizes the characteristic scale of the earthquake slip fault plane.

[0037] S302. The fault slip is calculated based on the fault radius, the fault stress drop, and the formation shear modulus of the area where the target well is located, which is obtained in advance.

[0038] It should be noted that: when obtaining the fault radius Then, the fault slip volume was further calculated. This requires incorporating the pre-obtained formation shear modulus of the target wellbore area. Shear Modulus (formation shear modulus). Fault slip can be determined through core mechanics experiments, or estimated through geophysical logging or regional crustal models. The formula for calculating fault slip is shown below: ; Assuming formation shear modulus The values ​​were determined through core mechanics experiments. Based on the calculations above , Substitute into the calculation of fault slip. In other engineering examples, the slip will vary depending on the stress drop or shear modulus used (e.g., when...). , hour, (Approximately 17.37 mm).

[0039] In this embodiment, by establishing the theoretical relationship between moment magnitude, stress drop, and fault radius, and further combining it with the formation shear modulus to calculate fault slip, seismic parameters (moment magnitude, stress drop) can be quantitatively converted into displacement boundary conditions that can be directly used in engineering. By pre-obtaining the formation shear modulus of the area where the target well is located and combining it with the calculated fault slip, the calculated fault slip can reflect the mechanical properties of the real strata, improve the scientific nature and regional adaptability of seismic slip load input, and lay the foundation for unified evaluation under different magnitude conditions.

[0040] In some embodiments of the present invention, such as Figure 4 As shown, step S103 includes: S401. Based on the wellbore structural parameters, the virtual formation block is established using a three-dimensional block structure, and the virtual casing and the virtual cement sheath are established using a coaxial concentric cylindrical structure.

[0041] It should be noted that, based on the wellbore dimensions and other geometric parameters in the wellbore structural parameters, a three-dimensional block structure is used to construct a virtual formation block to simulate the infinite formation environment surrounding the target wellbore. Specifically, based on the wellbore dimensions and the engineering estimate of the fault slip influence range, the horizontal range (along two horizontal directions) and axial length of the virtual formation block are set. To ensure that the influence of the outer boundary on the stress distribution near the wellbore is sufficiently attenuated, the outer boundary dimensions of the virtual formation block should be set to a sufficiently large multiple (e.g., more than 10 times) relative to the wellbore radius, thereby forming a stress environment of approximately infinite formation. In the finite element software, a three-dimensional deformable solid part is created, and a cuboid block is generated by extruded sketch rectangles; this block is the virtual formation block. The center point of this block is determined as the axis position of the target wellbore so that the virtual casing and virtual cement sheath can be placed coaxially and centered.

[0042] Based on the casing outer diameter, casing wall thickness, and other geometric structural parameters in the wellbore structure parameters, the outer and inner diameters of the solid casing are determined. In finite element software, a three-dimensional deformable cylindrical component is created, with its outer diameter equal to the casing outer diameter and its length consistent with the axial length of the virtual formation block. Then, a tubular geometric model of the casing is formed through Boolean subtraction (or by directly creating a hollow cylinder). This model is the virtual casing (corresponding to the solid casing of the target wellbore).

[0043] Based on the geometric parameters such as the outer diameter of the cement sheath and the outer diameter of the casing in the wellbore structural parameters, the outer and inner diameters of the solid cement sheath are determined: the inner diameter of the cement sheath is equal to the outer diameter of the casing, and the outer diameter is equal to the wellbore diameter. A hollow cylinder with an outer diameter equal to the outer diameter of the cement sheath and an inner diameter equal to the outer diameter of the casing is generated using the coaxial cylinder creation method. This model is the virtual cement sheath (corresponding to the solid cement sheath in the target wellbore).

[0044] The virtual casing and virtual cement sheath are coaxially assembled with the virtual formation block, ensuring that the axes of the three are coincident and that the virtual cement sheath is located precisely within the annular space between the outer wall of the virtual casing and the inner wall of the virtual formation block. During assembly, the virtual casing is kept centered, and it is assumed that the interface between the virtual casing and the virtual cement sheath is initially well bonded. In the above modeling process, it is assumed that the materials of the virtual formation block, the virtual cement sheath, and the virtual casing are all homogeneous isotropic media (e.g., when loads are applied to the casing from the axial, radial, and circumferential directions, its stress-strain relationship follows the same elastic modulus and Poisson's ratio; and the material properties remain unchanged from the inner wall to the outer wall of the casing). Such media materials include concrete, glass, plastics, and casting resin. Simultaneously, it is assumed that there are initially no gaps between the virtual casing and the virtual cement sheath, and between the virtual cement sheath and the virtual formation block, and that the contact surfaces can automatically determine whether to press or separate based on the mechanical state throughout the analysis process.

[0045] S402. Based on the material mechanical parameters, a linear elastic constitutive model is assigned to the virtual casing, and an elastoplastic constitutive model based on the Mohr-Coulomb strength criterion is assigned to the virtual cement sheath and the virtual formation block to obtain the initial model.

[0046] It should be noted that, based on the material data of the actual casing of the target wellbore (usually steel), a linear elastic constitutive model is defined for the virtual casing in the FEM (Finite Element Method) software to describe the elastic response of the virtual casing (corresponding to the solid casing) under seismic slip loads. Based on the material data of the actual cement sheath and the actual formation (both typically brittle or soil-like materials), elastoplastic constitutive models based on the Mohr-Coulomb Strength Criterion are defined for the virtual cement sheath and the virtual formation block, respectively, enabling them to simulate yielding, cracking, or plastic flow. Among them, FEM software is a type of computer program based on FEM, used to solve partial differential equations in engineering and physics problems. By discretizing continuous objects (such as well shafts and formations) into a finite number of interconnected elements (mesh), and describing physical quantities (such as displacement and stress) in each element with approximate functions (shape functions), the continuous problem with infinite degrees of freedom is transformed into a system of algebraic equations with finite degrees of freedom. Finally, an approximate solution is obtained through computer numerical solution.

[0047] The virtual casing with linear elastic constitutive model, the virtual cement sheath with elastoplastic constitutive model, and the virtual formation block are combined in the same finite element model. Ensuring the correct geometric positions of each component (coaxial and concentric, interface contact ready) yields the initial model, which includes geometric shape and material properties. All parameters can be derived from field design data, wellbore structure design documents, or core mechanics experimental test results.

[0048] S403. An interface contact relationship is established between the virtual casing and the virtual cement sheath, and between the virtual formation block and the virtual cement sheath in the initial model. The interface friction coefficient between the virtual casing and the virtual cement sheath is set to be less than the interface friction coefficient between the virtual formation block and the virtual cement sheath, thereby establishing the three-dimensional coupling model. The tangential behavior of the interface contact is simulated using the Coulomb friction model, and the normal behavior of the interface contact is simulated using the hard contact model.

[0049] It should be noted that: for the contact between the dummy casing and the dummy cement sheath, the outer wall surface of the dummy casing is defined as the master surface, and the inner wall surface of the dummy cement sheath is defined as the slave surface, forming the first contact pair. For the contact between the dummy formation block and the dummy cement sheath, the inner wall surface of the dummy formation block is defined as the master surface, and the outer wall surface of the dummy cement sheath is defined as the slave surface, forming the second contact pair.

[0050] Tangential behavior is used to simulate the relative sliding resistance of the contact surfaces in the direction parallel to the interface. For this purpose, the Coulomb friction model is used to simulate the tangential behavior of the interface contact. The Coulomb friction model assumes that the maximum tangential stress that the interface can withstand is proportional to the normal contact pressure, and the proportionality coefficient is the friction coefficient. When the shear stress does not reach this maximum value, the interface is in an adhesive state. Once it reaches this maximum value, the interface will slip relative to each other.

[0051] Normal behavior is used to simulate the pressure transmission and separation characteristics of the contact surface in the direction perpendicular to the interface. Therefore, a hard contact model is used to simulate the normal behavior of the interface contact. The hard contact model assumes that: when the interface is in a compressed state, it can transmit any magnitude of normal pressure; when the interface exhibits a tensile tendency, it cannot transmit normal tension; once the normal contact pressure drops to zero, the interface immediately separates and no longer transmits any normal force. Based on engineering experience, the interfacial friction coefficient between the virtual casing and the virtual cement sheath is set to be less than that between the virtual formation block and the virtual cement sheath to reflect the physical characteristics of the relatively smooth casing surface and the relatively rough formation surface. The above tangential and normal contact attributes are assigned to the first and second contact pairs, respectively. After completing geometric modeling, material assignment, and interface contact settings, the initial model is meshed. Figure 5 As shown, the virtual formation block is discretized using structured hexahedral elements, with the element size gradually sparser from the inside out. The virtual casing is uniformly divided along the radial and axial directions. The virtual cement sheath, as the key analysis area, is locally refined in both the radial and axial directions, especially near the fault slip surface to ensure the calculation accuracy of stress concentration areas. Through the above meshing, a discretized model suitable for finite element solution is obtained. After completing the above meshing and interface contact settings, the initial model has the ability to simulate nonlinear interface behavior, thus establishing a three-dimensional coupled model that can be used for subsequent load application and finite element solution.

[0052] In this embodiment, by accurately constructing geometric models of the virtual formation block, virtual casing, and virtual cement sheath using three-dimensional blocks and coaxial concentric cylinders based on actual wellbore structural parameters, the concentric multi-layered structural characteristics of the wellbore can be realistically reflected, providing an accurate geometric basis for subsequent stress field analysis and avoiding distortion of spatial stress distribution caused by simplified two-dimensional models. Furthermore, by assigning linear elastic and elastoplastic constitutive models based on material mechanics parameters, the different mechanical responses of the casing, cement sheath, and formation under shear loads (casing linear elasticity, cement sheath, and formation elastoplasticity) can be accurately described, thereby capturing the yielding and damage evolution process of the cement sheath. Further still, by introducing Coulomb friction and hard contact models at the interface and setting reasonable friction coefficient relationships, the nonlinear behavior of the interface during shear slip (tangential slip, normal separation) can be simulated, making the stress transmission path and local stress concentration around the well closer to engineering reality, significantly improving the prediction accuracy of cement sheath fracturing, tensile fracturing, and interface debonding risks.

[0053] In some embodiments of the present invention, such as Figure 6 As shown, step S104 includes: S601. Based on the fault slip amount, apply shear displacement boundary conditions to the boundary of the virtual stratum block; the shear displacement boundary conditions include applying a pre-set fully constrained boundary condition to one end of the virtual stratum block and applying a shear displacement component corresponding to the fault slip amount to the other end of the virtual stratum block.

[0054] It should be noted that, based on the calculated fault slip, shear displacement boundary conditions are applied to the boundaries of the virtual stratigraphic block to simulate stratigraphic displacement caused by earthquake fault slip. For example... Figure 7 As shown, the specific operation is as follows: On one end boundary of the virtual stratigraphic block along the shear direction (e.g., the left end face), set fully constrained boundary conditions, that is, fix all translational degrees of freedom of all nodes on this end face, and use it as the displacement reference datum. Then, on the other end boundary of the virtual stratigraphic block (e.g., the right end face), apply a shear displacement component corresponding to the fault slip. The direction of this shear displacement component is consistent with the fault slip direction, and its magnitude is obtained by vector decomposition based on the fault slip, the angle between the actual fault slip direction and the model coordinate axes. For example, assuming... L =11 mm, to simulate oblique slip, along the model's X direction and Displacement components are applied in the Z direction: Ux = L ·cosθ,Uz= L ·sinθ, assuming θ = 45°, then Ux = Uz ≈ 7.78 mm, the magnitude and value of the displacements of Ux and Uz are equal to LIn this way, one end of the virtual formation block is completely constrained, while the other end generates a predetermined shear displacement, thus forming a shear displacement field with a clear direction around the wellbore. This boundary condition directly reflects the direction of the seismic fault slip on the target wellbore structure.

[0055] S602. Apply the hydrostatic pressure to the inner wall of the virtual sleeve and apply the in-situ stress field to the outermost boundary of the three-dimensional coupled model.

[0056] It should be noted that, based on the hydrostatic pressure value in the well completion parameters, a uniformly distributed hydrostatic pressure is applied to the inner wall of the virtual casing in the 3D coupled model. The hydrostatic pressure is perpendicular to the inner wall surface of the virtual casing and points towards the center of the virtual casing (i.e., simulating the supporting effect of the fluid inside the target wellbore on the virtual casing). The magnitude of the hydrostatic pressure is determined based on the completion fluid density and wellbore depth, and remains constant during loading to reflect the internal fluid pressure environment of the target wellbore under normal production or shut-in conditions.

[0057] Based on the in-situ stress field data in the well completion parameters, an in-situ stress field is applied to the outermost boundary of the 3D coupled model (i.e., all outer surfaces of the virtual formation block). The in-situ stress field includes three components: vertical principal stress, maximum horizontal principal stress, and minimum horizontal principal stress. The vertical principal stress is applied perpendicularly to the horizontal plane to the top and bottom surfaces of the 3D coupled model, while the maximum and minimum horizontal principal stresses are applied to their respective side surfaces. These stress components act vertically on the outer surfaces of the 3D coupled model in the form of pressure, reflecting the actual formation environment of the target wellbore. The magnitudes of the three stress components satisfy the normal fault stress state, i.e., the vertical principal stress is greater than the maximum horizontal principal stress, and the maximum horizontal principal stress is greater than the minimum horizontal principal stress. After applying the above loads, the 3D coupled model possesses complete boundary conditions and an initial stress field, which can be used for subsequent finite element solutions.

[0058] S603. Solve the model using the finite element method to extract the radial stress distribution and the circumferential stress distribution of the virtual cement ring in the three-dimensional coupled model.

[0059] After applying all the boundary conditions and loads, the FEM algorithm was used to numerically solve the three-dimensional coupled model. Static analysis was performed using finite element software (such as the ABAQUS / Standard solver), considering both geometric and contact nonlinearities. The solver used automatic time stepping, iterating within each increment until the results met the convergence criteria. After solving, the radial and circumferential stress distributions of the virtual cement ring in the three-dimensional coupled model were extracted. To accurately extract the stress components of the cylindrical structure, a local cylindrical coordinate system was first created in the finite element software. The Z-axis of this coordinate system was aligned with the axis of the virtual cement ring in the three-dimensional coupled model (i.e., the shaft axis), the radial direction (R-axis) was perpendicular to the axis pointing outwards, and the circumferential direction (T-axis) was determined according to the right-hand rule. Then, the calculation results (stress tensors) were transformed into this local cylindrical coordinate system. For the target region of the virtual cement ring, the radial normal stress component (i.e., the stress along the R-axis) in the transformed coordinate system is extracted to obtain the radial stress value at each node or element integration point of the entire virtual cement ring, thus obtaining the radial stress distribution; the circumferential normal stress component (i.e., the stress along the T-axis) in the transformed coordinate system is extracted to obtain the circumferential stress distribution.

[0060] In this embodiment, by applying full constraints at one end of the virtual formation block based on fault slip and shear displacement components at the other end, seismic parameters can be directly converted into displacement boundary conditions for the finite element model. This allows for the quantitative reproduction of the shear effect of fault slip on the wellbore. Applying hydrostatic pressure to the inner wall of the virtual casing and an in-situ in-situ stress field to the outermost boundary of the model couples the long-term foundation load under completion conditions with the sudden seismic slip load, making the initial stress state of the cement sheath closer to reality. This avoids evaluation bias caused by considering only a single load and significantly improves the accuracy of cement sheath evaluation. Furthermore, by using the finite element algorithm to solve and extract the radial and circumferential stress distribution of the virtual cement sheath, the stress concentration areas and their variation along the well axis can be accurately identified, improving the reliability of the wellbore cement sheath integrity evaluation.

[0061] In some embodiments of the present invention, such as Figure 8 As shown, step S105 includes: S801. The radial stress distribution is compared with the compressive strength in the strength parameters to obtain a first comparison result.

[0062] It should be noted that: for each unit (or each node) of the virtual cement ring, its radial stress value is read and compared with the cement ring compressive strength determined in advance through experiments to obtain the corresponding first comparison result.

[0063] S802. The circumferential stress distribution is compared with the tensile strength in the strength parameters to obtain a second comparison result.

[0064] It should be noted that: for each element (or each node) of the virtual cement ring, its circumferential stress value is read. Since the cement ring is a brittle material, the tensile stress (positive value) is the main concern, so it is necessary to distinguish between tensile stress and compressive stress: for the circumferential tensile stress, it is compared with the tensile strength of the cement ring that has been experimentally determined in advance to obtain the corresponding second comparison result.

[0065] S803. Monitor the first interface contact pressure between the dummy casing and the dummy cement sheath, and the second interface contact pressure between the dummy formation block and the dummy cement sheath.

[0066] It should be noted that contact pairs include the contact pair between the dummy casing and the dummy cement sheath (first contact pair) and the contact pair between the dummy formation block and the dummy cement sheath (second contact pair). The contact pressure distribution of each contact pair at each moment during the analysis is extracted. Specifically, for the first interface contact pressure, "CPRESS" (or the corresponding contact pressure variable in the software) is selected in the contact output variables, and the normal contact pressure values ​​at each node or element integration point along the contact surface of the first contact pair are extracted and defined as the first interface contact pressure. Similarly, for the second interface contact pressure, the contact pressure values ​​are extracted on the second contact pair and defined as the second interface contact pressure. By monitoring whether these contact pressures drop to zero and simultaneously observing whether relative displacement (slippage or opening) occurs between the contact pairs, it can be determined whether debonding or slip failure has occurred at the interface.

[0067] S804. Based on the first comparison result, the second comparison result, the first interface contact pressure, and the second interface contact pressure, the evaluation result is obtained.

[0068] It should be noted that the integrity evaluation results of the target wellbore cement sheath under seismic fault slip are formed based on the first comparison results, the second comparison results, and the monitoring of the contact pressure at the first and second interfaces.

[0069] In this embodiment, by comparing the radial stress distribution obtained from finite element analysis with the compressive strength of the cement sheath point by point, the specific areas and extent of the cement sheath fracture under shear load can be quantitatively identified. By comparing the circumferential stress distribution with the tensile strength of the cement sheath, the cracking risk of the brittle cement sheath under tensile stress can be accurately captured, and the axial length of the tensile fracture zone can be determined, providing a quantitative basis for preventing radial cracks. Furthermore, by monitoring the changes in the interfacial contact pressure between the dummy casing and the dummy cement sheath, as well as the changes in the interfacial contact pressure between the dummy formation block and the dummy cement sheath, it is possible to determine whether debonding failure has occurred at the interface, improving the ability to capture interfacial slippage and separation phenomena, thereby enhancing the reliability of the cement sheath evaluation results.

[0070] In some embodiments of the present invention, step S804 includes: S8041. If the first comparison result indicates that the radial stress is greater than or equal to the compressive strength, it is determined that the evaluation result includes the cement sheath of the target wellbore having a risk of fracturing at the corresponding location.

[0071] It should be noted that: if the first comparison result indicates that the radial stress is greater than or equal to the compressive strength of the cement ring ( σr ≥ σ c If the evaluation result indicates that the cement sheath of the target wellbore has a risk of fracturing at the corresponding location, then the evaluation result is determined. When the risk type is fracturing risk, it corresponds to the volumetric failure of the cement sheath under strong shear compression, which may lead to loss of sealing capacity. Of course, if the first comparison result indicates that the radial stress is less than the compressive strength of the cement sheath (…), then… σr < σc The evaluation results include that the cement sheath of the target wellbore does not pose a risk of fracturing at the corresponding location.

[0072] S8042. If the second comparison result indicates that the circumferential stress is greater than or equal to the tensile strength, it is determined that the evaluation result includes the cement sheath of the target wellbore having a risk of tensile cracking at the corresponding location.

[0073] It should be noted that: if the second comparison result indicates that the circumferential stress is greater than or equal to the tensile strength of the cement ring ( σθ ≥ σ t The evaluation results indicate that the cement sheath in the target wellbore has a risk of tensile fracture at the corresponding location. A risk type of tensile fracture suggests that tensile stress may induce radial microcracks, weakening the sealing integrity of the cement sheath. Of course, if the second comparison result indicates that the circumferential stress is less than the tensile strength of the cement sheath (…), then the evaluation results include the risk of tensile fracture at the corresponding location. σθ < σt The evaluation results include that the cement sheath of the target wellbore does not have a risk of cracking at the corresponding location.

[0074] S8043. If the first interface contact pressure drops to zero and a relative displacement occurs between the dummy casing and the dummy cement sheath, the evaluation result is determined to include the risk of interface debonding between the cement sheath and the casing of the target wellbore.

[0075] It should be noted that if the monitored first interface contact pressure (between the dummy casing and the dummy cement sheath) drops to zero, and relative displacement (i.e., tangential slippage or normal separation) is simultaneously observed between the dummy casing and the dummy cement sheath, indicating local slippage or debonding at the interface, the evaluation result includes a risk of interface debonding between the cement sheath and the casing in the target wellbore. Conversely, if the first interface contact pressure is always greater than zero (i.e., the interface remains compressed), or if the first interface contact pressure fluctuates but never drops to zero, or drops to zero but without relative displacement, it indicates that there is no risk of interface debonding between the cement sheath and the casing in the target wellbore. In this case, the evaluation result includes that there is no risk of interface debonding between the cement sheath and the casing in the target wellbore.

[0076] S8044. If the second interface contact pressure drops to zero and a relative displacement occurs between the virtual formation block and the virtual cement sheath, the evaluation result is determined to include the risk of interface debonding between the cement sheath and the formation block in the target wellbore.

[0077] It should be noted that if the monitored second interface contact pressure (between the virtual formation block and the virtual cement sheath) drops to zero, and relative displacement is simultaneously observed between the virtual formation block and the virtual cement sheath, indicating local slippage or debonding at the interface, the evaluation result includes a risk of interface debonding between the cement sheath and the formation block in the target wellbore. Conversely, if the second interface contact pressure remains consistently greater than zero (i.e., the interface remains consistently compressed), or if the second interface contact pressure fluctuates but never drops to zero, or drops to zero without accompanying relative displacement, indicating no risk of interface debonding between the cement sheath and the formation block in the target wellbore, the evaluation result includes no risk of interface debonding between the cement sheath and the formation block in the target wellbore.

[0078] Finally, the evaluation results from the above steps can be summarized to generate a complete evaluation report. The evaluation report includes the risk type (compressive fracturing, tensile fracturing, casing-cement sheath debonding, formation-cement sheath debonding), the axial location and extent of each risk, and risk level recommendations. The evaluation report can serve as a direct basis for cementing design optimization (such as improving the tensile strength of the cement sheath and improving the surface roughness of the casing to increase the interfacial friction coefficient).

[0079] In this embodiment, by directly mapping the comparison result of radial stress and the compressive strength of the cement sheath to the fracturing risk assessment, the ability to identify the specific location and extent of volumetric failure of the cement sheath under shear load is improved. Furthermore, by mapping the comparison result of circumferential stress and tensile strength to the tensile fracturing risk assessment, the accuracy of identifying weak sections of the cement sheath where radial cracks occur is improved. Even further, by using both zero interfacial contact pressure and relative displacement as debonding criteria, the objectivity of interfacial state assessment is improved, misjudgment is avoided, and the protection of the casing is enhanced. Cement interface and formation The ability to differentiate between different debonding risks at the cement interface enhances the targeted nature of interface strengthening measures (such as adjusting the water loss of cement paste and using interface modifiers).

[0080] In some embodiments of the present invention, such as Figure 9 As shown, after calculating the radial and circumferential stress distributions of the virtual cement ring, the process includes: S901. Based on the radial stress distribution and the circumferential stress distribution, identify the stress concentration region along the axial direction of the target wellbore.

[0081] It should be noted that, based on the extracted radial and circumferential stress distribution data, the stress extrema on each cross-section are extracted along the axial direction of the virtual cement sheath in the three-dimensional coupled model (i.e., the depth direction of the wellbore). By comparing the radial stress... σr The ratio of peak value to average value, and circumferential stress. σθ The location of the peak tensile stress is identified, and the area where the stress increases significantly is identified as the stress concentration area.

[0082] S902. Determine the axial length of the stress concentration region, and add the identified stress concentration region and its axial length as potential failure segments to the evaluation results.

[0083] It should be noted that: based on the boundaries of the identified stress concentration areas, their axial lengths (i.e., the length extending along the wellbore axis) are calculated. These axial lengths include the first axial length of the radial stress concentration area and the second axial length of the circumferential tensile stress concentration area. Considering that cement sheath failure is often caused by the combined effects of radial hydraulic fracturing and circumferential tensile fracturing, the larger of the first and second axial lengths is taken as the length of the overall potential failure zone. The identified stress concentration areas and their axial lengths are added as supplementary information to the generated evaluation results as potential failure zones.

[0084] In this embodiment, by analyzing the radial and circumferential stress distributions along the wellbore axial direction, stress concentration areas with significantly increased stress peaks can be identified, thereby improving the accuracy of failure location. Furthermore, by quantifying the axial length of the stress concentration area and explicitly adding this area and its length to the evaluation results, the evaluation results are enhanced to provide direct guidance for cementing design (e.g., providing the length of well sections requiring key monitoring, the range that may require perforation avoidance, etc.), improving the engineering operability of the evaluation results. Moreover, since the concentration effects of radial and circumferential stresses are considered simultaneously, the identified potential failure zones can comprehensively cover both hydraulic and tensile fracturing failure modes, improving the comprehensiveness of failure mode identification and enhancing the reliability of deepwater oil and gas well integrity management and risk control decision-making.

[0085] In some embodiments of the present invention, such as Figure 10 As shown, it also includes: S1001. Adjust at least one parameter in the three-dimensional coupled model, such as the elastic modulus of the cement ring, the fault dip angle, the seismic moment magnitude, or the interface friction coefficient, to obtain multiple new evaluation results.

[0086] It should be noted that: keeping the well structure, material constitutive model and boundary conditions in the benchmark embodiment unchanged, at least one of the cement sheath elastic modulus, fault dip angle, seismic moment magnitude or interface friction coefficient is adjusted respectively, and steps S101 to S105 are repeated to obtain multiple sets of new evaluation results.

[0087] S1002. Based on the multiple evaluation results, identify the key parameters that cause the cement sheath of the target wellbore to be damaged.

[0088] It should be noted that: all the evaluation results obtained will be compared and analyzed to identify the parameter combination that poses the greatest risk of damaging the integrity of the cement ring (i.e., the most dangerous working condition), and the sensitivity rules of each parameter will be summarized.

[0089] In this embodiment, by adjusting key parameters such as the elastic modulus of the cement sheath, fault dip angle, seismic moment magnitude, and interfacial friction coefficient, evaluation results of the cement sheath under different working conditions can be obtained, enhancing the ability to analyze cement sheaths with different parameter combinations. Furthermore, by comparing multiple sets of evaluation results, the parameter combinations that lead to the greatest risks of hydraulic fracturing, tensile fracturing, and interfacial debonding, as well as the sensitive ranges of each parameter, are identified. The identified key parameter combinations are output as design recommendations, enabling this evaluation method not only to assess the integrity of a specific wellbore under a specific earthquake but also to guide the optimization design direction when facing uncertain geological conditions. This significantly improves the engineering applicability and foresight of the method in deep-water complex geomorphological areas, providing a scientific decision-making tool for wellbore integrity risk management.

[0090] Furthermore, by comparing multiple sets of evaluation results, the key parameters that lead to the greatest risks of hydraulic fracturing, tensile fracturing, and interface debonding are identified, guiding the direction of optimization design when facing uncertain geological conditions, and significantly improving the engineering applicability and foresight in deep-water complex geomorphic areas.

[0091] In all specific embodiments of this application, when processing data related to user identity or characteristics, such as user information, user behavior data, user historical data, and user location information, user permission or consent is obtained first. Furthermore, the collection, use, and processing of this data comply with relevant laws, regulations, and standards. Additionally, when embodiments of this application require access to sensitive personal information, separate permission or consent from the user is obtained through pop-ups or redirects to confirmation pages. Only after obtaining the user's separate permission or consent is the necessary user-related data required for the proper functioning of these embodiments acquired.

[0092] The following section describes the method for evaluating the integrity of wellbore cement sheaths under deep-water seismic slip conditions, as described in this invention, using a specific engineering example. The specific evaluation process includes: S1. Engineering Parameter Acquisition and Cement Sheath Strength Parameter Determination: Acquire the wellbore structural parameters and completion condition parameters of the target wellbore, including geometric structural parameters such as casing outer diameter, casing wall thickness, cement sheath outer diameter, cement sheath thickness, and wellbore dimensions. Simultaneously, acquire the basic mechanical parameters of the casing, cement sheath, and formation materials, including elastic parameters such as elastic modulus and Poisson's ratio. When using an elastoplastic model, strength parameters such as the internal friction angle and cohesion of the materials also need to be acquired. These parameters can be obtained from field design data, wellbore structural design documents, or core mechanics test results. Determine the compressive strength σc and tensile strength σt of the cement sheath through laboratory mechanical testing or field cement slurry system performance evaluation experiments. These strength parameters serve as an important basis for subsequent cement sheath integrity assessment, used to determine whether the cement sheath has undergone compressive or tensile fracturing failure under different loads. By establishing a cement sheath material strength database, integrity evaluation under different cement system conditions can be achieved. This embodiment uses a deep-water oil and gas well in the South China Sea as the research object to quantitatively evaluate the integrity of the wellbore cement sheath under seismic slip. Specific parameters are assumed as follows: casing outer diameter 254 mm, wall thickness 16.13 mm; cement sheath outer diameter 330.2 mm, thickness 76.2 mm. Casing elastic modulus 20 GPa, Poisson's ratio 0.30. Cement sheath elastic modulus 4.6 GPa, Poisson's ratio 0.17, internal friction angle 27.4°, cohesion 11.2 MPa, compressive strength 28 MPa, tensile strength 2.68 MPa. Formation elastic modulus 5 GPa, Poisson's ratio 0.45, internal friction angle 40.5°, cohesion 1 MPa.

[0093] S2. Calculation of Seismic Moment Magnitude and Fault Slip: Based on seismic activity data of the study area or the seismic conditions set in the engineering design, input the seismic moment magnitude Mw and the fault stress drop Δσ. Based on the theoretical relationship between seismic moment magnitude and fault geometric parameters, a mathematical model is established between the fault radius r, shear modulus G, stress drop Δσ, and fault slip distance L to calculate the fault slip under the corresponding magnitude conditions. In actual calculations, slip calculation tables or empirical formulas can be established according to different magnitude ranges to solve for the slip amount for typical magnitudes such as Mw 0.5, 1.0, 1.5, 2.0, and 2.5, and obtain the fault slip distance under different stress drop conditions. This step converts the energy released by seismic activity into engineering-usable stratum slip displacement, providing quantitative input conditions for subsequent numerical simulations. Continuing the above example, selecting moment magnitude Mw=1.0 and stress drop Δσ=2–10MPa, the calculated fault slip is approximately 17.37mm.

[0094] S3. Establishment of a 3D Coupled Model of Casing-Cement Sheath-Formation: A 3D coupled model of "casing-cement sheath-formation" is established in the finite element numerical simulation platform to simulate the mechanical response of the wellbore structure under seismic slip. The virtual formation block is modeled as a 3D block structure, with its outer boundary dimensions set to a sufficiently large ratio relative to the wellbore radius to ensure that the influence of the outer boundary on the stress distribution near the wellbore is sufficiently attenuated, thus forming a stress environment of approximately infinite formation. The virtual casing and virtual cement sheath are modeled using a coaxial concentric cylindrical geometry to maintain the axisymmetric characteristics of the wellbore structure. Regarding material constitutive modeling, the virtual casing material adopts a linear elastic constitutive model, and its mechanical behavior is described by the elastic modulus and Poisson's ratio; the virtual cement sheath and formation material adopt an elastoplastic constitutive model, and their yield criterion adopts the Mohr-Coulomb strength criterion to reflect the yielding behavior and potential failure tendency of the material under shear. In the model, it is assumed that the formation, virtual cement sheath, and virtual casing are all homogeneous and isotropic media. It is also assumed that the virtual casing is centrally located and that the virtual casing-virtual cement sheath interface is initially well-bonded to reduce the interference of non-critical factors on the analysis results. Continuing the above example, a three-dimensional coupled model is established in ABAQUS. The virtual formation block has dimensions of 3m × 3m × 10m, and the virtual casing and virtual cement sheath are coaxial and concentric cylinders. The material constitutive models are as described above.

[0095] S4. Interface Contact Relationship and Friction Parameter Setting: Surface contact relationships are set between the virtual casing-virtual cement sheath interface and the formation-virtual cement sheath interface to simulate the mechanical transmission behavior between interfaces. The tangential interface behavior adopts the Coulomb friction model to allow relative slippage under shear loads. When the interface shear stress exceeds the friction limit, the interface will slip, thereby changing the wellbore stress distribution. The normal interface behavior adopts a hard contact model, where the interface remains in contact and transmits normal stress under compression, while allowing interface separation when the interface contact pressure drops to zero or a tensile tendency appears. In a preferred embodiment, the friction coefficient of the virtual casing-cement interface is set to 0.15, and the friction coefficient of the formation-cement interface is set to 0.6 to reflect the friction characteristics under different interface roughness and material matching conditions. Continuing with the above example, the friction coefficient of the virtual casing-cement interface is set to 0.15, and the friction coefficient of the formation-cement interface is set to 0.6.

[0096] S5. Applying Equivalent Shear Displacement Boundary Conditions for Seismic Slip: The fault slip L calculated in step S2 is equivalent to a shear displacement boundary condition acting on the boundary of the virtual strata block to simulate the strata displacement process caused by seismic slip. Specifically, a fully constrained boundary condition is applied as a reference at one end of the virtual strata block (i.e., the strata portion in the three-dimensional coupled model), while a shear displacement boundary condition is applied at the other end, for example... X direction and A displacement component is applied in the Z direction, thereby forming a directional shear displacement field around the wellbore. Furthermore, hydrostatic pressure is applied to the inner wall of the virtual casing to simulate the continuous support of the well fluid on the virtual casing; an in-situ stress field is applied to the outer boundary of the entire three-dimensional coupled model (i.e., all outer surfaces of the virtual formation block) to reflect the actual stress environment of the wellbore. These loads are automatically transferred through the virtual casing-virtual cement sheath contact and the virtual cement sheath-virtual formation block contact within the model, allowing the virtual cement sheath to obtain the corresponding stress response in the S6 solution. In one embodiment, the in-situ formation stress satisfies the normal fault stress state of vertical principal stress Sv > maximum horizontal principal stress SHmax > minimum horizontal principal stress Shmin. Continuing the above example, one end of the formation is fully constrained, and a shear displacement component (in the -X and -Z directions) is applied to the other end. Hydrostatic pressure is applied to the inner wall of the virtual casing, and an in-situ stress field (Sv > SHmax > Shmin) is applied to the outer surface of the three-dimensional coupled model.

[0097] S6. Finite Element Calculation and Wellbore Stress Distribution Acquisition: After establishing the 3D coupled model, meshing, and applying boundary conditions, the 3D coupled model was numerically calculated using a finite element solver to obtain the stress distribution of the virtual cement sheath around the wellbore. The focus was on extracting the radial stress σr and circumferential stress σθ distribution of the virtual cement sheath along the wellbore axial direction, and analyzing their maximum values ​​and corresponding locations. Simultaneously, stress concentration areas and potential plastic deformation areas in the virtual cement sheath were identified to determine critical locations where failure might occur. Continuing with the previous example, a structured hexahedral mesh was used: 11520 elements for the formation, 4800 elements for the virtual casing, and 22560 elements for the virtual cement sheath (radial minimum 0.08m), with axial refinement in the middle. The stress distribution of the virtual cement sheath was obtained: the region with the maximum radial stress exceeding 28MPa is distributed within approximately 0.45m before and after the slip surface, and the region with the maximum circumferential tensile stress exceeding 2.68MPa is distributed within approximately 0.55m near the slip surface.

[0098] S7. Integrity Evaluation and Risk Zone Determination of the Virtual Cement Ring: Based on the finite element analysis results, the radial stress σr of the virtual cement ring is compared with its compressive strength σc. When σr ≥ σc, the area is determined to have a risk of radial crushing or crushing. Simultaneously, the circumferential tensile stress σθ of the virtual cement ring is compared with its tensile strength σt. When σθ ≥ σt, the area is determined to have a risk of circumferential tensile cracking, which may induce radial cracks and affect the sealing performance of the virtual cement ring. Furthermore, when the interfacial contact pressure drops to zero and is accompanied by significant interfacial slippage or separation, the area is determined to have a risk of interfacial debonding or interfacial failure. Continuing with the above example, the evaluation results show a risk of crushing within 0.45m before and after the slippage face, a risk of tensile cracking within 0.55m, and a risk of localized interfacial slippage / debonding.

[0099] S8. Output Evaluation Results and Engineering Application Recommendations: Based on the above analysis results, output a wellbore cement sheath integrity evaluation report, including the cement sheath risk location, risk type, and influencing factor analysis results. The evaluation results may include the axial risk range of the cement sheath, the circumferential stress concentration location, and the potential failure area in the thickness direction. Further analysis can be conducted on the influence of key parameters such as earthquake magnitude, fault dip angle, cement sheath elastic modulus, and interfacial friction coefficient on cement sheath integrity. This evaluation method can provide quantitative technical basis for wellbore cementing design, cement material selection, and wellbore integrity management in deep-water complex geological areas. Continuing with the above example, the evaluation results indicate that under Mw=1.0 seismic slip conditions, the cement sheath near the fault faces risks of radial fracturing, circumferential tensile fracturing, and interfacial debonding. Optimization of cement sheath material properties and interfacial conditions is recommended.

[0100] This invention establishes a quantitative conversion relationship between seismic moment magnitude, fault slip, and wellbore shear displacement. It can convert the energy released by seismic activity into equivalent slip displacement of the formation surrounding the wellbore through a mathematical model, thereby achieving an engineering expression of the impact of seismic action on the wellbore structure. Compared with traditional methods that rely solely on empirical judgment or qualitative analysis, this invention enables quantitative input of seismic slip loads, allowing for a unified evaluation of the cement sheath stress state under different magnitudes, and improving the scientific rigor and comparability of wellbore integrity analysis. By establishing a three-dimensional coupled model of casing-cement sheath-formation and introducing surface contact and Coulomb friction relationships at the interface, this invention can realistically simulate the stress transfer process in a multi-material concentric structure system. Compared with traditional two-dimensional plane strain models or simplified analytical models, this invention can more accurately reflect the three-dimensional stress field distribution characteristics of the wellbore structure under seismic slip action, particularly identifying local stress concentration areas near the wellbore and their variation along the well axis, thus significantly improving the accuracy of cement sheath failure risk prediction. This invention proposes a cement sheath integrity evaluation criterion system based on radial and circumferential stress. By comparing the radial stress calculated by finite element method with the compressive strength of the cement sheath, and comparing the circumferential tensile stress with the tensile strength of the cement sheath, it can identify multiple failure modes of the cement sheath, such as compressive fracturing, tensile fracturing, and interface debonding. It can not only determine whether cement sheath failure has occurred, but also clarify the type of failure and its spatial distribution, providing a more targeted risk assessment basis for engineering design. This invention analyzes the stress distribution of the cement sheath along the wellbore axial direction to determine the stress concentration zone and its axial length near the slip surface, thereby identifying key sections of the cement sheath where compressive or tensile fracturing may occur. Compared to traditional evaluation methods that only provide an overall safety factor, this invention can directly output specific risk locations, providing clear engineering references for wellbore structure design, cementing construction optimization, and subsequent integrity monitoring, and can quantitatively identify the spatial range of potential cement sheath failure areas. This invention, by changing parameters such as the cement sheath elastic modulus, fault dip angle, earthquake magnitude, and interface friction coefficient, can obtain the stress response change trend of the cement sheath under different operating conditions, thereby identifying key control factors affecting the risk of cement sheath failure. The research results show that increasing the elastic modulus of the cement sheath enhances the structural stiffness and increases the degree of local stress concentration, while changes in fault dip angle and magnitude significantly alter the distribution of shear load around the well. These patterns provide important basis for the design and structural optimization of cement systems in deep water wells, enabling a systematic analysis of the influence of key engineering parameters on the integrity of the cement sheath.This invention, through numerical simulation analysis, reveals that shear displacement caused by fault slip creates a significant asymmetric stress field near the wellbore, leading to localized stress concentration in the cement sheath near the slip surface and inducing failure modes such as radial fracturing or circumferential tensile fracturing. This addresses the insufficient understanding of the damage mechanism of wellbore cement sheaths under the chain reaction of "earthquake-landslide-fault slip" in existing technologies, and can reveal the cement sheath failure mechanism under deep-water seismic slip conditions. This invention can be used not only for safety analysis in the cementing design stage of deep-water oil and gas wells, but also for wellbore integrity assessment of production wells, injection wells, and underground gas storage facilities, thus providing reliable technical support for the safe development and long-term operation of deep-water oil and gas fields. It is applicable to wellbore integrity evaluation under different earthquake magnitudes, formation dip angles, and cement material parameters, exhibiting good versatility and scalability. This invention establishes a complete quantitative evaluation process for wellbore integrity, enabling comprehensive analysis from seismic parameter input, slip calculation, 3D numerical simulation to risk zone identification. It provides a systematic and standardized process for wellbore integrity evaluation in deep-water complex geomorphic areas, effectively improving the safety and reliability of cementing design for deep-water oil and gas wells. This invention establishes a quantitative relationship between seismic magnitude, fault slip, and wellbore shear displacement, combined with 3D finite element numerical simulation, and equates slip to wellbore shear displacement boundary conditions. Simultaneously, it employs a 3D coupled model capable of describing the nonlinearity of multi-material concentric structures and interface contact to obtain the spatial distribution of radial and circumferential stresses in the cement sheath. Furthermore, it constructs failure criteria based on experimental parameters such as the compressive and tensile strength of the cement sheath, outputting risk zones and failure modes such as fracturing, tensile fracturing, and interface peeling. This provides repeatable and quantifiable technical means for cementing design, cement material selection, and wellbore integrity management in deep-water complex geomorphic areas. A systematic evaluation of the stress response and failure risk of wellbore cement sheaths under seismic slip conditions in deep-water complex geomorphic areas is conducted. This method can achieve quantitative assessment of wellbore integrity under different earthquake magnitudes, fault dip angles, and material parameters, providing engineering basis for cementing design and cement system optimization in deepwater oil and gas wells.

[0101] To better implement the evaluation method for wellbore cement sheath under seismic fault slip conditions in the embodiments of the present invention, based on the evaluation method for wellbore cement sheath under seismic fault slip conditions, correspondingly, as follows: Figure 11 As shown, this embodiment of the invention also provides an evaluation system 1100 for wellbore cement sheath under seismic fault slip conditions. The evaluation system 1100 for wellbore cement sheath under seismic fault slip conditions includes: The parameter acquisition module 1101 is used to acquire the wellbore structure parameters, material mechanical parameters, completion condition parameters, and cement sheath strength parameters of the target wellbore. The target wellbore includes a casing, a cement sheath surrounding the casing, and formation blocks surrounding the cement sheath. The completion condition parameters include hydrostatic pressure and in-situ stress field. Data acquisition module 1102 is used to acquire the seismic moment magnitude and fault stress drop of the area where the target well is located, and to calculate the fault slip. The model creation module 1103 is used to establish a three-dimensional coupled model based on the wellbore structural parameters and the material mechanical parameters; the three-dimensional coupled model includes virtual casing, virtual cement sheath and virtual formation block corresponding to the casing, cement sheath and formation block of the target wellbore; The calculation module 1104 is used to calculate the radial stress distribution and circumferential stress distribution of the virtual cement ring based on the fault slip, the hydrostatic pressure applied to the inner wall of the virtual casing, and the in-situ stress field applied to the outermost boundary of the three-dimensional coupled model, using the finite element algorithm. Evaluation module 1105 is used to obtain the evaluation results of the cement sheath of the target wellbore under earthquake-induced fault slip based on the radial stress distribution, the circumferential stress distribution and the strength parameters.

[0102] The wellbore cement sheath evaluation system 1100 provided in the above embodiments can realize the technical solutions described in the above embodiments of the wellbore cement sheath evaluation method under earthquake fault slip conditions. The specific implementation principles of each module or unit can be found in the corresponding content in the above embodiments of the wellbore cement sheath evaluation method under earthquake fault slip conditions, and will not be repeated here.

[0103] like Figure 12 As shown, the present invention also provides an electronic device 1200. The electronic device 1200 includes a processor 1201, a memory 1202, and a display 1203. Figure 12 Only some components of the electronic device 1200 are shown, but it should be understood that it is not required to implement all the components shown, and more or fewer components may be implemented instead.

[0104] In some embodiments, processor 1201 may be a central processing unit (CPU), microprocessor, or other data processing chip, used to run program code stored in memory 1202 or process data, such as the evaluation method for wellbore cement sheath under seismic fault slip conditions in this invention.

[0105] In some embodiments, processor 1201 may be a single server or a group of servers. The server group may be centralized or distributed. In some embodiments, processor 1201 may be local or remote. In some embodiments, processor 1201 may be implemented on a cloud platform. In one embodiment, the cloud platform may include a private cloud, public cloud, hybrid cloud, community cloud, distributed cloud, internal cloud, multi-cloud, etc., or any combination thereof.

[0106] In some embodiments, memory 1202 may be an internal storage unit of electronic device 1200, such as a hard disk or memory of electronic device 1200. In other embodiments, memory 1202 may also be an external storage device of electronic device 1200, such as a plug-in hard disk, smart media card (SMC), secure digital (SD) card, flash card, etc. equipped on electronic device 1200.

[0107] Furthermore, the memory 1202 may include both internal storage units of the electronic device 1200 and external storage devices. The memory 1202 is used to store application software and various types of data installed on the electronic device 1200.

[0108] In some embodiments, display 1203 may be an LED display, a liquid crystal display, a touch-sensitive liquid crystal display, or an OLED (Organic Light-Emitting Diode) touchscreen. Display 1203 is used to display information from electronic device 1200 and to display a visual user interface. Components 1201-1203 of electronic device 1200 communicate with each other via a system bus.

[0109] In one embodiment, when the processor 1201 executes the evaluation program for wellbore cement sheath under seismic fault slip conditions stored in the memory 1202, the following steps can be implemented: The wellbore structural parameters, material mechanical parameters, completion condition parameters, and cement sheath strength parameters of the target wellbore are obtained. The target wellbore includes a casing, a cement sheath surrounding the casing, and formation blocks surrounding the cement sheath. The completion condition parameters include hydrostatic pressure and in-situ stress field. Obtain the seismic moment magnitude and fault stress drop of the area where the target well is located, and calculate the fault slip. A three-dimensional coupled model is established based on the wellbore structural parameters and the material mechanical parameters; the three-dimensional coupled model includes virtual casing, virtual cement sheath and virtual formation block corresponding to the casing, cement sheath and formation block of the target wellbore; Based on the fault slip, the hydrostatic pressure applied to the inner wall of the virtual casing, and the in-situ stress field applied to the outermost boundary of the three-dimensional coupled model, the radial stress distribution and circumferential stress distribution of the virtual cement ring are calculated using the finite element algorithm. Based on the radial stress distribution, the circumferential stress distribution, and the strength parameters, the evaluation results of the cement sheath of the target wellbore under earthquake-induced fault slip are obtained.

[0110] It should be understood that when the processor 1201 executes the evaluation program for wellbore cement sheath under seismic fault slip conditions in the memory 1202, in addition to the functions mentioned above, it can also perform other functions, as detailed in the description of the corresponding method embodiments above.

[0111] Furthermore, the embodiments of the present invention do not specifically limit the type of the electronic device 1200 mentioned. The electronic device 1200 can be a mobile phone, tablet computer, personal digital assistant (PDA), wearable device, laptop computer, or other portable electronic device. Exemplary embodiments of portable electronic devices include, but are not limited to, portable electronic devices running iOS, Android, Microsoft, or other operating systems. The aforementioned portable electronic device can also be other portable electronic devices, such as a laptop computer with a touch-sensitive surface (e.g., a touch panel). It should also be understood that in some other embodiments of the present invention, the electronic device 1200 may not be a portable electronic device, but rather a desktop computer with a touch-sensitive surface (e.g., a touch panel).

[0112] Those skilled in the art will understand that all or part of the processes of the methods described in the above embodiments can be implemented by a computer program instructing related hardware (such as a processor, controller, etc.), and the computer program can be stored in a computer-readable storage medium. The computer-readable storage medium may be a disk, optical disk, read-only memory, or random access memory, etc.

[0113] The above provides a detailed description of the evaluation method, system, and equipment for wellbore cement sheath under seismic fault slip conditions provided by this invention. Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this invention. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A method for evaluating wellbore cement sheaths under seismic fault slip conditions, characterized in that, include: The wellbore structural parameters, material mechanical parameters, completion condition parameters, and cement sheath strength parameters of the target wellbore are obtained. The target wellbore includes a casing, a cement sheath surrounding the casing, and formation blocks surrounding the cement sheath. The completion condition parameters include hydrostatic pressure and in-situ stress field. Obtain the seismic moment magnitude and fault stress drop of the area where the target well is located, and calculate the fault slip. A three-dimensional coupled model is established based on the wellbore structural parameters and the material mechanical parameters; the three-dimensional coupled model includes virtual casing, virtual cement sheath and virtual formation block corresponding to the casing, cement sheath and formation block of the target wellbore; Based on the fault slip, the hydrostatic pressure applied to the inner wall of the virtual casing, and the in-situ stress field applied to the outermost boundary of the three-dimensional coupled model, the radial stress distribution and circumferential stress distribution of the virtual cement ring are calculated using the finite element algorithm. Based on the radial stress distribution, the circumferential stress distribution, and the strength parameters, the evaluation results of the cement sheath of the target wellbore under earthquake-induced fault slip are obtained.

2. The evaluation method for wellbore cement sheath under seismic fault slip conditions according to claim 1, characterized in that, The calculation of fault slip includes: The fault radius is calculated based on the earthquake moment magnitude and the fault stress drop. The fault slip is calculated based on the fault radius, the fault stress drop, and the formation shear modulus of the area where the target well is located, which is obtained in advance.

3. The evaluation method for wellbore cement sheath under seismic fault slip conditions according to claim 1, characterized in that, The establishment of a three-dimensional coupled model based on the wellbore structural parameters and the material mechanical parameters includes: Based on the wellbore structural parameters, the virtual formation block is established using a three-dimensional block structure, and the virtual casing and the virtual cement sheath are established using a coaxial concentric cylindrical structure. Based on the material mechanics parameters, a linear elastic constitutive model is assigned to the virtual casing, and an elastoplastic constitutive model based on the Mohr-Coulomb strength criterion is assigned to the virtual cement sheath and the virtual formation block to obtain the initial model; An interface contact relationship is established between the virtual casing and the virtual cement sheath, and between the virtual formation block and the virtual cement sheath in the initial model. The interface friction coefficient between the virtual casing and the virtual cement sheath is set to be less than that between the virtual formation block and the virtual cement sheath, thereby establishing the three-dimensional coupled model. The tangential behavior of the interface contact is simulated using the Coulomb friction model, and the normal behavior of the interface contact is simulated using the hard contact model.

4. The evaluation method for wellbore cement sheath under seismic fault slip conditions according to claim 1, characterized in that, Based on the fault slip, the hydrostatic pressure applied to the inner wall of the virtual casing, and the in-situ stress field applied to the outermost boundary of the three-dimensional coupled model, the radial and circumferential stress distributions of the virtual cement sheath are calculated using the finite element method, including: Based on the fault slip, a shear displacement boundary condition is applied to the boundary of the virtual stratum block; the shear displacement boundary condition includes applying a pre-set fully constrained boundary condition at one end of the virtual stratum block and applying a shear displacement component corresponding to the fault slip at the other end of the virtual stratum block. The hydrostatic pressure is applied to the inner wall of the virtual sleeve, and the in-situ stress field is applied to the outermost boundary of the three-dimensional coupled model. The radial stress distribution and circumferential stress distribution of the virtual cement ring in the three-dimensional coupled model are extracted by solving the problem using the finite element method.

5. The evaluation method for wellbore cement sheath under seismic fault slip conditions according to claim 1, characterized in that, The evaluation results of the cement sheath of the target wellbore under earthquake-induced fault slip, based on the radial stress distribution, the circumferential stress distribution, and the strength parameters, include: The radial stress distribution is compared with the compressive strength in the strength parameters to obtain a first comparison result; A second comparison result is obtained by comparing the circumferential stress distribution with the tensile strength in the strength parameters. Monitor the first interface contact pressure between the dummy casing and the dummy cement sheath, and the second interface contact pressure between the dummy formation block and the dummy cement sheath; The evaluation result is obtained based on the first comparison result, the second comparison result, the first interface contact pressure, and the second interface contact pressure.

6. The evaluation method for wellbore cement sheath under seismic fault slip conditions according to claim 5, characterized in that, The step of obtaining the evaluation result based on the first comparison result, the second comparison result, the first interface contact pressure, and the second interface contact pressure includes: If the first comparison result indicates that the radial stress is greater than or equal to the compressive strength, it is determined that the evaluation result includes the cement sheath of the target wellbore having a risk of fracturing at the corresponding location; If the second comparison result indicates that the circumferential stress is greater than or equal to the tensile strength, it is determined that the evaluation result includes the risk of tensile cracking of the cement sheath at the corresponding location in the target wellbore; If the first interface contact pressure drops to zero and a relative displacement occurs between the dummy casing and the dummy cement sheath, the evaluation result is determined to include the risk of interface debonding between the cement sheath and the casing of the target wellbore. If the second interface contact pressure drops to zero and a relative displacement occurs between the virtual formation block and the virtual cement sheath, the evaluation result is determined to include the risk of interface debonding between the cement sheath and the formation block in the target wellbore.

7. The evaluation method for wellbore cement sheath under seismic fault slip conditions according to claim 1, characterized in that, After calculating the radial and circumferential stress distributions of the virtual cement ring, the process includes: Based on the radial stress distribution and the circumferential stress distribution, stress concentration areas along the axial direction of the target wellbore are identified; The axial length of the stress concentration region is determined, and the identified stress concentration region and its axial length are added to the evaluation results as potential failure zones.

8. The evaluation method for wellbore cement sheath under seismic fault slip conditions according to any one of claims 1 to 7, characterized in that, Also includes: By adjusting at least one parameter in the three-dimensional coupled model, such as the elastic modulus of the cement sheath, the fault dip angle, the seismic moment magnitude, or the interface friction coefficient, multiple new evaluation results can be obtained. Based on multiple evaluation results, key parameters leading to the destruction of the cement sheath in the target wellbore were identified.

9. An evaluation system for wellbore cement sheath under seismic fault slip conditions, characterized in that, include: The parameter acquisition module is used to acquire the wellbore structural parameters, material mechanical parameters, completion condition parameters, and cement sheath strength parameters of the target wellbore. The target wellbore includes a casing, a cement sheath surrounding the casing, and formation blocks surrounding the cement sheath. The completion condition parameters include hydrostatic pressure and in-situ stress field. The data acquisition module is used to acquire the seismic moment magnitude and fault stress drop of the area where the target well is located, and to calculate the fault slip. The model creation module is used to establish a three-dimensional coupled model based on the wellbore structural parameters and the material mechanical parameters; the three-dimensional coupled model includes virtual casing, virtual cement sheath and virtual formation block corresponding to the casing, cement sheath and formation block of the target wellbore; The calculation module is used to calculate the radial and circumferential stress distributions of the virtual cement ring based on the fault slip, the hydrostatic pressure applied to the inner wall of the virtual casing, and the in-situ stress field applied to the outermost boundary of the three-dimensional coupled model, using the finite element algorithm. The evaluation module is used to obtain the evaluation results of the cement sheath of the target wellbore under earthquake-induced fault slip based on the radial stress distribution, the circumferential stress distribution, and the strength parameters.

10. An electronic device, characterized in that, Including memory and processor, among which, The memory is used to store programs; The processor, coupled to the memory, is used to execute the program stored in the memory to implement the steps in the evaluation method of wellbore cement sheath under seismic fault slip conditions as described in any one of claims 1 to 8.

Images