Thermal-seepage coupling cement sheath stress and integrity prediction method, equipment and medium

Abstract

The invention provides a thermal-seepage coupling cement sheath stress and integrity prediction method, equipment and a medium, and belongs to the field of casing well cementation. The cement sheath integrity prediction method comprises the following steps: solving a shaft assembly initial stress calculation equation set, a shaft assembly stress increment calculation equation set, a shaft assembly temperature calculation equation set and a shaft assembly boundary condition equation set, and determining full life cycle stress distribution of a shaft assembly at a specified depth; based on the full-life-cycle stress distribution of the shaft assembly at the specified depth, determining a strength calculation result required for guaranteeing the integrity of the cement sheath at the specified depth; the strength calculation result and the strength actual measurement result are compared, and the failure risk at the designated depth is determined; and based on the failure risks at different depths, determining the integrity failure risk of the target well in the full life cycle. By means of the method, the stress state of the shaft assembly can be accurately simulated, and then the sealing failure risk of the shaft assembly is accurately analyzed and pre-judged.

Description

Technical Field

[0001] The present invention relates to the technical field of casing cementing, and in particular to a thermal-permeability coupling cement ring stress prediction method, a thermal-permeability coupling cement ring integrity prediction method, an electronic device and a computer-readable storage medium. Background Art

[0002] With the increasing proportion of high-temperature and high-pressure gas wells, unconventional oil and gas wells, gas storage wells, deep wells and ultra-deep wells, higher requirements are placed on the long-term sealing of wellbore assemblies. The cement ring of cementing is an important barrier to ensure the integrity of oil and gas wells. In order to achieve long-term sealing, the cement ring needs to adapt to changes in temperature and pressure during drilling and production, as well as resist corrosion from formation fluids. The failure of cement ring sealing and the failure of wellbore integrity can be caused by a variety of reasons. Among them, the stress damage to the cement ring and interface of the wellbore assembly due to changes in wellbore stress is an important reason for the failure of wellbore integrity sealing.

[0003] As exploration and development continue to move deeper into deep and unconventional resources, geological conditions and downhole conditions are becoming increasingly complex, and conditions where wellbore temperature and pressure change significantly are becoming more and more common, mainly manifested in three situations: First, the fluid density in the wellbore changes greatly during different drilling, test production, and production processes, and the wellbore pressure changes significantly; second, during pressure testing and fracturing, the wellbore pressure increases significantly in a short period of time and the ground stress is redistributed; third, during the production process (especially deep wells, thermal wells, etc.), the wellbore temperature changes significantly over time. Therefore, accurately analyzing and determining the stress state of the wellbore assembly at different stages of the entire life cycle of oil and gas wells is of great practical significance for judging how the wellbore integrity will fail and studying countermeasures to prevent the failure of the wellbore integrity.

[0004] In the prior art, in order to determine the stress state of the wellbore assembly under downhole conditions, researchers generally use analytical or numerical analysis methods to establish a mechanical model of the wellbore assembly according to the actual wellbore structure, analyze the stress state of each part of the wellbore assembly under different working conditions, and then study the failure mechanism of the wellbore assembly. These analysis methods are generally based on elastic or elastoplastic mechanics theory and steady-state heat transfer model for modeling. They do not consider the impact of the dynamic change of cement sheath pore pressure in the assembly and the change of cement sheath temperature during the dynamic heat transfer process on the integrity of the wellbore assembly. They can only quantitatively calculate the stress and temperature distribution of the wellbore assembly during fracturing and production. However, with the deepening of research on cementing cement, more and more experiments have shown that cement is a typical porous medium material, and its mechanical behavior has obvious porous medium material characteristics. On the one hand, the change of cement pore pressure has an important influence on its deformation and failure process. On the other hand, the temperature change of cement sheath will cause pore pressure fluctuations, which in turn affects the mechanical behavior.

[0005] In summary, the existing mechanical model of the wellbore assembly has some defects and is inconsistent with the actual downhole working conditions. It does not consider the influence of the changes in the pore pressure of the cement stone and the temperature of the cement sheath on the stress state of the wellbore assembly. Its simulation results are difficult to accurately reflect the stress state of the wellbore assembly, and it is also difficult to accurately analyze and predict the risk of sealing failure of the wellbore assembly. Summary of the invention

[0006] In view of the technical problem that the mechanical model of the wellbore assembly in the prior art does not take into account the influence of the change of cement stone pore pressure and the change of cement sheath temperature on the stress state of the wellbore assembly, and its simulation result is difficult to accurately reflect the stress state of the wellbore assembly, the present invention provides a thermal-permeability coupled cement sheath stress prediction method, which can accurately simulate the stress distribution of the cement sheath under the condition of wellbore temperature and pressure changes.

[0007] In order to solve the technical problem that the analysis results of the stress state of the wellbore assembly in the prior art do not conform to the actual stress conditions of the wellbore assembly, resulting in the inability to accurately predict the risk of sealing failure of the wellbore assembly, the present invention provides a thermal-permeability coupled cement ring integrity prediction method, which can accurately predict the risk of sealing failure of the wellbore assembly.

[0008] To achieve the above-mentioned purpose, the first aspect of the present invention provides a thermal-permeability coupling cement sheath stress prediction method, which comprises the following steps: by solving the integrity analysis model of the multi-layer casing wellbore assembly, determining the initial stress distribution of the wellbore assembly at a specified depth before drilling or cementing, and determining the stress increment of the wellbore assembly at a specified depth under different construction conditions; linearly accumulating the initial stress distribution of the wellbore assembly at the specified depth with the stress increment under different construction conditions to obtain the full life cycle stress distribution of the wellbore assembly at the specified depth; wherein the integrity analysis model of the multi-layer casing wellbore assembly comprises: a group of equations for calculating the initial stress of the wellbore assembly, a group of equations for calculating the stress increment of the wellbore assembly considering the mechanical properties of porous media, a group of equations for calculating the temperature of the wellbore assembly, and a group of equations for the boundary conditions of the wellbore assembly; the different construction conditions include: after cementing, completion fracturing, and production.

[0009] In an exemplary embodiment of the present invention, the initial stress calculation equation group of the wellbore assembly may include: a calculation expression for the stress condition of the casing and a calculation expression for the stress condition of the formation;

[0010] The calculation expression of casing stress is:

[0011] The calculation expression of the formation stress is:

[0012] in, is the radial stress of the casing; is the casing circumferential stress; is the radial stress of the formation; is the circumferential stress of the formation; r in is the inner radius of the casing; p in is the pressure of the liquid column on the inner side of the casing; r1 is the outer radius of the casing; r2 is the outer radius of the cement ring; r o is the outer radius of the formation; p d is the annular liquid column pressure on the outside of the casing; r is the calculated radius.

[0013] In an exemplary embodiment of the present invention, the wellbore assembly stress increment calculation equation group may include: casing stress and strain calculation expression, first cement sheath stress and strain calculation expression, second cement sheath stress and strain calculation expression and formation stress and strain calculation expression; wherein, the first cement sheath stress and strain calculation expression is used to calculate the stress and strain generated by the cement sheath connected to the formation, and the second cement sheath stress and strain calculation expression is used to calculate the stress and strain generated by the cement sheath between two layers of casing;

[0014] The calculation expressions of casing stress and strain are:

[0015]

[0016]

[0017]

[0018] The calculation expression of the first cement sheath stress and strain is:

[0019]

[0020]

[0021]

[0022]

[0023]

[0024]

[0025] The calculation expression of the stress and strain of the second cement sheath is:

[0026]

[0027]

[0028]

[0029]

[0030]

[0031]

[0032]

[0033] The calculation expressions of formation stress and strain are:

[0034]

[0035]

[0036]

[0037]

[0038]

[0039]

[0040] in, is the radial stress of the casing; is the casing circumferential stress; G cas is the shear modulus of the casing; is the radial strain of the casing; is the circumferential strain of the casing; ν cas is the Poisson's ratio of the casing; ε cas is the casing volume strain, and is the linear thermal expansion coefficient of the casing; ΔT cas is the difference between the casing calculation temperature and the casing initial temperature; a cas is the thermal diffusion coefficient of the casing; F cas1 is the first calculation parameter of the casing; F cas2 is the second calculation parameter of the casing; F cas3 is the third calculation parameter of the casing; F cas4 is the fourth calculation parameter of the casing; is the radial stress of cement sheath; is the circumferential stress of cement ring; G cem is the shear modulus of cement sheath; is the radial strain of cement sheath; is the circumferential strain of the cement sheath; ν cem is the Poisson's ratio of cement ring drainage; ε cem is the cement sheath volume strain, and is the linear thermal expansion coefficient of cement sheath; ΔTcem is the difference between the cement sheath calculation temperature and the cement sheath initial temperature; α cem is the Biot coefficient of cement ring; p cem is the pore pressure of cement sheath; F cem1 is the first calculation parameter of the first cement sheath; F cem2 is the second calculation parameter of the first cement sheath; F cem3 is the third calculation parameter of the first cement sheath; F cem4 is the fourth calculation parameter of the first cement sheath; F cem5 is the fifth calculation parameter of the first cement sheath; is the constant strain specific heat of cement sheath under drainage condition; is the thermal conductivity of the cement sheath; is the parameter of cement sheath strain that is independent of radius; is the volume of fluid flowing through the porous material of the cement sheath per unit area per unit time; κ cem is the permeability coefficient of cement sheath; is the thermal permeability coefficient of cement sheath; F cem11 is the first calculation parameter of the second cement sheath; F cem12 is the second calculation parameter of the second cement sheath; F cem13 The third calculation parameter for the second cement sheath; is the radial stress of the formation; is the circumferential stress of the formation; G rock is the formation shear modulus; is the radial strain of the formation; is the circumferential strain of the formation; ν rock is the Poisson's ratio of the formation; ε rock is the volume strain of the formation annulus, and is the linear thermal expansion coefficient of the formation; ΔT rock is the difference between the formation temperature at the calculation point and the formation initial temperature; α rock is the formation Biot coefficient; p rock is the formation pore pressure; F rock1 is the first formation calculation parameter; F rock2 is the second formation calculation parameter; F rock3 is the third formation calculation parameter; F rock4 F is the fourth calculation parameter of the formation; rock5 is the fifth calculation parameter of the formation; A1 is the first intermediate parameter; A2 is the second intermediate parameter; A3 is the third intermediate parameter; A4 is the fourth intermediate parameter; A5 is the fifth intermediate parameter; A6 is the sixth intermediate parameter; is the constant strain specific heat of the formation under drainage conditions; is the thermal conductivity of the formation; is a parameter of formation strain that is independent of radius; is the volume of fluid flowing through the porous material per unit area of ​​the formation per unit time; rock is the permeability coefficient of the formation; is the thermal permeability coefficient of the formation; ΔT rock is the difference between the temperature at the calculation point of the formation and the initial temperature of the formation; s is the parameter introduced by Laplace transform; r is the calculation radius; K0 is the standard solution of the second kind of modified Bessel function corresponding to the n-order modified Bessel equation when n=0; K1 is the standard solution of the second kind of modified Bessel function corresponding to the n-order modified Bessel equation when n=1; I0 is the standard solution of the first kind of modified Bessel function corresponding to the n-order modified Bessel equation when n=0; I1 is the standard solution of the first kind of modified Bessel function corresponding to the n-order modified Bessel equation when n=1.

[0041] In an exemplary embodiment of the present invention, the wellbore assembly temperature calculation equation group may include: a casing temperature calculation expression, a first cement ring temperature calculation expression, a second cement ring temperature calculation expression and a formation temperature calculation expression; wherein the first cement ring temperature calculation expression is used to calculate the temperature change generated by the cement ring connected to the formation, and the second cement ring temperature calculation expression is used to calculate the temperature change generated by the cement ring between two layers of casing;

[0042] The casing temperature calculation expression is:

[0043]

[0044] The calculation expression of the first cement ring temperature is:

[0045]

[0046]

[0047] The calculation expression of the second cement ring temperature is:

[0048]

[0049]

[0050] The formation temperature calculation expression is:

[0051]

[0052]

[0053] Where, ΔT cas F is the difference between the casing calculation temperature and the casing initial temperature; cas1 is the first calculation parameter of the casing; a cas is the thermal diffusion coefficient of the casing; F cas2is the second calculation parameter of the casing; ΔT cem is the difference between the temperature at the cement sheath calculation point and the initial temperature of the cement sheath; F is the heat flowing through the pores of cement ring per unit area per unit time; cem1 is the first calculation parameter of the first cement sheath; F cem2 is the second calculation parameter of the first cement sheath; F cem11 is the first calculation parameter of the second cement sheath; F cem12 is the second calculation parameter of the second cement sheath; is the constant strain specific heat of cement sheath under drainage condition; is the thermal conductivity of the cement sheath; ΔT rock F is the difference between the formation calculation temperature and the formation initial temperature; rock1 is the first formation calculation parameter; F rock2 is the second formation calculation parameter; is the constant strain specific heat of the formation under drainage conditions; is the thermal conductivity of the formation; is the amount of heat flowing through the pores per unit area of ​​the formation per unit time; s is the parameter introduced by Laplace transform; r is the calculation radius; I0 is the standard solution of the first kind of modified Bessel function corresponding to the n-order modified Bessel equation when n=0; K0 is the standard solution of the second kind of modified Bessel function corresponding to the n-order modified Bessel equation when n=0; I1 is the standard solution of the first kind of modified Bessel function corresponding to the n-order modified Bessel equation when n=1; K1 is the standard solution of the second kind of modified Bessel function corresponding to the n-order modified Bessel equation when n=1.

[0054] In an exemplary embodiment of the present invention, the wellbore assembly boundary condition equation group may include: a boundary condition equation of the inner wall of the casing, a boundary condition equation of the interface between the casing and the cement sheath, a boundary condition equation of the interface between the cement sheath and the formation, and a boundary condition equation of the formation at infinity;

[0055] The boundary condition equation of the inner wall of the casing is:

[0056] The boundary condition equation of the interface between casing and cement sheath is:

[0057] The boundary condition equation of the interface between cement sheath and formation is:

[0058] The boundary condition equation for the infinitely far stratum is:

[0059] in, is the radial stress of the casing; p in is the pressure of the liquid column on the inner side of the casing; ΔT casΔT1 is the difference between the calculated temperature of the casing and the initial temperature of the casing; cas is the temperature change of the inner wall of the casing; r is the calculation radius; r in is the inner radius of the casing; is the radial stress of cement sheath; is the radial displacement of the casing; is the radial displacement of cement sheath; ΔT cem is the difference between the temperature at the cement sheath calculation point and the initial temperature of the cement sheath; is the volume of fluid flowing through the porous material of the cement sheath per unit area per unit time; is the heat flowing through the cement ring per unit area per unit time; is the heat flowing through the pores of cement sheath per unit area per unit time; r is the calculation radius; r1 is the outer radius of casing; is the radial stress of the formation; is the radial displacement of the formation; ΔT rock is the difference between the formation temperature at the calculation point and the formation initial temperature; p cem is the pore pressure of cement sheath; p rock is the formation pore pressure; is the volume of fluid flowing through the porous material of the formation per unit area per unit time; is the heat flowing through the pores per unit area of ​​the formation per unit time; r2 is the outer radius of the cement ring; ε rock is the volume strain of the formation ring; r o is the outer radius of the formation.

[0060] A second aspect of the present invention provides a thermal-permeability coupling cement ring integrity prediction method, which comprises the following steps: using the above-mentioned thermal-permeability coupling cement ring stress prediction method to determine the full life cycle stress distribution of the wellbore assembly at a specified depth; based on the full life cycle stress distribution of the wellbore assembly at the specified depth, determine the strength calculation result required to ensure the integrity of the cement ring at the specified depth; compare the strength calculation result required to ensure the integrity of the cement ring at the specified depth with the actual strength measurement result of the cement stone at the specified depth, and determine the failure risk of the wellbore assembly at the specified depth; based on the failure risk of the wellbore assemblies at different depths, determine the wellbore assembly integrity failure risk of the target well in the full life cycle; wherein, the strength calculation result required to ensure the integrity of the cement ring includes: at least one of the strength calculation value to ensure that the cement ring does not produce shear failure, the strength calculation value to ensure that the cement ring does not produce tensile failure, and the strength calculation value to ensure that the cement ring does not produce micro-annulus; the actual strength measurement result of the cement stone includes: at least one of the actual shear failure strength of the cement stone, the actual tensile failure strength of the cement stone, and the actual bonding strength between the cement stone and the casing.

[0061] In another exemplary embodiment of the present invention, the comparison of the calculated strength result required to ensure the integrity of the cement sheath at the specified depth and the measured strength result of the cement stone at the specified depth to determine the failure risk of the wellbore assembly at the specified depth may include: determining the shear failure risk coefficient of the cement sheath of the wellbore assembly at the specified depth based on the calculated strength value to ensure that the cement sheath does not produce shear failure at the specified depth and the measured shear failure strength value of the cement stone at the specified depth; and when it is determined that the shear failure risk coefficient of the cement sheath at the specified depth is greater than the shear failure risk threshold of the cement sheath, determining that the cement sheath of the wellbore assembly at the specified depth has a shear failure risk.

[0062] In another exemplary embodiment of the present invention, the comparing the strength calculation result required to ensure the integrity of the cement sheath at the specified depth and the actual measured strength result of the cement stone at the specified depth to determine the failure risk of the wellbore assembly at the specified depth may also include: determining the tensile failure risk coefficient of the cement sheath of the wellbore assembly at the specified depth based on the strength calculation value to ensure that the cement sheath does not produce tensile failure at the specified depth and the actual measured value of the tensile failure strength of the cement stone at the specified depth; when it is determined that the tensile failure risk coefficient of the cement sheath is greater than the tensile failure risk threshold of the cement sheath, determining that the cement sheath of the wellbore assembly at the specified depth has a tensile failure risk.

[0063] In another exemplary embodiment of the present invention, the comparison of the strength calculation result required to ensure the integrity of the cement ring at the specified depth and the actual measured strength result of the cement stone at the specified depth to determine the failure risk of the wellbore assembly at the specified depth may also include: determining the cement ring micro-annulus failure risk coefficient of the wellbore assembly at the specified depth based on the strength calculation value to ensure that the cement ring does not produce micro-annuli at the specified depth and the actual measured value of the bond strength between the cement stone and the casing at the specified depth; when it is determined that the cement ring micro-annulus failure risk coefficient at the specified depth is greater than the cement ring micro-annulus failure risk threshold, determining that the cement ring of the wellbore assembly at the specified depth has a micro-annulus failure risk.

[0064] In another exemplary embodiment of the present invention, the comparison of the strength calculation results required to ensure the integrity of the cement sheath at a specified depth and the actual measured strength results of the cement stone at the specified depth to determine the failure risk of the wellbore assembly at the specified depth may also include: comparing the cement shear failure risk coefficient, the cement sheath tensile failure risk coefficient and the cement sheath micro-annulus failure risk coefficient of the wellbore assembly at the specified depth to determine the maximum failure risk coefficient; and determining the cement sheath failure risk corresponding to the maximum failure risk coefficient as the maximum failure risk of the wellbore assembly at the specified depth.

[0065] A third aspect of the present invention provides an electronic device, comprising a processor and a memory, wherein the memory stores at least one computer program, and the at least one computer program is loaded and executed by one or more of the above-mentioned processors to enable the processor to execute the above-mentioned thermal-permeability coupled cement ring stress prediction method, or the above-mentioned thermal-permeability coupled cement ring integrity prediction method.

[0066] A fourth aspect of the present invention provides a computer-readable storage medium, which stores at least one program code, and the program code is loaded and executed by a processor to enable the computer to execute the above-mentioned thermal-permeability coupled cement sheath stress prediction method, or the above-mentioned thermal-permeability coupled cement sheath integrity prediction method.

[0067] Through the technical solution provided by the present invention, the present invention has at least the following technical effects:

[0068] (1) The thermal-permeability coupled cement sheath stress prediction method provided by the present invention introduces porous media mechanics and heat transfer theory, considers the influence of dynamic temperature-pore pressure on the integrity of the wellbore assembly, and establishes a multi-layer casing wellbore assembly integrity analysis and calculation model. The stress state of the wellbore assembly predicted by the model is more accurate and closer to the actual stress condition of the wellbore assembly;

[0069] (2) The thermal-permeability coupled cement sheath integrity prediction method provided by the present invention uses a multi-layer casing wellbore assembly integrity analysis calculation model to carry out a single-layer / multi-layer wellbore assembly stress analysis and determine the integrity failure risk point and form, which can accurately simulate the stress distribution and failure risk of the cement sheath under the wellbore temperature and pressure change conditions;

[0070] (3) The thermal-permeability coupling cement sheath stress prediction method and the thermal-permeability coupling cement sheath integrity prediction method of the present invention fully consider the influence of dynamic heat transfer and thermal-permeability coupling, and can be widely used in the wellbore assembly integrity analysis and prediction of unconventional wells such as high-temperature and high-pressure gas wells, unconventional oil and gas wells, gas storage wells, deep wells and ultra-deep wells;

[0071] (4) The wellbore assembly integrity analysis and prediction results of the present invention can be used to ensure the mechanical properties of cement paste for the integrity of the wellbore assembly, guide the design of cementing slurry, and ensure the long-term effective sealing of the wellbore assembly.

[0072] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0073] The accompanying drawings are used to provide a further understanding of the embodiments of the present invention and constitute a part of the specification. Together with the following specific implementations, they are used to explain the embodiments of the present invention, but do not constitute a limitation on the embodiments of the present invention. In the accompanying drawings:

[0074] Figure 1 A schematic flow chart of a method for predicting cement sheath stress by thermal-permeability coupling provided in the first embodiment of the present invention;

[0075] Figure 2 A schematic structural diagram of a wellbore assembly provided in accordance with a first embodiment of the present invention;

[0076] Figure 3 A schematic flow chart of a thermal-permeability coupled cement sheath integrity prediction method provided in a second embodiment of the present invention;

[0077] Figure 4 A schematic structural diagram of an electronic device provided in a third embodiment of the present invention.

[0078] Description of Reference Numerals

[0079] 201 - processor, 202 - memory. DETAILED DESCRIPTION

[0080] The specific implementation of the embodiment of the present invention is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described here is only used to illustrate and explain the embodiment of the present invention, and is not used to limit the embodiment of the present invention.

[0081] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0082] In the present invention, unless otherwise specified, the directional words used, such as "upper, lower, top, bottom", are usually used to describe the relative positional relationship of the components in terms of the directions shown in the drawings or in terms of the vertical, perpendicular or gravity directions. "First", "second", etc. are only used for the convenience of description and distinction, and cannot be understood as indicating or implying relative importance.

[0083] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0084] Embodiment 1

[0085] Please refer to Figure 1 The first embodiment of the present invention provides a method for predicting cement sheath stress by thermal-permeability coupling, the method comprising the following steps:

[0086] Step S101: by solving the multi-layer casing wellbore assembly integrity analysis model, determine the initial stress distribution of the wellbore assembly at a specified depth before drilling or cementing, and determine the stress increment of the wellbore assembly at a specified depth under different construction conditions.

[0087] Here, the multi-layer casing wellbore assembly integrity analysis model includes: a wellbore assembly initial stress calculation equation group, a wellbore assembly stress increment calculation equation group, a wellbore assembly temperature calculation equation group and a wellbore assembly boundary condition equation group.

[0088] Step S102: linearly add the initial stress distribution of the wellbore assembly at the specified depth and the stress increments under different construction conditions to obtain the full life cycle stress distribution of the wellbore assembly at the specified depth.

[0089] Here, different construction conditions should include: cementing and solidification, completion fracturing and production.

[0090] It should be noted that the present invention is based on the actual well construction process and wellbore structure, and is based on the plane strain principle to establish different casing layer calculation models such as casing-cement sheath-formation (single-layer casing), casing-cement sheath-casing-cement sheath-formation (double-layer casing) at a specified depth, thereby jointly forming the multi-layer casing wellbore assembly integrity analysis model described in step S101. During the establishment process of the multi-layer casing wellbore assembly integrity analysis model, the influence of dynamic temperature and dynamic seepage on cement sheath and formation is comprehensively considered, and the coupling relationship between cement sheath temperature, pore pressure and total stress is added to the wellbore assembly stress increment calculation equation group and the wellbore assembly temperature calculation equation group. By solving the multi-layer casing wellbore assembly integrity analysis model as a whole, the stress conditions of the wellbore assembly under different temperature, pore pressure and stress conditions can be obtained.

[0091] In addition, in step S101, since different wellbore structures are formed by different wellbore assemblies, before solving the multi-layer casing wellbore assembly integrity analysis model, the number of casing layers and calculation conditions of the wellbore assembly at a specified depth need to be determined according to the wellbore structure.

[0092] The specified depth here refers to the proposed calculation well depth, and the calculation condition refers to the construction process experienced by the wellbore assembly throughout its entire life cycle. In other words, before using the multi-layer casing wellbore assembly integrity analysis model to determine the life cycle stress distribution of the wellbore assembly at the proposed calculation well depth, it is necessary to first determine whether the wellbore assembly is a single-layer casing, double-layer casing or multi-layer casing, as well as the construction conditions experienced during the establishment of the wellbore assembly and the subsequent construction conditions.

[0093] For example, Figure 2As shown in the figure, a well in a certain block has a four-open wellbore structure. If the depth to be calculated is Figure 2 As shown by the green line in the figure, the wellbore assembly is a single-layer casing model. The wellbore assembly consists of a single-layer casing, a single-layer cement ring and a formation. The construction process experienced by the wellbore assembly mainly includes drilling, cementing, completion fracturing and production.

[0094] If the depth to be calculated is Figure 2 As shown by the red line in the figure, the wellbore assembly is a double-casing model. The wellbore assembly consists of an outer casing (i.e., surface casing), an inner casing (i.e., production casing), an outer cement ring, an inner cement ring and formations. The construction process experienced by the wellbore assembly mainly includes outer casing drilling, cementing, inner casing drilling, cementing, completion fracturing and production.

[0095] If the depth to be calculated is Figure 2 As shown by the blue line in the figure, the wellbore assembly is a multi-layer casing model. The wellbore assembly consists of an outer casing, an inner casing, an intermediate casing (i.e., supplementary casing), an outer cement ring, an inner cement ring, a middle cement ring and formations. The construction process experienced by the wellbore assembly mainly includes outermost casing drilling, cementing, intermediate casing drilling, cementing, inner casing drilling, cementing, completion fracturing and production, and so on.

[0096] When the wellbore assembly is determined to be a single-layer casing assembly, the stress distribution of the wellbore assembly before drilling / cementing is first calculated. The stress in the annulus (i.e., cement ring) is the static liquid column pressure of the annulus slurry, the casing inner wall stress is the static liquid column pressure of the casing slurry, the casing outer wall / formation inner wall stress is the annulus slurry static liquid column pressure, and the formation outer wall stress is the initial ground stress. The above stress distribution is used as the initial stress of the wellbore assembly during the well construction process. Under the subsequent working conditions such as cementing, completion fracturing and production, the dynamic temperature and dynamic seepage of the cement ring and the formation are considered. For the casing, only elastic deformation is considered. The stress conditions of the casing, cement ring and formation are calculated respectively according to the boundary pressure and temperature variables of the wellbore assembly, and then the full life cycle stress distribution of the wellbore assembly at the specified depth (i.e., the calculation depth) is obtained by linear accumulation.

[0097] For example, for a single-layer casing assembly, the calculation process of the full life cycle stress distribution of the wellbore assembly at a specified depth is as follows:

[0098] (a1) Calculate the stress of the wellbore assembly at a specified depth before drilling / cementing for a single layer of casing.

[0099] During the drilling / cementing process, the inner side of the single-layer casing is subjected to the pressure of the liquid column inside the casing. in The outer side of the casing and the inner side of the formation are subjected to the annular liquid column pressure pd The outer side of the formation is subjected to the ground stress p out At this time, the stress state of the casing and the formation satisfies the Lame formula, and the elastic modulus of the casing is E cas , the elastic modulus of the formation is E rock .

[0100] At this time, the stress condition of the single-layer casing is calculated using the casing stress condition calculation expression, which is:

[0101]

[0102] In formula (1), is the radial stress of the casing; is the casing circumferential stress; r in is the inner radius of the casing; p in is the pressure of the liquid column on the inner side of the casing; r1 is the outer radius of the casing; p d is the annular liquid column pressure on the outside of the casing; r is the calculated radius.

[0103] The stress condition of the stratum is calculated using the calculation expression of the stratum stress condition, which is:

[0104]

[0105] In formula (2), is the radial stress of the formation; is the circumferential stress of the formation; r2 is the outer radius of the cement ring; r o is the outer radius of the formation; p d is the annular liquid column pressure on the outside of the casing; p out is the ground stress on the outside of the stratum; r is the calculation radius.

[0106] (a2) Based on the principles of pore mechanics, calculate the stress conditions of the wellbore assembly at a specified depth under subsequent working conditions such as cementing, completion, fracturing and production.

[0107] By simultaneously solving the equations for calculating the stress increment of the wellbore assembly, the equations for calculating the temperature of the wellbore assembly, and the equations for the boundary conditions of the wellbore assembly, the stress changes and temperature changes of a single-layer casing, a single-layer cement sheath, and the formation at a specified depth under different construction conditions (such as after cementing, completion fracturing, and production processes) can be determined respectively.

[0108] It should be noted that for a single-layer casing assembly, the initial stress calculation equation group of the wellbore assembly includes: the casing stress calculation expression and the formation stress calculation expression. The stress increment calculation equation group of the wellbore assembly includes: the casing stress and strain calculation expression, the first cement sheath stress and strain calculation expression, and the formation stress and strain calculation expression. The temperature calculation equation group of the wellbore assembly includes: the casing temperature calculation expression, the first cement sheath temperature calculation expression, and the formation temperature calculation expression. The boundary condition equation group of the wellbore assembly includes: the boundary condition equation of the inner wall of the casing, the boundary condition equation of the interface between the casing and the cement sheath, the boundary condition equation of the interface between the cement sheath and the formation, and the boundary condition equation of the formation at infinity.

[0109] In addition, in the process of calculating temperature and stress for casing, cement sheath and formation, multiple intermediate parameters can be set to simplify the expression. In the process of calculating temperature and stress for casing, cement sheath and formation respectively, multiple unknown calculation parameters will be generated. By applying these calculation parameters to the boundary conditions for solution, and then substituting the solution results of each calculation parameter into the expressions of stress, strain, temperature, pore water pressure, etc., the final calculation results of stress, strain, temperature and pore water pressure corresponding to casing, cement sheath and formation can be obtained.

[0110] Multiple intermediate parameters include A1, A2, A3, A4, A5 and A6; multiple calculation parameters include F cas1 、F cas2 、F cas3 、F cas4 、F cem1 、F cem2 、F cem3 、F cem4 、F cem5 、F rock1 、F rock2 、F rock3 、F rock4 and F rock5 .

[0111] The calculation formulas for multiple intermediate parameters can be found in the following formulas (3) to (8).

[0112]

[0113]

[0114]

[0115]

[0116]

[0117]

[0118] In formulas (3) to (8), A1 is the first intermediate parameter; κ cem is the permeability coefficient of cement sheath; M cem is the Biot modulus of cement paste; G cem is the shear modulus of cement sheath; α cem is the Biot coefficient of cement sheath; ν cem is the Poisson's ratio of cement ring drainage; A2 is the second intermediate parameter; is the thermal permeability coefficient of cement sheath; is the constant strain specific heat of cement sheath under drainage condition; is the thermal conductivity of cement sheath; α cem is the Biot coefficient of cement ring; is the linear thermal expansion coefficient of cement sheath; A3 is the third intermediate parameter; A4 is the fourth intermediate parameter; κ rock is the permeability coefficient of the formation; M rock is the Biot modulus of the formation; G rock is the formation shear modulus; α rock is the formation Biot coefficient; ν rock is the Poisson's ratio of the formation; A5 is the fifth intermediate parameter; is the thermal permeability coefficient of the formation; is the constant strain specific heat of the formation under drainage conditions; is the thermal conductivity of the formation; is the volumetric thermal expansion coefficient of the fluid content under constant skeleton volume conditions; is the linear thermal expansion coefficient of the formation; A6 is the sixth intermediate parameter.

[0119] The calculation expression of casing temperature can be found in the following formula (9).

[0120]

[0121] In formula (9), ΔT cas F is the difference between the casing calculation temperature and the casing initial temperature; cas1 is the calculation parameter of the first casing; I0 is the standard solution of the first modified Bessel function corresponding to the nth order modified Bessel equation when n=0; s is the parameter introduced by Laplace transform; r is the calculation radius; a cas is the thermal diffusion coefficient of the casing; F cas2 is the calculation parameter of the second casing; K0 is the standard solution of the second kind of modified Bessel function corresponding to the nth order modified Bessel equation when n=0.

[0122] The calculation expressions of casing stress and strain can be found in the following equations (10) to (12).

[0123]

[0124]

[0125]

[0126] In formulas (10) to (12), is the radial stress of the casing; is the casing circumferential stress; G cas is the shear modulus of the casing; is the radial strain of the casing; is the circumferential strain of the casing; ν cas is the Poisson's ratio of the casing; ε cas is the casing volume strain, and is the linear thermal expansion coefficient of the casing; ΔT cas F is the difference between the casing calculation temperature and the casing initial temperature; cas1 is the first calculation parameter of the casing; I0 is the standard solution of the first modified Bessel function corresponding to the nth order modified Bessel equation when n=0; a cas is the thermal diffusion coefficient of the casing; s is the parameter introduced by Laplace transform; r is the calculation radius; F cas2 is the second calculation parameter of the casing; K0 is the standard solution of the second modified Bessel function corresponding to the n-order modified Bessel equation when n=0; K1 is the standard solution of the second modified Bessel function corresponding to the n-order modified Bessel equation when n=1; F cas3 is the third calculation parameter of the casing; F cas4 is the fourth calculation parameter of the casing; I1 is the standard solution of the first kind of modified Bessel function corresponding to the nth order modified Bessel equation when n=1.

[0127] The calculation expression of the first cement sheath (cement sheath connected to the stratum) temperature can be referred to in the following equations (13) to (14). The calculation expression of the first cement sheath temperature is used to calculate the temperature change generated by the cement sheath connected to the stratum.

[0128]

[0129]

[0130] In formulas (13) and (14), ΔT cem is the difference between the temperature at the cement sheath calculation point and the initial temperature of the cement sheath; F is the heat flowing through the pores of cement ring per unit area per unit time; cem1 is the first calculation parameter of the first cement sheath; F cem2 is the second calculation parameter of the first cement sheath; I0 is the standard solution of the first modified Bessel function corresponding to the nth order modified Bessel equation when n=0; is the constant strain specific heat of cement sheath under drainage condition; is the thermal conductivity of the cement sheath; r is the calculation radius; K0 is the standard solution of the second kind of modified Bessel function corresponding to the n-order modified Bessel equation when n=0; s is the parameter introduced by Laplace transform; I1 is the standard solution of the first kind of modified Bessel function corresponding to the n-order modified Bessel equation when n=1; K1 is the standard solution of the second kind of modified Bessel function corresponding to the n-order modified Bessel equation when n=1.

[0131] The calculation expressions for the stress and strain of the first cement sheath (cement sheath connected to the stratum) can be referred to in the following equations (15) to (19). The calculation expressions for the stress and strain of the first cement sheath are used to calculate the stress and strain generated by the cement sheath connected to the stratum.

[0132]

[0133]

[0134]

[0135]

[0136]

[0137] In formulas (15) to (19), is the radial stress of cement sheath; is the circumferential stress of cement ring; G cem is the shear modulus of cement sheath; is the radial strain of cement sheath; is the circumferential strain of the cement sheath; ν cem is the Poisson's ratio of cement ring drainage; ε cem is the cement sheath volume strain, and is the linear thermal expansion coefficient of cement sheath; ΔT cem is the difference between the cement sheath calculation temperature and the cement sheath initial temperature; α cem is the Biot coefficient of cement ring; p cem is the pore pressure of cement sheath; F cem1 is the first calculation parameter of the first cement sheath; F cem2 is the second calculation parameter of the first cement sheath; F cem3 is the third calculation parameter of the first cement sheath; F cem4is the fourth calculation parameter of the first cement ring; I0 is the standard solution of the first modified Bessel function corresponding to the n-order modified Bessel equation when n=0; K0 is the standard solution of the second modified Bessel function corresponding to the n-order modified Bessel equation when n=0; A1 is the first intermediate parameter; A2 is the second intermediate parameter; A3 is the third intermediate parameter; s is the parameter introduced by Laplace transform; r is the calculation radius; is the constant strain specific heat of cement sheath under drainage condition; is the thermal conductivity of the cement sheath; is the parameter of cement sheath strain that is independent of radius; is the volume of fluid flowing through the porous material of the cement sheath per unit area per unit time; κ cem is the permeability coefficient of cement sheath; is the thermal permeability coefficient of cement sheath; F cem5 The fifth calculation parameter for the first cement sheath.

[0138] The expressions for calculating formation temperature can be found in the following equations (20) to (21).

[0139]

[0140]

[0141] In formulas (20) to (21), ΔT rock F is the difference between the formation calculation temperature and the formation initial temperature; rock1 is the first formation calculation parameter; F rock2 is the second formation calculation parameter; I0 is the first kind of standard solution of the modified Bessel function corresponding to the n-order modified Bessel equation when n=0; K0 is the second kind of standard solution of the modified Bessel function corresponding to the n-order modified Bessel equation when n=0; I1 is the first kind of standard solution of the modified Bessel function corresponding to the n-order modified Bessel equation when n=1; K1 is the second kind of standard solution of the modified Bessel function corresponding to the n-order modified Bessel equation when n=1; r is the calculation radius; s is the parameter introduced by Laplace transform; is the constant strain specific heat of the formation under drainage conditions; is the thermal conductivity of the formation; It is the amount of heat flowing through the pores per unit area of ​​the formation per unit time.

[0142] The calculation expressions of formation stress and strain can be found in the following equations (22) to (26).

[0143]

[0144]

[0145]

[0146]

[0147]

[0148] In formulas (22) to (26), is the radial stress of the formation; is the circumferential stress of the formation; G rock is the formation shear modulus; is the radial strain of the formation; is the circumferential strain of the formation; ν rock is the Poisson's ratio of the formation; ε rock is the volume strain of the formation annulus, and is the linear thermal expansion coefficient of the formation; ΔT rock is the difference between the formation temperature at the calculation point and the formation initial temperature; α rock is the formation Biot coefficient; p rock is the formation pore pressure; F rock1 is the first formation calculation parameter; F rock2 is the second formation calculation parameter; F rock3 is the third formation calculation parameter; F rock4 is the fourth calculation parameter of the formation; I0 is the standard solution of the first modified Bessel function corresponding to the n-order modified Bessel equation when n=0; K0 is the standard solution of the second modified Bessel function corresponding to the n-order modified Bessel equation when n=0; A4 is the fourth intermediate parameter; A5 is the fifth intermediate parameter; A6 is the sixth intermediate parameter; r is the calculation radius; s is the parameter introduced by Laplace transform; is the constant strain specific heat of the formation under drainage conditions; is the thermal conductivity of the formation; is a parameter of formation strain that is independent of radius; is the volume of fluid flowing through the porous material per unit area of ​​the formation per unit time; rock is the permeability coefficient of the formation; is the thermal permeability coefficient of the formation; ΔT rock F is the difference between the formation calculation temperature and the formation initial temperature; rock5 is the calculation parameter of the fifth formation; I1 is the standard solution of the first kind of modified Bessel function corresponding to the n-order modified Bessel equation when n=1; K1 is the standard solution of the second kind of modified Bessel function corresponding to the n-order modified Bessel equation when n=1.

[0149] Based on the above expressions of stress, temperature, strain, etc., a group of boundary condition equations for the assembly is established according to the boundary stress and temperature variables of the wellbore assembly.

[0150] The boundary condition equation of the inner wall of the casing is:

[0151]

[0152] In formula (27), is the radial stress of the casing; p in is the pressure of the liquid column on the inner side of the casing; ΔT cas ΔT1 is the difference between the calculated temperature of the casing and the initial temperature of the casing; cas is the temperature change of the inner wall of the casing; r is the calculation radius; r in is the inner radius of the casing.

[0153] The boundary condition equation of the interface between casing and cement sheath (interface 1) is:

[0154]

[0155] In formula (28), is the radial stress of the casing; is the radial stress of cement sheath; is the radial displacement of the casing; is the radial displacement of cement sheath; ΔT cas ΔT is the difference between the casing calculation temperature and the casing initial temperature; cem is the difference between the temperature at the cement sheath calculation point and the initial temperature of the cement sheath; is the volume of fluid flowing through the porous material of the cement sheath per unit area per unit time; is the heat flowing through the cement ring per unit area per unit time; is the heat flowing through the pores of cement sheath per unit area per unit time; r is the calculation radius; r1 is the outer radius of casing.

[0156] The boundary condition equation of the interface between cement sheath and formation (second interface) is:

[0157]

[0158] In formula (29), is the radial stress of cement sheath; is the radial stress of the formation; is the radial displacement of cement sheath; is the radial displacement of the formation; ΔT cem ΔT is the difference between the cement sheath calculation temperature and the cement sheath initial temperature; rock is the difference between the formation temperature at the calculation point and the formation initial temperature; p cem is the pore pressure of cement sheath; p rock is the formation pore pressure; is the volume of fluid flowing through the porous material of the cement sheath per unit area per unit time; is the volume of fluid flowing through the porous material of the formation per unit area per unit time; is the heat flowing through the pores of the cement sheath per unit area per unit time; is the amount of heat flowing through the pores per unit area of ​​the formation per unit time; r is the calculation radius; r2 is the outer radius of the cement ring.

[0159] The boundary condition equation for the infinitely far stratum is:

[0160]

[0161] In formula (30), ε rock is the volume strain of the formation ring; p rock is the formation pore pressure; ΔT rock is the difference between the formation calculation temperature and the formation initial temperature; r is the calculation radius; r o is the outer radius of the formation.

[0162] (a3) The stress distribution of the wellbore assembly during the entire life cycle is obtained by linear accumulation.

[0163] When the wellbore assembly is determined to be a double-casing assembly, it is first necessary to refer to the calculation method of the single-casing assembly to determine the stress distribution of the outer casing of the double-casing assembly before drilling, cementing and solidification, and after cementing; then calculate the stress distribution of the inner casing before drilling / cementing. The stress in the annulus is the static liquid column pressure of the annulus slurry, the inner wall stress of the inner casing is the static liquid column pressure of the slurry in the casing, the outer wall of the inner casing / the inner wall of the outer casing-cement sheath-formation assembly is the static liquid column pressure of the annulus slurry, and the outer wall stress of the outer casing-cement sheath-formation assembly is the initial ground stress. The above stress distribution is taken as the initial stress of the wellbore assembly during the well construction process. Under subsequent working conditions such as cementing, completion fracturing and production, the dynamic temperature and dynamic seepage of the cement sheath and the formation are considered. For the casing, only elastic deformation is considered. The stress conditions of the casing, cement sheath and formation are calculated respectively according to the boundary pressure and temperature variables of the wellbore assembly. Then, the full life cycle stress distribution of the wellbore assembly at a specified depth is obtained by linear accumulation.

[0164] For example, for a double-casing assembly, the calculation process of the stress distribution of the wellbore assembly over its entire life cycle at a specified depth is as follows:

[0165] (b1) Calculate the stress on the outer casing at the specified depth of the wellbore assembly before drilling / cementing.

[0166] The stress condition of the wellbore assembly at a specified depth before drilling / cementing can be determined by referring to the calculation method of the stress condition of the wellbore assembly at the same depth before drilling / cementing with a single casing (i.e., formula (1) to formula (2)).

[0167] (b2) Calculate the stress conditions of the wellbore assembly at a specified depth under subsequent working conditions such as after the outer casing cementing, completion fracturing and production.

[0168] The stress condition of the wellbore assembly at a specified depth after cementing, completion, fracturing and production, etc. can be determined by referring to the calculation method of the stress condition of the wellbore assembly at a specified depth after cementing, completion, fracturing and production, etc. (i.e., formula (3) to formula (30)).

[0169] (b3) Calculate the stress conditions of the inner casing at the wellbore assembly at a specified depth before drilling / cementing.

[0170] During the drilling / cementing process, the inner side of the inner casing is subjected to a liquid column pressure of p in2 The outer side of the inner casing is subjected to annular fluid pressure change of p d2 The pressure change of the annular liquid column on the outer layer assembly is Δp d2 The ground stress on the outer side of the formation changes to p out2 .

[0171] At this time, the stress state of the inner casing can be determined by referring to the stress calculation method of the single-layer casing before drilling / cementing (i.e., formula (1) to formula (2)).

[0172] The stress state of the outer casing assembly can be determined by referring to the stress calculation method of the single-layer casing under subsequent working conditions such as cementing, completion fracturing and production (i.e., equations (3) to (30)).

[0173] (b4) Calculate the stress conditions of the wellbore assembly at a specified depth under subsequent working conditions such as cementing, completion, fracturing and production.

[0174] For the inner casing, outer casing, outer cement sheath and formation, relevant calculations can be performed by referring to the stress expressions (i.e., equations (3) to (30)) under subsequent working conditions such as single-layer casing cementing, completion fracturing and production.

[0175] For the inner cement sheath, since the boundary conditions are different from those of the single-layer casing cement sheath, that is, the cement sheath has no seepage in the radial direction, it is necessary to establish new temperature and stress expressions for the inner cement sheath (i.e., the second cement sheath temperature calculation expression and the second cement sheath stress and strain calculation expression). The newly added calculation parameters include F cem11 、F cem12 and F cem13 .

[0176] The second cement ring temperature calculation expression (the cement ring between two layers of casing) can be referred to in the following equations (31) to (32). The second cement ring temperature calculation expression is used to calculate the temperature change of the cement ring between two layers of casing.

[0177]

[0178]

[0179] In formulas (31) to (32), ΔT cem is the difference between the temperature at the cement sheath calculation point and the initial temperature of the cement sheath; F is the heat flowing through the pores of cement ring per unit area per unit time; cem11 is the first calculation parameter of the second cement sheath; F cem12 is the second calculation parameter of the second cement sheath; I0 is the standard solution of the first kind of modified Bessel function corresponding to the nth order modified Bessel equation when n=0; is the constant strain specific heat of cement sheath under drainage condition; is the thermal conductivity of the cement sheath; r is the calculation radius; K0 is the standard solution of the second kind of modified Bessel function corresponding to the n-order modified Bessel equation when n=0; s is the parameter introduced by Laplace transform; I1 is the standard solution of the first kind of modified Bessel function corresponding to the n-order modified Bessel equation when n=1; K1 is the standard solution of the second kind of modified Bessel function corresponding to the n-order modified Bessel equation when n=1.

[0180] The second cement sheath (cement sheath between two layers of casing) stress and strain calculation expressions can be found in the following equations (33) to (37). The second cement sheath stress and strain calculation expressions are used to calculate the stress and strain generated by the cement sheath between two layers of casing.

[0181]

[0182]

[0183]

[0184]

[0185]

[0186] In formulas (33) to (37), is the radial stress of cement sheath; is the circumferential stress of cement ring; G cem is the shear modulus of cement sheath; is the radial strain of cement sheath; is the circumferential strain of the cement sheath; ν cem is the Poisson's ratio of cement ring drainage; εcem is the cement sheath volume strain, and is the linear thermal expansion coefficient of cement sheath; ΔT cem is the difference between the cement sheath calculation temperature and the cement sheath initial temperature; α cem is the Biot coefficient of cement ring; p cem is the pore pressure of cement sheath; F cem11 is the first calculation parameter of the second cement sheath; F cem12 is the second calculation parameter of the second cement sheath; F cem13 is the third calculation parameter of the second cement ring; I0 is the standard solution of the first modified Bessel function corresponding to the n-order modified Bessel equation when n=0; K0 is the standard solution of the second modified Bessel function corresponding to the n-order modified Bessel equation when n=0; A1 is the first intermediate parameter; A2 is the second intermediate parameter; A3 is the third intermediate parameter; s is the parameter introduced by Laplace transform; r is the calculation radius; is the constant strain specific heat of cement sheath under drainage condition; is the thermal conductivity of the cement sheath; is the parameter of cement sheath strain that is independent of radius; is the volume of fluid flowing through the porous material of the cement sheath per unit area per unit time; κ cem is the permeability coefficient of cement sheath; is the thermal permeability coefficient of the cement sheath.

[0187] That is to say, for the double-layer casing assembly, the initial stress calculation equation group of the wellbore assembly includes: the casing stress calculation expression and the formation stress calculation expression. The stress increment calculation equation group of the wellbore assembly includes: the casing stress and strain calculation expression, the first cement sheath stress and strain calculation expression, the second cement sheath stress and strain calculation expression, and the formation stress and strain calculation expression. The temperature calculation equation group of the wellbore assembly includes: the casing temperature calculation expression, the first cement sheath temperature calculation expression, the second cement sheath temperature calculation expression, and the formation temperature calculation expression. The boundary condition equation group of the wellbore assembly includes: the boundary condition equation of the inner wall of the casing, the boundary condition equation of the interface between the casing and the cement sheath, the boundary condition equation of the interface between the cement sheath and the formation, and the boundary condition equation of the formation at infinity.

[0188] (b5) The stress distribution of the wellbore assembly during the entire life cycle is obtained by linear accumulation.

[0189] For example, when the wellbore assembly is determined to be a multi-layer casing assembly, the stress distribution of the wellbore assembly over the entire life cycle can be calculated by referring to the calculation method of a double-layer casing assembly.

[0190] Furthermore, in a possible implementation, the thermal-permeability coupled cement sheath stress prediction method further includes step S103: determining the life cycle stress distribution of the entire target wellbore assembly based on the life cycle stress distribution of the wellbore assembly at different depths.

[0191] In addition, the implementation environment of this embodiment includes at least one terminal and a server, and the method is executed on the terminal or the server respectively. The terminal and the server can be connected in communication to realize the interactive transmission of information.

[0192] Among them, the terminal can be any electronic product that can interact with the user through one or more methods such as keyboard, touchpad, touch screen, voice interaction, etc., such as PC (Personal Computer), PPC (Pocket Personal Computer), tablet computer, etc.

[0193] The server can be a single server or a server cluster composed of multiple servers. It can also be a cloud server that provides basic cloud computing services such as cloud services, cloud databases, cloud computing, cloud functions, cloud storage, network services, cloud communications, middleware services, domain name services, security services, CDN (Content Delivery Network), as well as big data and artificial intelligence platforms.

[0194] Embodiment 2

[0195] Please refer to Figure 3 The second embodiment of the present invention provides a method for predicting the integrity of a cement sheath by coupling heat and seepage, the method comprising the following steps:

[0196] Step S201: According to the multi-layer casing wellbore assembly integrity analysis model, simulate and determine the full life cycle stress distribution of the wellbore assembly at a specified depth.

[0197] Step S202: Based on the full life cycle stress distribution of the wellbore assembly at the specified depth, determine the strength calculation result required to ensure the integrity of the cement sheath at the specified depth.

[0198] Step S203: Compare the strength calculation result required to ensure the integrity of the cement sheath at the specified depth with the actual strength measurement result of the cement stone at the specified depth to determine the failure risk of the wellbore assembly at the specified depth.

[0199] Step S204: Based on the failure risks of the wellbore assemblies at different depths, determine the wellbore assembly integrity failure risk of the target well over the entire life cycle.

[0200] It should be noted that in step S203, the strength calculation results required to ensure the integrity of the cement ring include: at least one of the strength calculation value for ensuring that the cement ring does not produce shear failure, the strength calculation value for ensuring that the cement ring does not produce tensile failure, and the strength calculation value for ensuring that the cement ring does not produce micro-annular gaps; the actual measured strength results of the cement stone include: at least one of the actual measured value of the shear failure strength of the cement stone, the actual measured value of the tensile failure strength of the cement stone, and the actual measured value of the bonding strength between the cement stone and the casing.

[0201] Furthermore, in a possible implementation, in step S203, the failure risk coefficient of the cement sheath at a specified depth can be calculated using the strength calculation results and the actual strength measurement results, and the failure risk coefficient of the cement sheath can be compared with the corresponding failure risk coefficient threshold to determine the failure risk of the wellbore assembly at the specified depth.

[0202] For example, the ratio of the strength calculation result required to ensure the integrity of the cement sheath at a specified depth to the measured strength result of the cement stone at a specified depth can be determined as the failure risk coefficient of the cement sheath. In this case, the calculation expression of the failure risk coefficient of the cement sheath is:

[0203]

[0204] In formula (38), σ n is the strength calculation result required to ensure the integrity of the cement sheath at a specified depth, MPa; σ t is the measured strength result of cement paste at the specified depth, MPa; β is the failure risk coefficient of cement sheath, dimensionless.

[0205] Further, in a possible implementation, the failure risk of the wellbore assembly may include at least one of a shear failure risk, a tensile failure risk, and a micro-annulus failure risk.

[0206] For the shear failure risk, the shear failure risk coefficient of the cement sheath of the wellbore assembly at the specified depth can be calculated based on the strength calculation results and the actual strength measurement results; then, if it is determined that the shear failure risk coefficient of the cement sheath at the specified depth is greater than the shear failure risk threshold of the cement sheath, it is determined that there is a shear failure risk for the cement sheath of the wellbore assembly at the specified depth.

[0207] For example, the ratio of the calculated strength value that ensures that the cement sheath does not fail in shear at a specified depth to the measured shear failure strength of the cement stone at a specified depth can be determined as the risk coefficient of cement shear failure. In this case, the calculation expression of the risk coefficient of cement shear failure is:

[0208]

[0209] In formula (39), σ sThe strength required to ensure that the cement sheath does not fail in shear at a specified depth, MPa; σ st is the measured value of cement paste shear failure strength at a specified depth, MPa; β s is the risk factor of cement sheath shear failure, dimensionless.

[0210] Since the shear failure of cement sheath is based on the cement paste satisfying the Mohr-Coulomb failure criterion, the shear failure of cement sheath can be determined based on the experimentally measured c and To determine σ st , and σ obtained from simulation calculations rr and σ θθ To determine σ s Therefore, the calculation expression of cement sheath shear failure risk coefficient can also be simplified as:

[0211]

[0212]

[0213] In formulas (40) and (41), c is the cohesion of cement paste measured by experiment, is the internal friction angle of cement paste measured in the test, σ rr is the strength required to ensure that the cement sheath does not produce micro-annulus at the specified depth, σ θθ The strength required to ensure that the cement sheath does not fail in tension at a specified depth.

[0214] The cement sheath shear failure risk threshold can be set to 1, if β s >1, it is judged that the cement sheath is at risk of shear failure.

[0215] For the risk of tensile failure, the tensile failure risk coefficient of the cement sheath of the wellbore assembly at the specified depth can be calculated based on the strength calculation results and the actual strength measurement results; then, if it is determined that the tensile failure risk coefficient of the cement sheath at the specified depth is greater than the tensile failure risk threshold of the cement sheath, it is determined that the cement sheath of the wellbore assembly at the specified depth has a tensile failure risk.

[0216] For example, the ratio of the calculated strength value that ensures that the cement sheath does not produce tensile failure at a specified depth to the measured tensile failure strength of cement stone at a specified depth can be determined as the tensile failure risk coefficient of the cement sheath. In this case, the calculation expression of the tensile failure risk coefficient of the cement sheath is:

[0217]

[0218] In formula (42), σ d The calculated strength value required to ensure that the cement sheath does not produce tensile failure at a specified depth, MPa; σ dtis the measured value of the tensile strength of cement paste at a specified depth, MPa; β d is the risk factor of cement sheath tensile failure, dimensionless.

[0219] Here, the strength calculation value required to ensure that the cement sheath does not produce tensile failure at a specified depth can be determined as σ obtained by the wellbore assembly integrity analysis model. θθ The measured value of the tensile strength of cement paste at a specified depth can be obtained through the pore mechanics test of cement paste.

[0220] The cement sheath tensile failure risk threshold can be set to 1, if β t >1, it is judged that the cement sheath is at risk of tensile failure.

[0221] With regard to the microannulus failure risk, the microannulus failure risk coefficient of the cement sheath of the wellbore assembly at the specified depth can be calculated based on the strength calculation results and the actual strength measurement results; then, if it is determined that the microannulus failure risk coefficient of the cement sheath at the specified depth is greater than the microannulus failure risk threshold of the cement sheath, it is determined that the cement sheath of the wellbore assembly at the specified depth has a microannulus failure risk.

[0222] For example, the ratio of the calculated strength value that ensures that the cement sheath does not produce micro-annulus failure at a specified depth to the measured value of the bonding strength between the cement stone and the casing at a specified depth can be determined as the cement sheath micro-annulus failure risk coefficient. At this time, the calculation expression of the cement sheath micro-annulus failure risk coefficient is:

[0223]

[0224] In formula (42), σ b The strength calculation value required to ensure that the cement sheath does not produce micro-annulus failure at a specified depth, MPa; σ bt is the measured value of the bonding strength between cement stone and casing at a specified depth, MPa; β a is the failure risk coefficient of micro-annulus of cement sheath, dimensionless.

[0225] Here, the strength calculation value required to ensure that the cement sheath does not produce micro-annulus failure at a specified depth can be determined as σ obtained by the wellbore assembly integrity analysis model. rr The measured value of the bond strength between cement paste and casing at a specified depth can be obtained through the casing-cement paste bond test.

[0226] The failure risk threshold of cement sheath micro-annulus can be set to 1. a >1, it is judged that there is a risk of micro-annulus failure in the cement sheath.

[0227] Furthermore, in a possible implementation, the cement sheath shear failure risk coefficient, cement sheath tensile failure risk coefficient and cement sheath microannulus failure risk coefficient of the wellbore assembly at a specified depth can be compared to determine the maximum failure risk coefficient; and the cement sheath failure risk corresponding to the maximum failure risk coefficient can be determined as the maximum failure risk of the wellbore assembly at the specified depth.

[0228] For example, we can comprehensively compare β s , β t and β a The maximum value among them is taken, and the main failure risk at this depth is determined as the failure risk category corresponding to the maximum value of the failure risk coefficient.

[0229] In addition, the implementation environment of this embodiment includes at least one terminal and a server, and the method is executed on the terminal or the server respectively. The terminal and the server can be connected in communication to realize the interactive transmission of information.

[0230] Among them, the terminal can be any electronic product that can interact with the user through one or more methods such as keyboard, touchpad, touch screen, voice interaction, etc., such as PC (Personal Computer), PPC (Pocket Personal Computer), tablet computer, etc.

[0231] The server can be a single server or a server cluster composed of multiple servers. It can also be a cloud server that provides basic cloud computing services such as cloud services, cloud databases, cloud computing, cloud functions, cloud storage, network services, cloud communications, middleware services, domain name services, security services, CDN (Content Delivery Network), as well as big data and artificial intelligence platforms.

[0232] Embodiment 3

[0233] The third embodiment of the present invention further provides an electronic device, see Figure 4 The electronic device includes a processor 201 and a memory 202, wherein at least one computer program is stored in the memory, and the at least one computer program is loaded and executed by one or more of the above-mentioned processors to enable the processor to implement the thermal-permeability coupling cement sheath stress prediction method described in the first embodiment, or the thermal-permeability coupling cement sheath integrity prediction method described in the second embodiment.

[0234] Of course, the electronic device may also have components such as a wired or wireless network interface, a keyboard, and an input / output interface for input and output. The electronic device may also include other components for realizing various functions of the device, which will not be described in detail here.

[0235] The third embodiment of the present invention also provides a computer-readable storage medium, which stores at least one program code. The program code is loaded and executed by a processor to enable the computer to implement the thermal-permeability coupled cement ring stress prediction method described in the first embodiment or the thermal-permeability coupled cement ring integrity prediction method described in the second embodiment.

[0236] Optionally, the computer readable storage medium may be a read-only memory (ROM), a random access memory (RAM), a compact disc (CD-ROM), a magnetic tape, a floppy disk, and an optical disc data storage device. Those skilled in the art may understand that all or part of the steps in the above-mentioned embodiment method can be completed by instructing the relevant hardware through a program, and the program is stored in a storage medium, including several instructions to enable a single-chip microcomputer, a chip or a processor to execute all or part of the steps of the method described in each embodiment of the present application. The aforementioned storage medium includes: various media that can store program codes, such as a USB flash drive, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk or an optical disc.

[0237] The preferred embodiments of the present invention are described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0238] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0239] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A method for predicting cement sheath stress by thermal-permeability coupling, characterized in that: The thermal-permeability coupled cement sheath stress prediction method comprises: By solving the integrity analysis model of the multi-layer casing wellbore assembly, the initial stress distribution of the wellbore assembly at a specified depth before drilling or cementing is determined, and the stress increment of the wellbore assembly at a specified depth under different construction conditions is determined; The initial stress distribution of the wellbore assembly at the specified depth is linearly accumulated with the stress increments under different construction conditions to obtain the full life cycle stress distribution of the wellbore assembly at the specified depth; The multi-layer casing wellbore assembly integrity analysis model includes: a wellbore assembly initial stress calculation equation group, a wellbore assembly stress increment calculation equation group considering the mechanical properties of porous media, a wellbore assembly temperature calculation equation group and a wellbore assembly boundary condition equation group; The different construction conditions include: cementing and solidification, completion and fracturing, and production.

2. The thermal-permeability coupled cement sheath stress prediction method according to claim 1 is characterized in that: The initial stress calculation equation group of the wellbore assembly includes: a calculation expression for the stress condition of the casing and a calculation expression for the stress condition of the formation; The calculation expression of casing stress is: The calculation expression of the formation stress is: in, is the radial stress of the casing; is the casing circumferential stress; is the radial stress of the formation; is the circumferential stress of the formation; r in is the inner radius of the casing; p in is the pressure of the liquid column on the inner side of the casing; r1 is the outer radius of the casing; r2 is the outer radius of the cement ring; r o is the outer radius of the formation; p d is the annular liquid column pressure on the outside of the casing; r is the calculated radius.

3. The thermal-permeability coupled cement sheath stress prediction method according to claim 2 is characterized in that: The wellbore assembly stress increment calculation equation group includes: casing stress and strain calculation expression, first cement sheath stress and strain calculation expression, second cement sheath stress and strain calculation expression and formation stress and strain calculation expression; The first cement sheath stress and strain calculation expression is used to calculate the stress and strain generated by the cement sheath connected to the formation, and the second cement sheath stress and strain calculation expression is used to calculate the stress and strain generated by the cement sheath between two layers of casing; The calculation expressions of casing stress and strain are: The calculation expression of the first cement sheath stress and strain is: The calculation expression of the stress and strain of the second cement sheath is: The calculation expressions of formation stress and strain are: in, is the radial stress of the casing; is the casing circumferential stress; G cas is the shear modulus of the casing; is the radial strain of the casing; is the circumferential strain of the casing; ν cas is the Poisson's ratio of the casing; ε cas is the casing volume strain, and is the linear thermal expansion coefficient of the casing; ΔT cas is the difference between the casing calculation temperature and the casing initial temperature; a cas is the thermal diffusion coefficient of the casing; F cas1 is the first calculation parameter of the casing; F cas2 is the second calculation parameter of the casing; F cas3 is the third calculation parameter of the casing; F cas4 is the fourth calculation parameter of the casing; is the radial stress of cement sheath; is the circumferential stress of cement ring; G cem is the shear modulus of cement sheath; is the radial strain of cement sheath; is the circumferential strain of the cement sheath; ν cem is the Poisson's ratio of cement ring drainage; ε cem is the cement sheath volume strain, and is the linear thermal expansion coefficient of cement sheath; ΔT cem is the difference between the cement sheath calculation temperature and the cement sheath initial temperature; α cem is the Biot coefficient of cement ring; p cem is the pore pressure of cement sheath; F cem1 is the first calculation parameter of the first cement sheath; F cem2 is the second calculation parameter of the first cement sheath; F cem3 is the third calculation parameter of the first cement sheath; F cem4 is the fourth calculation parameter of the first cement sheath; F cem5 is the fifth calculation parameter of the first cement sheath; is the constant strain specific heat of cement sheath under drainage condition; is the thermal conductivity of the cement sheath; is the parameter of cement sheath strain that is independent of radius; is the volume of fluid flowing through the porous material of the cement sheath per unit area per unit time; κ cem is the permeability coefficient of cement sheath; is the thermal permeability coefficient of cement sheath; F cem11 is the first calculation parameter of the second cement sheath; F cem12 is the second calculation parameter of the second cement sheath; F cem13 The third calculation parameter for the second cement sheath; is the radial stress of the formation; is the circumferential stress of the formation; G rock is the formation shear modulus; is the radial strain of the formation; is the circumferential strain of the formation; ν rock is the Poisson's ratio of the formation; ε rock is the volume strain of the formation annulus, and is the linear thermal expansion coefficient of the formation; ΔT rock is the difference between the formation temperature at the calculation point and the formation initial temperature; α rock is the formation Biot coefficient; p rock is the formation pore pressure; F rock1 is the first formation calculation parameter; F rock2 is the second formation calculation parameter; F rock3 is the third formation calculation parameter; F rock4 F is the fourth calculation parameter of the formation; rock5 is the fifth calculation parameter of the formation; A1 is the first intermediate parameter; A2 is the second intermediate parameter; A3 is the third intermediate parameter; A4 is the fourth intermediate parameter; A5 is the fifth intermediate parameter; A6 is the sixth intermediate parameter; is the constant strain specific heat of the formation under drainage conditions; is the thermal conductivity of the formation; is a parameter of formation strain that is independent of radius; is the volume of fluid flowing through the porous material per unit area of ​​the formation per unit time; rock is the permeability coefficient of the formation; is the thermal permeability coefficient of the formation; ΔT rock is the difference between the temperature at the calculation point of the formation and the initial temperature of the formation; s is the parameter introduced by Laplace transform; r is the calculation radius; K0 is the standard solution of the second kind of modified Bessel function corresponding to the n-order modified Bessel equation when n=0; K1 is the standard solution of the second kind of modified Bessel function corresponding to the n-order modified Bessel equation when n=1; I0 is the standard solution of the first kind of modified Bessel function corresponding to the n-order modified Bessel equation when n=0; I1 is the standard solution of the first kind of modified Bessel function corresponding to the n-order modified Bessel equation when n=1.

4. The thermal-permeability coupled cement sheath stress prediction method according to claim 3 is characterized in that: The wellbore assembly temperature calculation equation group includes: a casing temperature calculation expression, a first cement ring temperature calculation expression, a second cement ring temperature calculation expression and a formation temperature calculation expression; The first cement ring temperature calculation expression is used to calculate the temperature change of the cement ring connected to the formation, and the second cement ring temperature calculation expression is used to calculate the temperature change of the cement ring between two layers of casing; The casing temperature calculation expression is: The calculation expression of the first cement ring temperature is: The calculation expression of the second cement ring temperature is: The formation temperature calculation expression is: Where, ΔT cas F is the difference between the casing calculation temperature and the casing initial temperature; cas1 is the first calculation parameter of the casing; a cas is the thermal diffusion coefficient of the casing; F cas2 is the second calculation parameter of the casing; ΔT cem is the difference between the temperature at the cement sheath calculation point and the initial temperature of the cement sheath; F is the heat flowing through the pores of cement ring per unit area per unit time; cem1 is the first calculation parameter of the first cement sheath; F cem2 is the second calculation parameter of the first cement sheath; F cem11 is the first calculation parameter of the second cement sheath; F cem12 is the second calculation parameter of the second cement sheath; is the constant strain specific heat of cement sheath under drainage condition; is the thermal conductivity of the cement sheath; ΔT rock F is the difference between the formation calculation temperature and the formation initial temperature; rock1 is the first formation calculation parameter; F rock2 is the second formation calculation parameter; is the constant strain specific heat of the formation under drainage conditions; is the thermal conductivity of the formation; is the amount of heat flowing through the pores per unit area of ​​the formation per unit time; s is the parameter introduced by Laplace transform; r is the calculation radius; I0 is the standard solution of the first kind of modified Bessel function corresponding to the n-order modified Bessel equation when n=0; K0 is the standard solution of the second kind of modified Bessel function corresponding to the n-order modified Bessel equation when n=0; I1 is the standard solution of the first kind of modified Bessel function corresponding to the n-order modified Bessel equation when n=1; K1 is the standard solution of the second kind of modified Bessel function corresponding to the n-order modified Bessel equation when n=1.

5. The thermal-permeability coupled cement sheath stress prediction method according to claim 4 is characterized in that: The boundary condition equation group of the wellbore assembly includes: boundary condition equations of the inner wall of the casing, boundary condition equations of the interface between the casing and the cement sheath, boundary condition equations of the interface between the cement sheath and the formation, and boundary condition equations of the formation at infinity; The boundary condition equation of the inner wall of the casing is: The boundary condition equation of the interface between casing and cement sheath is: The boundary condition equation of the interface between cement sheath and formation is: The boundary condition equation for the infinitely far stratum is: in, is the radial stress of the casing; p in is the pressure of the liquid column on the inner side of the casing; ΔT cas ΔT1 is the difference between the calculated temperature of the casing and the initial temperature of the casing; cas is the temperature change of the inner wall of the casing; r is the calculation radius; r in is the inner radius of the casing; is the radial stress of cement sheath; is the radial displacement of the casing; is the radial displacement of cement sheath; ΔT cem is the difference between the temperature at the cement sheath calculation point and the initial temperature of the cement sheath; is the volume of fluid flowing through the porous material of the cement sheath per unit area per unit time; is the heat flowing through the cement ring per unit area per unit time; is the heat flowing through the pores of cement sheath per unit area per unit time; r is the calculation radius; r1 is the outer radius of casing; is the radial stress of the formation; is the radial displacement of the formation; ΔT rock is the difference between the formation temperature at the calculation point and the formation initial temperature; p cem is the pore pressure of cement sheath; p rock is the formation pore pressure; is the volume of fluid flowing through the porous material of the formation per unit area per unit time; is the heat flowing through the pores per unit area of ​​the formation per unit time; r2 is the outer radius of the cement ring; ε rock is the volume strain of the formation ring; r o is the outer radius of the formation.

6. A thermal-permeability coupled cement sheath integrity prediction method, characterized in that: The thermal-permeability coupled cement sheath integrity prediction method comprises: Using the thermal-permeability coupled cement sheath stress prediction method described in any one of claims 1 to 5, the full life cycle stress distribution of the wellbore assembly at a specified depth is determined; Based on the full life cycle stress distribution of the wellbore assembly at the specified depth, determine the strength calculation results required to ensure the integrity of the cement sheath at the specified depth; Compare the strength calculation results required to ensure the integrity of the cement sheath at the specified depth with the measured strength results of the cement stone at the specified depth to determine the failure risk of the wellbore assembly at the specified depth; Based on the failure risk of wellbore assemblies at different depths, determine the wellbore assembly integrity failure risk of the target well over its entire life cycle; The strength calculation result required to ensure the integrity of the cement sheath includes: at least one of the strength calculation value for ensuring that the cement sheath does not produce shear failure, the strength calculation value for ensuring that the cement sheath does not produce tensile failure, and the strength calculation value for ensuring that the cement sheath does not produce micro-annular gaps; The measured results of the strength of the cement paste include: at least one of the measured value of the cement paste shear failure strength, the measured value of the cement paste tensile failure strength, and the measured value of the bonding strength between the cement paste and the casing.

7. The thermal-permeability coupled cement sheath integrity prediction method according to claim 6 is characterized in that: The method of comparing the strength calculation result required to ensure the integrity of the cement sheath at the specified depth with the actual strength measurement result of the cement stone at the specified depth to determine the failure risk of the wellbore assembly at the specified depth includes: Based on the calculated strength value of the cement sheath at the specified depth to ensure that the cement sheath does not fail in shear and the measured value of the cement stone shear failure strength at the specified depth, the risk factor of the cement sheath shear failure of the wellbore assembly at the specified depth is determined; When it is determined that the cement sheath shear failure risk coefficient at the specified depth is greater than the cement sheath shear failure risk threshold, it is determined that the cement sheath of the wellbore assembly at the specified depth has a shear failure risk.

8. The thermal-permeability coupled cement sheath integrity prediction method according to claim 7 is characterized in that: The step of comparing the strength calculation result required to ensure the integrity of the cement sheath at the specified depth with the actual strength measurement result of the cement stone at the specified depth to determine the failure risk of the wellbore assembly at the specified depth also includes: Based on the calculated strength value for ensuring that the cement sheath does not produce tensile failure at the specified depth and the measured tensile failure strength value of the cement stone at the specified depth, the tensile failure risk factor of the cement sheath of the wellbore assembly at the specified depth is determined; When it is determined that the cement sheath tensile failure risk coefficient is greater than the cement sheath tensile failure risk threshold, it is determined that the cement sheath of the wellbore assembly at the specified depth has a tensile failure risk.

9. The thermal-permeability coupled cement sheath integrity prediction method according to claim 8, characterized in that: The step of comparing the strength calculation result required to ensure the integrity of the cement sheath at the specified depth with the actual strength measurement result of the cement stone at the specified depth to determine the failure risk of the wellbore assembly at the specified depth also includes: Based on the calculated strength value of the cement sheath at the specified depth to ensure that no micro-annulus is generated and the measured strength value of the cement stone and casing at the specified depth, the micro-annulus failure risk coefficient of the cement sheath of the wellbore assembly at the specified depth is determined; When it is determined that the cement sheath micro-annulus failure risk coefficient at the specified depth is greater than the cement sheath micro-annulus failure risk threshold, it is determined that the cement sheath of the wellbore assembly at the specified depth has a micro-annulus failure risk.

10. The thermal-permeability coupled cement sheath integrity prediction method according to claim 9, characterized in that: The step of comparing the strength calculation result required to ensure the integrity of the cement sheath at the specified depth with the actual strength measurement result of the cement stone at the specified depth to determine the failure risk of the wellbore assembly at the specified depth also includes: Compare the cement sheath shear failure risk factor, cement sheath tensile failure risk factor and cement sheath micro-annulus failure risk factor of the wellbore assembly at a specified depth to determine the maximum failure risk factor; The cement sheath failure risk corresponding to the maximum failure risk coefficient is determined as the maximum failure risk of the wellbore assembly at a specified depth.

11. An electronic device, characterized in that: The electronic device includes a processor and a memory, wherein at least one computer program is stored in the memory, and the at least one computer program is loaded and executed by one or more of the above processors, so that the processor executes the thermal-permeability coupled cement sheath stress prediction method described in any one of claims 1 to 5, or the thermal-permeability coupled cement sheath integrity prediction method described in any one of claims 6 to 10.

12. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores at least one program code, which is loaded and executed by a processor to enable a computer to execute the thermal-permeability coupled cement sheath stress prediction method described in any one of claims 1 to 5, or the thermal-permeability coupled cement sheath integrity prediction method described in any one of claims 6 to 10.

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