Defective casing isolated grid reconstruction and evaluation method based on multi-arm logging

Abstract

A defect casing isolated grid reconstruction and evaluation method based on multi-arm logging, comprising: reading the discrete polar radius sequence collected by the multi-arm caliper under the well, and constructing a discrete three-point array data set containing an axial sampling depth set and a circumferential probe arm angle set; a space mapping equation is established, a shear ellipticity factor is introduced, the discrete three-point array data set is converted into inner and outer wall discrete point cloud data in a three-dimensional global Cartesian coordinate system and is subjected to micro chamfer smoothing processing, to generate an inner wall topology pure node group and an outer wall topology pure node group; a space block surrounded by adjacent depth layers and adjacent probes is extracted, and an eight-node linear reduced integration three-dimensional solid element is constructed; the circumferential physical closed loop and the model packaging are completed by using the modulo operation; the finite element input file is imported into the finite element solver, the three-dimensional stress distribution characteristics under the complex real damage morphology are analyzed, and the extreme stress concentration area is extracted for integrity evaluation.

Description

Technical Field

[0001] This invention belongs to the field of image data processing technology, specifically relating to a method for reconstructing and evaluating isolated grids of defective casing based on multi-arm logging. Background Technology

[0002] In oil and gas well integrity assessment, the degradation of the load-bearing capacity of defective casing due to complex deformation and corrosion is a key factor threatening the safe operation of the wellbore. Utilizing discrete extreme diameter data acquired by a high-resolution multi-arm caliper (MIT) for refined mechanical analysis to assess the remaining strength of the casing is a core data foundation for ensuring the production safety of oil and gas wells. However, there has long been a lack of an efficient and accurate direct conversion path between the massive amounts of one-dimensional logging signals and the finite element mechanical model capable of quantitative calculations. Existing technical approaches mainly fall into two categories: qualitative imaging methods based on graphics and visualization technologies, and finite element modeling methods based on traditional CAD geometric transitions. Both of these methods have their own shortcomings.

[0003] Qualitative imaging methods based on graphics and visualization technologies often rely on data utilization at a superficial level, focusing on graphical interpretation and qualitative identification. The resulting topographic images are essentially just zero-thickness visualization point clouds of the inner surface, which cannot be directly coupled into finite element mechanics solvers for quantitative strength verification and bearing capacity calculation. For example, the "Development of Downhole Casing Deformation Simulation Software in Daqing Oilfield" published in the Journal of Daqing Petroleum Institute, 2009, 33(4): 103-106, 144, utilizes graphics rendering engines such as OpenGL or DirectX to directly render well diameter data as three-dimensional color topographic images, achieving intuitive display and qualitative interpretation of casing damage.

[0004] Finite element modeling methods based on traditional CAD geometry transitions rely excessively on traditional CAD geometric solid modeling. They require cumbersome intermediate geometric surface construction and secondary mesh generation steps such as skinning, surface fitting, or Boolean cutting, resulting in low data inversion and modeling efficiency and severe real-time insufficiency. Secondly, when faced with extremely irregular sharp-angled pits and asymmetric distortions in real well logging point clouds, CAD Boolean modeling is prone to topological overlap, mesh penetration, and mesh generation failure. This leads to conventional simulation models typically having to use idealized regular geometric shapes (such as regular spherical or ellipsoidal pits) as substitutes, thus masking the local extreme stress concentration effects induced by real irregular defects. For example, the "Research on Finite Element Geometric Modeling of Three-Dimensional Casing Deformation Wells" published in the Journal of Southwest Petroleum University (Natural Science Edition), 2010, 32(3): 172-175, uses a technique that extracts discrete point data of multi-arm well diameter, constructs a solid geometric model of the casing by means of geometric operations such as curve fitting, skinning, surface fitting, and Boolean cutting, and then generates a finite element mesh through secondary mesh generation.

[0005] In summary, existing methods are limited to graphical visualization or intermediate CAD formats, lacking a direct physical bridge to map one-dimensional discrete well logging point cloud data from the field directly to a three-dimensional high-precision finite element solver. This prevents massive amounts of high-resolution well logging data from being directly used for quantitative strength calculations. They cannot faithfully reproduce the irregular and asymmetric corrosion morphology under real service conditions, and the calculation models have long been based on idealized regular geometric assumptions, leading to inaccurate residual strength predictions. Traditional methods such as skinning, surface fitting, and Boolean cutting are prone to geometric topological overlap, mesh penetration, and mesh generation failure when dealing with extremely irregular sharp-angled pits in real well logging point clouds, resulting in a serious technical gap between measured conditions and mechanical assessments. Summary of the Invention

[0006] The technical problem to be solved by this invention is to overcome the shortcomings of the prior art and provide a method for reconstruction and evaluation of isolated grids of defective casing based on multi-arm logging, which has high geometric reconstruction accuracy, high modeling efficiency, and high mechanical evaluation fidelity.

[0007] The technical solution adopted to solve the above-mentioned technical problems is: a method for reconstruction and evaluation of isolated grids of defective casing based on multi-arm logging, including the following steps:

[0008] Step 1. Read the discrete extreme diameter sequence collected downhole by the multi-arm caliper and construct a discrete ternary lattice dataset containing the axial sampling depth set and the circumferential probe angle set;

[0009] Step 2. Establish a spatial mapping equation, introduce the eccentricity component representing the well trajectory and the shear ellipticity factor representing the non-uniform stress compression, and transform the discrete ternary lattice dataset into discrete point cloud data of the inner and outer walls in a three-dimensional global Cartesian coordinate system, including the coordinates of the discrete point clouds of the inner and outer walls and their topological connection relationships.

[0010] Step 3. Combining the physical resolution limit of the multi-arm caliper, perform microscopic chamfering and smoothing on the discrete nodes of the discrete point cloud data of the inner and outer walls. While preserving the maximum macroscopic corrosion depth, filter out high-frequency geometric noise from the topological bottom layer to generate a topologically pure node group for the inner wall and a topologically pure node group for the outer wall.

[0011] Step 4. Based on the topologically pure node groups of the inner wall and the topologically pure node groups of the outer wall, extract the spatial blocks enclosed by adjacent depth layers and adjacent probes, establish a one-to-one topological mapping matrix between the inner wall node groups and the outer wall node groups, and construct an eight-node linear reduction integral three-dimensional solid element.

[0012] Step 5. Use the modulus operation to complete the seamless connection and addressing of circumferential nodes, realize the three-dimensional physical closed loop of the sleeve circumference, automatically encapsulate the node topology and element definition, and directly output the finite element input file containing the complete geometry set and surface isolated mesh standard;

[0013] Step 6. Import the finite element input file into the finite element solver, assign constitutive parameters to the casing material and apply service loads and equivalent boundary constraints, quantitatively analyze the three-dimensional stress distribution characteristics under complex real damage morphology, and extract the extreme stress concentration area for integrity evaluation.

[0014] As a preferred technical solution, the underlying physical structure of the scattered ternary matrix dataset in step 1 is as follows: numerical matrix, The total number of sampling depths. This represents the total number of probes.

[0015] As a preferred technical solution, the coordinates of the discrete point cloud of the inner wall are:

[0016]

[0017] In the formula, Let be the coordinates of the discrete nodes on the inner wall in the three-dimensional global Cartesian coordinate system; This refers to the axial depth layer number. ; For the circumferential probe serial number, ; For the first The absolute circumferential angle of the probe arm. For the first Axial depth logging values ​​of the layer In depth With angle The true value of the extreme diameter of the inner wall of the casing measured at the location; The eccentricity of the multi-arm caliper relative to the geometric center of the casing in the x and y directions;

[0018] The coordinates of the discrete point cloud of the outer wall are:

[0019]

[0020] In the formula, The three-dimensional spatial coordinates of the nodes on the outer wall of the casing are given. The initial nominal inner diameter of the casing. This is the initial nominal wall thickness of the casing. , where is the ellipticity deformation scaling factor of the casing in the x and y directions respectively when subjected to ground stress compression.

[0021] As a preferred technical solution, in step 3, the micro-chamfering smoothing method is as follows: utilizing the spatial circumferential angle step size of adjacent probes. As a filtering feature size, it enables the circumferential first-order linear approximation surface to perform microscopic transition smoothing on infinitely sharp corrosion edges, eliminating the distortion of the finite element Jacobian matrix and the divergent pseudo-stress peaks caused by the theoretical radius of curvature approaching zero in CAD Boolean solid cutting.

[0022] As a preferred technical solution, the eight-node linear reduced integral three-dimensional solid element is a fully hexahedral C3D8R element.

[0023] As a preferred technical solution, the fully hexahedral C3D8R unit is:

[0024]

[0025] In the formula, For the first Layer and First A single C3D8R hexahedral element generated within an angular range; This constitutes the inner wall space node group that forms the inner surface of the unit; This constitutes the spatial node group on the outer wall of the unit's outer surface.

[0026] As a preferred technical solution, the modulus calculation method in step 5 is as follows: when the circumferential probe number is traversed to... When, let the next adjacent angle number be... The modulo operation automatically assigns a value of 1, i.e., forces the value to be 1. This enables seamless closure and braided stitching of the circumferential cross-sectional nodes of the casing.

[0027] As a preferred technical solution, in step 5, the finite element input file format is .inp.

[0028] As a preferred technical solution, in step 6, the method of applying service load and equivalent boundary constraint is as follows: apply ultimate working internal pressure or external extrusion stress load to the irregular inner wall surface of the generated isolated mesh model, apply displacement axial constraint at both ends of the pipe column, and enable the nonlinear geometry option in the finite element solver to capture the geometric nonlinear mechanical characteristics under complex irregular damage geometric abrupt changes.

[0029] The beneficial effects of this invention are as follows:

[0030] This invention bypasses the traditional CAD geometric entity modeling stage by combining spatial homogeneous mapping with topological isomorphic stitching, achieving fully automated, high-fidelity, and second-level reconstruction from raw one-dimensional logging signals to isolated three-dimensional finite element meshes. Compared with existing technologies, it significantly improves geometric accuracy, modeling efficiency, and mechanical fidelity.

[0031] This invention uses a purely mathematical spatial mapping to ensure that the absolute error strictly converges to 10. -6 The error is at the mm level (the global average error is only 9.85×10). -4 The microscopic morphology of lunulae wear and asymmetric corrosion pits was replicated almost without any artificial modification or intervention (μm).

[0032] This invention completes mesh topology stitching directly within seconds, fundamentally eliminating mesh distortion and penetration errors caused by geometric interference. Compared to the traditional inefficient and cumbersome chain of "point cloud-surface fitting-CAD solid-Boolean cutting", it greatly improves modeling efficiency.

[0033] The reconstructed model of this invention can be seamlessly imported into the finite element solver to carry out nonlinear analysis, accurately capturing the local extreme stress concentration phenomenon induced by real micro-geometric mutations (wall thickness reduction zone), and providing a reliable three-dimensional mechanical benchmark for the evaluation of the ultimate bearing capacity of complex tubular columns. Attached Figure Description

[0034] Figure 1 This is a flowchart illustrating the method for reconstructing and evaluating isolated grids of defective casing based on multi-arm logging, as described in this invention.

[0035] Figure 2 This is a flowchart of the isolated grid inversion algorithm of the present invention.

[0036] Figure 3 This is a schematic diagram of the multi-arm logging data acquisition and processing process of the present invention.

[0037] Figure 4 This is the node coordinate space mapping diagram of the present invention.

[0038] Figure 5 This is a spatial construction diagram of the hexahedral unit of the present invention.

[0039] Figure 6 This is a casing defect illustration derived from the inversion of benchmark data according to the present invention.

[0040] Figure 7 This is the histogram of the geometric reconstruction error distribution of the present invention.

[0041] Figure 8 This is a real 40-arm multi-arm logging data dot matrix diagram of the present invention.

[0042] Figure 9 This is a diagram illustrating the overall results of this invention.

[0043] Figure 10 This is a finite element model of the actual defective inner wall of the casing generated by the inversion method of this invention.

[0044] Figure 11 This is a three-dimensional stress cloud view of the inversion model containing real defects after loading, according to the present invention.

[0045] Figure 12 This is another view of the three-dimensional stress cloud after loading of the inversion model containing real defects in this invention.

[0046] Figure 13 This is a correlation analysis diagram of the complex defect morphology and mechanical response of the present invention. Detailed Implementation

[0047] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments, but the present invention is not limited to the following embodiments.

[0048] Example

[0049] exist Figure 1 , 2 The method for reconstructing and evaluating isolated grids of defective casing based on multi-arm logging in this embodiment includes the following steps:

[0050] Step 1. Construct a discrete ternary matrix dataset

[0051] like Figure 3 As shown, discrete polar diameter sequences acquired downhole by a multi-arm caliper are read to construct a discrete ternary lattice dataset containing axial sampling depth sets and circumferential probe angle sets. Its underlying physical structure is as follows: numerical matrix, The total number of sampling depths. This embodiment represents the total number of probes. =40;

[0052] Step 2. Generate discrete point cloud data for the inner and outer walls.

[0053] like Figure 4 As shown, a spatial mapping equation is established, introducing the eccentricity component characterizing the wellbore trajectory and the shear ellipticity factor characterizing non-uniform stress compression. This transforms the discrete ternary lattice dataset into discrete point cloud data of the inner and outer walls in a three-dimensional global Cartesian coordinate system, including the coordinates of the inner and outer wall discrete point clouds and their topological connectivity, where:

[0054] The coordinates of the discrete point cloud of the inner wall are:

[0055]

[0056] In the formula, Let be the coordinates of the discrete nodes on the inner wall in the three-dimensional global Cartesian coordinate system; This refers to the axial depth layer number. ; For the circumferential probe serial number, ; For the first The absolute circumferential angle of the probe arm. For the first Axial depth logging values ​​of the layer In depth With angle The true value of the extreme diameter of the inner wall of the casing measured at the location; The eccentricity of the multi-arm caliper relative to the geometric center of the casing in the x and y directions;

[0057] The coordinates of the discrete point cloud on the outer wall are:

[0058]

[0059] In the formula, The three-dimensional spatial coordinates of the nodes on the outer wall of the casing are given. The initial nominal inner diameter of the casing. This is the initial nominal wall thickness of the casing. , where is the ellipticity deformation scaling factor of the casing in the x and y directions respectively when subjected to ground stress compression.

[0060] Step 3. Generate a topologically pure node group for the inner and outer walls.

[0061] Combining the physical resolution limit of the multi-arm caliper, the discrete nodes of the discrete point cloud data of the inner and outer walls are subjected to microscopic chamfering and smoothing. While preserving the maximum macroscopic corrosion depth, high-frequency geometric noise is filtered out from the topological bottom layer to generate a topologically pure node group for the inner wall and a topologically pure node group for the outer wall.

[0062] The micro-bevel smoothing method is as follows: utilizing the spatial circumferential angle step size between adjacent probes. As a filter feature size, it enables the circumferential first-order linear approximation surface to perform microscopic transition smoothing on infinitely sharp corrosion edges, eliminating the distortion of the finite element Jacobian matrix and the divergent pseudo-stress peaks caused by the theoretical radius of curvature approaching zero in CAD Boolean solid cutting.

[0063] Step 4. Construct 3D solid units

[0064] like Figure 5 As shown, based on the topologically pure node groups of the inner and outer walls, spatial blocks enclosed by adjacent depth layers and adjacent probes are extracted. A one-to-one topological mapping matrix between the inner and outer wall node groups is established, and an eight-node linear reduced integral three-dimensional solid element is constructed, specifically a fully hexahedral C3D8R element.

[0065]

[0066] In the formula, For the first Layer and First A single C3D8R hexahedral element generated within an angular range; This constitutes the inner wall space node group that forms the inner surface of the unit; This constitutes the spatial node group on the outer wall of the unit's outer surface.

[0067] Step 5. Circumferential Physical Loop Closure and Model Encapsulation

[0068] The seamless connection and addressing of circumferential nodes are achieved using modulo operations, realizing a three-dimensional physical closed loop in the circumferential direction of the casing. Specifically, when the circumferential probe number traverses to... When, let the next adjacent angle number be... The modulo operation automatically assigns a value of 1, i.e., forces the value to be 1. This achieves seamless closure and braided stitching of the circumferential cross-section nodes of the casing;

[0069] It automatically encapsulates node topology and element definitions, and directly outputs a standard finite element input file containing a complete geometry set and surface, in .inp format;

[0070] Step 6. Mechanical Response Analysis and Safety Assessment

[0071] Import the finite element input file into the finite element solver, assign constitutive parameters to the casing material and apply service loads and equivalent boundary constraints, quantitatively analyze the three-dimensional stress distribution characteristics under complex real damage morphology, and extract the extreme stress concentration area for integrity evaluation.

[0072] The method for applying service loads and equivalent boundary constraints is as follows: apply ultimate working internal pressure or external extrusion stress load to the irregular inner wall surface of the generated isolated mesh model, apply displacement axial constraints at both ends of the pipe column, and enable the nonlinear geometry option in the finite element solver to capture the geometric nonlinear mechanical characteristics under complex irregular damage geometric abrupt changes.

[0073] experiment

[0074] To verify the beneficial effects of the present invention, the inventors conducted the following simulation experiments using the method of the embodiments of the present invention:

[0075] Experimental Step 1. Extract the original discrete polar diameter dataset of a real 40-arm caliper imaging logging operation section of an oil well, determine the azimuth angle and measurement radius of each depth layer, and use this as the basic discrete ternary lattice dataset (axial sampling depth set, circumferential probe angle set, and measurement radius set). For example... Figure 6To comprehensively evaluate the topological adaptability of the method of this invention to different morphologies, four representative downhole damage features—lunar wear, long grooves, standard spherical erosion, and ellipsoidal pits—were sequentially implanted at the global axial depth (Z-axis) of the casing using Boolean cutting technology. Subsequently, a new discrete ternary lattice dataset containing defects was extracted using a virtual multi-arm logging scanning algorithm to match the geometric truth. This data simultaneously includes wellbore inclination and ellipticity information.

[0076] Experimental Step 2. Based on the above discrete polar diameter dataset, an eight-node linear reduced integral three-dimensional solid element was constructed using the method of this embodiment of the invention. This accurately reproduced complex defect morphologies such as long grooves, crescent wear, spherical erosion, and ellipsoidal pits. Figure 6 ;

[0077] To quantify the accuracy of the global reconstruction, a total of 11,820 three-dimensional mesh nodes were extracted from the entire pipe section of the inversion model (including complex morphologies such as crescent wear, long grooves, standard spherical erosion, and ellipsoidal pits). A point-to-point absolute error analysis was then performed between the inversely calculated extreme diameter and the 60-arm baseline true value, resulting in an error distribution histogram, as shown below. Figure 7 The global average error is only 9.85×10. -4 μm, converges to 10 -6 The millimeter level verifies the ultra-high geometric fidelity of this invention.

[0078] To verify the reliability of the inversion reconstruction algorithm in practical engineering, the comprehensive interpretation results of a real 40-arm logging operation from an oilfield are introduced, such as... Figure 8 , 9 The results show that the inversion model based on real field data accurately replicates the large-area irregular corrosion pits on the inner wall revealed by the well logging data, proving the reliability of the algorithm in actual complex service environments.

[0079] After importing the finite element input file generated by this invention into the finite element solver software and applying material properties, boundary conditions, and loads, the result is... Figure 11 and Figure 12 The stress cloud diagram shows that after applying equivalent boundary constraints and loads, the stress distribution is uniform in the macroscopically intact areas of the model, while in the actual defect evolution areas (such as areas with severe wall thinning and irregular pits), there are significant and concentrated high stress zones, which intuitively reflect the local deterioration effect of complex geometric changes on the bearing state of the casing.

[0080] After calculation, the nodal equivalent stress (Von-Mises) distribution data of the section with the most severe casing defects (depth Z = 424–425 mm) were extracted, and a circumferential full-angle (0°–360°) depth benchmark analysis was performed with the extreme diameter data recorded by the original logging probe. Figure 13It can be seen that the three-dimensional model reconstructed based on the inversion algorithm has a very high spatial synchronicity between its micro-geometric deformation distribution and macro-mechanical response field, and the geometric shape and local stress field closely match in terms of trend distribution, which fully verifies the strong spatial coupling relationship between "deformation-stress".

[0081] In summary, the method of this invention not only achieves accurate replication and ultra-high precision reconstruction of geometric features, but also ensures the physical authenticity of downstream mechanical evaluation.

Claims

1. A method for reconstructing and evaluating isolated grids of defective casing based on multi-arm logging, characterized in that, Includes the following steps: Step 1. Read the discrete extreme diameter sequence collected downhole by the multi-arm caliper, and construct a discrete ternary lattice dataset containing the axial sampling depth set and the circumferential arm angle set. The underlying physical structure of the discrete ternary lattice dataset is as follows: numerical matrix, The total number of sampling depths. Total number of probes; Step 2. Establish a spatial mapping equation, introduce the eccentricity component representing the well trajectory and the shear ellipticity factor representing the non-uniform stress compression, and transform the discrete ternary lattice dataset into discrete point cloud data of the inner and outer walls in a three-dimensional global Cartesian coordinate system, including the coordinates of the discrete point clouds of the inner and outer walls and their topological connection relationships. Step 3. Combining the physical resolution limit of the multi-arm caliper, perform microscopic chamfering and smoothing on the discrete nodes of the discrete point cloud data of the inner and outer walls. While preserving the maximum macroscopic corrosion depth, filter out high-frequency geometric noise from the topological bottom layer to generate a topologically pure node group for the inner wall and a topologically pure node group for the outer wall. The micro-chamfering and smoothing method is as follows: Utilizing the spatial circumferential angle step size between adjacent probes. As a filter feature size, it enables the circumferential first-order linear approximation surface to perform microscopic transition smoothing on infinitely sharp corrosion edges, eliminating the distortion of the finite element Jacobian matrix and the divergent pseudo-stress peaks caused by the theoretical radius of curvature approaching zero in CAD Boolean solid cutting. Step 4. Based on the topologically pure node groups of the inner wall and the topologically pure node groups of the outer wall, extract the spatial blocks enclosed by adjacent depth layers and adjacent probes, establish a one-to-one topological mapping matrix between the inner wall node groups and the outer wall node groups, and construct an eight-node linear reduction integral three-dimensional solid element. Step 5. Use the modulus operation to complete the seamless connection and addressing of circumferential nodes, realize the three-dimensional physical closed loop of the sleeve circumference, automatically encapsulate the node topology and element definition, and directly output the finite element input file containing the complete geometry set and surface isolated mesh standard; Step 6. Import the finite element input file into the finite element solver, assign constitutive parameters to the casing material and apply service loads and equivalent boundary constraints, quantitatively analyze the three-dimensional stress distribution characteristics under complex real damage morphology, and extract the extreme stress concentration area for integrity evaluation.

2. The method for reconstructing and evaluating isolated grids of defective casing based on multi-arm logging according to claim 1, characterized in that, The coordinates of the discrete point cloud of the inner wall are: In the formula, Let be the coordinates of the discrete nodes on the inner wall in the three-dimensional global Cartesian coordinate system; This refers to the axial depth layer number. ; For the circumferential probe serial number, ; For the first The absolute circumferential angle of the probe arm. For the first Axial depth logging values ​​of the layer In depth With angle The true value of the extreme diameter of the inner wall of the casing measured at the location; The eccentricity of the multi-arm caliper relative to the geometric center of the casing in the x and y directions; The coordinates of the discrete point cloud of the outer wall are: In the formula, The three-dimensional spatial coordinates of the nodes on the outer wall of the casing are given. The initial nominal inner diameter of the casing. This is the initial nominal wall thickness of the casing. , where is the ellipticity deformation scaling factor of the casing in the x and y directions respectively when subjected to ground stress compression.

3. The method for reconstructing and evaluating isolated grids of defective casing based on multi-arm logging according to claim 2, characterized in that, The eight-node linear reduced integral three-dimensional solid element is a fully hexahedral C3D8R element.

4. The method for reconstructing and evaluating isolated grids of defective casing based on multi-arm logging according to claim 3, characterized in that, The fully hexahedral C3D8R element is: In the formula, For the first Layer and First A single C3D8R hexahedral element generated within an angular range; This constitutes the inner wall space node group that forms the inner surface of the unit; This constitutes the spatial node group on the outer wall of the unit's outer surface.

5. The method for reconstruction and evaluation of isolated grids of defective casing based on multi-arm logging according to claim 4, characterized in that, The modulo operation method in step 5 is as follows: when the circumferential probe number is traversed to... When, let the next adjacent angle number be... The modulo operation automatically assigns a value of 1, i.e., forces the value to be 1. This enables seamless closure and braided stitching of the circumferential cross-sectional nodes of the casing.

6. The method for reconstructing and evaluating isolated grids of defective casing based on multi-arm logging according to claim 1, characterized in that: In step 5, the finite element input file is in .inp format.

7. The method for reconstruction and evaluation of isolated grids of defective casing based on multi-arm logging according to claim 1, characterized in that, In step 6, the method for applying service loads and equivalent boundary constraints is as follows: apply ultimate working internal pressure or external extrusion stress loads to the irregular inner wall surface of the generated isolated mesh model, apply displacement axial constraints at both ends of the pipe column, and enable the nonlinear geometry option in the finite element solver to capture the geometric nonlinear mechanical characteristics under complex irregular damage geometric abrupt changes.

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