Oil field well casing residual strength evaluation method and system based on numerical simulation

Abstract

The invention provides an oil field well casing residual strength evaluation method and system based on numerical simulation, and relates to the technical field of oil field development casing safety evaluation. Based on the casing damage evaluation basic data of the target oil field block, establishing a block scale fluid-solid coupling numerical model reflecting an injection-production dynamic and formation mechanical response coupling relationship, and obtaining redistributed crustal stress field data around a shaft; redistributed crustal stress field data are used as boundary conditions, a three-dimensional coupling mechanical model containing a stratum, a cement sheath and a casing pipe is established in combination with the casing pipe structure and material parameters, and the stress distribution and the maximum equivalent stress of the casing pipe under the injection-production load effect are obtained through numerical simulation; and based on the maximum equivalent stress and the yield strength of the casing material, performing residual strength evaluation and damage risk grading on the casing according to the strength utilization rate and the residual strength coefficient. Therefore, the accuracy and the dynamic prediction capability of the residual strength evaluation of the oil field casing are improved, and a scientific decision basis is provided for casing damage treatment.

Description

Technical Field

[0001] This invention relates to the field of oilfield well casing safety evaluation technology, and in particular to a method and system for evaluating the remaining strength of oilfield well casing based on numerical simulation. Background Technology

[0002] Today, major oilfields worldwide are characterized by diverse reservoir types, complex structures, and wide distributions of burial depths. During oilfield development, the difficulty of replenishing formation energy and the "injection failure, production failure" problem is common in water-driven low-permeability reservoirs. Pressure-driven fracturing and hydraulic displacement (PFD) technologies are effective methods to address this issue. These technologies induce the generation and expansion of reservoir fracture networks under pressures exceeding or near formation fracture levels, driving oil flow through high-volume water injection. However, in PFD and fracturing operations on older wells in low-permeability reservoirs, casing damage is becoming increasingly prominent. Casing damage can lead to injection-production failure, reduced production, and even well abandonment, severely impacting oilfield safety and development efficiency. Furthermore, casing damage is a complex geological engineering problem with multiple influencing factors and mechanisms. Casing damage is often the result of multiple factors acting together, including engineering factors such as water injection pressure and corrosion defects, as well as geological factors such as changes in geostress and fault slip. Therefore, researching casing residual strength evaluation models and methods during injection-production processes is of great significance for the prevention and control of casing damage in oilfields.

[0003] Currently, casing remaining strength evaluation technology has significant shortcomings: First, the evaluation method is static, relying heavily on empirical formulas, static strength verification, or local testing. The evaluation method lacks systematicity, dynamism, and predictability, making it difficult to accurately assess the safety status and remaining life of the casing during injection and production. Second, in terms of finite element technology, although some studies have used numerical simulation methods to analyze casing stress, they are mostly limited to single wellbore or simplified models. They do not consider the combined effects of multiple factors such as the evolution of the overall geostress field in the block injection and production, multi-well synergy, fracture / fault slip, and corrosion defects. This results in a large deviation between the evaluation results and the actual engineering situation, making it impossible to form a closed-loop technical system from mechanism analysis and dynamic simulation to safety evaluation. Summary of the Invention

[0004] To address the aforementioned issues, this invention proposes a numerical simulation-based method and system for evaluating the remaining strength of oilfield well casing. This system transforms the evaluation of remaining casing strength from static analysis to dynamic prediction, and from assessing the consequences of casing damage to providing risk warnings. It can not only accurately assess the current safety status of in-service casing, but also predict the evolution of casing damage risks in oil and water wells under different production scenarios.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for evaluating the remaining strength of oilfield well casing based on numerical simulation, comprising: Based on the basic data of casing damage evaluation of the target oilfield block, a block-scale fluid-structure coupling numerical model reflecting the coupling relationship between injection and production dynamics and formation mechanical response is established to simulate the dynamic evolution of formation pore pressure and geostress field during long-term injection and production, and obtain the geostress field data redistributed around the wellbore. Using the redistributed geostress field data as boundary conditions, and combining the casing structure and material parameters, a three-dimensional coupled mechanical model including the formation, cement sheath, and casing is established. The stress distribution and maximum equivalent stress of the casing under injection and production loads are obtained through numerical simulation calculation. Based on the maximum equivalent stress and the yield strength of the casing material, the remaining strength of the casing is evaluated and the damage risk level is classified by using the strength utilization rate and the remaining strength coefficient in combination with the set safety factor.

[0006] Secondly, the present invention provides a numerical simulation-based system for evaluating the remaining strength of oilfield well casing, comprising: The injection-production simulation module is configured to establish a block-scale fluid-structure coupling numerical model that reflects the coupling relationship between injection-production dynamics and formation mechanical response based on the casing damage evaluation data of the target oilfield block, simulate the dynamic evolution of formation pore pressure and geostress field during long-term injection-production process, and obtain the redistributed geostress field data around the wellbore. The stress analysis module is configured to use the redistributed geostress field data as boundary conditions, and combine the casing structure and material parameters to establish a three-dimensional coupled mechanical model including the formation, cement sheath and casing, and obtain the stress distribution and maximum equivalent stress of the casing under injection and production load through numerical simulation calculation. The strength evaluation module is configured to evaluate the remaining strength and classify the damage risk level of the casing based on the maximum equivalent stress and the yield strength of the casing material, using the strength utilization rate and the remaining strength coefficient in combination with the set safety factor.

[0007] Thirdly, the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps in the numerical simulation-based method for evaluating the residual strength of oilfield well casing as described in the first aspect.

[0008] Fourthly, the present invention provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the steps in the numerical simulation-based method for evaluating the remaining strength of oilfield well casing described in the first aspect.

[0009] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) This invention achieves dynamic and precise evaluation of the remaining strength of casing through the synergistic application of block-scale fluid-structure interaction simulation and three-dimensional coupled mechanical modeling. By integrating multi-source basic data, it replicates the evolution of the geostress field and the mechanical response of the casing throughout the injection and production process. Based on the quantitative analysis of strength utilization rate and remaining strength coefficient, it accurately identifies wells and dangerous locations at risk of casing damage. This invention breaks through the limitations of static evaluation and has the capabilities of mechanism tracing, dynamic prediction, and system evaluation. It not only provides a scientific basis for oilfield casing damage management but also flexibly adapts to blocks with different geological and development conditions, effectively reducing casing damage risk and management costs, and promoting the upgrading of oilfield casing safety management towards systematization and refinement.

[0010] (2) This invention realizes multi-scale coupled analysis from block scale to wellbore scale, coupled the evolution of geostress field throughout the injection and production cycle, and realizes dynamic tracking evaluation rather than static evaluation. The evaluation results are closer to the actual engineering situation.

[0011] (3) This invention dynamically reflects the evolution of the geostress field and casing stress during the injection and production process, and has been verified by the actual engineering of the Niu 23-A block of Niuzhuang Oilfield. It has a high accuracy rate in casing damage prediction and has the ability to provide risk warning.

[0012] (4) The present invention integrates multi-source data such as geology, engineering, and materials, as well as various types of damage causes, to form a closed-loop evaluation system, thereby improving the scientificity, reliability and comprehensiveness of the evaluation.

[0013] (5) This invention can provide direct decision support for the optimization of injection and production parameters, casing selection, well network layout and casing damage control. It provides sufficient theoretical support and technical tools for the scientific optimization of oilfield injection and production schemes and the formulation of casing damage control measures. It is of great significance for ensuring the safe, efficient and long-term development of oilfield blocks.

[0014] Advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0015] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute a limitation thereof.

[0016] Figure 1 The main flowchart of a method for evaluating the remaining strength of oilfield well casing based on numerical simulation provided in an embodiment of the present invention; Figure 2 A flowchart illustrating a method for evaluating the remaining strength of oilfield well casing based on numerical simulation, provided in an embodiment of the present invention. Figure 3This is a schematic diagram of the injection and extraction model for the Niu23-A block provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of the formation-cement sheath-casing coupling model provided in an embodiment of the present invention; Figure 5 A flowchart for evaluating the remaining strength of the casing provided in an embodiment of the present invention. Detailed Implementation

[0017] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0018] Example 1 like Figure 1 As shown in the figure, this embodiment discloses a method for evaluating the remaining strength of oilfield well casing based on numerical simulation, including the following steps: S1: Based on the basic data of casing damage evaluation of the target oilfield block, establish a block-scale fluid-solid coupling numerical model that reflects the coupling relationship between injection and production dynamics and formation mechanical response, simulate the dynamic evolution of formation pore pressure and geostress field during long-term injection and production, and obtain the geostress field data redistributed around the wellbore. S2: Using the redistributed geostress field data as boundary conditions, and combining the casing structure and material parameters, a three-dimensional coupled mechanical model including the formation, cement sheath and casing is established. The stress distribution and maximum equivalent stress of the casing under injection and production loads are obtained through numerical simulation calculation. S3: Based on the maximum equivalent stress and the yield strength of the casing material, the remaining strength of the casing is evaluated and the damage risk level is classified by using the strength utilization rate and the remaining strength coefficient in combination with the set safety factor.

[0019] Next, combined Figure 2 This embodiment provides a detailed description of a numerical simulation-based method for evaluating the remaining strength of oilfield well casing.

[0020] In oilfield development, the casing of oil and water wells is a crucial structural barrier ensuring wellbore stability and enabling safe and efficient oil and gas extraction. However, during long-term enhanced extraction processes such as water injection and pressure drive, the pore pressure and geostress field of the underground reservoir undergo continuous dynamic changes, leading to rock deformation, slippage, and even failure. This, in turn, generates complex loads on the casing, such as non-uniform extrusion and shearing, causing a series of damage problems including casing deformation, breakage, and corrosion. These issues seriously affect normal oilfield production and pose safety and environmental risks.

[0021] Traditional casing damage prediction methods often rely on macroscopic statistics or single mechanical assumptions, making it difficult to accurately reflect the dynamic damage mechanism involving multi-field coupling and cross-scale transmission of "formation-fluid-casing" during actual injection and production processes. Therefore, this invention introduces finite element numerical simulation technology to construct a quantifiable and dynamically evolving analytical model encompassing the entire chain from the geological engineering characteristics of oilfield blocks to the mechanical response of single-well casing. This model enables early identification, accurate location, and scientific assessment of casing damage risks, providing systematic technical support for oilfield casing integrity management, from macroscopic decision-making to microscopic maintenance.

[0022] (I) Research on the mechanism of hedging losses; First, we collect and analyze the geological structure, geostress field, fluid properties, historical drilling engineering parameters, and annual casing damage logging data of the target oilfield block, and identify the main mechanisms leading to casing damage.

[0023] Specifically, basic data for casing damage assessment of the target oilfield block is collected, including basic geological data of the block, well network and well location data, injection and production engineering parameters, casing basic data, and historical casing damage data.

[0024] Among them, the basic geological data of the block is used to describe the underground geological environment of the oilfield, including the distribution of formation permeability (non-uniformity), geostress field parameters (direction, initial geostress field magnitude), formation Young's modulus, Poisson's ratio, porosity, hydraulic fractures (length, distribution direction), etc.

[0025] Well network and well location data are used to describe the distribution and basic information of oilfield wells, including well network layout, well type and number, well depth, etc.

[0026] Injection and production engineering parameters are used to describe oilfield production operations, including water injection pressure at the wellhead of water injection wells, production pressure at the wellhead of oil production wells, water injection volume, and injection and production time.

[0027] The casing basic data is used to describe the casing's own properties, including the casing material steel grade, yield strength, ultimate tensile strength, wall thickness, perforation parameters, etc.

[0028] Historical casing damage data is used to describe past casing damage, including the proportion of damaged wells, the number of damaged wells, and the type of casing failure.

[0029] As one implementation method, this embodiment takes the Niu23-A block of Niuzhuang Oilfield as the research object.

[0030] By reviewing relevant literature and official data from the Niuzhuang Oilfield, it was learned that 30% of the water injection wells in the Niuzhuang Oilfield suffered casing damage. Geological information of the Niu 23-A block was also collected, such as the uneven distribution of formation permeability in the structure, the overall geostress of the block trending southeast to northwest, and the well network mostly using the inverse nine-point method. Well history data and the current main casing damage well numbers of the Niu 23-A block were obtained.

[0031] Based on a survey of the basic data of injection and production casing in the hydraulically driven / fractured well groups of Niuzhuang Oilfield, the main failure types of casing include shear failure, extrusion failure, tensile failure, corrosion failure, and thermal stress failure.

[0032] Meanwhile, the most basic and common form of casing damage in Niuzhuang Oilfield, namely the casing damage mechanism, is the deterioration of the stress state of the casing caused by changes in the geostress field due to injection and production: high-pressure liquid is continuously pumped into the formation, the rock strength is weakened, the geostress around the wellbore is redistributed, and the casing is damaged and deformed by non-uniform geostress.

[0033] The above research content serves as the basis for the evaluation model and methods, providing direction for subsequent implementation steps.

[0034] In this embodiment, by systematically integrating geological, engineering, and historical casing loss data, a multi-dimensional evaluation foundation covering geological environment, well network layout, production operations, and casing attributes was constructed for the first time at the block scale. This breaks through the limitations of fragmented data and one-sided analysis in traditional methods, providing comprehensive and accurate input for subsequent numerical simulations. It ensures the objectivity and relevance of casing loss mechanism analysis from the source, giving subsequent model building and evaluation conclusions a solid realistic basis.

[0035] (ii) Block injection and production simulation; By performing block injection-production simulation, a numerical model is established that reflects the coupling relationship between injection-production dynamics and formation mechanical response, transforming geological and engineering insights into quantifiable mechanical environment data.

[0036] Specifically, based on the basic geological data, well network and well location data, and injection and production engineering parameters of the block collected in the early stage, a fluid-structure interaction model based on the well network distribution of the block was established using the multi-field coupling finite element software COMSOL.

[0037] This model starts with the initial geostress field of the block and, by inputting injection and production data such as injection volume, production pressure, and injection and production time, simulates the dynamic evolution of formation pore pressure and geostress field throughout the entire production cycle. It also outputs the redistribution of the geostress field near the wellbore. This transforms the oilfield injection and production operations into external loads acting on the casing, providing accurate, time-varying boundary conditions for subsequent casing stress analysis.

[0038] As one implementation method, based on the collected geological structural characteristics, non-uniform permeability distribution, initial geostress field trending southeast-northwest, inverse nine-point well network layout, and detailed well history and injection-production pressure data of the Niu 23-A block, a multi-field coupled finite element model covering the entire target block was constructed. The model's geometric scale was set to 6571m × 3750m, including 10 water injection wells (such as Niu 23-47 well) and 29 oil production wells (such as Niu 23-46 well). The depth of all wells was set to 3000 meters. Based on the actual data of the block, hydraulic fracture geometry with specific lengths and orientations was introduced into some wells to realistically represent the impact of pressure-driven development.

[0039] The key to model construction lies in the refined handling of formation heterogeneity and boundary conditions.

[0040] First, based on the stratigraphic permeability contour maps in the block's basic geological data, the model area is divided into multiple subdomains with different permeability attributes, thereby characterizing the anisotropic features of permeability, such as... Figure 3 As shown.

[0041] Secondly, the mechanical boundary conditions of the model are strictly set according to the study of the geostress field: the model boundary is subjected to corresponding stress loads in the direction of maximum horizontal principal stress (set as the X direction) and the direction of minimum horizontal principal stress (set as the Y direction), and all external boundaries are subject to normal displacement constraints to simulate the constraint effect of far-field strata. The fluid flow boundary is related to wellbore operation. The wellhead pressure of the water injection well is set in a dynamic range of 20MPa to 40MPa based on historical data, and the wellhead production pressure of the oil production well is set at approximately 1.5MPa.

[0042] The initial conditions of the model, including key parameters such as formation pore pressure, Young's modulus of rock, and Poisson's ratio, were all derived from core experimental data, well logging interpretation results, and reservoir description reports provided by the oilfield.

[0043] After completing the model establishment and parameter assignment, a transient fluid-structure interaction numerical simulation was performed. This simulation started with the initial geostress field and pore pressure field, and then progressively applied a year-long injection-production process. The calculation process solved for the pore pressure changes caused by fluid seepage in the porous medium, as well as the resulting changes in effective stress in the rock skeleton and solid deformation. Simultaneously, the solid deformation reacted on the pore space and the seepage field, forming a complete coupled feedback system.

[0044] Through this process, the model dynamically calculates the spatiotemporal distribution evolution of pore pressure and geostress field in the block throughout the entire production cycle.

[0045] This simulation step extracts the redistributed geostress field data at the casing location at the end of the simulation period for each target wellbore, including the magnitude and direction of the three principal stresses. Specifically, the three principal stresses refer to the maximum, minimum, and vertical principal stresses, which are perpendicular to each other, acting on the underground rock at that point. Their magnitudes and directions are directly obtained by solving the stress tensor at that location and calculating its eigenvalues ​​and eigenvectors using the post-processing function of the finite element software (COMSOL). These data are no longer static, idealized theoretical values, but rather a relatively stable dynamic mechanical state that incorporates the effects of injection and production disturbances over time. This series of specific, quantified wellbore stress data, used as time-varying boundary conditions, is directly input into the subsequent casing stress analysis module, thereby transferring the macroscopic block production dynamics into microscopic mechanical loads acting on the casing of a single well, laying a solid foundation for accurately assessing the stress state of the casing.

[0046] This embodiment establishes a block-scale fluid-structure interaction model reflecting injection-production dynamics, enabling dynamic simulation of the spatiotemporal evolution of formation pore pressure and geostress field during long-term production. It overcomes the traditional assumption of simplifying casing loads to static or uniformly distributed pressure, and for the first time quantifies the disturbance process of macroscopic production operations on the wellbore mechanical environment. This provides accurate, time-varying mechanical boundary conditions for subsequent casing analysis, achieving a crucial transformation from production parameters to mechanical loads.

[0047] (III) Casing stress analysis; Based on the completion of block injection-production simulation and the acquisition of wellbore redistribution geostress field data, further casing stress analysis is performed to transform the macroscopic formation mechanical environment into a refined mechanical response of the casing body.

[0048] This step uses the research results from the previous two stages as direct input to construct a locally refined finite element model that can truly reflect the mechanical state of the wellbore after injection and production.

[0049] Specifically, using the general-purpose finite element software ABAQUS, a three-dimensional coupled solid model of the formation-cement sheath-casing system was established based on the previously determined casing foundation data (such as material steel grade P110, wall thickness 9.54mm, perforation parameters, etc.) and key output data extracted from the block injection and production simulation.

[0050] The model focuses on a typical section of a single wellbore, with overall dimensions of 4m × 4m × 0.5m, designed to ensure computational efficiency while fully covering the surrounding formation range sufficient to influence the casing's mechanical behavior. The model is assembled from three solid components: the overlying and surrounding rock formations, the cement sheath, and the casing. The casing component is precisely modeled with its geometric features, including wall thickness and the spirally arranged perforation structure (in this embodiment, 10 perforations with a diameter of 10mm and a phase angle of 60°). Figure 4As shown, the contact relationships between the components, especially the interfaces between the cement sheath and the formation, and between the cement sheath and the casing, are set as "bonded" constraints to simulate a good cementing condition and ensure effective load transfer.

[0051] This step transforms the output of the block injection-production simulation—that is, the redistributed geostress field, including the effects of injection-production disturbances, experienced by the target wellbore at the end of the simulation period—into the precise mechanical boundary conditions of this model.

[0052] Specifically, the magnitude and direction of the three principal stresses (maximum horizontal principal stress, minimum horizontal principal stress, and vertical principal stress) at the calculated point are converted into pressure loads in the corresponding directions and applied to the corresponding surfaces on the outer boundary of the model strata.

[0053] Simultaneously, based on the well's production status (water injection well or oil production well), corresponding fluid pressures (such as water injection pressure or production flow pressure) are applied to the inner wall of the casing. Fixed constraints are applied to the bottom of the model to simulate the support of the underlying formation; on the sides of the formation model, normal displacement constraints are applied on the plane of symmetry according to the direction of stress application. All material properties, including the formation's elastic modulus and Poisson's ratio, the mechanical parameters of the cement sheath, and the elastic parameters of the casing steel, are assigned values ​​based on the initially collected casing damage assessment baseline data.

[0054] Following the modeling and load application described above, a static numerical simulation was then performed. This calculation directly solves the structural equilibrium equations under these complex boundary conditions, ultimately outputting detailed stress contour maps, deformation patterns, and displacement fields of the target well casing. The analysis results clearly reveal the stress distribution on the casing body, particularly the location and severity of stress concentration areas (such as around perforation holes and at casing wall thickness variations), and quantitatively provide the maximum equivalent stress (such as von Mises stress) value and its location.

[0055] Therefore, this step yields refined stress state and deformation information of the casing under actual injection and production loads, quantifying the macroscopic block production dynamics (characterized by changes in the geostress field) described in the block injection and production simulation and reflecting it as the specific mechanical response of the well casing. This provides an indispensable and accurate quantitative input for the next step of directly comparing the stress level of the casing with its material strength, thereby conducting residual strength evaluation and damage risk assessment.

[0056] This embodiment establishes a refined three-dimensional coupled mechanical model of the formation-cement sheath-casing and applies a realistic non-uniform load obtained from upstream simulation. For the first time, it achieves a refined simulation of the casing's mechanical response under real formation constraints and injection-production disturbances. It can accurately identify the stress concentration areas, maximum stress values, and deformation patterns of the casing, directly converting macroscopic stress changes into the casing's microscopic mechanical state. This provides a direct and reliable stress input for strength evaluation and is a core link connecting the macroscopic environment and microscopic failure.

[0057] (iv) Evaluation of remaining strength of the casing; Based on the completed detailed analysis of casing stress, the final evaluation of remaining casing strength is then performed.

[0058] This step determines the maximum von Mises equivalent stress value of the target casing under actual injection and production loads. The data includes the yield strength and its distribution as input data, combined with basic data for loss assessment (such as yield strength). This involves quantitatively comparing the current stress state of the casing with its inherent bearing limit to assess its safety margin or damage risk level.

[0059] Specifically, such as Figure 5 As shown, the maximum von Mises stress value appearing on the target well casing is first extracted from the finite element analysis results of the casing stress analysis. Then, the classic von Mises yield criterion is applied, and the extracted stress value is compared with the yield strength of the obtained casing material. Two core engineering evaluation indicators are used in the calculation: strength utilization rate (η) and residual strength coefficient (RSF).

[0060] The formula for calculating strength utilization rate is: (1) The formula for calculating the residual strength coefficient is: (2) in, It is the maximum Mises stress of the casing. This refers to the yield strength of the casing. Strength utilization rate describes the proportion of the current loads (such as ground stress and internal pressure) on the casing relative to its ultimate bearing capacity, where the ultimate bearing capacity refers to the yield strength of the casing material.

[0061] The calculation of strength utilization rate directly reflects the proportion of the casing material's yield strength consumed under current complex load conditions. The closer the value is to 100%, the closer the casing is to the yield state. The calculation of residual strength coefficient, on the other hand, characterizes the safety margin of the casing under the current state from another perspective. A value greater than 1 indicates that the casing still has a certain safety reserve.

[0062] This embodiment does not use the above single indicator in isolation, but combines the two with a recognized engineering safety factor (SF, which is taken as 1.125 in this embodiment according to the general standard) to form a set of composite criteria: if the strength utilization rate of a well casing is greater than or equal to 100% (i.e., it has reached or exceeded the yield limit) and its residual strength coefficient is less than or equal to 1 (i.e., the safety margin is lower than the baseline), then the well casing is judged to have failed or is in a "casing damage" state; if the strength utilization rate is less than 100% but the residual strength coefficient is close to or lower than the safety factor, then it can be judged as a high-risk well and needs to be closely monitored.

[0063] By applying this method to calculate and evaluate target wells in the Niu 23-A block, this embodiment obtained clear casing safety status classification results. Numerical calculations and evaluations show that the evaluation results of wells with known actual casing damage (such as Niu 23-47 and Niu 25-25) meet the "casing damage" criterion; while the residual strength coefficients of wells in a high-risk state (such as Niu 25-44 and Niu Geng 42) are also significantly lower, which is highly consistent with the on-site observations. This verifies the reliability and accuracy of the entire technical chain from data collection, mechanism analysis, multi-scale simulation to final strength evaluation.

[0064] Therefore, this embodiment ultimately yields a quantitative and graded evaluation conclusion on the safety status of the casing of each target well (e.g., safe, high-risk, failed), as well as key values ​​for the remaining strength coefficient and strength utilization rate. This result condenses all the aforementioned complex mechanistic analysis and numerical simulation into a clear guide that can be directly used for on-site engineering decision-making, thus providing a direct scientific basis for formulating differentiated casing damage prevention, monitoring, and repair measures. It achieves closed-loop management of wellbore integrity from "macro-risk assessment" to "micro-quantitative evaluation" and then to "precise countermeasure support."

[0065] At this point, all specific implementation schemes of the present invention have been completed. Because the implementation is highly targeted to oilfields, the present invention is not only applicable to Niuzhuang Oilfield, but can also be extended to other oilfield blocks with different geological conditions and pressure drive / fracturing methods, so as to achieve systematic, dynamic and precise management of casing safety.

[0066] This specific embodiment, through a block-scale fluid-structure interaction model, for the first time incorporates multiple factors such as multi-well collaboration, geostress field evolution, and fracture distribution into the simulation, overcoming the limitations of single-well or simplified models. Using a dynamically evolving redistributed geostress field as the load input, combined with a high-fidelity three-dimensional coupled mechanical model, it significantly improves the consistency between evaluation results and engineering realities. Simultaneously, it abandons traditional empirical formulas and static verification, achieving dynamic tracking and lifetime prediction of casing safety status throughout the injection and production cycle. This fills the gaps in existing technologies regarding systematicity, dynamism, and predictability, forming a widely applicable closed-loop evaluation system.

[0067] Example 2 This embodiment provides a numerical simulation-based system for evaluating the remaining strength of oilfield well casing, including: The injection-production simulation module is configured to establish a block-scale fluid-structure coupling numerical model that reflects the coupling relationship between injection-production dynamics and formation mechanical response based on the casing damage evaluation data of the target oilfield block, simulate the dynamic evolution of formation pore pressure and geostress field during long-term injection-production process, and obtain the redistributed geostress field data around the wellbore. The stress analysis module is configured to use the redistributed geostress field data as boundary conditions, and combine the casing structure and material parameters to establish a three-dimensional coupled mechanical model including the formation, cement sheath and casing, and obtain the stress distribution and maximum equivalent stress of the casing under injection and production load through numerical simulation calculation. The strength evaluation module is configured to evaluate the remaining strength and classify the damage risk level of the casing based on the maximum equivalent stress and the yield strength of the casing material, using the strength utilization rate and the remaining strength coefficient in combination with the set safety factor.

[0068] Example 3 This embodiment provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the steps in the numerical simulation-based oilfield well casing residual strength evaluation method described in Embodiment 1 above.

[0069] Example 4 This embodiment provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, it implements the steps in the numerical simulation-based oilfield well casing residual strength evaluation method described in Embodiment 1 above.

[0070] The steps or modules involved in Embodiments 2 to 4 above correspond to those in Embodiment 1. For specific implementation details, please refer to the relevant description section of Embodiment 1. The term "computer-readable storage medium" should be understood as a single medium or multiple media including one or more instruction sets; it should also be understood as including any medium capable of storing, encoding, or carrying an instruction set for execution by a processor and enabling the processor to perform any of the methods in this invention.

[0071] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for evaluating the remaining strength of oilfield well casing based on numerical simulation, characterized in that, include: Based on the basic data of casing damage evaluation of the target oilfield block, a block-scale fluid-structure coupling numerical model reflecting the coupling relationship between injection and production dynamics and formation mechanical response is established to simulate the dynamic evolution of formation pore pressure and geostress field during long-term injection and production, and obtain the geostress field data redistributed around the wellbore. Using the redistributed geostress field data as boundary conditions, and combining the casing structure and material parameters, a three-dimensional coupled mechanical model including the formation, cement sheath, and casing is established. The stress distribution and maximum equivalent stress of the casing under injection and production loads are obtained through numerical simulation calculation. Based on the maximum equivalent stress and the yield strength of the casing material, the remaining strength of the casing is evaluated and the damage risk level is classified by using the strength utilization rate and the remaining strength coefficient in combination with the set safety factor.

2. The method for evaluating the remaining strength of oilfield well casing based on numerical simulation as described in claim 1, characterized in that, The basic data for casing damage assessment includes basic geological data of the block, well network and well location data, injection and production engineering parameters, casing basic data, and historical casing damage data.

3. The method for evaluating the remaining strength of oilfield well casing based on numerical simulation as described in claim 2, characterized in that, The establishment of a block-scale fluid-structure coupled numerical model reflecting the coupling relationship between injection-production dynamics and formation mechanical response, to simulate the dynamic evolution of formation pore pressure and geostress field during long-term injection-production processes, and to obtain redistributed geostress field data around the wellbore, specifically includes: Based on the aforementioned casing damage evaluation data, a finite element model covering the geological structure, well network distribution, and non-uniform permeability characteristics of the target block is constructed. The mechanical boundary conditions of the model are set based on the geostress field parameters, and the fluid flow boundary conditions are set based on the injection and production engineering parameters. Perform transient fluid-structure interaction numerical simulation to calculate the distribution of formation pore pressure and geostress field after long-term injection and production; Extract the redistributed geostress field data at the end of the simulation period for each target well location, which includes the magnitude and direction of the three principal stresses, including the maximum horizontal principal stress, the minimum horizontal principal stress, and the vertical principal stress.

4. The method for evaluating the remaining strength of oilfield well casing based on numerical simulation as described in claim 1, characterized in that, Using the redistributed geostress field data as boundary conditions, and combining the casing structure and material parameters, a three-dimensional coupled mechanical model including the formation, cement sheath, and casing is established. Numerical simulation calculations are then used to obtain the stress distribution and maximum equivalent stress of the casing under injection-production loads. Specifically, this includes: A three-dimensional solid finite element model of the formation-cement sheath-casing was established based on the casing foundation data. The redistributed geostress field data is converted into pressure loads and applied to the corresponding direction of the outer boundary of the model strata; Apply appropriate fluid pressure to the inner wall of the casing according to the well's production status; Displacement constraints are set for the model, and material properties are assigned to each component based on the basic data of casing damage evaluation; Perform static numerical simulation to obtain the stress cloud diagram, deformation state and maximum equivalent stress value of the casing.

5. The method for evaluating the remaining strength of oilfield well casing based on numerical simulation as described in claim 1, characterized in that, Based on the maximum equivalent stress and the yield strength of the casing material, the remaining strength of the casing is evaluated and the damage risk level is classified using the strength utilization rate, the remaining strength coefficient, and a set safety factor. Specifically, this includes: The strength utilization rate of the casing is calculated based on the ratio of the maximum equivalent stress to the yield strength, and the residual strength coefficient of the casing is calculated based on the ratio of the yield strength to the maximum equivalent stress. The strength utilization rate and the remaining strength coefficient are compared with the preset safety factor. If the strength utilization rate is greater than or equal to 100% and the remaining strength coefficient is less than or equal to 1, it is determined to be a loss. Otherwise, different levels of risk status are classified based on how close the residual strength coefficient is to the safety factor.

6. A numerical simulation-based system for evaluating the remaining strength of oilfield well casing, characterized in that, include: The injection-production simulation module is configured to establish a block-scale fluid-structure coupling numerical model that reflects the coupling relationship between injection-production dynamics and formation mechanical response based on the casing damage evaluation data of the target oilfield block, simulate the dynamic evolution of formation pore pressure and geostress field during long-term injection-production process, and obtain the redistributed geostress field data around the wellbore. The stress analysis module is configured to use the redistributed geostress field data as boundary conditions, and combine the casing structure and material parameters to establish a three-dimensional coupled mechanical model including the formation, cement sheath and casing, and obtain the stress distribution and maximum equivalent stress of the casing under injection and production load through numerical simulation calculation. The strength evaluation module is configured to evaluate the remaining strength and classify the damage risk level of the casing based on the maximum equivalent stress and the yield strength of the casing material, using the strength utilization rate and the remaining strength coefficient in combination with the set safety factor.

7. The oilfield well casing residual strength evaluation system based on numerical simulation as described in claim 6, characterized in that, The basic data for casing damage assessment includes basic geological data of the block, well network and well location data, injection and production engineering parameters, casing basic data, and historical casing damage data.

8. The oilfield well casing residual strength evaluation system based on numerical simulation as described in claim 7, characterized in that, The establishment of a block-scale fluid-structure coupled numerical model reflecting the coupling relationship between injection-production dynamics and formation mechanical response, to simulate the dynamic evolution of formation pore pressure and geostress field during long-term injection-production processes, and to obtain redistributed geostress field data around the wellbore, specifically includes: Based on the aforementioned casing damage evaluation data, a finite element model covering the geological structure, well network distribution, and non-uniform permeability characteristics of the target block is constructed. The mechanical boundary conditions of the model are set based on the geostress field parameters, and the fluid flow boundary conditions are set based on the injection and production engineering parameters. Perform transient fluid-structure interaction numerical simulation to calculate the distribution of formation pore pressure and geostress field after long-term injection and production; Extract the redistributed geostress field data at the end of the simulation period for each target well location, which includes the magnitude and direction of the three principal stresses, including the maximum horizontal principal stress, the minimum horizontal principal stress, and the vertical principal stress.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by the processor, it implements the steps in the numerical simulation-based method for evaluating the remaining strength of oilfield well casing as described in any one of claims 1-5.

10. A computer device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the program, it implements the steps in the method for evaluating the residual strength of oilfield well casing based on numerical simulation as described in any one of claims 1-5.

Images