A method for quantitatively evaluating microstructure damage of argillaceous cap rock of underground gas storage
By establishing a particle flow numerical model and a multiple linear regression equation, the microstructural damage of the mudstone caprock of underground gas storage is quantitatively evaluated, which solves the problem that existing technologies cannot accurately predict the lifespan and pressure limit of gas storage facilities, and achieves more accurate prediction results.
Patent Information
- Application Number
- CN202411710634.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-27
- Publication Date
- 2025-11-25
- Estimated Expiration
- 2044-11-27
AI Technical Summary
Existing research methods cannot accurately and quantitatively characterize the degree of microstructural damage in the mudstone caprock of underground gas storage facilities, which makes it impossible to accurately predict the lifespan and pressure limit of gas storage facilities.
By establishing a particle flow numerical model, cyclic loading and unloading processes under different stress conditions are simulated, the number of cracks and damage within the caprock are calculated, and a multiple linear regression equation is constructed to predict the damage level and lifespan of the gas storage facility.
A method is provided that can accurately evaluate the microstructural damage of argillaceous caprock, predict the lifespan and pressure limit of gas storage facilities, and consider multiple factors, thereby improving the accuracy and applicability of the prediction.
Smart Images
Figure CN119578091B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of oil and gas exploration technology, and in particular relates to a method for quantitative evaluation of microstructural damage in the mudstone caprock of underground gas storage. Background Technology
[0002] Macroscopic damage to the caprock is an external manifestation of the accumulation of internal microstructural damage; therefore, the degree of microstructural damage in argillaceous caprock determines its sealing capacity. Quantitative characterization models of rock microstructural damage are not only of significant guiding importance for the operation and design of gas storage facilities, but also serve as the theoretical basis for designing long-term stable operating parameters for underground gas storage facilities. Currently, quantitative characterization methods are mainly used to characterize the degree of rock microstructural damage based on the operating pressure and loading / unloading cycle of the gas storage facility.
[0003] Previous studies have primarily employed indoor experiments and numerical simulations to investigate microstructural damage in argillaceous caprocks, identifying stress level and cycle time as crucial factors influencing their microstructure. However, a consensus has not been reached on the quantitative characterization of this damage. Furthermore, current research focuses on single-factor analysis, failing to accurately predict the lifespan and pressure limit of gas storage facilities. Therefore, a quantitative evaluation method for microstructural damage in argillaceous caprocks is urgently needed to predict gas storage facility lifespan and pressure limit, providing theoretical guidance for the design of gas storage facility operating parameters. Summary of the Invention
[0004] To address the shortcomings of existing technologies, the technical problem this invention aims to solve is that existing research methods cannot quantitatively or accurately characterize the degree of microscopic damage to rocks. This invention proposes a quantitative evaluation method for the microscopic structural damage of mudstone caprock in underground gas storage facilities, which can quantitatively characterize the microscopic structural damage of rocks in underground gas storage facilities, predict the lifespan of gas storage facilities, and has high accuracy and wide applicability.
[0005] To solve the aforementioned technical problem, the technical solution adopted by the present invention is as follows:
[0006] This invention provides a method for quantitatively evaluating the microstructural damage of the mudstone caprock in an underground gas storage facility, comprising:
[0007] Step S1: Based on the mineral composition of the core, establish a particle flow numerical model of the caprock core; adjust the parameter settings in the particle flow numerical model until they match the results of the triaxial compression test of the core; fix the lower limit stress ratio and conduct cyclic loading and unloading numerical simulations under different upper limit stress ratios to obtain the corresponding number N of cracks generated inside the caprock. β Calculate the damage S generated within the model during the i-th iteration. i ;
[0008] Step S2: When the number of internal cracks in the model reaches N under specific cyclic stress conditions βWhen the model generates N cracks, the corresponding damage amount D is calculated. The specimen is close to failure when the model generates N cracks. N is defined as the crack threshold for specimen failure. At this time, the damage amount D is 1.
[0009] Step S3: Calculate S for the i-th iteration. i The percentage D of damage amount reaching 1 in the nth instance i ;
[0010] Step S4: Select damage amounts under different cycle counts and upper limit stress ratios to construct a quantitative evaluation model for microstructural damage in argillaceous caprock.
[0011] Step S5: Based on actual working conditions, analyze the fatigue life of the caprock when the damage reaches 0.85 under a specific upper limit stress ratio, and predict the maximum upper limit stress ratio that the gas storage tank can withstand when the cycle is 60 times and the damage is 0.85.
[0012] Preferably, in step S1, the S i It is calculated using the following formula:
[0013]
[0014] In the above formula, N β Let β be the number of internal cracks corresponding to the strain at point β. i Let d be the strain at the i-th cycle point. β This is the differential of the number of internal cracks corresponding to the strain at β.
[0015] Preferably, step S1 specifically includes: establishing a particle flow numerical model of the caprock core based on the mineral composition of the caprock core, adjusting the parameter settings in the particle flow numerical model until it matches the results of the triaxial compression test of the core; conducting cyclic loading and unloading numerical simulations under different cycle periods and different stress levels to obtain the corresponding number of cracks, evaluating the damage development of the rock during the entire fatigue process by analyzing the change of the number of cracks inside the caprock with strain, observing the microscopic damage at each peak point under different stress ratio conditions by the number of cracks N generated under different stress ratio conditions, and calculating the damage Si generated inside the model in the i-th cycle according to formula (1).
[0016] Preferably, in step S2, D is calculated using the following formula:
[0017]
[0018] In the above formula, n is the number of cycles when the number of cracks generated inside the model is N under a specific stress level, where D = 1.
[0019] Preferably, in step S3, the Di It is calculated using the following formula:
[0020]
[0021] In the above formula, i is the number of iterations. When i = n, D i =1.
[0022] Preferably, step S4 specifically includes: statistically analyzing the damage amount D generated during i cycles under different upper limit stress conditions. i A quantitative evaluation model for microstructural damage in argillaceous caprock was constructed based on different cycle counts, stress conditions, and damage amounts.
[0023] Preferably, step S4 further includes: establishing a microstructure damage cloud map based on the number of cycles when the damage amount reaches 1 under different upper limit stress conditions and the damage amount generated under the corresponding number of cycles; and establishing a multiple linear regression equation among the damage amount, the number of cycles, and the upper limit stress based on the damage cloud map.
[0024] Preferably, step S5 further includes: using the multiple linear regression equation between the damage amount, the number of cycles, and the upper limit stress to calculate, with a fixed upper limit stress ratio, the maximum cycle injection-production period that the caprock can withstand when the damage amount is 0.85; and the maximum upper limit stress ratio that the caprock can withstand when the damage amount is 0.85 and the cycle period is 60 times, to provide guidance for the design of the upper limit pressure of the gas storage facility.
[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0026] This invention proposes a quantitative evaluation method for the microstructural damage of argillaceous caprock in underground gas storage facilities. It utilizes the variation of the number of internal cracks in the caprock with strain to quantitatively evaluate the degree of microstructural damage in the argillaceous caprock, thereby predicting the lifespan of the gas storage facility. This method offers the following advantages:
[0027] In addition to considering the operating pressure of the gas storage facility, the injection and production cycle of the gas storage facility is also taken into account. Furthermore, by comprehensively considering various factors, deviations caused by using one or more of these factors can be avoided.
[0028] The impact of rock microstructure damage on the sealing capacity of the caprock was fully considered, and a quantitative characterization model was constructed to make the characterization results more accurate. Attached Figure Description
[0029] Figure 1 This invention provides a flowchart for the quantitative evaluation of microstructural damage in the mudstone caprock of an underground gas storage facility. Detailed Implementation
[0030] The technical solutions in specific embodiments of the present invention will now be described in detail and completely with reference to the accompanying drawings. Obviously, the described embodiments are merely some specific implementations of the overall technical solution of the present invention, and not all implementations. Based on the overall concept of the present invention, all other embodiments obtained by those skilled in the art fall within the protection scope of the present invention.
[0031] This invention provides a method for quantitatively evaluating the microstructural damage of the mudstone caprock in underground gas storage facilities, such as... Figure 1 As shown, it includes:
[0032] Step S1: Based on the mineral composition of the core, establish a particle flow numerical model of the caprock core; adjust the parameter settings in the particle flow numerical model until they match the results of the triaxial compression test of the core; fix the lower limit stress ratio and conduct cyclic loading and unloading numerical simulations under different upper limit stress ratios to obtain the corresponding number N of cracks generated inside the caprock. β Calculate the damage S generated within the model during the i-th iteration. i Among them, S i It is calculated using the following formula:
[0033]
[0034] In the above formula, N β Let β be the number of internal cracks corresponding to the strain at point β. i Let d be the strain at the i-th cycle point. β This is the differential of the number of internal cracks corresponding to the strain at β.
[0035] In a preferred embodiment, step S1 specifically includes: establishing a particle flow numerical model of the caprock core based on its mineral composition; adjusting the parameter settings in the particle flow numerical model until it matches the results of the triaxial compression test of the core; conducting cyclic loading and unloading numerical simulations under different cycle periods and stress levels to obtain the corresponding number of cracks; evaluating the damage development of the rock during the entire fatigue process by analyzing the change in the number of cracks inside the caprock with strain; observing the microscopic damage at each peak point under each cycle i under different stress ratio conditions by using the number of cracks N generated under different stress ratio conditions; and calculating the damage S generated inside the model in the i-th cycle according to formula (1). i .
[0036] Step S2: When the number of internal cracks in the model reaches N under specific cyclic stress conditions β When the model generates N cracks, the corresponding damage amount D is calculated. The specimen approaches failure when the model generates N cracks. N is defined as the crack threshold for specimen failure, at which point the damage amount D is 1. The damage amount D generated inside the model after n cycles is calculated using the following formula:
[0037]
[0038] In the above formula, n is the number of cycles when the number of cracks generated inside the model is N under a specific stress level, where D = 1.
[0039] Step S3: Calculate S for the i-th iteration. i The percentage D of damage amount reaching 1 in the nth instance i Specifically, the proportion D of the microscopic damage amount reaching 1 in the nth cycle is calculated using formula (3). i :
[0040]
[0041] In the above formula, i is the number of iterations. When i = n, D i =1.
[0042] Step S4: Select damage amounts under different cycle counts and upper limit stress ratios to construct a quantitative evaluation model for the microstructural damage of the argillaceous caprock; specifically including:
[0043] The damage amount D generated during i cycles under different upper stress limits is statistically analyzed. i A quantitative evaluation model for microstructural damage in argillaceous caprock was constructed based on different cycle counts, stress conditions, and damage amounts.
[0044] Based on the number of cycles required to reach damage 1 under different upper stress conditions and the damage amount generated under the corresponding number of cycles, a microstructural damage cloud map is established. Based on the damage cloud map, a multiple linear regression equation is established among damage amount, number of cycles, and upper stress.
[0045] Step S5: Based on actual working conditions, analyze the fatigue life of the caprock when the damage reaches 0.85 under a specific upper limit stress ratio, and predict the maximum upper limit stress ratio that the gas storage tank can withstand when the cycle is 60 times and the damage is 0.85.
[0046] In a preferred embodiment, step S5 further includes: using a multiple linear regression equation among the damage amount, number of cycles, and upper limit stress to calculate, with a fixed upper limit stress ratio, the maximum cyclic injection-production cycle that the caprock can withstand when the damage amount is 0.85; and the maximum upper limit stress ratio that the caprock can withstand when the damage amount is 0.85 and the cycle is 60 times, to provide guidance for the design of the upper limit pressure of the gas storage facility.
[0047] The aforementioned quantitative evaluation method for the microstructural damage of the argillaceous caprock of underground gas storage facilities utilizes the variation of the number of internal cracks in the caprock with strain to quantitatively evaluate the degree of microstructural damage and thus predict the lifespan of the gas storage facility. This method offers the following advantages: it considers not only the operating pressure of the gas storage facility but also its injection-production cycle, and by comprehensively considering multiple factors, it avoids biases arising from using only one or a few factors; it fully considers the impact of rock microstructural damage on the caprock's sealing capacity, thereby constructing a quantitative characterization model that results in more accurate characterization results. This method can quantitatively characterize the rock microstructural damage of underground gas storage facilities, predict their lifespan, and has high accuracy and wide applicability.
[0048] To provide a clearer and more detailed description of the quantitative evaluation method for microstructural damage in the mudstone caprock of underground gas storage provided in this invention, specific embodiments will be described below.
[0049] Example 1
[0050] Taking the Baogu 2 oil reservoir in the Nanpu Depression as the study area and the Sha-1 section of the proposed reservoir as the target layer, we carried out quantitative characterization of the microstructure damage of the mudstone caprock of the Baogu 2 gas reservoir.
[0051] (1) Numerical simulation was conducted based on the data obtained from triaxial compression tests and cyclic loading and unloading tests carried out in the study area. The damage development of the rock during the entire fatigue process was studied by observing the change of the number of internal cracks in the overburden rock with strain in the numerical simulation. The number of cracks N generated under different stress ratios was used to observe the microscopic damage at each peak point under each cycle i under different stress ratios. The damage S generated inside the model in the i-th cycle was calculated according to formula (1). i .
[0052] (2) According to the model, the specimen is close to failure when N cracks are generated. N is defined as the crack threshold for specimen failure, and the damage amount D is defined as 1. D is calculated according to formula (2). When the number of cracks generated inside the model is N after n cycles, D = 1.
[0053] (3) Based on the proportion of micro-damage in the rock under different cycle numbers, the micro-damage S at each peak point under different stress conditions was used. i The corresponding stress conditions generate up to N crack damage values D, which are calculated according to formula (3).
[0054] (4) Selecting a fixed lower limit stress, under different upper limit stress levels, determine the number of cycles required for crack initiation to reach point N, and predict the number of cycles required to reach damage 1 under different upper limit stress levels; the corresponding number of cycles and the resulting damage S. i .
[0055] (5) Based on the number of cycles when the damage reaches 1 under different upper stress conditions and the damage generated at the corresponding number of cycles, a microstructural damage cloud map is established. Based on the damage cloud map, a multiple linear regression equation is established among the damage, the number of cycles, and the upper stress:
[0056] y=6.451x1+0.0116x2-5.542 (4)
[0057] In the formula, y is the damage amount, x1 is the upper limit stress ratio, and x2 is the cycle period.
[0058] (6) Using formula (4), when the upper limit stress ratio is 0.466 (the upper limit stress currently used) and the damage amount is 0.85, the maximum cycle injection and production cycle that the caprock can withstand is 291 times, indicating that the gas storage has a large pressure-boosting space; while when the cycle is 60 times and the damage amount is 1, the corresponding upper limit stress ratio is 0.90, and when the damage amount is 0.85, the corresponding upper limit stress ratio is 0.88.
[0059] (7) The lifespan of the Baogu 2 underground gas storage facility was predicted. When the caprock damage was 0.8 and the number of cycles was 60, the maximum cyclic stress ratio that the mudstone caprock in the Baogu 2 block could withstand was 0.875. In addition, the mudstone caprock exhibited strong sealing capacity when the maximum cyclic stress ratio was 0.8, the minimum cyclic stress ratio was 0.3, and the cycle period did not exceed 120 times.
Claims
1. A method for quantitatively evaluating the microstructural damage of argillaceous caprock in underground gas storage facilities, characterized in that, include: Step S1: Based on the mineral composition of the core, establish a numerical model of the grain flow of the caprock core; Adjust the parameter settings in the particle flow numerical model until they match the results of the triaxial compression test of the core; fix the lower limit stress ratio and conduct cyclic loading and unloading numerical simulations under different upper limit stress ratios to obtain the corresponding number N of cracks generated inside the caprock. β Calculate the damage S generated within the model during the i-th iteration. i ; Step S2: When the number of internal cracks in the model reaches N under specific cyclic stress conditions β When the model generates N cracks, the corresponding damage amount D is calculated. The specimen is close to failure when the model generates N cracks. N is defined as the crack threshold for specimen failure. At this time, the damage amount D is 1. Step S3: Calculate S for the i-th iteration. i The percentage D of damage amount reaching 1 in the nth instance i ; Step S4: Select damage amounts under different cycle counts and upper limit stress ratios to construct a quantitative evaluation model for microstructural damage in argillaceous caprock. Step S5: Based on actual working conditions, analyze the fatigue life of the caprock when the damage reaches 0.85 under a specific upper limit stress ratio, and predict the maximum upper limit stress ratio that the gas storage tank can withstand when the cycle period is 60 times and the damage is 0.
85. In step S1, the S i It is calculated using the following formula: In the above formula, N β Let β be the number of internal cracks corresponding to the strain at point β. i Let d be the strain at the i-th cycle point. β The derivative of the number of internal cracks corresponding to the strain at β; In step S2, D is calculated using the following formula: In the above formula, n is the number of cycles when the number of cracks generated inside the model is N under a specific stress level, at which point D = 1; In step S3, the D i It is calculated using the following formula: In the above formula, i is the number of iterations. When i = n, D i =1; Step S4 specifically includes: The damage amount D generated during i cycles under different upper stress limits is statistically analyzed. i A quantitative evaluation model for microstructural damage in argillaceous caprock was constructed based on different cycle counts, stress conditions, and damage amounts. Step S4 further includes: Based on the number of cycles when the damage reaches 1 under different upper stress conditions and the damage generated under the corresponding number of cycles, a microstructural damage cloud map is established. Based on the damage cloud map, a multiple linear regression equation is established among the damage, the number of cycles, and the upper stress.
2. The method for quantitative evaluation of microstructural damage in the mudstone caprock of an underground gas storage facility according to claim 1, characterized in that, Step S1 specifically includes: establishing a particle flow numerical model of the caprock core based on its mineral composition; adjusting the parameter settings in the particle flow numerical model until it matches the results of the triaxial compression test of the core; conducting cyclic loading and unloading numerical simulations under different cycle periods and stress levels to obtain the corresponding number of cracks; evaluating the damage development of the rock during the entire fatigue process by analyzing the change in the number of cracks inside the caprock with strain; observing the microscopic damage at each peak point under each cycle i under different stress ratio conditions by using the number of cracks N generated under different stress ratio conditions; and calculating the damage S generated inside the model in the i-th cycle according to formula (1). i .
3. The method for quantitative evaluation of microstructural damage in the mudstone caprock of an underground gas storage facility according to claim 1, characterized in that, Step S5 further includes: using the multiple linear regression equation between the damage amount, the number of cycles, and the upper limit stress to calculate, with a fixed upper limit stress ratio, the maximum cycle injection-production cycle that the caprock can withstand when the damage amount is 0.85; and the maximum upper limit stress ratio that the caprock can withstand when the damage amount is 0.85 and the cycle is 60 times, to provide guidance for the design of the upper limit pressure of the gas storage facility.