Quantitative evaluation method for integrity risk of shaft of carbon dioxide flooding injection well

Abstract

The invention relates to the technical field of wellbore risk evaluation, in particular to a carbon dioxide flooding injection well wellbore integrity risk quantitative evaluation method, which comprises the following steps: constructing an injection well integrity evaluation hierarchical structure model; determining a weight coefficient of each risk index; respectively evaluating each risk index; and calculating a total risk grade score and determining a risk grade. Through the hierarchical model and the determination of the weight coefficient, various risk factors can be comprehensively considered, and detailed evaluation of the integrity of the shaft is realized. Acquisition of real-time data and parameter correction ensure the accuracy and timeliness of an evaluation result, in addition, the method can recognize a high-risk area in advance, early warning and timely treatment are achieved, and the problem that in the prior art, due to the fact that an integrity analysis evaluation method is large in subjectivity, the accuracy and timeliness of the evaluation result are poor is effectively solved. Therefore, the problem of low evaluation accuracy caused by the fact that the integrity risk of the shaft cannot be evaluated more objectively and quantitatively is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of wellbore risk assessment, and in particular to a method for quantitatively assessing the wellbore integrity risk of a carbon dioxide injection well. Background Art

[0002] With the profound impact of global climate change on the environment and society, and the increasing attention of the international community to reducing greenhouse gas emissions, carbon dioxide capture, utilization and storage technology (CCUS) has gradually become one of the key technologies for achieving a low-carbon economy. As an important part of the energy structure, the oil and gas industry is facing the challenge of transformation and upgrading, and needs to reduce environmental impact while improving energy efficiency. Technological progress and innovation have provided new tools for the traditional energy industry, making it possible to achieve green development and environmental protection while ensuring energy security. The guidance of policies and regulations, coupled with the market and investors' preference for environmentally friendly technologies, have jointly promoted the development and application of CCUS technology. Against this background, the development of a quantitative assessment method for the wellbore integrity risk of carbon dioxide injection wells is not only of great significance to improving the safety and economic benefits of CCUS projects, but also an important practice to respond to the global emission reduction trend and achieve sustainable development goals.

[0003] Integrity failure problems were common in the early development of CCUS test areas, including risks such as annular pressure, wellhead lifting, casing damage, and gas leakage. The process for evaluating integrity of domestic and foreign companies is mainly to obtain wellbore parameters through wellbore pressure testing or engineering logging, and then conduct integrity risk assessment through manual qualitative analysis. In general, the current integrity analysis and evaluation methods still have the problem of significant subjective influence, which makes it impossible to conduct a more objective quantitative evaluation of wellbore integrity risks, thereby affecting the standard type of integrity evaluation. Summary of the invention

[0004] To this end, the present invention provides a method for quantitatively evaluating the wellbore integrity risk of a carbon dioxide injection well, so as to overcome the problem of low evaluation accuracy caused by the high subjectivity of the integrity analysis evaluation method in the prior art, which makes it impossible to conduct a more objective quantitative evaluation of the wellbore integrity risk.

[0005] To achieve the above object, the present invention provides a method for quantitatively evaluating the wellbore integrity risk of a carbon dioxide injection well, comprising:

[0006] According to the on-site production situation of CCUS pilot area, a hierarchical model for injection well integrity evaluation is constructed, and several risk indicators are determined;

[0007] Determine the weight coefficient of each risk indicator through the hierarchical analysis method;

[0008] Evaluate each risk indicator separately;

[0009] The total risk level score is calculated based on the evaluation results of each risk indicator and the weight coefficient of each risk indicator, and the risk level is determined based on the total risk level score and a number of preset standard level score ranges;

[0010] Among them, several risk indicators include downhole tool strength, pipe corrosion risk, residual strength of oil casing, thread corrosion risk, gas tree sealing, casing thread air tightness and cement ring sealing. The standard grade scoring range includes the first scoring range, the second scoring range, the third scoring range and the fourth scoring range. The risk levels include slight risk, medium risk, more serious risk and serious risk.

[0011] Among them, the evaluation of the air tightness of the casing thread includes obtaining in real time the first interference contact pressure caused by the casing thread make-up, the second interference contact pressure caused by the internal pressure, and the working internal pressure of the test area working condition, correcting the first interference contact pressure according to the first interference contact pressure and the preset standard pressure range, and calculating the casing thread sealing quantitative evaluation value according to the corrected first interference contact pressure, the second interference contact pressure, and the working internal pressure of the test area working condition;

[0012] Among them, the evaluation of the sealing performance of the cement ring includes real-time acquisition of the formation temperature, injection pressure difference and actual high-quality bonding section length in the well, correction of the cement ring bonding index according to the formation temperature and the preset standard temperature range, and calculation of the minimum sealing length of the cement ring according to the corrected cement ring bonding index and injection pressure difference, and calculation of the quantitative evaluation value of the cement ring sealing performance according to the minimum sealing length of the cement ring and the actual high-quality bonding section length.

[0013] Furthermore, the hierarchical model of injection well integrity evaluation is constructed based on the field production situation of the CCUS pilot area, including:

[0014] According to the on-site production conditions in the CCUS pilot area, a three-level injection well integrity evaluation hierarchical model was established. The target layer is the injection well integrity risk, the criterion layer is the strength, corrosion and sealing that affect the wellbore integrity, and the solution layer is the oil casing strength, downhole tool strength, pipe corrosion, thread corrosion, gas tree sealing, casing thread sealing and cement ring sealing.

[0015] Furthermore, the weight coefficients of each risk indicator determined by the hierarchical analysis method include:

[0016] The 1-9 scale comparison method is used to compare the risk indicators at the scheme level and the criterion level in pairs to form a comparison matrix. The weight coefficient of each risk indicator is determined by calculating the maximum eigenvalue and corresponding eigenvector of the comparison matrix.

[0017] Furthermore, the strength evaluation of downhole tools includes:

[0018] The Wellcat software was used to build a model for the tubing string, and the pressure profile was established according to the production conditions. The force verification was carried out according to the working conditions of the test area to obtain the maximum pressure difference, maximum force, rated pressure bearing capacity and rated tensile pressure bearing capacity of the tool. The quantitative evaluation value of the downhole tool strength was calculated based on the obtained results.

[0019] Furthermore, the evaluation of the residual strength of the oil casing includes:

[0020] A mechanical model was established based on the tubing structure and geological parameters of the test area. Mechanical verification and analysis of the water-gas alternating injection conditions were carried out according to the CCUS Phase I industrial construction plan. The standard safety factor was obtained by verifying the original design tubing parameters. The current safety factor was obtained by verifying the parameters of the current tubing after corrosion and thinning. The quantitative evaluation value of the residual strength of the oil casing was calculated based on the standard safety factor and the current safety factor.

[0021] Furthermore, the evaluation of pipe corrosion risk and thread corrosion risk includes:

[0022] Obtain carbon dioxide partial pressure, temperature, corrosion product film and flow rate in real time during production operations, and calculate the quantitative evaluation value of pipe corrosion risk based on the obtained results;

[0023] The corrosion rate, corrosion depth and corrosion area of ​​the threads during the production process are acquired in real time, and the quantitative evaluation value of the thread corrosion risk is calculated based on the acquired results.

[0024] Furthermore, the evaluation of the sealing performance of the gas tree includes:

[0025] The wellhead pressure of the gas injection condition and the rated pressure bearing capacity of the gas tree in the test area are obtained, and the quantitative evaluation value of the gas tree sealing is calculated based on the obtained results.

[0026] Further, correcting the first interference contact pressure according to the first interference contact pressure and a preset standard pressure range includes:

[0027] Adjusting the first interference contact pressure according to the first interference contact pressure that is less than the minimum value of the preset standard pressure range and the standard pressure range;

[0028] The first interference contact pressure is adjusted according to the first interference contact pressure being greater than the maximum value of the preset standard pressure range and the standard pressure range being reduced.

[0029] Furthermore, the cement sheath bonding index is corrected according to the formation temperature and the preset standard temperature range, including:

[0030] Adjusting the cement sheath bonding index according to the formation temperature being less than the minimum value of the preset standard temperature range and the standard temperature range increasing;

[0031] The cement sheath bonding index is adjusted according to the formation temperature being greater than the maximum value of the preset standard temperature range and the standard temperature range being reduced.

[0032] Furthermore, the total risk level score is calculated based on the evaluation results of each risk indicator and the weight coefficient of each risk indicator, including:

[0033] The quantitative evaluation value of casing thread sealing, the quantitative evaluation value of cement ring sealing, the quantitative evaluation value of downhole tool strength, the quantitative evaluation value of oil casing residual strength, the quantitative evaluation value of pipe corrosion risk, the quantitative evaluation value of thread corrosion risk and the quantitative evaluation value of gas tree sealing are multiplied by the corresponding weight coefficients and summed up to obtain the total risk level score.

[0034] Compared with the prior art, the beneficial effect of the present invention is that, through the determination of hierarchical models and weight coefficients, multiple risk factors can be comprehensively considered to achieve a detailed assessment of wellbore integrity. Real-time data acquisition and parameter correction ensure the accuracy and timeliness of the evaluation results. In addition, the method can identify high-risk areas in advance, achieve early warning and timely governance, thereby reducing the possibility of risk occurrence and management costs, and improving the economic benefits and safety of CCUS engineering projects. It effectively solves the problem of low evaluation accuracy caused by the integrity analysis and evaluation method in the prior art due to its high subjectivity, which makes it impossible to conduct a more objective quantitative evaluation of wellbore integrity risks.

[0035] Furthermore, by quantifying the integrity risk of injection wells, factors that may affect wellbore safety can be more accurately identified and evaluated. The determination of weight coefficients enhances objectivity and transparency in the decision-making process. It not only helps to optimize resource allocation and reduce potential risks, but also improves the overall safety and efficiency of CCUS projects.

[0036] Furthermore, the correction can ensure that the interference contact pressure of the casing thread and the bonding index of the cement sheath are within an optimized range, thereby improving the sealing and integrity of the wellbore. The adaptability to downhole working conditions is enhanced, ensuring that sufficient sealing performance can be maintained under different conditions. In addition, it helps prevent downhole equipment damage or failure due to excessive or low pressure, reduces operational risks, and improves the safety performance of CCUS projects. Through real-time monitoring and timely adjustments, the integrity of the wellbore can be controlled more accurately, providing guarantees for long-term and stable CCUS operations.

[0037] Furthermore, through risk identification and prioritization, the contribution of various risk factors to the overall risk level can be identified, which helps to determine the priority of risk management. Through quantitative evaluation, the efficiency and effectiveness of risk management are improved, and the reliance on qualitative judgment is reduced. It is helpful to take preventive measures and reduce the possibility of accidents, thereby ensuring operational safety and extending the service life of the wellbore. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a flow chart of the method for quantitatively evaluating the wellbore integrity risk of a carbon dioxide injection well in this embodiment;

[0039] Figure 2 It is a schematic diagram of the injection well integrity evaluation hierarchical model of this embodiment;

[0040] Figure 3 A determination logic diagram for correcting the first interference contact pressure in this embodiment;

[0041] Figure 4 This is the decision logic diagram for correcting the cement sheath bonding index in this embodiment. DETAILED DESCRIPTION

[0042] In order to make the objects and advantages of the present invention more clearly understood, the present invention is further described below in conjunction with embodiments; it should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0043] The preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood by those skilled in the art that these embodiments are only used to explain the technical principles of the present invention and are not intended to limit the protection scope of the present invention.

[0044] It should be noted that, in the description of the present invention, terms such as "up", "down", "left", "right", "inside" and "outside" indicating directions or positional relationships are based on the directions or positional relationships shown in the drawings. This is merely for the convenience of description and does not indicate or imply that the device or element must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it cannot be understood as a limitation on the present invention.

[0045] In addition, it should be noted that in the description of the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0046] See also Figure 1 As shown, it is a flow chart of the method for quantitatively evaluating the wellbore integrity risk of carbon dioxide injection wells in this embodiment;

[0047] This embodiment provides a method for quantitatively evaluating the wellbore integrity risk of a carbon dioxide injection well, comprising:

[0048] According to the on-site production situation of CCUS pilot area, a hierarchical model for injection well integrity evaluation is constructed, and several risk indicators are determined;

[0049] Determine the weight coefficient of each risk indicator through the hierarchical analysis method;

[0050] Evaluate each risk indicator separately;

[0051] The total risk level score is calculated based on the evaluation results of each risk indicator and the weight coefficient of each risk indicator, and the risk level is determined based on the total risk level score and a number of preset standard level score ranges;

[0052] Among them, several risk indicators include downhole tool strength, pipe corrosion risk, residual strength of oil casing, thread corrosion risk, gas tree sealing, casing thread air tightness and cement ring sealing. The standard grade scoring range includes the first scoring range, the second scoring range, the third scoring range and the fourth scoring range. The risk levels include slight risk, medium risk, more serious risk and serious risk.

[0053] Among them, the evaluation of the air tightness of the casing thread includes obtaining in real time the first interference contact pressure caused by the casing thread make-up, the second interference contact pressure caused by the internal pressure, and the working internal pressure of the test area working condition, correcting the first interference contact pressure according to the first interference contact pressure and the preset standard pressure range, and calculating the casing thread sealing quantitative evaluation value according to the corrected first interference contact pressure, the second interference contact pressure, and the working internal pressure of the test area working condition;

[0054] Among them, the evaluation of the sealing performance of the cement ring includes real-time acquisition of the formation temperature, injection pressure difference and actual high-quality bonding section length in the well, correction of the cement ring bonding index according to the formation temperature and the preset standard temperature range, and calculation of the minimum sealing length of the cement ring according to the corrected cement ring bonding index and injection pressure difference, and calculation of the quantitative evaluation value of the cement ring sealing performance according to the minimum sealing length of the cement ring and the actual high-quality bonding section length.

[0055] Through the determination of hierarchical models and weight coefficients, multiple risk factors can be fully considered to achieve a detailed assessment of wellbore integrity. Real-time data acquisition and parameter correction ensure the accuracy and timeliness of the evaluation results. In addition, this method can identify high-risk areas in advance, achieve early warning and timely governance, thereby reducing the possibility of risk occurrence and management costs, and improving the economic benefits and safety of CCUS engineering projects. It effectively solves the problem of low evaluation accuracy caused by the high subjectivity of the integrity analysis and evaluation method in the existing technology, which makes it impossible to conduct a more objective quantitative evaluation of the wellbore integrity risk.

[0056] Please continue reading Figure 2 As shown, it is a schematic diagram of the injection well integrity evaluation hierarchical model of this embodiment;

[0057] Specifically, the hierarchical model of injection well integrity evaluation based on the field production situation in the CCUS pilot area includes:

[0058] According to the on-site production situation of the Daqing CCUS test area, a three-level injection well integrity evaluation hierarchical model is established. The target layer is the injection well integrity risk, the criterion layer is the three factors affecting the wellbore integrity, namely strength, corrosion, and sealing, and the solution layer is the seven risk indicators of oil casing strength, downhole tool strength, pipe corrosion, thread corrosion, gas tree sealing, casing thread sealing, and cement ring sealing;

[0059] Specifically, the weight coefficients of each risk indicator determined by the hierarchical analysis method include:

[0060] By comparing the seven risk indicators of wellbore safety risk of carbon dioxide injection wells, the 1-9 scale comparison method is used to compare the factors of the bottom layer and the middle layer in pairs, forming a comparison matrix, as shown in Tables 1-5;

[0061] Table 1 Comparison of wellbore integrity risk factor scales

[0062] scale meaning i is the same as j i / j=1 i is slightly stronger than j i / j=3 i is stronger than j i / j=5 i is much stronger than j i / j=7 i is much stronger than j i / j=9 i is between the above levels i / j=2, 4, 6, 8, 10 i is slightly weaker than j, weak, very weak, extremely weak i / j=1 / 3, 1 / 5, 1 / 7, 1 / 9

[0063] Table 2 Strength judgment matrix

[0064] Criteria layer (strength) Oil casing strength Downhole tool strength Oil casing strength 1 3 Downhole tool strength 1 / 3 1

[0065] Table 3 Corrosion judgment matrix

[0066] Criteria layer (corrosion) Pipe corrosion Thread corrosion Pipe corrosion 1 1 / 7 Thread corrosion 7 1

[0067] Table 4 Sealing judgment matrix

[0068]

[0069] Table 5 Wellbore integrity risk judgment matrix

[0070]

[0071] By calculation, we can get the maximum eigenvalue λ of the strength judgment matrix = 2, and the eigenvector corresponding to the maximum eigenvalue is W MAX =(0.9487, 0.3162) T ;

[0072] The maximum eigenvalue of the corrosion judgment matrix is ​​λ=2, and the eigenvector corresponding to the maximum eigenvalue is W MAX =(0.1414, 0.9899) T ;

[0073] The maximum eigenvalue of the sealing judgment matrix is ​​λ=3.0858, and the eigenvector corresponding to the maximum eigenvalue is W MAX =(0.1352, 0.9048, 0.4038) T ;

[0074] The maximum eigenvalue of the wellbore integrity risk judgment matrix is ​​λ=3.0037, and the eigenvector corresponding to the maximum eigenvalue is W MAX =(0.1640, 0.4629, 0.8711) T .

[0075] The weights corresponding to each factor are as follows:

[0076] Table 6 Risk indicator weights

[0077] Risk Indicators Weight Oil casing strength 0.0822 Downhole tool strength 0.0274 Pipe corrosion 0.0386 Thread corrosion 0.2705 Gas tree sealing 0.0560 Casing thread sealing 0.1652 Cement ring sealing 0.3600

[0078] By quantifying the integrity risk of injection wells, factors that may affect wellbore safety can be more accurately identified and evaluated. The determination of weight coefficients enhances objectivity and transparency in the decision-making process. It not only helps to optimize resource allocation and reduce potential risks, but also improves the overall safety and efficiency of CCUS projects.

[0079] Specifically, the evaluation of downhole tool strength includes:

[0080] Common downhole tools used in gas wells include production packers and downhole safety valves.

[0081] Strength of production packers: reasons of the packer itself, influence of wellbore and formation stress, and influence of operation construction.

[0082] Strength of downhole safety valve: reasons of downhole safety valve itself, influence of pressure in pipeline, influence of operation and construction.

[0083] For the strength of downhole tools, Wellcat software was used to model the string, establish the pressure profile according to the production conditions, and verify it according to the conditions of the test area. The results of the force verification showed that the maximum pressure difference of the tool was B. C1 , Maximum force B C2 , the rated pressure bearing capacity of the tool is B 1 , Rated tensile pressure capacity is B 2 , quantitative evaluation value R of downhole tool strength 2 The calculation is as follows:

[0084]

[0085] Specifically, the evaluation of the residual strength of oil casing includes:

[0086] During the production of oil and gas wells after cementing, the main factors affecting the residual strength of the casing are the external squeeze force, followed by the axial tension and internal pressure. When the external squeeze force on the casing is greater than the casing's collapse strength at that time, the casing will be squeezed and destroyed. Secondly, the elastic modulus, Poisson's ratio, thickness, non-uniformity of ground stress, perforation, etc. of the cement sheath will enhance or weaken the collapse strength of the casing.

[0087] A mechanical model was established based on the pipe string structure and geological parameters of the test area. According to the CCUS Phase I industrial construction plan, a mechanical verification analysis of the water-gas alternating injection condition was carried out. The safety factor A was obtained by verifying the original design pipe string parameters. 0 The current safety factor A is obtained by checking the parameters after the corrosion and thinning of the pipe column. C , quantitative evaluation value of residual strength of oil casing R 1 The calculation is as follows:

[0088]

[0089] Specifically, the evaluation of pipe corrosion risk and thread corrosion risk includes:

[0090] Obtain the carbon dioxide partial pressure, temperature, corrosion product film and flow rate in the production process in real time, multiply the obtained results by the corresponding weights and sum them up to calculate the quantitative evaluation value of pipe corrosion risk. The corresponding weight is determined based on the specific requirements of the production process;

[0091] In the process of oil and gas production, the Christmas tree often suffers from severe corrosion, which causes great harm to the production operation on site. Through the analysis of mixed water samples in the block, the content of corrosive media, the physical and chemical properties of materials, and the analysis of corrosion products, it can be found that the corrosion of pipes is related to the following factors: carbon dioxide partial pressure, temperature, corrosion product film, and flow rate.

[0092] For the carbon dioxide corrosion resistance of the selected pipe, the carbon dioxide downhole corrosion rate is measured on site, and then according to the four-level classification method of corrosion severity in the NACE SP 0775 standard, its quantitative evaluation R3 is divided into four levels, as shown in Table 7:

[0093] Table 7 Evaluation standards for corrosion resistance of pipes

[0094]

[0095] In the case where the casing string connection is not properly buckled or the string is subjected to excessive tensile or bending loads, extremely small gaps will be formed at locations such as the torque shoulder surface, and concentration cells will be formed inside and outside the gap, causing local corrosion.

[0096] The corrosion rate, corrosion depth and corrosion area of ​​the thread in the production process are obtained in real time. The obtained results are multiplied by the corresponding weights and summed to calculate the quantitative evaluation value of the thread corrosion risk. The corresponding weight is determined based on the specific requirements of the production process. For the thread crevice corrosion risk, the electrochemical corrosion simulation experiment results are used. According to the four-level classification method of corrosion severity in the NACE SP 0775 standard, its quantitative evaluation R4 is divided into four levels, as shown in Table 8:

[0097] Table 8 Evaluation standard of thread corrosion resistance

[0098]

[0099] Specifically, the evaluation of the sealing performance of the gas tree includes:

[0100] When characterizing the integrity of oil and gas wells, the gas tree seal is divided into two aspects: internal leakage and external leakage.

[0101] External leakage of pipe: mainly divided into the following three forms: leakage, puncture leakage, and open welding. The leakage points and manifestations of different external leakage forms are as follows: Leakage: annular space, production decline, unstable pressure, liquid level cannot be pumped down; top thread sealing ring, white crystalline objects appear, water leakage, oil stains. Puncture leakage: large flange steel ring, oil stains, mist leakage; clamp steel ring, oil stains, seepage water. Open welding: surface casing and production casing, shaking, upward movement, will rise during hot washing.

[0102] Internal leakage of the pipe body: After investigation, it was found that the valve plate and valve seat are the places where internal leakage often occurs. The main reasons for the internal leakage of the valve plate and valve seat are divided into two aspects: first, manufacturing factors, which are mainly reflected in whether the parameters such as size (mm), surface roughness (dimensionless), flatness (mm), parallelism (mm) match the standard parameters; second, bearing capacity, which is mainly reflected in whether its maximum bearing pressure (MPa) exceeds the material tensile strength (MPa) and yield strength (MPa).

[0103] For the sealing of the gas tree, the wellhead pressure of the gas injection condition in the test area is E C , the rated pressure bearing capacity of the gas tree is E 0 , then the quantitative evaluation value of the gas tree sealing performance is R 5 The calculation is as follows:

[0104]

[0105] Specifically, the evaluation of the air tightness of the casing thread includes obtaining in real time the first interference contact pressure caused by the casing thread make-up, the second interference contact pressure caused by the internal pressure, and the working internal pressure of the test area working condition, correcting the first interference contact pressure according to the first interference contact pressure and the preset standard pressure range, and calculating the quantitative evaluation value of the casing thread sealing according to the corrected first interference contact pressure, the second interference contact pressure, and the working internal pressure of the test area working condition;

[0106] Compared with the water injection process, the injection pressure of the carbon dioxide injection oil recovery process is higher, which increases the risk of casing damage. Therefore, the process of converting water drive to carbon dioxide oil recovery faces a very high risk of wellbore integrity failure. The old water drive wells have been in service for many years, and all use round thread buckles. The casing strength and sealing performance after the conversion to carbon dioxide injection wells are unclear, so the round thread buckle is one of the important factors affecting the casing gas sealing. At the same time, factors such as casing damage, surface defects and the anti-crevice corrosion performance of the joints need to be considered.

[0107] For the casing thread sealing, the interference contact pressure caused by the make-up is determined as G 1 The interference contact pressure caused by the internal pressure is G 2 The sum of the two is used as the thread seal pressure bearing capacity index. The working internal pressure of the test area is G C , then the quantitative evaluation value of casing thread sealing is R 6 The calculation is as follows:

[0108]

[0109] Please continue reading Figure 3 As shown, it is a judgment logic diagram for correcting the first interference contact pressure in this embodiment;

[0110] Wherein, correcting the first interference contact pressure according to the first interference contact pressure and a preset standard pressure range includes:

[0111] Adjusting the first interference contact pressure according to the first interference contact pressure that is less than the minimum value of the preset standard pressure range and the standard pressure range;

[0112] The first interference contact pressure is adjusted according to the first interference contact pressure being greater than the maximum value of the preset standard pressure range and the standard pressure range being reduced.

[0113] Specifically, the evaluation of cement sheath sealing performance includes obtaining the formation temperature, injection pressure difference and actual high-quality cementing section length in the well in real time, correcting the cement sheath bonding index according to the formation temperature and the preset standard temperature range, and calculating the minimum cement sheath sealing length according to the corrected cement sheath bonding index and injection pressure difference, and calculating the cement sheath sealing performance quantitative evaluation value according to the minimum cement sheath sealing length and the actual high-quality cementing section length;

[0114] There are three main factors that affect the sealing performance of cement sheath, namely, the degree of cement bonding, the length of the bonding section and the corrosion of cement sheath.

[0115] Based on the self-developed full-scale high-temperature and high-pressure cement ring sealing integrity evaluation device, the simulation function of the full-scale, full-temperature range and full-pressure system is realized, and in conjunction with the self-developed 8-sector cementing quality detector, an evaluation test of the cement ring sealing capacity with different cementing indices is carried out. The experimental results show that the cement ring sealing capacity is linearly related to the cement ring height. When the cementing quality is excellent, the cement ring sealing capacity of 0.2m, 0.6m and 1m heights is 1.8MPa, 2.4MPa and 3.7MPa, respectively. With the increase of the cement ring bonding index, the cement ring sealing capacity shows a linear increase trend. The breakthrough pressures of cement rings with bonding indexes of 0.21, 0.42, 0.61 and 0.82 are 0.7MPa, 1.6MPa, 2.3MPa and 2.9MPa, respectively.

[0116] The calculation formula for the minimum sealing length of cement sheath is as follows:

[0117] h= <h2 style=";text-align:left;direction:ltr">f-0.02-1.3B<h2 style=";text-align:left;direction:ltr"> I

[0118] 0.027+2.5B I ;

[0119] Where, f is the injection pressure difference, MPa; B I is the cement sheath bonding index; h is the minimum isolation length (m).

[0120] Based on the on-site formation data and injection condition data of the test area, it was calculated that the minimum isolation length for safe operation of the wells in the test area under the condition of 4F18 cementing quality and 19MPa injection pressure is 7.5m; the minimum isolation length for safe operation of the wells in the test area under the condition of high-quality cementing quality and 20MPa injection pressure is 8.2m.

[0121] The corrosion risk is mainly due to the micro-gaps generated in the cement ring under the action of alternating temperature and pressure loads. Carbon dioxide extends along the micro-gaps, creating a carbon dioxide corrosion environment, causing the cement ring to fail to seal, further exacerbating the risk of cement ring sealing failure.

[0122] In order to explore the corrosion expansion law of cement ring perforation holes under carbon dioxide, a small-sized cement ring sealing evaluation device was developed to simulate the carbon dioxide phase under the temperature and pressure conditions of the on-site formation, and cement ring corrosion expansion tests with different corrosion times were carried out. The cement ring specimens were subjected to corrosion tests using supercritical carbon dioxide for corrosion times of 2, 5, 7, 14, 21, and 28 days. The experimental results showed that the corrosion time no longer expanded significantly after 3 months, and the corrosion expansion range reached a maximum value in June, and then almost stopped expanding. The expansion depth reached a maximum value of 16.84mm in 6 months;

[0123] The actual high-quality bonding section length is set as H C (m), and finally determine the quantitative evaluation value R of cement sheath sealing 7 The calculation is as follows:

[0124]

[0125] Among them, the correction of cement sheath bonding index according to the formation temperature and the preset standard temperature range includes:

[0126] Please continue reading Figure 4 As shown, it is a judgment logic diagram for correcting the cement sheath bonding index in this embodiment;

[0127] Adjusting the cement sheath bonding index according to the formation temperature being less than the minimum value of the preset standard temperature range and the standard temperature range increasing;

[0128] The cement sheath bonding index is adjusted according to the formation temperature being greater than the maximum value of the preset standard temperature range and the standard temperature range being reduced.

[0129] Through real-time monitoring and quantitative analysis of key parameters, potential risk points of wellbore integrity can be more accurately identified and evaluated. This not only helps to take preventive measures to improve the safety and reliability of the wellbore, but also provides clearer guidance for maintenance decisions and optimizes the planning and scheduling of maintenance and repair work through quantitative evaluation values.

[0130] During the evaluation process, the correction of the first interference contact pressure is achieved by comparing it with the preset standard pressure range. If the actual measured first interference contact pressure is lower than the minimum value of the standard range, the pressure will be adjusted upward based on this difference to ensure that it reaches at least the lower limit of the standard pressure range. On the contrary, if the first interference contact pressure is greater than the maximum value of the standard range, it needs to be adjusted downward to ensure that it does not exceed the upper limit. A similar strategy is also adopted for the correction of the cement sheath bonding index. According to the comparison results of the actual formation temperature with the preset standard temperature range, the bonding index is adjusted accordingly to increase or decrease. This correction ensures that the evaluation parameters can be within a safe and effective operating range, thereby improving the accuracy and reliability of the evaluation.

[0131] The correction can ensure that the interference contact pressure of the casing thread and the bonding index of the cement sheath are within an optimized range, thereby improving the sealing and integrity of the wellbore. It enhances the adaptability to downhole working conditions and ensures that sufficient sealing performance can be maintained under different conditions. In addition, it helps prevent downhole equipment damage or failure due to excessive or low pressure, reduces operational risks, and improves the safety performance of CCUS projects. Through real-time monitoring and timely adjustments, the integrity of the wellbore can be controlled more accurately, providing guarantees for long-term and stable CCUS operations.

[0132] Specifically, the total risk level score is calculated based on the evaluation results of each risk indicator and the weight coefficient of each risk indicator, including:

[0133] The casing thread sealing quantitative evaluation value, cement ring sealing quantitative evaluation value, downhole tool strength quantitative evaluation value, casing residual strength quantitative evaluation value, pipe corrosion risk quantitative evaluation value, thread corrosion risk quantitative evaluation value and gas tree sealing quantitative evaluation value are multiplied by the corresponding weight coefficients and summed to obtain the total risk level score ZF;

[0134] Where ZF = 0.0822 × R 1 +0.0274×R 2 +0.0386×R 3 +0.2705×R 4 +0.0560×R 5 +0.1652×R 6 +0.3600×R 7 ;

[0135] In the process of risk quantitative evaluation, each independent wellbore integrity influencing factor (including casing thread sealing, cement ring sealing, downhole tool strength, oil casing residual strength, pipe corrosion risk, thread corrosion risk and gas tree sealing) is firstly quantitatively evaluated in detail to obtain the respective quantitative evaluation values. Subsequently, according to the weight coefficient of each risk factor determined by the analytic hierarchy process, the quantitative evaluation value of each factor is multiplied by its corresponding weight coefficient. Finally, these products are summed to obtain a comprehensive total risk level score, which fully reflects the risk level of wellbore integrity.

[0136] Through risk identification and prioritization, we can identify the contribution of various risk factors to the overall risk level, help determine the priority of risk management, and through quantitative assessment, improve the efficiency and effectiveness of risk management, reduce reliance on qualitative judgments, and help take preventive measures to reduce the possibility of accidents, thereby ensuring operational safety and extending the service life of the wellbore.

[0137] Wellbore safety risk level classification:

[0138] According to the on-site production situation of the Daqing CCUS test area, the risks brought by the wellbore integrity factor are divided into 4 levels, namely, slight, moderate, serious and severe, as shown in Table 9:

[0139] Table 9 Wellbore integrity quantitative scores and risk levels

[0140] Risk Level Completeness Quantification Score slight 0.8-1.0 (excluding 0.8) medium 0.6-0.8 (excluding 0.6) More serious 0.4-0.6 (excluding 0.4) serious 0-0.4

[0141] For example, a. Residual strength of oil casing

[0142] Using WELLCAT mechanical analysis software, a pipe string model was established based on the well logging results, and the wall thickness of the weak point at 145 meters was 6 meters. The strength of the injection well casing was mechanically checked and analyzed. The minimum safety factor of the whole well was 1.629, and the risk point was located at the wellhead. The evaluation value R was calculated according to the quantitative evaluation formula for the residual strength of the oil casing. 1 =1.6 / 1.629=0.982;

[0143] b. Downhole tool strength

[0144] This well is a general injection well with no packer or safety valve. The quantitative evaluation of downhole tool strength takes the highest evaluation value R 2 =1;

[0145] c. Pipe corrosion risk

[0146] The well uses J-55 ordinary carbon steel pipes. The gas inside the pipe column is high-concentration carbon dioxide. The corrosion simulation evaluation experiment is carried out using the hanging piece weight loss method. The corrosion rate is calculated to be 0.04mm / a. Substituting it into the calculation formula, the quantitative score R of the pipe carbon dioxide corrosion resistance is obtained. 3 =1, as shown in Table S1;

[0147] Table S1 Casing corrosion simulation evaluation test results

[0148]

[0149] d. The casing thread of the well is made of J-55 ordinary carbon steel. The gas inside the pipe string is high-concentration carbon dioxide. The corrosion process is simulated by ECE software, and the corrosion rate is measured to be 0.0283mm / a. Substituting it into the calculation formula, the quantitative score R of the pipe carbon dioxide corrosion resistance is obtained. 4 =1;

[0150] e. The gas tree model of the well is ZQ65 / 35-FF. According to the production conditions of the YSL test area with a wellhead pressure of 22MPa, the quantitative evaluation value R of the gas tree sealing performance is calculated. 5 =0.37;

[0151] f. The casing of this well adopts API long round thread. Calculation parameters: Long round thread size table E S =137.246mm, round thread casing coupling size W = 160.02mm, d = outer diameter - 2 × wall thickness = 139.7-2 × 9.17 = 121.36mm, refer to API 5B standard hand-tightening pitch number N = 3, p = 3.175mm (long round thread has 8 threads per inch, pitch is 25.4mm / 8 = 3.175mm), T d =0.0625 (the taper of the round thread is 1 / 16), Young's modulus E = 210;

[0152] Interference contact pressure caused by make-up:

[0153]

[0154] (Unit: MPa), which is within the preset standard pressure range (15.273MPa-18.667MPa) and does not require correction;

[0155] Interference contact pressure caused by internal pressure:

[0156] (Unit: MPa);

[0157] The sum of the two is used as the thread seal pressure bearing capacity index. The working internal pressure of the test area is GC = 22MPa. The quantitative evaluation value of the casing thread sealing is R 6=0.205;

[0158] g. Cement sheath cementing quality evaluation

[0159] Based on the logging data of Well 11Y68-58 in Yushulin Oilfield, the cement ring bonding test results show that the longest high-quality section of continuous cement ring above the perforation section is 168m, located at a well depth of 1490m-1628m. Under the condition of high-quality cementing quality, the minimum isolation length for safe operation under the injection pressure of 20MPa in the YSL test area well is 8.2m. The dynamic evaluation value of cement ring sealing R is calculated according to the quantitative evaluation formula of cement ring sealing 7 =20.075, due to (0≤R 7 ≤1), then take R 7 Maximum value 1;

[0160] h. Based on the quantitative scoring of the seven risk factors, we substituted them into the numerical evaluation formula for wellbore risk and calculated the risk value B = 0.0807 + 0.0274 + 0.0386 + 0.2705 + 0.0207 + 0.0034 + 0.36 = 0.8013. The well was classified as a slight risk well according to the risk level.

[0161] So far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it is easy for those skilled in the art to understand that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will fall within the protection scope of the present invention.

[0162] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for quantitatively evaluating the wellbore integrity risk of a carbon dioxide injection well, characterized in that: include: According to the on-site production situation of CCUS pilot area, a hierarchical model for injection well integrity evaluation is constructed, and several risk indicators are determined; Determine the weight coefficient of each risk indicator through the hierarchical analysis method; Evaluate each risk indicator separately; Calculate the total risk level score based on the evaluation results of each risk indicator and the weight coefficient of each risk indicator, and determine the corresponding risk levels based on the total risk level score and the preset standard level score ranges; Among them, several risk indicators include downhole tool strength, pipe corrosion risk, residual strength of oil casing, thread corrosion risk, gas tree sealing, casing thread air tightness and cement ring sealing. The standard grade scoring range includes the first scoring range, the second scoring range, the third scoring range and the fourth scoring range. The risk levels include slight risk, medium risk, more serious risk and serious risk. Among them, the evaluation of the air tightness of the casing thread includes obtaining in real time the first interference contact pressure caused by the casing thread make-up, the second interference contact pressure caused by the internal pressure, and the working internal pressure of the test area working condition, correcting the first interference contact pressure according to the first interference contact pressure and the preset standard pressure range, and calculating the casing thread sealing quantitative evaluation value according to the corrected first interference contact pressure, the second interference contact pressure, and the working internal pressure of the test area working condition; Among them, the evaluation of the sealing performance of the cement ring includes real-time acquisition of the formation temperature, injection pressure difference and actual high-quality bonding section length in the well, correction of the cement ring bonding index according to the formation temperature and the preset standard temperature range, and calculation of the minimum sealing length of the cement ring according to the corrected cement ring bonding index and injection pressure difference, and calculation of the quantitative evaluation value of the cement ring sealing performance according to the minimum sealing length of the cement ring and the actual high-quality bonding section length.

2. The method for quantitatively evaluating the wellbore integrity risk of carbon dioxide injection wells according to claim 1, characterized in that: The hierarchical model of injection well integrity evaluation based on the field production of CCUS pilot area includes: According to the on-site production conditions in the CCUS pilot area, a three-level injection well integrity evaluation hierarchical model was established. The target layer is the injection well integrity risk, the criterion layer is the strength, corrosion and sealing that affect the wellbore integrity, and the solution layer is the oil casing strength, downhole tool strength, pipe corrosion, thread corrosion, gas tree sealing, casing thread sealing and cement ring sealing.

3. The method for quantitatively evaluating the wellbore integrity risk of carbon dioxide injection wells according to claim 2, characterized in that: The weight coefficients of each risk indicator determined by analytic hierarchy process include: The 1-9 scale comparison method is used to compare the risk indicators at the scheme level and the criterion level in pairs to form a comparison matrix. The weight coefficient of each risk indicator is determined by calculating the maximum eigenvalue and corresponding eigenvector of the comparison matrix.

4. The method for quantitatively evaluating the wellbore integrity risk of carbon dioxide injection wells according to claim 3, characterized in that: Evaluation of downhole tool strength includes: Wellcat software was used to build a model for the tubing string, and a pressure profile was established according to production conditions. A force check was performed according to the conditions in the test area to obtain the maximum pressure difference, maximum force, rated pressure bearing capacity, and rated tensile pressure bearing capacity of the tool. The quantitative evaluation value of the downhole tool strength was calculated based on the obtained results.

5. The method for quantitatively evaluating the wellbore integrity risk of carbon dioxide injection wells according to claim 4, characterized in that: The evaluation of the residual strength of oil casing includes: A mechanical model was established based on the tubing structure and geological parameters of the test area. Mechanical verification and analysis of the water-gas alternating injection conditions were carried out according to the CCUS Phase I industrial construction plan. The standard safety factor was obtained by verifying the original design tubing parameters. The current safety factor was obtained by verifying the parameters of the current tubing after corrosion and thinning. The quantitative evaluation value of the residual strength of the oil casing was calculated based on the standard safety factor and the current safety factor.

6. The method for quantitatively evaluating the wellbore integrity risk of carbon dioxide injection wells according to claim 5, characterized in that: The evaluation of pipe corrosion risk and thread corrosion risk includes: Obtain carbon dioxide partial pressure, temperature, corrosion product film and flow rate in real time during production operations, and calculate the quantitative evaluation value of pipe corrosion risk based on the obtained results; The corrosion rate, corrosion depth and corrosion area of ​​the threads during the production process are acquired in real time, and the quantitative evaluation value of the thread corrosion risk is calculated based on the acquired results.

7. The method for quantitatively evaluating the wellbore integrity risk of carbon dioxide injection wells according to claim 6, characterized in that: The evaluation of the sealing performance of the gas tree includes: The wellhead pressure of the gas injection condition and the rated pressure bearing capacity of the gas tree in the test area are obtained, and the quantitative evaluation value of the gas tree sealing is calculated based on the obtained results.

8. The method for quantitatively evaluating the wellbore integrity risk of carbon dioxide injection wells according to claim 7, characterized in that: Correcting the first interference contact pressure according to the first interference contact pressure and a preset standard pressure range includes: Adjusting the first interference contact pressure according to the first interference contact pressure that is less than the minimum value of the preset standard pressure range and the standard pressure range; The first interference contact pressure is adjusted according to the first interference contact pressure being greater than the maximum value of the preset standard pressure range and the standard pressure range being reduced.

9. The method for quantitatively evaluating the wellbore integrity risk of carbon dioxide injection wells according to claim 8, characterized in that: Correction of cement sheath bonding index according to formation temperature and preset standard temperature range includes: Adjusting the cement sheath bonding index according to the formation temperature being less than the minimum value of the preset standard temperature range and the standard temperature range increasing; The cement sheath bonding index is adjusted according to the formation temperature being greater than the maximum value of the preset standard temperature range and the standard temperature range being reduced.

10. The method for quantitatively evaluating the wellbore integrity risk of carbon dioxide injection wells according to claim 9, characterized in that: The total risk level score is calculated based on the evaluation results of each risk indicator and the weight coefficient of each risk indicator, including: The quantitative evaluation value of casing thread sealing, the quantitative evaluation value of cement ring sealing, the quantitative evaluation value of downhole tool strength, the quantitative evaluation value of oil casing residual strength, the quantitative evaluation value of pipe corrosion risk, the quantitative evaluation value of thread corrosion risk and the quantitative evaluation value of gas tree sealing are multiplied by the corresponding weight coefficients and summed up to obtain the total risk level score.

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