Method and system for determining sealing capacity of corrosion cement sheath of layered gas injection well

Abstract

The invention relates to the technical field of petroleum engineering well cementation, and provides a method and system for determining the sealing capacity of a corrosion cement sheath of a layered gas injection well, and the method comprises the steps: determining well bore parameters of a target layered gas injection well; analyzing the compressive strength, the tensile strength and the relationship between the elastic modulus and the corrosion time of the corroded set cement at different ages; a casing-cement sheath-stratum combination mechanical model is established, and the corrosion cement sheath stress distribution situation changing along with corrosion time in the layered gas injection process is obtained through analysis; comparing the stress with compressive strength and tensile strength of the corrosion cement sheath, analyzing a sealing failure form of the corrosion cement sheath according to a comparison result, and determining the sealing capability of the corrosion cement sheath of the layered gas injection well. According to the method, the corrosion effect of CO2 on the well cementation cement sheath in the gas injection process of the layered gas injection well and the compressive strength, tensile strength and elastic modulus degradation rule of the corrosion cement sheath are considered, dynamic analysis of the sealing capacity of the corrosion cement sheath is achieved, and the sealing failure form and the sealing failure moment of the corrosion cement sheath are quantified.

Description

Technical Field

[0001] The invention relates to the technical field of petroleum engineering cementing, and in particular to a method and system for determining the sealing capacity of a corroded cement ring of a layered gas injection well. Background Art

[0002] Gas injection is an important means to improve the oil and gas recovery rate of oil and gas wells, and stratified gas injection is a key technology to achieve simultaneous improvement of oil and gas recovery rates in multiple production layers of oil and gas wells. In recent years, in order to implement the national dual carbon goals, CO2 is often used as the gas medium for gas injection; however, the injection of CO2 will cause carbonization corrosion of the wellbore cement ring, which will lead to its strength decline and performance degradation. The cement ring is a key barrier to ensure the isolation of the wellbore layers. The sealing ability of the corroded cement ring is directly related to whether stratified gas injection can be implemented safely and efficiently. Therefore, it is very necessary to scientifically predict and evaluate the sealing ability of the corroded cement ring in stratified gas injection wells.

[0003] In order to judge the sealing ability of corroded cement ring, most traditional schemes use cement stone corrosion test to analyze the corrosion depth of cement stone at different corrosion times to evaluate the corrosion degree of underground cement ring; by evaluating the degradation law of cement stone compressive strength at different corrosion times, the corrosion resistance of cement stone is qualitatively evaluated. It can be found that the current evaluation of the sealing ability of corroded cement ring is mostly qualitative evaluation, which is difficult to achieve quantitative analysis.

[0004] For stratified gas injection wells, the wellbore load is approximately constant during the gas injection process, and the cement sheath is in a relatively stable stress environment. However, due to the influence of CO2 corrosion, the elastic modulus and strength of the cement sheath continue to deteriorate. Under a constant wellbore load, the changing elastic modulus will also cause the stress distribution of the corroded cement sheath to change continuously; at the same time, due to the continuous deterioration of the strength of the corroded cement sheath, the cement sheath that meets the wellbore load requirements under initial conditions may also suffer strength damage during the stratified gas injection process. Summary of the invention

[0005] The purpose of the present invention is to solve at least one technical problem in the background technology and to provide a method and system for determining the sealing capacity of corroded cement ring in a stratified gas injection well.

[0006] To achieve the above object, the present invention provides a method for determining the sealing ability of corroded cement sheath in a stratified gas injection well, comprising:

[0007] Determine the wellbore parameters of the target stratified gas injection well;

[0008] Carry out CO2 corrosion maintenance of cement paste, test and analyze the relationship between the compressive strength, tensile strength and elastic modulus of cement paste corroded at different ages and the corrosion time;

[0009] A casing-cement sheath-formation combination mechanical model is established based on the wellbore parameters of the target stratified gas injection well, and the relationship between the elastic modulus and corrosion time of corroded cement stone at different ages is substituted into the casing-cement sheath-formation combination mechanical model to analyze and obtain the stress distribution of the corroded cement sheath that changes with the corrosion time during the stratified gas injection process;

[0010] The stress of the corroded cement sheath that changes with corrosion time is compared with the compressive strength and tensile strength at the corresponding corrosion time. The failure form of the corroded cement sheath seal is analyzed based on the comparison results, and the sealing capacity of the corroded cement sheath in the stratified gas injection well is determined.

[0011] According to one aspect of the present invention, the target stratified gas injection wellbore parameters include:

[0012] The bottom hole temperature of the target stratified gas injection well, the wellbore structural parameters, the mechanical parameters of the casing, the mechanical parameters of the cement sheath, the mechanical parameters of the formation, the formation confining pressure and the stratified gas injection pressure;

[0013] The wellbore structural parameters are the dimensions of the casing, cement ring and the inner wall of the formation;

[0014] The mechanical parameters of the casing are the elastic modulus and Poisson's ratio of the casing;

[0015] The mechanical parameters of the cement sheath are the elastic modulus and Poisson's ratio of the cement sheath;

[0016] The mechanical parameters of the formation are elastic modulus and Poisson's ratio of the formation;

[0017] The formation confining pressure is the pore pressure of the formation rock.

[0018] According to one aspect of the present invention, the relationship between the compressive strength, tensile strength and elastic modulus of corroded cement paste at different ages and the corrosion time is obtained by fitting different corrosion ages with the test results after testing the uniaxial compressive strength, uniaxial tensile strength and triaxial compressive strength of the corroded cement paste after corrosion curing for 3 days, 7 days, 14 days and 28 days respectively. The expression is:

[0019] Y = at + b;

[0020] Wherein, Y is the compressive strength, tensile strength or elastic modulus of the corroded cement paste; t is the corrosion time; a and b are fitting coefficients.

[0021] According to one aspect of the present invention, the mechanical model of the casing-cement sheath-formation assembly is:

[0022]

[0023] Where σs r is the radial stress at r in the casing; σsθ is the circumferential stress at r in the casing; r isis the inner wall size of the casing; r os is the outer wall size of the casing; psi is the pressure at the inner wall of the casing; pso is the pressure at the outer wall of the casing; r r is the radius of any position r of the casing, cement sheath or formation; σc r is the radial stress at r in the cement sheath; σcθ is the circumferential stress at r in the cement sheath; r ic is the inner wall size of cement ring; r oc is the size of the outer wall of the cement sheath; pc i is the pressure at the inner wall of the cement sheath; pco is the pressure at the outer wall of the cement sheath; σf r is the radial stress at r in the formation; σfθ is the circumferential stress at r in the formation; r if is the size of the inner wall of the formation; r of is the size of the outer wall of the formation; pf i is the pressure at the inner wall of the formation; pf o is the pressure at the outer wall of the formation.

[0024] According to one aspect of the present invention, the relationship between the elastic modulus of cement stone corroded at different ages and the corrosion time is substituted into the mechanical model of the casing-cement sheath-formation combination, and the stress distribution of the corroded cement sheath changing with the corrosion time during the stratified gas injection process is analyzed and obtained, including:

[0025] When solving the mechanical model of the casing-cement sheath-stratum combination, displacement continuity conditions and stress continuity conditions need to be introduced;

[0026] The displacement continuity condition expression is:

[0027] In the formula, is the displacement of the outer wall of the casing, is the displacement of the inner wall of the cement sheath, is the displacement of the outer wall of the cement sheath, is the displacement at the inner wall of the formation;

[0028] The stress continuity condition expression is:

[0029] The casing-cement sheath-formation combination mechanical model solves the contact pressure between the inner wall and the outer wall of the cement sheath. The expression of the contact pressure between the inner wall and the outer wall of the cement sheath after the solution is as follows:

[0030]

[0031] in,

[0032]

[0033] In the formula, E s is the elastic modulus of the casing; E c is the elastic modulus of cement sheath; E f is the formation elastic modulus; vs is the casing Poisson's ratio; v c is the Poisson's ratio of cement sheath; v f is the formation Poisson’s ratio;

[0034] The relationship between the elastic modulus of cement stone corroded at different ages and the corrosion time is substituted into the mechanical model of casing-cement sheath-formation combination to replace the elastic modulus of cement sheath E. c , the stress distribution of the corroded cement sheath changing with corrosion time during the stratified gas injection process is obtained;

[0035] The stress distribution of the corroded cement ring includes the radial stress distribution of the corroded cement ring and the circumferential stress distribution of the corroded cement ring. The stress distribution of the corroded cement ring changes with the corrosion time.

[0036] According to one aspect of the present invention, the comparison of the corrosion cement sheath stress varying with the corrosion time with the compressive strength and tensile strength corresponding to the corrosion time, analyzing the corrosion cement sheath sealing failure form according to the comparison result, and determining the sealing capacity of the corrosion cement sheath of the stratified gas injection well includes:

[0037] When the radial stress of the corroded cement sheath is tensile stress and the tensile stress exceeds the tensile strength of the corroded cement sheath, the corroded cement sheath will suffer radial tensile failure.

[0038] When the radial stress of the corroded cement sheath is compressive stress and the compressive stress exceeds the compressive strength of the corroded cement sheath, the corroded cement sheath will suffer radial compression failure.

[0039] When the circumferential stress of the corroded cement sheath is tensile stress and the tensile stress exceeds the tensile strength of the corroded cement sheath, the corroded cement sheath will suffer circumferential tensile failure.

[0040] When the circumferential stress of the corroded cement sheath is compressive stress and the compressive stress exceeds the compressive strength of the corroded cement sheath, the corroded cement sheath undergoes circumferential compression failure.

[0041] When the corroded cement sheath suffers radial tensile failure, radial compression failure, circumferential tensile failure or circumferential compression failure, the sealing ability of the corroded cement sheath in the stratified gas injection well fails.

[0042] To achieve the above object, the present invention also provides a system for determining the sealing ability of corroded cement sheath in a stratified gas injection well, comprising:

[0043] A wellbore parameter determination module, which determines the wellbore parameters of the target stratified gas injection well;

[0044] The relationship determination module conducts CO2 corrosion maintenance of cement paste, tests and analyzes the relationship between the compressive strength, tensile strength and elastic modulus of cement paste corroded at different ages and the corrosion time;

[0045] A stress distribution determination module is used to establish a casing-cement sheath-formation combination mechanical model based on the wellbore parameters of the target stratified gas injection well, substitute the relationship between the elastic modulus and corrosion time of corroded cement stone of different ages into the casing-cement sheath-formation combination mechanical model, and analyze and obtain the stress distribution of the corroded cement sheath that changes with the corrosion time during the stratified gas injection process;

[0046] The corrosion cement ring sealing capacity determination module compares the corrosion cement ring stress that changes with corrosion time with the compressive strength and tensile strength of the corresponding corrosion time, analyzes the corrosion cement ring sealing failure form based on the comparison results, and determines the corrosion cement ring sealing capacity of the stratified gas injection well.

[0047] To achieve the above objectives, the present invention also provides an electronic device, including a processor, a memory, and a computer program stored in the memory and executable on the processor, wherein the computer program, when executed by the processor, implements the method for determining the sealing capability of corroded cement ring of a stratified gas injection well as described above.

[0048] To achieve the above objectives, the present invention also provides a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the method for determining the sealing capacity of corroded cement sheath in a stratified gas injection well as described above.

[0049] According to the scheme of the present invention, the present invention takes into account the corrosion effect of CO2 on the cementing cement ring during the gas injection process of the stratified gas injection well, as well as the degradation law of the compressive strength, tensile strength and elastic modulus of the corroded cement ring, realizes the dynamic analysis of the sealing ability of the corroded cement ring, and quantifies the sealing failure form and sealing failure time of the corroded cement ring.

[0050] The method for determining the sealing ability of corroded cement ring in stratified gas injection wells provided by the present invention can make up for the deficiency that current research can only qualitatively evaluate the corrosion resistance of cement stone but cannot quantitatively evaluate the sealing ability of corroded cement ring in underground wells, and realize real-time analysis of the sealing ability of corroded cement ring in stratified gas injection process. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 A flow chart schematically showing a method for determining the sealing capability of a corroded cement sheath in a stratified gas injection well according to an embodiment of the present invention;

[0052] Figure 2 This is a schematic diagram of the relationship between corrosion time and compressive strength of Example 1 of the present invention;

[0053] Figure 3 This is a schematic diagram of the relationship between corrosion time and tensile strength of Example 1 of the present invention;

[0054] Figure 4This is a schematic diagram of the relationship between the corrosion time and the elastic modulus of Example 1 of the present invention;

[0055] Figure 5 and Figure 6 This is a schematic diagram of cement sheath stress distribution that changes with corrosion time in Example 1 of the present invention. DETAILED DESCRIPTION

[0056] The present invention will now be discussed with reference to exemplary embodiments. It should be understood that the embodiments discussed are only to enable those skilled in the art to better understand and thus implement the present invention, rather than implying any limitation on the scope of the present invention.

[0057] As used herein, the term “including” and variations thereof are to be interpreted as open-ended terms meaning “including, but not limited to.” The term “based on” is to be interpreted as “based, at least in part, on.” The terms “one embodiment” and “an embodiment” are to be interpreted as “at least one embodiment.”

[0058] Figure 1 The flowchart schematically shows a method for determining the sealing capability of corroded cement sheath in a stratified gas injection well according to an embodiment of the present invention. Figure 1 As shown, in this embodiment, the method for determining the sealing ability of the corroded cement sheath of a stratified gas injection well includes:

[0059] Determine the wellbore parameters of the target stratified gas injection well;

[0060] Carry out CO2 corrosion maintenance of cement paste, test and analyze the relationship between the compressive strength, tensile strength and elastic modulus of cement paste corroded at different ages and the corrosion time;

[0061] Based on the wellbore parameters of the target stratified gas injection well, a mechanical model of the casing-cement sheath-formation combination is established. The relationship between the elastic modulus of corroded cement stone of different ages and the corrosion time is substituted into the mechanical model of the casing-cement sheath-formation combination, and the stress distribution of the corroded cement sheath changing with the corrosion time during the stratified gas injection process is analyzed.

[0062] The stress of the corroded cement sheath that changes with corrosion time is compared with the compressive strength and tensile strength at the corresponding corrosion time. The failure form of the corroded cement sheath seal is analyzed based on the comparison results, and the sealing capacity of the corroded cement sheath in the stratified gas injection well is determined.

[0063] Among them, the cement ring is composed of cement stone, that is, annular cement stone.

[0064] According to one embodiment of the present invention, the target stratified gas injection wellbore parameters include:

[0065] The bottom hole temperature of the target stratified gas injection well, the wellbore structural parameters, the mechanical parameters of the casing, the mechanical parameters of the cement sheath, the mechanical parameters of the formation, the formation confining pressure and the stratified gas injection pressure;

[0066] Wellbore structural parameters are the dimensions of casing, cement sheath and inner wall of formation;

[0067] The mechanical parameters of the casing are the elastic modulus and Poisson's ratio of the casing;

[0068] The mechanical parameters of cement sheath are elastic modulus and Poisson's ratio of cement sheath;

[0069] The mechanical parameters of the formation are the elastic modulus and Poisson's ratio of the formation;

[0070] The confining pressure of the formation is the pore pressure of the formation rock.

[0071] Among other things, the elastic modulus can be a measure of a solid's stiffness or resistance to elastic deformation under load.

[0072] Further, according to an embodiment of the present invention, the relationship between the compressive strength, tensile strength and elastic modulus of corroded cement stone at different ages and the corrosion time is obtained by fitting different corrosion ages and the test results after testing the uniaxial compressive strength, uniaxial tensile strength and triaxial compressive strength of the corroded cement stone after corrosion curing for 3 days, 7 days, 14 days and 28 days respectively. The expression is:

[0073] Y = at + b;

[0074] Wherein, Y is the compressive strength, tensile strength or elastic modulus of the corroded cement paste, in MPa; t is the corrosion time, in days (d); a and b are fitting coefficients.

[0075] In this embodiment, the CO2 corrosion curing conditions of cement paste need to be determined according to the CO2 concentration injected into the target stratified gas injection well, the CO2 dry gas / wet gas type, and the bottom hole temperature of the target stratified gas injection well.

[0076] The corroded cement pastes of different ages are generally cured under CO2 corrosion curing conditions for 3, 7, 14 and 28 days.

[0077] Corroded cement paste of each age needs to be tested for uniaxial compressive strength, uniaxial tensile strength and triaxial compressive strength.

[0078] The purpose of the uniaxial compressive strength test is to test the compressive strength of corroded cement paste.

[0079] The purpose of the uniaxial tensile strength test is to test the tensile strength of corroded cement paste.

[0080] The purpose of the triaxial compressive strength test is to obtain the stress-strain curve of the corroded cement paste and obtain the elastic modulus of the cement paste.

[0081] Further, according to one embodiment of the present invention, the mechanical model of the casing-cement sheath-formation assembly is:

[0082]

[0083] Where, σs r is the radial stress at r in the casing, in MPa; σsθ is the circumferential stress at r in the casing, in MPa; r is is the inner wall size of the casing, in mm; r os is the outer wall size of the casing, in mm; psi is the pressure at the inner wall of the casing, in MPa; pso is the pressure at the outer wall of the casing, in MPa; r r is the radius of any position r of the casing, cement sheath or formation, in mm; σc r is the radial stress at r in the cement sheath, in MPa; σcθ is the circumferential stress at r in the cement sheath, in MPa; r ic is the inner wall size of cement ring, in mm; r oc is the size of the outer wall of the cement sheath, in mm; pc i is the pressure at the inner wall of the cement sheath, in MPa; pc o is the pressure at the outer wall of the cement sheath, in MPa; σf r is the radial stress at r in the formation, in MPa; σfθ is the circumferential stress at r in the formation, in MPa; r if is the size of the inner wall of the formation, in mm; r of is the size of the outer wall of the formation, in mm; pfi is the pressure at the inner wall of the formation, in MPa; pfo is the pressure at the outer wall of the formation, in MPa.

[0084] Further, according to an embodiment of the present invention, the relationship between the elastic modulus of corroded cement stone at different ages and the corrosion time is substituted into the above-mentioned casing-cement sheath-formation combination mechanical model, and the stress distribution of the corroded cement sheath changing with the corrosion time during the stratified gas injection process is analyzed and obtained, including:

[0085] When solving the mechanical model of casing-cement sheath-stratum combination, it is necessary to introduce displacement continuity conditions and stress continuity conditions;

[0086] The displacement continuity condition expression is:

[0087] In the formula, is the displacement of the outer wall of the casing, is the displacement of the inner wall of the cement sheath, is the displacement of the outer wall of the cement sheath, is the displacement at the inner wall of the formation; that is, the displacement at the outer wall of the casing is equal to the displacement at the inner wall of the cement sheath, and the displacement at the outer wall of the cement sheath is equal to the displacement at the inner wall of the formation;

[0088] The stress continuity condition expression is: That is, the radial stress at the outer wall of the casing is equal to the radial stress at the inner wall of the cement sheath, and the radial stress at the outer wall of the cement sheath is equal to the radial stress at the inner wall of the formation;

[0089] The casing-cement sheath-formation combination mechanical model solves the contact pressure between the inner and outer walls of the cement sheath. The expression of the contact pressure between the inner and outer walls of the cement sheath after the solution is as follows:

[0090]

[0091] in,

[0092]

[0093] In the formula, E s is the elastic modulus of the casing, in MPa; E c is the elastic modulus of cement sheath, in MPa; E f is the formation elastic modulus, in MPa; v s is the casing Poisson's ratio; v c is the Poisson's ratio of cement sheath; v f is the formation Poisson’s ratio;

[0094] The relationship between the elastic modulus of cement stone corroded at different ages and the corrosion time is substituted into the mechanical model of casing-cement sheath-formation combination to replace the elastic modulus of cement sheath E. c , the stress distribution of the corroded cement sheath changing with corrosion time during the stratified gas injection process is obtained;

[0095] The stress distribution of the corroded cement ring includes the radial stress distribution of the corroded cement ring and the circumferential stress distribution of the corroded cement ring, and the stress distribution of the corroded cement ring changes with the corrosion time.

[0096] Further, according to an embodiment of the present invention, the stress of the corroded cement sheath changing with the corrosion time is compared with the compressive strength and tensile strength of the corresponding corrosion time, and the sealing failure form of the corroded cement sheath is analyzed according to the comparison result to determine the sealing capacity of the corroded cement sheath of the stratified gas injection well, including:

[0097] When the radial stress of the corroded cement sheath is tensile stress and the tensile stress exceeds the tensile strength of the corroded cement sheath, the corroded cement sheath will suffer radial tensile failure.

[0098] When the radial stress of the corroded cement sheath is compressive stress and the compressive stress exceeds the compressive strength of the corroded cement sheath, the corroded cement sheath will suffer radial compression failure.

[0099] When the circumferential stress of the corroded cement sheath is tensile stress and the tensile stress exceeds the tensile strength of the corroded cement sheath, the corroded cement sheath will suffer circumferential tensile failure.

[0100] When the circumferential stress of the corroded cement sheath is compressive stress and the compressive stress exceeds the compressive strength of the corroded cement sheath, the corroded cement sheath undergoes circumferential compression failure.

[0101] When the corroded cement sheath suffers radial tensile failure, radial compression failure, circumferential tensile failure or circumferential compression failure, the sealing ability of the corroded cement sheath in the stratified gas injection well fails.

[0102] In this embodiment, the relationship between corrosion time and compressive strength is a relationship in which the compressive strength gradually decreases as corrosion is applied.

[0103] The relationship between corrosion time and tensile strength is that the tensile strength gradually decreases as corrosion is applied.

[0104] The failure mode analysis of corroded cement ring seal is to compare the stress distribution that changes with corrosion time with the tensile strength and compressive strength that change with corrosion time.

[0105] According to the above scheme of the present invention, the present invention takes into account the corrosion effect of CO2 on the cementing cement ring during the gas injection process of the stratified gas injection well, as well as the degradation law of the compressive strength, tensile strength and elastic modulus of the corroded cement ring, realizes the dynamic analysis of the sealing ability of the corroded cement ring, and quantifies the sealing failure form and sealing failure time of the corroded cement ring.

[0106] The method for determining the sealing ability of corroded cement ring in stratified gas injection wells provided by the present invention can make up for the deficiency that current research can only qualitatively evaluate the corrosion resistance of cement stone but cannot quantitatively evaluate the sealing ability of corroded cement ring in underground wells, and realize real-time analysis of the sealing ability of corroded cement ring in stratified gas injection process.

[0107] Furthermore, in order to achieve the above-mentioned purpose, the present invention also provides a system for determining the sealing ability of corroded cement sheath in a stratified gas injection well, comprising:

[0108] A wellbore parameter determination module, which determines the wellbore parameters of the target stratified gas injection well;

[0109] The relationship determination module conducts CO2 corrosion maintenance of cement paste, tests and analyzes the relationship between the compressive strength, tensile strength and elastic modulus of cement paste corroded at different ages and the corrosion time;

[0110] A stress distribution determination module is used to establish a casing-cement sheath-formation combination mechanical model based on the wellbore parameters of the target stratified gas injection well, substitute the relationship between the elastic modulus and corrosion time of corroded cement stone of different ages into the casing-cement sheath-formation combination mechanical model, and analyze and obtain the stress distribution of the corroded cement sheath that changes with the corrosion time during the stratified gas injection process;

[0111] The corrosion cement ring sealing capacity determination module compares the corrosion cement ring stress that changes with corrosion time with the compressive strength and tensile strength of the corresponding corrosion time, analyzes the corrosion cement ring sealing failure form based on the comparison results, and determines the corrosion cement ring sealing capacity of the stratified gas injection well.

[0112] The system for determining the sealing capacity of corroded cement ring of a stratified gas injection well provided by the present invention can implement the above-mentioned method for determining the sealing capacity of corroded cement ring of a stratified gas injection well. The specific steps are as described above and will not be repeated here.

[0113] Furthermore, to achieve the above-mentioned purpose, the present invention also provides an electronic device, including a processor, a memory, and a computer program stored in the memory and executable on the processor, wherein when the computer program is executed by the processor, the method for determining the sealing capacity of the corroded cement ring of a stratified gas injection well as described above is implemented.

[0114] Furthermore, to achieve the above objectives, the present invention also provides a computer-readable storage medium, on which a computer program is stored, and when the computer program is executed by a processor, the method for determining the sealing capacity of corroded cement ring of a stratified gas injection well as described above is implemented.

[0115] Based on the above solution of the present invention, the technical solution of the present invention is described in detail in the following in combination with the accompanying drawings in the form of a specific embodiment.

[0116] Example 1

[0117] The depth of a target stratified gas injection well is 3769m, the vertical depth is 3722m, the casing size is 177.8mm, the drill bit size is 241.3mm, the formation confining pressure is 32MPa, the stratified gas injection pressure is 38MPa, and the bottom hole temperature is 150°C. The elastic moduli of the casing, cement sheath and formation are 210GPa, 6.5GPa, and 30GPa, respectively, and the Poisson's ratios are 0.3, 0.17, and 0.3, respectively.

[0118] The cement paste was cured by CO2 corrosion at 150℃ and 40MPa. After 3, 7, 14 and 28 days of curing, the uniaxial compressive strength, uniaxial tensile strength and triaxial compressive strength of the corroded cement paste were tested. The compressive strength, tensile strength and elastic modulus of the corroded cement paste were obtained. Figure 2-Figure 4 shown.

[0119] Among them, the relationship between the compressive strength, tensile strength and elastic modulus of cement paste corroded at different ages and the corrosion time is:

[0120] Compressive strength = -0.3061 days + 28.004;

[0121] Tensile strength = -0.0283 days + 2.5499;

[0122] Elastic modulus = -0.0499 days + 7.2764;

[0123] Based on the above mechanical model of casing-cement sheath-formation combination, the stress distribution of corroded cement sheath during stratified gas injection is analyzed by taking the relationship between the elastic modulus of corroded cement stone at different ages and corrosion time as an example. Figure 5 and Figure 6 It can be found that the corroded cement sheath has compressive stress in both radial and circumferential directions, which means that the corroded cement sheath will not suffer from radial tensile and circumferential tensile failure, but may only suffer from radial or circumferential compression failure.

[0124] By comparing the stress distribution that changes with corrosion time and the relationship between tensile strength, compressive strength and corrosion time, the time when the corroded cement sheath undergoes radial compression failure and circumferential compression failure is analyzed. The analysis found that the corroded cement sheath undergoes radial compression failure about 81 days later, and reaches the circumferential compression failure condition about 90 days later. Therefore, the sealing failure form of the corroded cement sheath in the target stratified gas injection well is radial compression failure, and the time when radial compression failure is expected to occur is 81 days after stratified gas injection.

[0125] Those skilled in the art will appreciate that the modules and algorithm steps described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention.

[0126] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working processes of the above-described devices and equipment can refer to the corresponding processes in the aforementioned method implementation methods, and will not be repeated here.

[0127] In the embodiments provided in the present application, it should be understood that the disclosed devices and methods can be implemented in other ways. For example, the device embodiments described above are only schematic. For example, the division of the modules is only a logical function division. There may be other division methods in actual implementation, such as multiple modules or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or modules, which can be electrical, mechanical or other forms.

[0128] The modules described as separate components may or may not be physically separated, and the components shown as modules may or may not be physical modules, that is, they may be located in one place or distributed on multiple network modules. Some or all of the modules may be selected according to actual needs to achieve the purpose of the embodiments of the present invention.

[0129] In addition, each functional module in the embodiment of the present invention may be integrated into one processing module, or each module may exist physically separately, or two or more modules may be integrated into one module.

[0130] If the functions are implemented in the form of software function modules and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention can be essentially or partly embodied in the form of a software product that contributes to the prior art. The computer software product is stored in a storage medium and includes several instructions for enabling a computer device (which can be a personal computer, server, or network device, etc.) to perform all or part of the steps of the energy-saving signal sending / receiving method of each embodiment of the present invention. The aforementioned storage medium includes: various media that can store program codes, such as USB flash drives, mobile hard disks, ROM, RAM, magnetic disks, or optical disks.

[0131] The above description is only a preferred embodiment of the present application and an explanation of the technical principles used. Those skilled in the art should understand that the scope of the invention involved in the present application is not limited to the technical solution formed by a specific combination of the above technical features, but should also cover other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the inventive concept. For example, the above features are replaced with the technical features with similar functions disclosed in this application (but not limited to) by each other.

[0132] It should be understood that the size of the serial numbers of each step in the content of the invention and the implementation methods of the present invention does not absolutely mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the implementation methods of the present invention.

Claims

1. A method for determining the sealing capacity of corroded cement sheath in a stratified gas injection well, characterized in that: include: Determine the wellbore parameters of the target stratified gas injection well; Carry out CO2 corrosion maintenance of cement paste, test and analyze the relationship between the compressive strength, tensile strength and elastic modulus of cement paste corroded at different ages and the corrosion time; A casing-cement sheath-formation combination mechanical model is established based on the wellbore parameters of the target stratified gas injection well, and the relationship between the elastic modulus and corrosion time of corroded cement stone at different ages is substituted into the casing-cement sheath-formation combination mechanical model to analyze and obtain the stress distribution of the corroded cement sheath that changes with the corrosion time during the stratified gas injection process; The stress of the corroded cement sheath that changes with corrosion time is compared with the compressive strength and tensile strength at the corresponding corrosion time. The failure form of the corroded cement sheath seal is analyzed based on the comparison results, and the sealing capacity of the corroded cement sheath in the stratified gas injection well is determined.

2. The method for determining the sealing ability of corroded cement sheath in stratified gas injection wells according to claim 1, characterized in that: The target stratified gas injection well body parameters include: The bottom hole temperature of the target stratified gas injection well, the wellbore structural parameters, the mechanical parameters of the casing, the mechanical parameters of the cement sheath, the mechanical parameters of the formation, the formation confining pressure and the stratified gas injection pressure; The wellbore structural parameters are the dimensions of the casing, cement ring and the inner wall of the formation; The mechanical parameters of the casing are the elastic modulus and Poisson's ratio of the casing; The mechanical parameters of the cement sheath are the elastic modulus and Poisson's ratio of the cement sheath; The mechanical parameters of the formation are elastic modulus and Poisson's ratio of the formation; The formation confining pressure is the pore pressure of the formation rock.

3. The method for determining the sealing ability of corroded cement sheath in stratified gas injection wells according to claim 1, characterized in that: The relationship between the compressive strength, tensile strength and elastic modulus of corroded cement paste at different ages and the corrosion time is obtained by fitting different corrosion ages with the test results after testing the uniaxial compressive strength, uniaxial tensile strength and triaxial compressive strength of the corroded cement paste after corrosion curing for 3 days, 7 days, 14 days and 28 days respectively. The expression is: Y = at + b; Wherein, Y is the compressive strength, tensile strength or elastic modulus of the corroded cement paste; t is the corrosion time; a and b are fitting coefficients.

4. The method for determining the sealing ability of corroded cement sheath in stratified gas injection wells according to claim 1, characterized in that: The mechanical model of the casing-cement sheath-formation combination is: Where σs r is the radial stress at r in the casing; σsθ is the circumferential stress at r in the casing; r is is the inner wall size of the casing; r os is the outer wall size of the casing; psi is the pressure at the inner wall of the casing; pso is the pressure at the outer wall of the casing; r r is the radius of any position r of the casing, cement sheath or formation; σc r is the radial stress at r in the cement sheath; σcθ is the circumferential stress at r in the cement sheath; r ic is the inner wall size of cement ring; r oc is the size of the outer wall of the cement sheath; pci is the pressure at the inner wall of the cement sheath; pc o is the pressure at the outer wall of the cement sheath; σf r is the radial stress at r in the formation; σfθ is the circumferential stress at r in the formation; r if is the size of the inner wall of the formation; r of is the size of the outer wall of the formation; pf i is the pressure at the inner wall of the formation; pf o is the pressure at the outer wall of the formation.

5. The method for determining the sealing ability of corroded cement sheath in stratified gas injection wells according to claim 4, characterized in that: The relationship between the elastic modulus of corroded cement stone at different ages and the corrosion time is substituted into the mechanical model of the casing-cement sheath-formation combination to analyze the stress distribution of the corroded cement sheath during the stratified gas injection process as the corrosion time changes, including: When solving the mechanical model of the casing-cement sheath-stratum combination, displacement continuity conditions and stress continuity conditions need to be introduced; The displacement continuity condition expression is: In the formula, is the displacement of the outer wall of the casing, is the displacement of the inner wall of the cement sheath, is the displacement of the outer wall of the cement sheath, is the displacement at the inner wall of the formation; The stress continuity condition expression is: The casing-cement sheath-formation combination mechanical model solves the contact pressure between the inner wall and the outer wall of the cement sheath. The expression of the contact pressure between the inner wall and the outer wall of the cement sheath after the solution is as follows: in, In the formula, E s is the elastic modulus of the casing; E c is the elastic modulus of cement sheath; E f is the formation elastic modulus; v s is the casing Poisson's ratio; v c is the Poisson's ratio of cement sheath; v f is the formation Poisson’s ratio; The relationship between the elastic modulus of cement stone corroded at different ages and the corrosion time is substituted into the mechanical model of casing-cement sheath-formation combination to replace the elastic modulus of cement sheath E. c , the stress distribution of the corroded cement sheath changing with corrosion time during the stratified gas injection process is obtained; The stress distribution of the corroded cement ring includes the radial stress distribution of the corroded cement ring and the circumferential stress distribution of the corroded cement ring. The stress distribution of the corroded cement ring changes with the corrosion time.

6. The method for determining the sealing ability of corroded cement sheath in stratified gas injection wells according to claim 5, characterized in that: The method of comparing the corrosion cement sheath stress varying with the corrosion time with the compressive strength and tensile strength at the corresponding corrosion time, analyzing the corrosion cement sheath sealing failure mode according to the comparison result, and determining the sealing capacity of the corrosion cement sheath of the stratified gas injection well includes: When the radial stress of the corroded cement sheath is tensile stress and the tensile stress exceeds the tensile strength of the corroded cement sheath, the corroded cement sheath will suffer radial tensile failure. When the radial stress of the corroded cement sheath is compressive stress and the compressive stress exceeds the compressive strength of the corroded cement sheath, the corroded cement sheath will suffer radial compression failure. When the circumferential stress of the corroded cement sheath is tensile stress and the tensile stress exceeds the tensile strength of the corroded cement sheath, the corroded cement sheath will suffer circumferential tensile failure. When the circumferential stress of the corroded cement sheath is compressive stress and the compressive stress exceeds the compressive strength of the corroded cement sheath, the corroded cement sheath undergoes circumferential compression failure. When the corroded cement sheath suffers radial tensile failure, radial compression failure, circumferential tensile failure or circumferential compression failure, the sealing ability of the corroded cement sheath in the stratified gas injection well fails.

7. A system for determining the sealing capacity of corroded cement sheath in stratified gas injection wells, characterized in that: include: A wellbore parameter determination module, which determines the wellbore parameters of the target stratified gas injection well; The relationship determination module conducts CO2 corrosion maintenance of cement paste, tests and analyzes the relationship between the compressive strength, tensile strength and elastic modulus of cement paste corroded at different ages and the corrosion time; A stress distribution determination module is used to establish a casing-cement sheath-formation combination mechanical model based on the wellbore parameters of the target stratified gas injection well, substitute the relationship between the elastic modulus and corrosion time of corroded cement stone of different ages into the casing-cement sheath-formation combination mechanical model, and analyze and obtain the stress distribution of the corroded cement sheath that changes with the corrosion time during the stratified gas injection process; The corrosion cement ring sealing capacity determination module compares the corrosion cement ring stress that changes with corrosion time with the compressive strength and tensile strength of the corresponding corrosion time, analyzes the corrosion cement ring sealing failure form based on the comparison results, and determines the corrosion cement ring sealing capacity of the stratified gas injection well.

8. An electronic device, characterized in that The method comprises a processor, a memory and a computer program stored in the memory and executable on the processor, wherein when the computer program is executed by the processor, the method for determining the sealing capability of the corroded cement ring of a stratified gas injection well as described in any one of claims 1 to 6 is implemented.

9. A computer-readable storage medium, characterized in that The computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the method for determining the sealing ability of the corroded cement sheath of a stratified gas injection well according to any one of claims 1 to 6 is implemented.

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