Cement sheath damage degree quantitative evaluation method under alternating load and storage medium
Through finite element analysis combining indoor tests and on-site explanations in high-temperature and high-pressure wells, the problem of inaccurate cement environmental assessment in the existing technology is solved, and scientific quantitative evaluation of the degree of cement ring damage is achieved, ensuring the safe and efficient production of the well.
Patent Information
- Application Number
- CN202310771011.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-06-28
- Publication Date
- 2024-12-31
AI Technical Summary
The prior art methods for evaluating the degree of plastic failure of cement rings under alternating loads in high-temperature and high-pressure wells have problems such as high cost, large differences in experiments and actual conditions, simplified numerical simulation and no consideration of the impact of high temperature, resulting in inaccurate evaluation results.
The mechanical parameters of the cement ring are obtained through uniaxial and triaxial compression tests at different indoor temperatures, combined with the on-site cementing quality interpretation results, a finite element analysis model of the plane strain of the formation-casing-cement ring is established, and numerical simulation is performed to obtain the cement ring. The plastic strain relationship curve of the inner wall was quantitatively evaluated to the degree of cement ring damage, and the plastic integral evaluation factor was used to evaluate the degree of damage.
It has achieved scientific and accurate evaluation of the degree of cement ring damage in high-temperature and high-pressure wells, provided safety production advice, and avoided the economic and social harm caused by cement ring failure.
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Figure CN119227437A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of oil and gas well safety evaluation, and in particular to a method for quantitatively evaluating the degree of cement sheath damage under alternating loads and a storage medium. Background Art
[0002] Cement sheath is one of the main materials that make up the consolidation body. It plays the role of connecting the casing and the formation. It plays the role of bearing pressure and resisting deformation when the internal pressure of the casing and the external pressure of the formation increase. Due to the nature of the cement sheath itself, the cement sheath itself is the most vulnerable to damage in the consolidation body. At present, as oil and gas production gradually moves towards deep and ultra-deep layers, the downhole pressure, temperature and production have increased significantly. The wellbore structure is complex and the cementing construction is difficult. Under extreme alternating pressure conditions such as perforating, plugging, withdrawal, fracturing, pump stop, well shut-in, and trial production, the plastic failure of the cement sheath of the production casing will occur, affecting the integrity of the cement seal, and ultimately causing annular pressure and failure of the well integrity. At present, there are few studies on the evaluation of the degree of plastic failure of cement sheath in high-temperature and high-pressure wells under alternating pressure, and most of the results obtained are based on qualitative and one-sided analysis. It is urgent to study the plastic failure law of cement sheath under alternating loads with different cementing qualities, and quantitatively evaluate its integrity and strength safety. This paper provides a scientific and reasonable comprehensive evaluation method for the plastic failure degree of cement sheath in high temperature and high pressure wells, which can avoid economic losses and social harm caused by cement sheath failure.
[0003] A cement sheath integrity evaluation method is disclosed in Chinese patent application document CN 110411679 A, comprising: obtaining gas storage well parameters and cement sheath parameters of a cement sheath to be tested, wherein the gas storage well parameters are used to indicate the alternating load of the stress environment at the bottom of the gas storage well during the gas injection and production process; applying an equivalent alternating load corresponding to the stress environment at the bottom of the gas storage well to the cement sheath based on a load equivalent model, the cement sheath parameters and the gas storage well parameters; testing the time corresponding to the sealing failure of the cement sheath under the action of the equivalent alternating load, and evaluating the life of the cement sheath under the stress cycle at the bottom of the gas storage well based on the measured time. The equivalent alternating load is applied periodically, and the cement ring parameters include the maximum deformation rate of the cement ring, wherein determining the time corresponding to the sealing failure of the cement ring under the equivalent alternating load and evaluating the life of the cement ring under stress cycling in the gas storage well based on the determined time includes: determining the load operation cycle in which the equivalent alternating load is applied based on the maximum deformation rate of the cement ring; counting the number of load operation cycles corresponding to the sealing failure of the cement ring under the equivalent alternating load according to the load operation cycles in which the equivalent alternating load is applied; and determining the threshold number of times the cement ring implements safe gas injection and production in the gas storage well according to the counted number of load operation cycles.
[0004] The prior art has at least the following deficiencies:
[0005] 1. The existing cement sheath damage evaluation usually adopts the similarity criterion method to carry out physical model tests close to the actual situation, which is costly and has certain differences from the actual situation on site because most of the experiments are destructive tests.
[0006] 2. The existing numerical analytical solution research has made a lot of simplifications in theoretical research and cannot reflect the actual stress conditions of cement sheath casing. In addition, the existing numerical simulation analysis method sets the material model of cement stone and other materials to a linear elastic mode and does not consider the influence of high temperature. It cannot match the actual field cementing interpretation data and cannot simulate the degree of damage to the formation cement sheath under actual alternating loads. Summary of the invention
[0007] In order to solve the problems existing in the prior art, the present invention provides a method for quantitatively evaluating the degree of cement sheath damage under alternating loads, comprising the following steps: obtaining the mechanical parameters of cement sheath at different temperatures when the cement bonding quality is excellent in the laboratory according to uniaxial and triaxial compression tests at different temperatures in the room and stress-strain tests under cyclic loads; combining the mechanical parameters of cement sheath in the laboratory, according to the cementing quality interpretation results of the on-site after-casing imaging instrument, and according to the preset quality grading system, quantitatively assigning the mechanical parameters of the cement sheath cementing quality of the entire well section; establishing a formation-casing-cement sheath plane strain finite element analysis model according to the in-situ stress parameters and the size models of different parts under different wellbore structures under different working conditions, performing numerical simulation, and obtaining the variation relationship curve of the plastic strain of the inner wall of the cement sheath along the circumference of the inner wall and the radial path of the cement sheath under different cement sheath bonding strengths in the entire wellbore; obtaining the plastic failure area of the cement sheath according to the variation relationship of the plastic strain of the inner wall of the cement sheath along the circumference of the inner wall and the radial path of the cement sheath under the same cement sheath bonding strength, and evaluating the degree of cement sheath damage under alternating loads according to the area of the plastic failure area of the cement sheath. The present invention can directly obtain the variation relationship of the plastic strain of the inner wall of the cement sheath along the circumferential direction of the inner wall and the radial path of the cement sheath under different cement sheath bonding strengths in the whole wellbore under alternating loads, which is closer to the actual working conditions, and the prediction results are scientific and accurate; the damage degree of the cement sheath is accurately evaluated, and suggestions on whether safe production is possible under different oil test and production test conditions are given, thereby ensuring safe and efficient oil test and production test in high-temperature and high-pressure wells, which is of great significance for avoiding economic losses and social harm caused by cement sheath failure, and has broad application prospects.
[0008] The present invention provides a method for quantitatively evaluating the degree of cement sheath damage under alternating loads, comprising the following steps:
[0009] The mechanical parameters of cement sheath at different temperatures when the cement bonding quality is good are obtained according to the uniaxial and triaxial compression tests at different temperatures in the room and the stress-strain tests under cyclic loads;
[0010] Combined with the mechanical parameters of the cement sheath in the laboratory, according to the cementing quality interpretation results of the on-site after-casing imaging instrument, the mechanical parameters of the cement sheath cementing quality of the entire well section are quantitatively assigned according to the preset quality grading system;
[0011] According to the ground stress parameters and the size models of different parts under different working conditions and different wellbore structures, a finite element analysis model of formation-casing-cement ring plane strain is established, and numerical simulation is performed to obtain the variation relationship curve of the plastic strain of the cement ring inner wall along the inner wall circumference and the radial path of the cement ring under different cement ring bonding strengths in the whole wellbore;
[0012] According to the variation relationship of the plastic strain of the inner wall of the cement sheath along the circumferential direction of the inner wall and the radial path of the cement sheath under the same cement sheath bonding strength, the plastic failure area of the cement sheath is obtained, and the degree of cement sheath damage under alternating load is evaluated according to the area of the plastic failure area of the cement sheath.
[0013] Preferably, the numerical simulation is specifically a numerical simulation of the mechanical strength of the cement sheath and the integrity of the cement sheath.
[0014] Preferably, the quantitative assignment of mechanical parameters for the cementing quality of the cement ring in the entire well section includes quantitative assignment of material parameters and block formation rock mechanical parameters, wherein the material parameters include calculation of the position formation rock mechanical parameters, position formation depth, elastic modulus of cement stone, Poisson's ratio of cement stone, cohesion of cement, friction angle of cement, elastic modulus of metal casing material and Poisson's ratio of metal casing material under the current working conditions; the block formation rock mechanical parameters include maximum principal stress, minimum principal stress and vertical stress gradient.
[0015] Preferably, the material parameters take into account the influence of high temperature, and are associated with the temperature of the entire well section under different working conditions. According to the temperature profile curves calculated under different working conditions, different material parameters are assigned when calculating the model at different well depths under different working conditions.
[0016] Preferably, the steps for establishing the formation-casing-cement sheath plane strain finite element model are as follows:
[0017] According to the ground stress parameters and the size models of different parts under different wellbore structures under different working conditions, the geometric model of formation-casing-cement sheath is established;
[0018] Selecting a high-order plane strain unit to divide the finite element unit; the high-order is greater than or equal to 2nd order;
[0019] Contact pairs are established between interfaces by contact mode, and real gap simulation is set. The gap between cement sheath and casing is simulated at some interface contacts, and no gap is set between cement sheath and casing at other interface contacts.
[0020] Preferably, the degree of cement sheath damage under alternating load is evaluated according to the area of the cement sheath plastic damage region, and the following formula is used to determine the plastic integral evaluation factor W, and the degree of cement sheath damage under alternating load is evaluated using the plastic integral evaluation factor:
[0021]
[0022]
[0023] in,
[0024] f(x) is the fitting relationship of the change relationship curve of the plastic strain of the inner wall of the cement ring along the circumferential path of the inner wall of the cement ring under different cement paste bonding strengths;
[0025] x is the circumferential path, 0≤x≤s;
[0026] R is the radius of the inner wall of the cement sheath;
[0027] θ is the maximum plastic failure angle in the circumferential direction;
[0028] s is the maximum plastic path range corresponding to the cement paste bonding strength.
[0029] Preferably, when the mechanical parameters of the cement sheath cementing quality of the entire well section are quantitatively assigned, the actual cement stone parameters are set according to the cement bonding quality grade displayed by the logging curve.
[0030] The cement bonding quality is "excellent", and the actual cement paste parameters are 95% to 100% of the laboratory parameters;
[0031] The cement bonding quality is "good", and the actual cement paste parameters are 80-95% of the laboratory parameters;
[0032] The cement bonding quality is "medium", and the actual cement paste parameters are 60-80% of the laboratory parameters;
[0033] The cement bonding quality is "poor", and the actual cement paste parameters are 50-60% of the laboratory parameters;
[0034] The cement bonding quality is "very poor" and the actual cement stone parameters are 30-50% of the laboratory parameters.
[0035] Preferably, different cement paste parameters are assigned to different layers according to the quality grades of the well logging curves.
[0036] Preferably, when performing numerical simulation, the change relationship curve of the plastic strain of the inner wall of the cement sheath along the circumferential direction of the inner wall and the radial path of the cement sheath under different cement sheath bonding strengths in the entire wellbore is obtained by applying boundary condition constraints and applying internal pressure. The applying boundary condition constraints and applying internal pressure are to impose symmetric constraints on symmetric boundaries; when the stress at the outer boundary is maximum and the ground stress is minimum, the wellbore internal pressure is applied to the inner wall of the wellbore.
[0037] The present invention also provides a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the steps of the above-mentioned method for quantitatively evaluating the degree of cement sheath damage under any alternating load.
[0038] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0039] 1. In the present invention, mechanical parameters such as internal friction angle and cohesion of cement stone under different conditions are obtained through indoor cement sheath mechanical performance experiments under different working conditions. The laboratory cement sheath test results and the on-site IBC cementing quality interpretation results are combined to achieve quantitative assignment of cement sheath in the entire well section according to the "excellent-medium-poor" grading system.
[0040] 2. The present invention determines the damage area according to the change data of the plastic strain of the inner wall of the cement sheath along the circumferential direction of the inner wall and the radial path of the cement sheath, introduces the plastic integral evaluation factor for the first time to quantitatively describe the damage degree of the cement sheath, accurately evaluates the damage degree of the cement sheath, and gives suggestions on whether safe production is possible under different oil test and trial production conditions, thereby ensuring the safe and efficient oil test and trial production of high-temperature and high-pressure wells, which is of great significance for avoiding economic losses and social harm caused by cement sheath failure, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS
[0041] Figure 1 It is a flow chart of a method for quantitatively evaluating the degree of cement sheath damage under alternating loads according to an embodiment of the present invention;
[0042] Figure 2 A schematic diagram of cement sheath thickness AB and inner wall ACD path according to an embodiment of the present invention;
[0043] Figure 3 is a curve showing a change of plastic strain along the circumferential ACD path according to an embodiment of the present invention;
[0044] Figure 4 is the change of plastic strain along the radial AB path of one embodiment of the present invention;
[0045] Figure 5 for Figure 2 The change of plastic strain of cement ring in a certain well along the circumferential ACD path is shown;
[0046] Figure 6 for Figure 2 The change of plastic strain of cement ring in a certain well along radial AB path is shown;
[0047] Figure 7 for Figure 2 The relationship between the plastic integral evaluation factor of the circumferential ACD path and the cement bonding strength is shown;
[0048] Figure 8 for Figure 2 The relationship between the radial AB path plastic integral evaluation factor and cement bond strength is shown. DETAILED DESCRIPTION
[0049] The specific implementation modes of the present invention are described in detail below in conjunction with the accompanying drawings.
[0050] The present invention provides a method for quantitatively evaluating the degree of cement sheath damage under alternating loads, comprising the following steps:
[0051] The mechanical parameters of cement sheath at different temperatures when the cement bonding quality is good are obtained according to the uniaxial and triaxial compression tests at different temperatures in the room and the stress-strain tests under cyclic loads;
[0052] Combined with the mechanical parameters of the cement sheath in the laboratory, according to the cementing quality interpretation results of the on-site after-casing imaging instrument, the mechanical parameters of the cement sheath cementing quality of the entire well section are quantitatively assigned according to the preset quality grading system;
[0053] According to the ground stress parameters and the size models of different parts under different working conditions and different wellbore structures, a finite element analysis model of formation-casing-cement ring plane strain is established, and numerical simulation is performed to obtain the variation relationship curve of the plastic strain of the cement ring inner wall along the inner wall circumference and the radial path of the cement ring under different cement ring bonding strengths in the whole wellbore;
[0054] According to the variation relationship of the plastic strain of the inner wall of the cement sheath along the circumferential direction of the inner wall and the radial path of the cement sheath under the same cement sheath bonding strength, the plastic failure area of the cement sheath is obtained, and the degree of cement sheath damage under alternating load is evaluated according to the area of the plastic failure area of the cement sheath.
[0055] According to a specific embodiment of the present invention, the numerical simulation is specifically a numerical simulation of the mechanical strength of the cement sheath and the integrity of the cement sheath.
[0056] According to a specific embodiment of the present invention, the mechanical parameter quantitative assignment of the cement sheath cementing quality of the entire well section includes quantitative assignment of material parameters and block formation rock mechanical parameters, wherein the material parameters include calculation of the position formation rock mechanical parameters, position formation depth, elastic modulus of cement stone, Poisson's ratio of cement stone, cohesion of cement, friction angle of cement, elastic modulus of metal casing material and Poisson's ratio of metal casing material under current working conditions; the block formation rock mechanical parameters include maximum principal stress, minimum principal stress and vertical stress gradient.
[0057] According to a specific embodiment of the present invention, the material parameters take into account the influence of high temperature, and the material parameters are associated with the temperature of the entire well section under different working conditions. According to the temperature profile curves calculated under different working conditions, different material parameters are assigned when calculating the model at different well depths under different working conditions.
[0058] According to a specific embodiment of the present invention, the steps for establishing the formation-casing-cement sheath plane strain finite element model are as follows:
[0059] According to the ground stress parameters and the size models of different parts under different wellbore structures under different working conditions, the geometric model of formation-casing-cement sheath is established;
[0060] Selecting a high-order plane strain unit to divide the finite element unit; the high-order is greater than or equal to 2nd order;
[0061] Contact pairs are established between interfaces by contact mode, and real gap simulation is set. The gap between cement sheath and casing is simulated at some interface contacts, and no gap is set between cement sheath and casing at other interface contacts.
[0062] According to a specific embodiment of the present invention, the degree of cement sheath damage under alternating load is evaluated according to the area of the cement sheath plastic failure zone, and the plastic integral evaluation factor W is determined by the following formula, and the degree of cement sheath damage under alternating load is evaluated by the plastic integral evaluation factor:
[0063]
[0064]
[0065] in,
[0066] f(x) is the fitting relationship of the change relationship curve of the plastic strain of the inner wall of the cement ring along the circumferential path of the inner wall of the cement ring under different cement paste bonding strengths;
[0067] x is the circumferential path, 0≤x≤s;
[0068] R is the radius of the inner wall of the cement sheath;
[0069] θ is the maximum plastic failure angle in the circumferential direction;
[0070] s is the maximum plastic path range corresponding to the cement paste bonding strength.
[0071] According to a specific implementation scheme of the present invention, when the mechanical parameters of the cement sheath cementing quality of the entire well section are quantitatively assigned, the actual cement stone parameters are set according to the cement bonding quality grade displayed by the logging curve.
[0072] The cement bonding quality is "excellent", and the actual cement paste parameters are 95% to 100% of the laboratory parameters;
[0073] The cement bonding quality is "good", and the actual cement paste parameters are 80-95% of the laboratory parameters;
[0074] The cement bonding quality is "medium", and the actual cement paste parameters are 60-80% of the laboratory parameters;
[0075] The cement bonding quality is "poor", and the actual cement paste parameters are 50-60% of the laboratory parameters;
[0076] The cement bonding quality is "very poor" and the actual cement stone parameters are 30-50% of the laboratory parameters.
[0077] According to a specific embodiment of the present invention, different cement paste parameters are assigned to different layers according to the quality grades of the well logging curves.
[0078] According to a specific embodiment of the present invention, when performing numerical simulation, the change relationship curve of the plastic strain of the inner wall of the cement ring along the circumferential direction of the inner wall and the radial path of the cement ring under different cement ring bonding strengths in the whole wellbore is obtained by applying boundary condition constraints and applying internal pressure. The applying boundary condition constraints and applying internal pressure are to impose symmetric constraints on the symmetric boundaries; when the stress at the outer boundary is maximum and the ground stress is minimum, the wellbore internal pressure is applied to the inner wall of the wellbore.
[0079] The present invention also provides a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the steps of the above-mentioned method for quantitatively evaluating the degree of cement sheath damage under any alternating load.
[0080] Example 1
[0081] According to a specific embodiment of the present invention, the quantitative evaluation method of the cement sheath damage degree under alternating load of the present invention is described in detail below.
[0082] The present invention provides a method for quantitatively evaluating the degree of cement sheath damage under alternating loads, comprising the following steps:
[0083] Based on the uniaxial and triaxial compression tests at different temperatures in the room and the stress-strain tests under cyclic load, the mechanical parameters of cement stone such as internal friction angle and cohesion at different temperatures under the condition of excellent cementing quality in the laboratory are obtained.
[0084] Combined with the mechanical parameters of cement sheath in the laboratory and according to the on-site IBC cementing quality interpretation results, the mechanical parameters of cement sheath cementing quality in the entire well section are quantitatively assigned according to the preset quality grading system.
[0085] Reference table for numerical simulation classification of cement bonding strength and bonding quality of a certain well
[0086]
[0087] According to the ground stress parameters, different working conditions and the size models of different parts under different wellbore structures, the geometric model of formation-casing-cement sheath is established.
[0088] According to the indoor experimental test data of cement sheath and combined with the actual IBC cementing quality interpretation results, the values of material parameters such as cohesion and internal friction angle are assigned to the cement sheath part of the model.
[0089] The geometric model of formation-casing-cement sheath is meshed, and high-order plane strain units are selected to finally obtain the formation-casing-cement sheath finite element unit. The different cement sheath bonding strengths C1~C 11 The relationship between the plastic strain of the cement sheath inner wall along the circumferential ACD and radial AB path is as follows: Figure 3 and Figure 4 as shown.
[0090] The contact method is used between interfaces to establish contact pairs, and gaps can be set to simulate the gap between cement sheath and casing. Some parts can also be set to have no gaps, which is more in line with the actual situation.
[0091] According to the alternating loads and formation stress of the actual on-site oil testing operation, corresponding periodic loads are applied to the inner and outer walls of the model;
[0092] Select the calculation method and submit the finite element calculation.
[0093] Extract and obtain the variation relationship curve of the plastic strain of the inner wall of the cement sheath along the circumferential path of the inner wall under different cement sheath bonding strengths in the whole wellbore; Figure 5 shown.
[0094] The plastic stress-strain cloud diagram of the cement sheath is extracted, and the damage area is determined according to the change data of the plastic strain of the inner wall of the cement sheath along the circumferential path of the inner wall. The area of the plastic damage area of the cement sheath is used to evaluate the degree of cement sheath damage under alternating loads, such as Figure 5 and 6 shown.
[0095] Among them, the plastic integral evaluation factor W is proposed, and the plastic integral evaluation factor is used to evaluate the degree of cement sheath damage under alternating loads:
[0096]
[0097]
[0098] in,
[0099] f(x) is the fitting relationship of the change relationship curve of the cement ring plastic strain along the circumferential path of the cement ring inner wall under different cement ring bonding strengths;
[0100] x is the circumferential path, 0≤x≤s;
[0101] R is the radius of the inner wall of the cement sheath;
[0102] θ is the maximum plastic failure angle in the circumferential direction;
[0103] s is the maximum plastic path range corresponding to the cement paste bonding strength.
[0104] Among them, f(x) can also represent the fitting relationship of the change relationship curve of the cement ring plastic strain along the radial path of the inner wall of the cement ring under different cement ring bonding strengths; x is the radial path (i.e., the path in the thickness direction of the cement ring); the radial and circumferential directions can also be considered at the same time.
[0105] from Figure 7 It can be seen that under the same extreme fracturing conditions, the cement bonding quality is "good" or above, that is, the bonding strength is (8-12) MPa, and its plasticity integral evaluation factor is (1.55-5.34)×10 -2 (mm.E), where E represents plastic strain and is a unitless quantity. When the cement bonding quality is "medium", that is, the bonding strength is (6-8) MPa, its plasticity integral evaluation factor is (5.34-14.08)×10 -2 (mm.E). When the cement bonding quality is “poor”, that is, the bonding strength is (4-6) MPa, the plasticity integral evaluation factor is (14.08-29.11)×10 -2 (mm.E), when the cement bonding quality is "extremely poor", that is, the bonding strength is (1-4) MPa, its plasticity integral evaluation factor is (29.11-53.04)×10 -2 (mm.E).
[0106] from Figure 8 It can be seen that under the same extreme fracturing conditions, the cement bonding quality is "good" or above, that is, the bonding strength is (8-12) MPa, and its plasticity integral evaluation factor is (1.43-6.92)×10 -3(mm.E), where E represents plastic strain and is a unitless quantity. When the cement bonding quality is "medium", that is, the bonding strength is (6-8) MPa, its plasticity integral evaluation factor is (6.92-20.74)×10 -3 (mm.E). When the cement bonding quality is “poor”, that is, the bonding strength is (4-6) MPa, the plasticity integral evaluation factor is (30.74-44.73)×10 -3 (mm.E), when the cement bonding quality is "extremely poor", that is, the bonding strength is (1-4) MPa, its plasticity integral evaluation factor is (44.73-106.44)×10 -3 (mm.E).
[0107] in,
[0108] When the mechanical parameters of the cementing quality of the cement sheath in the entire well section are quantitatively assigned, the cement stone parameters are set according to the cementing quality displayed by the logging curve:
[0109] The cement bonding quality is "excellent", and the actual cement paste parameters are 95% to 100% of the laboratory parameters;
[0110] The cement bonding quality is "good", and the actual cement paste parameters are 80-95% of the laboratory parameters;
[0111] The cement bonding quality is "medium", and the actual cement paste parameters are 60-80% of the laboratory parameters;
[0112] The cement bonding quality is "poor", and the actual cement paste parameters are 50-60% of the laboratory parameters;
[0113] The cement bonding quality is "very poor" and the actual cement stone parameters are 30-50% of the laboratory parameters.
[0114] The parameter assignment of cement stone is mainly based on the excellent situation shown by the actual on-site IBC cementing interpretation results, and different cement stone parameters are assigned in different layers.
[0115] In addition, the material parameters take into account the influence of high temperature, and the material parameters are related to the temperature of the entire well section under different working conditions. According to the temperature profile curves calculated under different working conditions, different material parameters are assigned when calculating the model at different well depths under different working conditions, which better reflects the actual situation.
[0116] 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 are included in the protection scope of the present invention.
Claims
1. A quantitative evaluation method for the degree of cement sheath damage under alternating loads, characterized in that: The steps include: The mechanical parameters of cement sheath at different temperatures when the cement bonding quality is good are obtained according to the uniaxial and triaxial compression tests at different temperatures in the room and the stress-strain tests under cyclic loads; Combined with the mechanical parameters of the cement sheath in the laboratory, according to the cementing quality interpretation results of the on-site after-casing imaging instrument, the mechanical parameters of the cement sheath cementing quality of the entire well section are quantitatively assigned according to the preset quality grading system; According to the ground stress parameters and the size models of different parts under different working conditions and different wellbore structures, a finite element analysis model of formation-casing-cement ring plane strain is established, and numerical simulation is performed to obtain the variation relationship curve of the plastic strain of the cement ring inner wall along the circumferential direction of the inner wall and the radial path of the cement ring under different cement ring bonding strengths in the whole wellbore; According to the variation relationship of the plastic strain of the inner wall of the cement sheath along the circumferential direction of the inner wall and the radial path of the cement sheath under the same cement sheath bonding strength, the plastic failure area of the cement sheath is obtained, and the degree of cement sheath damage under alternating load is evaluated according to the area of the plastic failure area of the cement sheath.
2. The method for quantitatively evaluating the degree of cement sheath damage under alternating load according to claim 1, characterized in that: The numerical simulation is specifically the numerical simulation of the mechanical strength of the cement sheath and the integrity of the cement sheath.
3. The method for quantitatively evaluating the degree of cement sheath damage under alternating load according to claim 2, characterized in that: The quantitative assignment of mechanical parameters to the cementing quality of the cement sheath in the entire well section includes the quantitative assignment of material parameters and block formation rock mechanical parameters, wherein the material parameters include the calculation of the position formation rock mechanical parameters, position formation depth, the elastic modulus of cement stone, the Poisson's ratio of cement stone, the cohesion of cement, the friction angle of cement, the elastic modulus of the metal casing material and the Poisson's ratio of the metal casing material under the current working conditions; the block formation rock mechanical parameters include the maximum principal stress, the minimum principal stress and the vertical stress gradient.
4. The method for quantitatively evaluating the degree of cement sheath damage under alternating load according to claim 3 is characterized in that: The material parameters take into account the influence of high temperature, and are associated with the temperature of the entire well section under different working conditions. According to the temperature profile curves calculated under different working conditions, different material parameters are assigned when calculating the model at different well depths under different working conditions.
5. The method for quantitatively evaluating the degree of cement sheath damage under alternating load according to claim 2, characterized in that: The steps for establishing the plane strain finite element model of formation-casing-cement sheath are as follows: According to the ground stress parameters and the size models of different parts under different wellbore structures under different working conditions, the geometric model of formation-casing-cement sheath is established; Selecting a high-order plane strain unit to divide the finite element unit; the high-order is greater than or equal to 2nd order; Contact pairs are established between interfaces by contact mode, and real gap simulation is set. The gap between cement sheath and casing is simulated at some interface contacts, and no gap is set between cement sheath and casing at other interface contacts.
6. The method for quantitatively evaluating the degree of cement sheath damage under alternating load according to claim 1, characterized in that: The degree of cement sheath damage under alternating loads is evaluated based on the area of the cement sheath plastic failure zone. Specifically, the plastic integral evaluation factor W is determined using the following formula, and the degree of cement sheath damage under alternating loads is evaluated using the plastic integral evaluation factor: in, f(x) is the fitting relationship of the change relationship curve of the plastic strain of the inner wall of the cement ring along the circumferential path of the inner wall of the cement ring under different cement paste bonding strengths; x is the circumferential path, 0≤x≤s; R is the radius of the inner wall of the cement sheath; θ is the maximum plastic failure angle in the circumferential direction; s is the maximum plastic path range corresponding to the cement paste bonding strength.
7. The method for quantitatively evaluating the degree of cement sheath damage under alternating load according to claim 1, characterized in that: When the mechanical parameters of the cement sheath cementing quality of the entire well section are quantitatively assigned, the actual cement stone parameters are set according to the cement bonding quality grade displayed by the logging curve. The cement bonding quality is "excellent", and the actual cement paste parameters are 95% to 100% of the laboratory parameters; The cement bonding quality is "good", and the actual cement paste parameters are 80-95% of the laboratory parameters; The cement bonding quality is "medium", and the actual cement paste parameters are 60-80% of the laboratory parameters; The cement bonding quality is "poor", and the actual cement paste parameters are 50-60% of the laboratory parameters; The cement bonding quality is "very poor" and the actual cement stone parameters are 30-50% of the laboratory parameters.
8. The method for quantitatively evaluating the degree of cement sheath damage under alternating load according to claim 3 or 7, characterized in that: Cement stone parameters are assigned different cement stone parameters in different layers according to the different quality levels of the logging curve.
9. The method for quantitatively evaluating the degree of cement sheath damage under alternating load according to claim 1, characterized in that: When performing numerical simulation, the relationship curve of the change of the plastic strain of the inner wall of the cement sheath along the circumferential direction of the inner wall and the radial path of the cement sheath under different cement sheath bonding strengths in the whole wellbore is obtained by applying boundary condition constraints and internal pressure. The imposition of boundary condition constraints and internal pressure is to impose symmetric constraints on symmetric boundaries; when the maximum stress and minimum ground stress are at the outer boundary, the wellbore internal pressure is applied to the inner wall of the wellbore.
10. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the steps of the method for quantitatively evaluating the degree of cement sheath damage under alternating loads as described in any one of claims 1 to 9 are implemented.