Judgment method for shaft integrity failure dangerous area in gas injection and production stages of gas reservoir type gas storage

Abstract

The invention discloses a method for judging a shaft integrity failure dangerous area in a gas injection and production stage of a gas reservoir type gas storage. According to the method, a stratum-cement sheath-casing geometric model is constructed in finite element simulation software according to design parameters of the gas reservoir type gas storage and geological data of a stratum where the stratum-cement sheath-casing geometric model is located, and the integrity failure process of a shaft in the gas production stage is simulated through the stratum-cement sheath-casing geometric model. The method comprises the following steps: respectively evaluating the integrity failure severity degree of a failed shaft and the integrity failure risk of a non-failed shaft of the gas reservoir based on a shaft integrity failure evaluation standard, and calculating shaft integrity failure danger level judgment indexes corresponding to each depth of the gas reservoir type gas reservoir; based on the dangerous area judgment standard of the integrity failure of the shaft of the gas reservoir type gas storage, the danger level of the integrity failure of the shaft in each area of the shaft in the gas injection and production stage of the gas reservoir type gas storage is comprehensively judged, and shaft integrity failure monitoring of key areas of the gas storage in the later period is facilitated.

Description

Technical Field

[0001] The present invention relates to the technical field of gas storage, and in particular to a method for determining a wellbore integrity failure risk area during the gas injection and production phase of a gas reservoir type gas storage. Background Art

[0002] Although gas reservoir-type underground gas storage is recognized as the best type of gas storage in the world, its complex geological conditions and frequent injection and production operation characteristics easily lead to wellbore integrity failure during the operation of gas reservoir-type underground gas storage, resulting in disasters such as annular pressure. Analysis of the wellbore integrity failure theory during the injection and production phase of gas reservoir-type gas storage shows that the risk of cement shear failure is greater during the injection phase, while the risk of cement shear tensile failure and casing strength failure is smaller. In the gas production phase, the risk of cement shear failure and cement sheath first and second interface bonding failure is greater, while the risk of casing strength failure is smaller.

[0003] In order to determine the dangerous areas prone to wellbore integrity failure during the injection and production of gas reservoir-type gas storages and improve the relevant wellbore integrity management and design standards, it is urgent to establish a method for determining the dangerous areas of wellbore integrity failure during the injection and production stages of gas reservoir-type gas storages. By establishing a severity assessment standard for wellbore integrity failures that have already failed and a risk assessment standard for wellbore integrity failures that have not yet failed, the dangerous areas of wellbore integrity failure can be comprehensively determined. Summary of the invention

[0004] In order to accurately determine the dangerous area of ​​wellbore integrity failure in gas reservoir type gas storage, the present invention proposes a method for determining the dangerous area of ​​wellbore integrity failure during the gas injection and production stage of gas reservoir type gas storage, which achieves accurate determination of the hazard level of wellbore integrity failure and lays a theoretical foundation for the optimization and protection of wellbore integrity of gas reservoir type gas storage.

[0005] The present invention specifically adopts the following technical solutions:

[0006] A method for determining a dangerous area of ​​wellbore integrity failure during the gas injection and production phase of a gas reservoir type gas storage facility specifically comprises the following steps:

[0007] Step 1, constructing a formation-cement sheath-casing geometric model using finite element software according to the design parameters of the gas reservoir type gas storage and the geological data of the formation where the gas reservoir type gas storage is located;

[0008] Step 2, setting the boundary conditions of the formation-cement sheath-casing geometric model, calculating the three-dimensional non-uniform geostress to which the formation-cement sheath-casing geometric model is subjected based on the relationship between the formation depth and the three-dimensional non-uniform geostress, applying the gas production pressure relief pressure to the formation-cement sheath-casing geometric model, setting the bonding strength of the first interface of the cement sheath and the second interface of the cement sheath in the formation-cement sheath-casing geometric model, and determining the wellbore integrity failure judgment criterion;

[0009] Step 3, setting the three-dimensional non-uniform ground stress on the formation-cement sheath-casing geometric model and the cement ring node of the formation-cement sheath-casing geometric model, using the formation-cement sheath-casing geometric model to simulate the gas production stage of the gas reservoir type gas storage, obtaining the mechanical simulation parameters of the formation-cement sheath-casing geometric model, and judging whether the formation-cement sheath-casing geometric model has a wellbore integrity failure based on the wellbore integrity failure judgment;

[0010] Step 4, establishing a wellbore integrity failure assessment standard, and evaluating the severity of wellbore integrity failure of gas reservoir-type gas storage based on the wellbore integrity failure assessment standard, to obtain failure severity assessment results of the gas reservoir-type gas storage during the gas production stage and non-failure risk assessment results of the gas reservoir-type gas storage during the gas production stage;

[0011] Step 5, according to the failure severity assessment results of the gas production stage of the gas reservoir type gas storage and the non-failure risk assessment results of the gas production stage of the gas reservoir type gas storage, calculate the wellbore integrity failure hazard index of each area in the wellbore of the gas reservoir type gas storage, and then determine the hazard level of the wellbore integrity failure area of ​​the gas reservoir type gas storage based on the wellbore integrity failure hazard index value of each area.

[0012] Preferably, in step 1, according to the design parameters of the gas reservoir type gas storage and the geological data of the stratum in which the gas reservoir type gas storage is located, a formation-cement sheath-casing geometric model is constructed using finite element software, and the formation-cement sheath-casing geometric model is swept meshed, and the cohesion contact model is applied to the formation-cement sheath-casing geometric model, so that the master and slave surface meshes of each contact surface in the formation-cement sheath-casing geometric model are aligned with each other and completely overlap.

[0013] Preferably, the design parameters of the gas reservoir type gas storage include the type, outer diameter, thickness, elastic modulus, Poisson's ratio, yield strength of the casing in the vertical well, and the type, outer diameter, thickness, elastic modulus, Poisson's ratio, compressive strength, tensile strength, cohesion, and internal friction coefficient of the cement ring in the vertical well; the geological data of the gas reservoir type gas storage include the type, elastic modulus, Poisson's ratio of the formation and the type, elastic modulus, and Poisson's ratio of the interlayer.

[0014] Preferably, the finite element software is Abaqus.

[0015] Preferably, in step 2, the relationship between the formation depth and the three-dimensional non-uniform ground stress is:

[0016] σ H =a1+a2×h+a3×h 2 +a4×h 3 +a5×h 4 (1)

[0017] σ h =b1+b2×h+b3×h 2 +b4×h 3 +b5×h 4 (2)

[0018] σ v =c1+c2×h+c3×h 2 +c4×h 3 +c5×h 4 (3)

[0019] In the formula, σ H is the maximum horizontal ground stress, in MPa; σ h is the minimum horizontal ground stress, in MPa; σ v is the vertical geostress, in MPa; h is the formation depth, in MPa; a1, a2, a3, a4, a5 are all the maximum horizontal geostress fitting coefficients; b1, b2, b3, b4, b5 are all the minimum horizontal geostress fitting coefficients; c1, c2, c3, c4, c5 are all the vertical geostress fitting coefficients;

[0020] According to the depth of the center of the formation-cement sheath-casing geometric model, the maximum horizontal ground stress, minimum horizontal ground stress and vertical ground stress of the formation-cement sheath-casing geometric model are calculated by using the relationship between the formation depth and the three-dimensional non-uniform ground stress;

[0021] Then, the gas production decompression pressure is applied to the formation-cement sheath-casing geometric model, and the bonding strength of the first cement sheath interface and the second cement sheath interface in the formation-cement sheath-casing geometric model are set to determine the wellbore integrity failure judgment criterion during the gas production stage of the gas reservoir type gas storage.

[0022] Preferably, the wellbore integrity failure judgment criteria include cement sheath shear failure criteria, cement sheath tensile failure criteria, casing integrity failure criteria, and cement sheath first interface and second interface integrity failure criteria;

[0023] in,

[0024] The cement sheath shear failure criterion is:

[0025] The minimum principal stress σ when the Mohr circle is tangent to the failure envelope 3f As the safety critical value, the minimum principal stress σ of the cement sheath min When it is less than the safety critical value, it indicates that the cement sheath has shear failure. The minimum principal stress σ when the Mohr circle is tangent to the failure envelope is 3f The calculation formula is:

[0026]

[0027] In the formula, σ 3f is the minimum principal stress when the Mohr circle is tangent to the failure envelope; σ max is the maximum principal stress; is the internal friction angle; C is the failure coefficient of cement sheath shear failure;

[0028] The tensile failure criterion of the cement sheath is:

[0029] Circumferential stress on cement sheath Not less than the tensile strength of the cement sheath;

[0030] The integrity failure criteria of the first interface and the second interface of the cement sheath are:

[0031] The relationship between the normal pressure of the interface, the first shear stress of the interface, and the second shear stress of the interface satisfies:

[0032]

[0033] In the formula, t n is the normal pressure at the interface; t s is the first shear stress at the interface; t t is the second shear stress at the interface; t n0 is the initial normal pressure of the interface; t s0 is the initial first shear stress of the interface; t t0 is the initial second shear stress of the interface;

[0034] The casing integrity failure criterion is:

[0035] The casing equivalent stress does not exceed the yield strength of the casing, wherein the casing equivalent stress calculation formula is:

[0036]

[0037] In the formula, σ e is the equivalent stress of the casing, in MPa; σ1 is the first principal stress, in MPa; σ2 is the second principal stress, in MPa; σ3 is the third principal stress, in MPa.

[0038] Preferably, the mechanical simulation parameters include the minimum principal stress σ of the cement sheath min , the maximum principal stress of cement sheath σ max , internal friction angle Normal pressure of the first interface of cement sheath, first shear stress of the first interface of cement sheath, second shear stress of the first interface of cement sheath, normal pressure of the second interface of cement sheath, first shear stress of the second interface of cement sheath, second shear stress of the second interface of cement sheath, equivalent stress of casing σ e , the yield strength of the casing σ s , first principal stress σ1, second principal stress σ2, third principal stress σ3.

[0039] Preferably, the wellbore integrity failure assessment process includes assessing the severity of wellbore integrity failures that have already failed and assessing the risk of wellbore integrity failures that have not yet failed, and the wellbore integrity failure assessment criteria include assessment criteria for the severity of wellbore integrity failures that are applicable to wellbore integrity failures that have already failed and assessment criteria for the risk of wellbore integrity failures that are applicable to wellbore integrity failures that have not yet failed.

[0040] Preferably, the failure severity assessment process applicable to the wellbore integrity failure that has failed includes the cement sheath shear failure severity assessment and the cement sheath interface bonding failure severity assessment;

[0041] in,

[0042] The evaluation of cement sheath shear failure severity is based on the number of cement sheath damaged nodes in a unit depth area. By counting the number of shear failure nodes in each area, the evaluation index of cement sheath shear failure severity at any depth is determined, as shown in formula (7):

[0043]

[0044] Where, F1 is the evaluation index of the severity of shear failure of cement sheath; si is the number of cement sheath shear failure nodes; f smax is the maximum number of cement sheath shear failure nodes in the entire area;

[0045] The evaluation of the severity of cement failure at the cement sheath interface is based on the secondary stress criterion, and the evaluation index of the severity of cement failure at the first cement sheath interface and the evaluation index of the severity of cement failure at the second cement sheath interface at any depth are determined as follows:

[0046] F2=f 1CSQUADSCRT (8)

[0047] F3=f 2CSQUADSCRT (9)

[0048] Where, F2 is the evaluation index of the severity of cement failure at the first interface of cement sheath; F3 is the evaluation index of the severity of cement failure at the second interface of cement sheath; 1CSQUADSCRT is the secondary contact stress damage value of the first interface of cement sheath; f 2CSQUADSCRT is the secondary contact stress damage value of the second interface of cement sheath;

[0049] The shear failure severity assessment index F1 of the cement sheath, the bonding failure severity assessment index F2 of the first interface of the cement sheath and the bonding failure severity assessment index F3 of the second interface of the cement sheath are respectively used as the wellbore integrity failure severity assessment index F. Based on the wellbore integrity failure severity assessment index F and combined with the wellbore integrity failure severity assessment standard applicable to wellbore integrity that has failed, the severity of the wellbore integrity failure that has failed is assessed.

[0050] Preferably, the failure severity assessment criteria applicable to wellbore integrity failures that have occurred are:

[0051] When the value of the wellbore integrity failure severity evaluation index F is [0, 25%], the wellbore integrity failure level is determined to be level one, and the wellbore integrity failure severity is light;

[0052] When the value of the wellbore integrity failure severity assessment index F is (25%, 50%], the wellbore integrity failure level is determined to be level 2, and the wellbore integrity failure severity is moderate;

[0053] When the value of the wellbore integrity failure severity evaluation index F is (50%, 75%], the wellbore integrity failure level is determined to be level three, and the wellbore integrity failure severity is relatively serious;

[0054] When the value of the wellbore integrity failure severity assessment index F is (75%, 100%], the wellbore integrity failure level is determined to be level 4, and the wellbore integrity failure severity is very severe.

[0055] Preferably, the wellbore integrity failure risk assessment process applicable to wellbore integrity failures that have not failed first divides the cement sheath into regions according to depth, and then obtains the average stress value in each region of the cement sheath based on the maximum allowable stress index of the material used for the cement sheath, and determines the cement sheath tensile failure risk assessment index or casing strength failure risk index used for wellbore integrity failure risk assessment, as shown in formula (10):

[0056]

[0057] Where, E is the tensile failure risk assessment index or casing strength failure risk index; f tiis the structural stress on the nodes in the cement sheath, in MPa; i is the serial number of the nodes in the cement sheath; n is the number of easily damaged nodes; T is the maximum allowable stress index of the cement sheath structure, in MPa.

[0058] Preferably, the failure risk assessment standard applicable to wellbore integrity that has not failed is:

[0059] When the tensile failure risk assessment index or the casing strength failure risk index is [0, 25%], the wellbore integrity failure risk level is determined to be level one, and the wellbore integrity failure risk is low;

[0060] When the tensile failure risk assessment index or the casing strength failure risk index is (25%, 50%], the wellbore integrity failure risk level is determined to be level 2, and the wellbore integrity failure risk is medium;

[0061] When the tensile failure risk assessment index or the casing strength failure risk index is (50%, 75%], the wellbore integrity failure risk level is determined to be level three, and the wellbore integrity failure risk is high;

[0062] When the tensile failure risk assessment index or the casing strength failure risk index is (75%, 100%], the wellbore integrity failure risk level is determined to be level 4, and the wellbore integrity failure risk is dangerous.

[0063] Preferably, in step 5, the calculation formula of the wellbore integrity failure risk index is:

[0064] d k =S k +F 2k +F 3k +E 1k +E 2k (11)

[0065] in,

[0066]

[0067] Where, d k is the wellbore integrity failure risk index at depth k of gas reservoir type gas storage; S k F is the failure severity index of cement sheath shear damage at depth k in gas reservoir type gas storage; 2k F is the evaluation index of the severity of cement failure at the first interface of cement sheath at the depth k of gas storage reservoir; 3k E is the evaluation index of the severity of cement failure at the second interface of the cement sheath at the depth k of the gas storage reservoir; 1k E is the risk assessment index of cement sheath tensile failure at depth k in gas storage; 2kis the casing strength failure risk index at the depth k of the gas storage reservoir; It is the minimum value of the average minimum principal stress in the wellbore cement sheath shear failure area;

[0068] According to the wellbore integrity failure risk index value corresponding to each depth of the gas reservoir type gas storage, the wellbore integrity failure risk level determination index value at each depth of the gas reservoir type gas storage is calculated, as shown in formula (13):

[0069]

[0070] Where D k is the indicator for determining the risk level of wellbore integrity failure at depth k of gas reservoir type gas storage; d max It is the maximum value of the wellbore integrity failure risk index occurring at depth k in a gas reservoir type gas storage facility.

[0071] Preferably, based on the wellbore integrity failure hazard level determination index value corresponding to each depth of the gas reservoir type gas storage reservoir, and according to the hazard area determination standard of wellbore integrity failure of the gas reservoir type gas storage reservoir, the hazard level of each area of ​​the gas reservoir type gas storage reservoir is determined;

[0072] The criteria for determining the dangerous area of ​​wellbore integrity failure in gas reservoir type gas storage are:

[0073] When the wellbore integrity failure risk level determination index D at the depth k of the gas reservoir type gas storage k When the value range of is [0,25%], the danger level of the area is determined to be level one, and the danger level of the area is low;

[0074] When the wellbore integrity failure risk level determination index D at the depth k of the gas reservoir type gas storage k When the value range of is (25%, 50%], the danger level of the area is determined to be level 2, and the danger level of the area is medium;

[0075] When the wellbore integrity failure risk level determination index D at the depth k of the gas reservoir type gas storage k When the value range of is (50%, 75%], the danger level of the area is determined to be level 3, and the regional danger level is high;

[0076] When the wellbore integrity failure risk level determination index D at the depth k of the gas reservoir type gas storage k When the value range of is (75%, 100%], the danger level of the area is determined to be level 4, and the danger level of the area is extremely high.

[0077] The present invention has the following beneficial effects:

[0078] The present invention proposes a method for determining the dangerous area of ​​wellbore integrity failure during the gas injection and production stage of a gas reservoir type gas storage. The method constructs a formation-cement sheath-casing geometric model based on the design parameters of the gas reservoir type gas storage and the geological data of the formation in which it is located in the finite element simulation software, and uses the formation-cement sheath-casing geometric model to simulate the wellbore integrity failure process during the gas production stage. The severity of the wellbore integrity failure of the gas storage that has failed and the risk of wellbore integrity failure of the wellbore that has not failed are evaluated respectively, and the danger level of wellbore integrity failure in various areas of the wellbore during the gas injection and production stage of the gas reservoir type gas storage is comprehensively determined. The present invention makes up for the problem that the existing technology cannot be used to determine the specific danger level of wellbore integrity failure, lays a theoretical foundation for the optimization and protection of wellbore integrity of gas reservoir type gas storage, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0079] Figure 1 It is a structural schematic diagram of the formation-cement ring-casing geometric model of the present invention.

[0080] Figure 2 This is a schematic diagram of the cement sheath shear failure node during the gas production stage of a gas reservoir-type gas storage facility.

[0081] Figure 3 Schematic diagram of the assessment results of the severity of wellbore integrity failure during the gas production stage of a gas reservoir-type gas storage.

[0082] Figure 4 Schematic diagram of the wellbore integrity failure risk assessment results during the gas production phase of a gas reservoir-type gas storage facility

[0083] Figure 5 This is a schematic diagram of the classification results of wellbore integrity failure risk levels during the gas production stage. DETAILED DESCRIPTION

[0084] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0085] Example 1

[0086] The present invention proposes a method for determining a dangerous area of ​​wellbore integrity failure during the gas injection and production phase of a gas reservoir type gas storage, which specifically comprises the following steps:

[0087] Step 1, based on the design parameters of the gas reservoir type gas storage and the geological data of the stratum in which the gas reservoir type gas storage is located, wherein the design parameters of the gas reservoir type gas storage include the type, outer diameter, thickness, elastic modulus, Poisson's ratio, and yield strength of the casing in the vertical well and the type, outer diameter, thickness, elastic modulus, Poisson's ratio, compressive strength, tensile strength, cohesion, and internal friction coefficient of the cement sheath in the vertical well; the geological data of the gas reservoir type gas storage include the type, elastic modulus, and Poisson's ratio of the stratum and the type, elastic modulus, and Poisson's ratio of the interlayer.

[0088] The finite element software is used to construct the formation-cement sheath-casing geometric model, and the swept meshing is performed on the formation-cement sheath-casing geometric model. The cohesion contact model is applied to the formation-cement sheath-casing geometric model, so that the master and slave surface meshes of each contact surface in the formation-cement sheath-casing geometric model are aligned with each other and completely overlapped.

[0089] Step 2: Set the boundary conditions of the formation-cement sheath-casing geometric model according to the relationship between the formation depth and the three-dimensional non-uniform ground stress, as shown in formulas (1) to (3):

[0090] σ H =a1+a2×h+a3×h 2 +a4×h 3 +a5×h 4 (1)

[0091] σ h =b1+b2×h+b3×h 2 +b4×h 3 +b5×h 4 (2)

[0092] σ v =c1+c2×h+c3×h 3 +c4×h 3 +c5×h 4 (3)

[0093] In the formula, σ H is the maximum horizontal ground stress, in MPa; σ h is the minimum horizontal ground stress, in MPa; σ v is the vertical geostress, in MPa; h is the formation depth, in MPa; a1, a2, a3, a4, and a5 are all the maximum horizontal geostress fitting coefficients; b1, b2, b3, b4, and b5 are all the minimum horizontal geostress fitting coefficients; c1, c2, c3, c4, and c5 are all the vertical geostress fitting coefficients.

[0094] The three-dimensional non-uniform geostress (including the maximum horizontal geostress, the minimum horizontal geostress and the vertical geostress) of the formation-cement sheath-casing geometric model is calculated, the gas production pressure relief pressure is applied to the formation-cement sheath-casing geometric model, and the bonding strength of the first interface of the cement sheath and the second interface of the cement sheath in the formation-cement sheath-casing geometric model is set to determine the wellbore integrity failure judgment criterion;

[0095] Then, the gas production decompression pressure is applied to the formation-cement sheath-casing geometric model, and the bonding strength of the first cement sheath interface and the second cement sheath interface in the formation-cement sheath-casing geometric model are set to determine the wellbore integrity failure judgment criterion during the gas production stage of the gas reservoir type gas storage.

[0096] In this embodiment, the wellbore integrity failure judgment criteria include cement sheath shear failure failure criteria, cement sheath tensile failure failure criteria, casing integrity failure criteria, and cement sheath first interface and second interface integrity failure criteria.

[0097] in,

[0098] The cement sheath shear failure criterion is:

[0099] The minimum principal stress σ when the Mohr circle is tangent to the failure envelope 3f As the safety critical value, the minimum principal stress σ of the cement sheath min When it is less than the safety critical value, it indicates that the cement sheath has shear failure. The minimum principal stress σ when the Mohr circle is tangent to the failure envelope is 3f The calculation formula is:

[0100]

[0101] In the formula, σ 3f is the minimum principal stress when the Mohr circle is tangent to the failure envelope; σ max is the maximum principal stress; is the internal friction angle; C is the failure coefficient of cement sheath shear failure;

[0102] The tensile failure criterion of the cement sheath is: the circumferential stress on the cement sheath Not less than the tensile strength of the cement sheath.

[0103] The integrity failure criteria of the first interface and the second interface of the cement sheath are:

[0104] The relationship between the normal pressure of the interface, the first shear stress of the interface, and the second shear stress of the interface satisfies:

[0105]

[0106] In the formula, t n is the normal pressure at the interface; t s is the first shear stress at the interface; t t is the second shear stress at the interface; t n0 is the initial normal pressure of the interface; t s0 is the initial first shear stress of the interface; t t0 is the initial second shear stress of the interface;

[0107] The casing integrity failure criterion is:

[0108] The casing equivalent stress does not exceed the yield strength of the casing, wherein the casing equivalent stress calculation formula is:

[0109]

[0110] In the formula, σ e is the equivalent stress of the casing, in MPa; σ1 is the first principal stress, in MPa; σ2 is the second principal stress, in MPa; σ3 is the third principal stress, in MPa.

[0111] Step 3, set the three-dimensional non-uniform ground stress on the formation-cement sheath-casing geometric model and the cement ring node of the formation-cement sheath-casing geometric model, use the formation-cement sheath-casing geometric model to simulate the gas production stage of the gas reservoir type gas storage, obtain the mechanical simulation parameters of the formation-cement sheath-casing geometric model, and accurately judge whether the formation-cement sheath-casing geometric model has a wellbore integrity failure based on the wellbore integrity failure judgment.

[0112] In this embodiment, the mechanical simulation parameters include the minimum principal stress σ of the cement sheath min , the maximum principal stress of cement sheath σ max , internal friction angle Normal pressure of the first interface of cement sheath, first shear stress of the first interface of cement sheath, second shear stress of the first interface of cement sheath, normal pressure of the second interface of cement sheath, first shear stress of the second interface of cement sheath, second shear stress of the second interface of cement sheath, equivalent stress of casing σ e , the yield strength of the casing σ s , first principal stress σ1, second principal stress σ2, third principal stress σ3.

[0113] Step 4: Establish a wellbore integrity failure assessment standard, and evaluate the severity of wellbore integrity failure of gas reservoir-type gas storage based on the wellbore integrity failure assessment standard to obtain the failure severity assessment results of the gas production stage of the gas reservoir-type gas storage and the non-failure risk assessment results of the gas production stage of the gas reservoir-type gas storage.

[0114] The wellbore integrity failure assessment process includes assessing the severity of wellbore integrity failures that have already failed and assessing the risk of wellbore integrity failures that have not yet failed. The wellbore integrity failure assessment criteria include assessment criteria for the severity of wellbore integrity failures that have already failed and assessment criteria for the risk of wellbore integrity failures that have not yet failed.

[0115] The failure severity assessment process applicable to a wellbore integrity failure that has already failed includes a cement sheath shear failure severity assessment and a cement sheath interface bonding failure severity assessment.

[0116] The evaluation of cement sheath shear failure severity is based on the number of cement sheath damaged nodes in a unit depth area. By counting the number of shear failure nodes in each area, the evaluation index of cement sheath shear failure severity at any depth is determined, as shown in formula (7):

[0117]

[0118] Where, F1 is the evaluation index of the severity of shear failure of cement sheath; si is the number of cement sheath shear failure nodes; f smax is the maximum number of cement sheath shear failure nodes in the entire area;

[0119] The evaluation of the severity of cement failure at the cement sheath interface is based on the secondary stress criterion, and the evaluation index of the severity of cement failure at the first cement sheath interface and the evaluation index of the severity of cement failure at the second cement sheath interface at any depth are determined as follows:

[0120] F2=f 1CSQUADSCRT (8)

[0121] F3=f 2CSQUADSCRT (9)

[0122] Where, F2 is the evaluation index of the severity of cement failure at the first interface of cement sheath; F3 is the evaluation index of the severity of cement failure at the second interface of cement sheath; 1CSQUADSCRT is the secondary contact stress damage value of the first interface of cement sheath; f 2CSQUADSCRT is the secondary contact stress damage value of the second interface of cement sheath.

[0123] The shear failure severity assessment index F1 of the cement sheath, the bonding failure severity assessment index F2 of the first interface of the cement sheath and the bonding failure severity assessment index F3 of the second interface of the cement sheath are respectively used as the wellbore integrity failure severity assessment index F. Based on the wellbore integrity failure severity assessment index F and combined with the wellbore integrity failure severity assessment standard applicable to wellbore integrity that has failed, the severity of the wellbore integrity failure that has failed is assessed.

[0124] The failure severity assessment criteria applicable to wellbore integrity failures that have occurred are:

[0125] When the value of the wellbore integrity failure severity evaluation index F is [0, 25%], the wellbore integrity failure level is determined to be level one, and the wellbore integrity failure severity is light;

[0126] When the value of the wellbore integrity failure severity assessment index F is (25%, 50%], the wellbore integrity failure level is determined to be level 2, and the wellbore integrity failure severity is moderate;

[0127] When the value of the wellbore integrity failure severity evaluation index F is (50%, 75%], the wellbore integrity failure level is determined to be level three, and the wellbore integrity failure severity is relatively serious;

[0128] When the value of the wellbore integrity failure severity assessment index F is (75%, 100%], the wellbore integrity failure level is determined to be level 4, and the wellbore integrity failure severity is very severe.

[0129] The wellbore integrity failure risk assessment process applicable to wellbore integrity failure that has not failed is to first divide the cement sheath into regions according to depth, and then obtain the average stress value in each region of the cement sheath based on the maximum allowable stress index of the material used for the cement sheath, and determine the cement sheath tensile failure risk assessment index or casing strength failure risk index used for wellbore integrity failure risk assessment, as shown in formula (10):

[0130]

[0131] Where, E is the tensile failure risk assessment index or casing strength failure risk index; f ti is the structural stress on the nodes in the cement sheath, in MPa; i is the serial number of the nodes in the cement sheath; n is the number of vulnerable nodes; T is the maximum allowable stress index of the cement sheath structure, in MPa;

[0132] The wellbore integrity failure risk assessment criteria applicable to wellbore integrity failures that have not occurred are:

[0133] When the tensile failure risk assessment index or the casing strength failure risk index is [0, 25%], the wellbore integrity failure risk level is determined to be level one, and the wellbore integrity failure risk is low;

[0134] When the tensile failure risk assessment index or the casing strength failure risk index is (25%, 50%], the wellbore integrity failure risk level is determined to be level 2, and the wellbore integrity failure risk is medium;

[0135] When the tensile failure risk assessment index or the casing strength failure risk index is (50%, 75%], the wellbore integrity failure risk level is determined to be level three, and the wellbore integrity failure risk is high;

[0136] When the tensile failure risk assessment index or the casing strength failure risk index is (75%, 100%], the wellbore integrity failure risk level is determined to be level 4, and the wellbore integrity failure risk is dangerous.

[0137] Step 5: According to the failure severity assessment results of the gas reservoir type gas storage during the gas production stage and the non-failure risk assessment results of the gas reservoir type gas storage during the gas production stage, the wellbore integrity failure risk index of each area in the wellbore of the gas reservoir type gas storage is calculated, as shown in formula (11):

[0138] d k =S k +F 2k +F 3k +E 1k +E 2k (11)

[0139] in,

[0140]

[0141] Where, d k is the wellbore integrity failure risk index at depth k of gas reservoir type gas storage; S k F is the failure severity index of cement sheath shear damage at depth k in gas reservoir type gas storage; 2k F is the evaluation index of the severity of cement failure at the first interface of cement sheath at the depth k of gas storage reservoir; 3k E is the evaluation index of the severity of cement failure at the second interface of the cement sheath at the depth k of the gas storage reservoir; 1k E is the risk assessment index of cement sheath tensile failure at depth k in gas storage; 2k is the casing strength failure risk index at the depth k of the gas storage reservoir; It is the minimum value of the average minimum principal stress in the wellbore cement sheath shear failure area;

[0142] According to the wellbore integrity failure risk index value corresponding to each depth of the gas reservoir type gas storage, the wellbore integrity failure risk level determination index value at each depth of the gas reservoir type gas storage is calculated, as shown in formula (13):

[0143]

[0144] Where D k is the indicator for determining the risk level of wellbore integrity failure at depth k of gas reservoir type gas storage; d max It is the maximum value of the wellbore integrity failure risk index occurring at depth k in a gas reservoir type gas storage facility.

[0145] The hazard level of each area of ​​the gas reservoir type gas storage is determined based on the wellbore integrity failure hazard index value of each area and the hazard zone determination standard of the wellbore integrity failure of the gas reservoir type gas storage.

[0146] In this embodiment, the criteria for determining the dangerous area of ​​failure of the wellbore integrity of the gas reservoir type gas storage are:

[0147] When the wellbore integrity failure risk level determination index D at the depth k of the gas reservoir type gas storage k When the value range of is [0,25%], the danger level of the area is determined to be level one, and the danger level of the area is low;

[0148] When the wellbore integrity failure risk level determination index D at the depth k of the gas reservoir type gas storage k When the value range of is (25%, 50%], the danger level of the area is determined to be level 2, and the danger level of the area is medium;

[0149] When the wellbore integrity failure risk level determination index D at the depth k of the gas reservoir type gas storage k When the value range of is (50%, 75%], the danger level of the area is determined to be level 3, and the regional danger level is high;

[0150] When the wellbore integrity failure risk level determination index D at the depth k of the gas reservoir type gas storage k When the value range of is (75%, 100%], the danger level of the area is determined to be level 4, and the danger level of the area is extremely high.

[0151] Example 2

[0152] This embodiment takes the vertical well S1-A of the SQ underground gas storage as an example, and adopts the method for determining the wellbore integrity failure danger zone of the gas reservoir type gas storage during the injection and production phase proposed in Embodiment 1 to make a determination, which specifically includes the following steps:

[0153] Step 1: Obtain the design parameters of the SQ underground gas storage and the geological data of the stratum where the SQ underground gas storage is located, as shown in Table 1.

[0154] Table 1 SQ underground gas storage parameters

[0155]

[0156] According to the design parameters of the SQ underground gas storage and the geological data of the stratum where the SQ underground gas storage is located, the finite element software ABAQUS is used to construct the formation-cement sheath-casing geometric model, such as Figure 1As shown, the formation-cement sheath-casing geometric model is swept meshed, and the cohesion contact model is applied to the formation-cement sheath-casing geometric model, so that the master and slave surface meshes of each contact surface in the formation-cement sheath-casing geometric model are aligned with each other and completely overlap.

[0157] Step 2, setting the boundary conditions of the formation-cement sheath-casing geometric model. In this embodiment, the relationship between the formation depth and the maximum horizontal ground stress, the minimum horizontal ground stress and the vertical ground stress is:

[0158] The relationship between the formation depth and the three-dimensional non-uniform ground stress is shown in formulas (1) to (3):

[0159] σ H =353.11-0.55×h+3.46×10 -4 ×h 2 -9.08×10 -8 ×h 3 +8.72×10 -12 ×h 4 (14)

[0161] σ h =101.52-0.148×h+9.99×10 -5 ×h 2 -2.62×10 -8 ×h 3 +2.5×10 -12 ×h 4 (15)

[0163] σ v =305.65-0.499×h+3.2×10 -4 ×h 2 -8.36×10 -8 ×h 3 +7.9×10 -12 ×h 4 (16)

[0165] In the formula, σ H is the maximum horizontal ground stress, in MPa; σ h is the minimum horizontal ground stress, in MPa; σ v is the vertical geostress, in MPa; h is the formation depth, in MPa.

[0166] The three-dimensional non-uniform geostress (including the maximum horizontal geostress, the minimum horizontal geostress and the vertical geostress) of the formation-cement sheath-casing geometric model is calculated, the gas production pressure relief pressure is applied to the formation-cement sheath-casing geometric model, and the bonding strength of the first interface of the cement sheath and the second interface of the cement sheath in the formation-cement sheath-casing geometric model is set to determine the wellbore integrity failure judgment criterion;

[0167] Then, the gas production decompression pressure is applied to the formation-cement sheath-casing geometric model, and the bonding strength of the first cement sheath interface and the second cement sheath interface in the formation-cement sheath-casing geometric model are set to determine the wellbore integrity failure judgment criterion during the gas production stage of the gas reservoir type gas storage.

[0168] In this embodiment, the wellbore integrity failure judgment criteria include cement sheath shear failure failure criteria, cement sheath tensile failure failure criteria, casing integrity failure criteria, and cement sheath first interface and second interface integrity failure criteria.

[0169] The failure criterion for cement sheath shear failure is: the minimum principal stress σ when the Mohr circle is tangent to the failure envelope 3f As the safety critical value, the minimum principal stress σ of the cement sheath min When it is less than the safety critical value, it indicates that the cement sheath has shear failure. The minimum principal stress σ when the Mohr circle is tangent to the failure envelope is 3f The calculation formula is:

[0170]

[0171] In the formula, σ 3f is the minimum principal stress when the Mohr circle is tangent to the failure envelope; σ max is the maximum principal stress; is the internal friction angle; C is the failure coefficient of cement sheath shear failure;

[0172] The tensile failure criterion of the cement sheath is: the circumferential stress on the cement sheath Not less than the tensile strength of the cement sheath.

[0173] The integrity failure criteria of the first interface and the second interface of the cement sheath are: the relationship between the normal pressure of the interface, the first shear stress of the interface and the second shear stress of the interface satisfies:

[0174]

[0175] Where, t n is the normal pressure at the interface; t s is the first shear stress at the interface; t t is the second shear stress at the interface; t n0is the initial normal pressure of the interface; t s0 is the initial first shear stress of the interface; t t0 is the initial second shear stress of the interface;

[0176] The casing integrity failure criterion is:

[0177] The casing equivalent stress does not exceed the yield strength of the casing, wherein the casing equivalent stress calculation formula is:

[0178]

[0179] In the formula, σ e is the equivalent stress of the casing, in MPa; σ1 is the first principal stress, in MPa; σ2 is the second principal stress, in MPa; σ3 is the third principal stress, in MPa.

[0180] Step 3, set the three-dimensional non-uniform ground stress on the formation-cement sheath-casing geometric model and the cement ring node of the formation-cement sheath-casing geometric model, use the formation-cement sheath-casing geometric model to simulate the gas production stage of the gas reservoir type gas storage, obtain the mechanical simulation parameters of the formation-cement sheath-casing geometric model, and accurately judge whether the formation-cement sheath-casing geometric model has a wellbore integrity failure based on the wellbore integrity failure judgment.

[0181] The mechanical simulation parameters include the minimum principal stress σ of the cement sheath: min , the maximum principal stress of cement sheath σ max , internal friction angle Normal pressure of the first interface of cement sheath, first shear stress of the first interface of cement sheath, second shear stress of the first interface of cement sheath, normal pressure of the second interface of cement sheath, first shear stress of the second interface of cement sheath, second shear stress of the second interface of cement sheath, equivalent stress of casing σ e , the yield strength of the casing σ s , first principal stress σ1, second principal stress σ2, third principal stress σ3.

[0182] In this embodiment, cement shear failure is taken as an example, and the maximum principal stress σ of each node of the cement sheath obtained by simulating the formation-cement sheath-casing geometric model is max Substituting into formula (4) to calculate the safety critical value σ of each node of cement sheath 3f , and then the safety critical value σ of each node of the cement sheath 3f and the minimum principal stress σ min For comparison, if the minimum principal stress σ min Less than the safety threshold σ 3f, indicating that the cement sheath has undergone shear failure. By distinguishing the nodes of the cement sheath, it was found that 492 nodes of the cement sheath had undergone shear failure when the gas storage was completed. Figure 2 As shown in the figure, the failure law of wellbore integrity is analyzed based on the position information of each failure node of the cement sheath.

[0183] Step 4: Establish a wellbore integrity failure assessment standard, and evaluate the severity of wellbore integrity failure of gas reservoir-type gas storage based on the wellbore integrity failure assessment standard to obtain the failure severity assessment results of the gas reservoir-type gas storage during the gas production stage and the non-failure risk assessment results of the gas reservoir-type gas storage during the gas production stage, such as Figure 3 and Figure 4 shown.

[0184] In this embodiment, the wellbore integrity failure assessment process includes assessing the severity of wellbore integrity failures that have already failed and assessing the risk of wellbore integrity failures that have not yet failed. The wellbore integrity failure assessment criteria include assessment criteria for the severity of wellbore integrity failures that are applicable to wellbore integrity failures that have already failed and assessment criteria for the risk of wellbore integrity failures that are applicable to wellbore integrity failures that have not yet failed.

[0185] The failure severity assessment process applicable to the wellbore integrity failure that has already failed includes the cement sheath shear failure severity assessment and the cement sheath interface bonding failure severity assessment.

[0186] The evaluation of cement sheath shear failure severity is based on the number of cement sheath damaged nodes in a unit depth area. By counting the number of shear failure nodes in each area, the evaluation index of cement sheath shear failure severity at any depth is determined, as shown in formula (7):

[0187]

[0188] Where, F1 is the evaluation index of the severity of shear failure of cement sheath; si is the number of cement sheath shear failure nodes; f smax is the maximum number of cement sheath shear failure nodes in the entire area;

[0189] The evaluation of the severity of cement failure at the cement sheath interface is based on the secondary stress criterion, and the evaluation index of the severity of cement failure at the first cement sheath interface and the evaluation index of the severity of cement failure at the second cement sheath interface at any depth are determined as follows:

[0190] F2=f 1CSQUADSCRT (8)

[0191] F3=f 2CSQUADSCRT (9)

[0192] Where, F2 is the evaluation index of the severity of cement failure at the first interface of cement sheath; F3 is the evaluation index of the severity of cement failure at the second interface of cement sheath; 1CSQUADSCRT is the secondary contact stress damage value of the first interface of cement sheath; f 2CSQUADSCRT is the secondary contact stress damage value of the second interface of cement sheath.

[0193] The shear failure severity assessment index F1 of the cement sheath, the bonding failure severity assessment index F2 of the first interface of the cement sheath and the bonding failure severity assessment index F3 of the second interface of the cement sheath are respectively used as the wellbore integrity failure severity assessment index F. Based on the wellbore integrity failure severity assessment index F and combined with the wellbore integrity failure severity assessment standard applicable to wellbore integrity that has failed, the severity of the wellbore integrity failure that has failed is assessed.

[0194] The failure severity assessment criteria applicable to wellbore integrity failures that have occurred are:

[0195] When the value of the wellbore integrity failure severity evaluation index F is [0, 25%], the wellbore integrity failure level is determined to be level one, and the wellbore integrity failure severity is light;

[0196] When the value of the wellbore integrity failure severity assessment index F is (25%, 50%], the wellbore integrity failure level is determined to be level 2, and the wellbore integrity failure severity is moderate;

[0197] When the value of the wellbore integrity failure severity evaluation index F is (50%, 75%], the wellbore integrity failure level is determined to be level three, and the wellbore integrity failure severity is relatively serious;

[0198] When the value of the wellbore integrity failure severity assessment index F is (75%, 100%], the wellbore integrity failure level is determined to be level 4, and the wellbore integrity failure severity is very severe.

[0199] The wellbore integrity failure risk assessment process applicable to wellbore integrity failure that has not failed is to first divide the cement sheath into regions according to depth, and then obtain the average stress value in each region of the cement sheath based on the maximum allowable stress index of the material used for the cement sheath, and determine the cement sheath tensile failure risk assessment index or casing strength failure risk index used for wellbore integrity failure risk assessment, as shown in formula (10):

[0200]

[0201] Where, E is the tensile failure risk assessment index or casing strength failure risk index; f tiis the structural stress on the nodes in the cement sheath, in MPa; i is the serial number of the nodes in the cement sheath; n is the number of vulnerable nodes; T is the maximum allowable stress index of the cement sheath structure, in MPa;

[0202] The wellbore integrity failure risk assessment criteria applicable to wellbore integrity failures that have not occurred are:

[0203] When the tensile failure risk assessment index or the casing strength failure risk index is [0, 25%], the wellbore integrity failure risk level is determined to be level one, and the wellbore integrity failure risk is low;

[0204] When the tensile failure risk assessment index or the casing strength failure risk index is (25%, 50%], the wellbore integrity failure risk level is determined to be level 2, and the wellbore integrity failure risk is medium;

[0205] When the tensile failure risk assessment index or the casing strength failure risk index is (50%, 75%], the wellbore integrity failure risk level is determined to be level three, and the wellbore integrity failure risk is high;

[0206] When the tensile failure risk assessment index or the casing strength failure risk index is (75%, 100%], the wellbore integrity failure risk level is determined to be level 4, and the wellbore integrity failure risk is dangerous.

[0207] Step 5: According to the failure severity assessment results of the gas reservoir type gas storage during the gas production stage and the non-failure risk assessment results of the gas reservoir type gas storage during the gas production stage, the wellbore integrity failure risk index of each area in the wellbore of the gas reservoir type gas storage is calculated, as shown in formula (11):

[0208] d k =S k +F 2k +F 3k +E 1k +E 2k (11)

[0209] in,

[0210]

[0211] Where, d k is the wellbore integrity failure risk index at depth k of gas reservoir type gas storage; S k F is the failure severity index of cement sheath shear damage at depth k in gas reservoir type gas storage; 2k F is the evaluation index of the severity of cement failure at the first interface of cement sheath at the depth k of gas storage reservoir; 3k E is the evaluation index of the severity of cement failure at the second interface of the cement sheath at the depth k of the gas storage reservoir;1k E is the risk assessment index of cement sheath tensile failure at depth k of gas storage; 2k is the casing strength failure risk index at the depth k of the gas storage reservoir; It is the minimum value of the average minimum principal stress in the wellbore cement sheath shear failure area;

[0212] According to the wellbore integrity failure risk index value corresponding to each depth of the gas reservoir type gas storage, the wellbore integrity failure risk level determination index value at each depth of the gas reservoir type gas storage is calculated, as shown in formula (13):

[0213]

[0214] Where D k is the indicator for determining the risk level of wellbore integrity failure at depth k of gas reservoir type gas storage; d max It is the maximum value of the wellbore integrity failure risk index occurring at depth k in a gas reservoir type gas storage facility.

[0215] The hazard level of each area of ​​the gas reservoir type gas storage is determined based on the wellbore integrity failure hazard index value of each area and the hazard zone determination standard of the wellbore integrity failure of the gas reservoir type gas storage.

[0216] In this embodiment, the criteria for determining the dangerous area of ​​failure of the wellbore integrity of the gas reservoir type gas storage are:

[0217] When the wellbore integrity failure risk level determination index D at the depth k of the gas reservoir type gas storage k When the value range of is [0,25%], the danger level of the area is determined to be level one, and the danger level of the area is low;

[0218] When the wellbore integrity failure risk level determination index D at the depth k of the gas reservoir type gas storage k When the value range of is (25%, 50%], the danger level of the area is determined to be level 2, and the danger level of the area is medium;

[0219] When the wellbore integrity failure risk level determination index D at the depth k of the gas reservoir type gas storage k When the value range of is (50%, 75%], the danger level of the area is determined to be level 3, and the regional danger level is high;

[0220] When the wellbore integrity failure risk level determination index D at the depth k of the gas reservoir type gas storage k When the value range of is (75%, 100%], the danger level of the area is determined to be level 4, and the danger level of the area is extremely high.

[0221] According to the established hazard zone determination standard for wellbore integrity failure of gas reservoir-type gas storage, the determination index of wellbore integrity failure hazard level at each depth is calculated to obtain the wellbore integrity failure hazard level and corresponding position of the vertical well of gas reservoir-type gas storage during the gas injection stage, such as Figure 5 As shown, the determination of the risk area of ​​wellbore integrity failure during the gas injection stage of a vertical well of a gas reservoir type gas storage is realized.

[0222] Depend on Figure 5 It can be seen that the wellbore integrity failure of vertical wells during the gas injection stage of gas reservoir-type gas storage mainly occurs in the middle and lower areas of the wellbore, and the wellbore integrity failure hazard level in most areas is level 2. Wellbore integrity monitoring and protection should be focused on these areas to prevent wellbore integrity failure from affecting the normal operation of gas reservoir-type gas storage.

[0223] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms used herein are only for describing specific embodiments, and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0224] In the present invention, the directions or positional relationships indicated by terms such as "upper", "lower", "bottom", "top", etc. are based on the directions or positional relationships shown in the accompanying drawings. They are relational words determined only for the convenience of describing the structural relationships of the various parts or elements of the present invention. They do not specifically refer to any part or element in the present invention and cannot be understood as limitations on the present invention.

[0225] In the present invention, terms such as "connected" and "connection" should be understood in a broad sense, indicating that the connection can be fixed, integral or detachable; it can be directly connected or indirectly connected through an intermediate medium. Relevant scientific research or technical personnel in this field can determine the specific meaning of the above terms in the present invention according to specific circumstances, and they should not be understood as limiting the present invention.

[0226] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A method for determining the risk area of ​​wellbore integrity failure during the gas injection and production phase of a gas reservoir type gas storage, characterized in that: The specific steps include: Step 1, constructing a formation-cement sheath-casing geometric model using finite element software according to the design parameters of the gas reservoir type gas storage and the geological data of the formation where the gas reservoir type gas storage is located; Step 2, setting the boundary conditions of the formation-cement sheath-casing geometric model, calculating the three-dimensional non-uniform geostress to which the formation-cement sheath-casing geometric model is subjected based on the relationship between the formation depth and the three-dimensional non-uniform geostress, applying the gas production pressure relief pressure to the formation-cement sheath-casing geometric model, setting the bonding strength of the first interface of the cement sheath and the second interface of the cement sheath in the formation-cement sheath-casing geometric model, and determining the wellbore integrity failure judgment criterion; Step 3, setting the three-dimensional non-uniform ground stress on the formation-cement sheath-casing geometric model and the cement ring node of the formation-cement sheath-casing geometric model, using the formation-cement sheath-casing geometric model to simulate the gas production stage of the gas reservoir type gas storage, obtaining the mechanical simulation parameters of the formation-cement sheath-casing geometric model, and judging whether the formation-cement sheath-casing geometric model has a wellbore integrity failure based on the wellbore integrity failure judgment; Step 4, establishing a wellbore integrity failure assessment standard, and evaluating the severity of wellbore integrity failure of gas reservoir-type gas storage based on the wellbore integrity failure assessment standard, to obtain failure severity assessment results of the gas reservoir-type gas storage during the gas production stage and non-failure risk assessment results of the gas reservoir-type gas storage during the gas production stage; Step 5, according to the failure severity assessment results of the gas production stage of the gas reservoir type gas storage and the non-failure risk assessment results of the gas production stage of the gas reservoir type gas storage, calculate the wellbore integrity failure hazard index of each area in the wellbore of the gas reservoir type gas storage, and then determine the hazard level of the wellbore integrity failure area of ​​the gas reservoir type gas storage based on the wellbore integrity failure hazard index value of each area.

2. The method for determining the risk area of ​​wellbore integrity failure during the gas injection and production phase of a gas reservoir type gas storage according to claim 1 is characterized in that: In the step 1, according to the design parameters of the gas reservoir type gas storage and the geological data of the stratum in which the gas reservoir type gas storage is located, a formation-cement sheath-casing geometric model is constructed using finite element software, and the formation-cement sheath-casing geometric model is swept meshed, and the cohesion contact model is applied to the formation-cement sheath-casing geometric model, so that the master and slave surface meshes of each contact surface in the formation-cement sheath-casing geometric model are aligned with each other and completely overlap.

3. The method for determining the risk area of ​​wellbore integrity failure during the gas injection and production phase of a gas reservoir type gas storage according to claim 2 is characterized in that: The design parameters of the gas reservoir type gas storage include the type, outer diameter, thickness, elastic modulus, Poisson's ratio, and yield strength of the casing in the vertical well, and the type, outer diameter, thickness, elastic modulus, Poisson's ratio, compressive strength, tensile strength, cohesion, and internal friction coefficient of the cement ring in the vertical well; the geological data of the gas reservoir type gas storage include the type, elastic modulus, Poisson's ratio of the formation, and the type, elastic modulus, and Poisson's ratio of the interlayer.

4. The method for determining the risk area of ​​wellbore integrity failure during the gas injection and production phase of a gas reservoir type gas storage according to claim 3 is characterized in that: The finite element software is Abaqus.

5. The method for determining the risk area of ​​wellbore integrity failure during the gas injection and production phase of a gas reservoir type gas storage according to claim 2 is characterized in that: In step 2, the relationship between the formation depth and the three-dimensional non-uniform ground stress is: s H =a1+a2×h+a3×h 2 +a4×h 3 +a5×h 4 (1)s h =b1+b2×h+b3×h 2 +b4×h 3 +b5×h 4 (2)s v =c1+c2×h+c3×h 2 +c4×h 3 +c5×h 4 (3) In the formula, σ H is the maximum horizontal ground stress, in MPa; σ h is the minimum horizontal ground stress, in MPa; σ v is the vertical geostress, in MPa; h is the formation depth, in MPa; a1, a2, a3, a4, a5 are all the maximum horizontal geostress fitting coefficients; b1, b2, b3, b4, b5 are all the minimum horizontal geostress fitting coefficients; c1, c2, c3, c4, c5 are all the vertical geostress fitting coefficients; According to the depth of the center of the formation-cement sheath-casing geometric model, the maximum horizontal ground stress, minimum horizontal ground stress and vertical ground stress of the formation-cement sheath-casing geometric model are calculated by using the relationship between the formation depth and the three-dimensional non-uniform ground stress; Then, the gas production decompression pressure is applied to the formation-cement sheath-casing geometric model, and the bonding strength of the first cement sheath interface and the second cement sheath interface in the formation-cement sheath-casing geometric model are set to determine the wellbore integrity failure judgment criterion during the gas production stage of the gas reservoir type gas storage.

6. The method for determining the risk area of ​​wellbore integrity failure during the gas injection and production phase of a gas reservoir type gas storage according to claim 5 is characterized in that: The wellbore integrity failure judgment criteria include cement sheath shear failure criteria, cement sheath tensile failure criteria, casing integrity failure criteria, and cement sheath first interface and second interface integrity failure criteria; in, The cement sheath shear failure criterion is: The minimum principal stress σ when the Mohr circle is tangent to the failure envelope 3f As the safety critical value, the minimum principal stress σ of the cement sheath mun When it is less than the safety critical value, it indicates that the cement sheath has shear failure. The minimum principal stress σ when the Mohr circle is tangent to the failure envelope is 3f The calculation formula is: In the formula, σ 3f is the minimum principal stress when the Mohr circle is tangent to the failure envelope; σ max is the maximum principal stress; is the internal friction angle; C is the failure coefficient of cement sheath shear failure; The tensile failure criterion of the cement sheath is: Circumferential stress on cement sheath Not less than the tensile strength of the cement sheath; The integrity failure criteria of the first interface and the second interface of the cement sheath are: The relationship between the normal pressure of the interface, the first shear stress of the interface, and the second shear stress of the interface satisfies: Where, t n is the normal pressure at the interface; t s is the first shear stress at the interface; t t is the second shear stress at the interface; t n0 is the initial normal pressure of the interface; t s0 is the initial first shear stress of the interface; t t0 is the initial second shear stress of the interface; The casing integrity failure criterion is: The casing equivalent stress does not exceed the yield strength of the casing, wherein the casing equivalent stress calculation formula is: In the formula, σ e is the equivalent stress of the casing, in MPa; σ1 is the first principal stress, in MPa; σ2 is the second principal stress, in MPa; σ3 is the third principal stress, in MPa.

7. The method for determining the risk area of ​​wellbore integrity failure during the gas injection and production phase of a gas reservoir type gas storage according to claim 6, characterized in that: The mechanical simulation parameters include the minimum principal stress σ of the cement sheath min , the maximum principal stress of cement sheath σ max , internal friction angle Normal pressure of the first interface of cement sheath, first shear stress of the first interface of cement sheath, second shear stress of the first interface of cement sheath, normal pressure of the second interface of cement sheath, first shear stress of the second interface of cement sheath, second shear stress of the second interface of cement sheath, equivalent stress of casing σ e , the yield strength of the casing σ s , first principal stress σ1, second principal stress σ2, third principal stress σ3.

8. The method for determining the risk area of ​​wellbore integrity failure during the gas injection and production phase of a gas reservoir type gas storage according to claim 6, characterized in that: The wellbore integrity failure assessment process includes assessing the severity of wellbore integrity failures that have already failed and assessing the risk of wellbore integrity failures that have not yet failed. The wellbore integrity failure assessment criteria include assessment criteria for the severity of wellbore integrity failures that have already failed and assessment criteria for the risk of wellbore integrity failures that have not yet failed.

9. The method for determining the risk area of ​​wellbore integrity failure during the gas injection and production phase of a gas reservoir type gas storage according to claim 8, characterized in that: The failure severity assessment process applicable to the wellbore integrity failure that has already failed includes the cement sheath shear failure severity assessment and the cement sheath interface bonding failure severity assessment; in, The evaluation of cement sheath shear failure severity is based on the number of cement sheath damaged nodes in a unit depth area. By counting the number of shear failure nodes in each area, the evaluation index of cement sheath shear failure severity at any depth is determined, as shown in formula (7): Where, F1 is the evaluation index of the severity of shear failure of cement sheath; si is the number of cement sheath shear failure nodes; f smax is the maximum number of cement sheath shear failure nodes in the entire area; The evaluation of the severity of cement failure at the cement sheath interface is based on the secondary stress criterion, and the evaluation index of the severity of cement failure at the first cement sheath interface and the evaluation index of the severity of cement failure at the second cement sheath interface at any depth are determined as follows: F2=f 1CSQUADSCRT (8) <h2 style=";text-align:left;direction:ltr">F3=f<h2 style=";text-align:left;direction:ltr"> 2CSQUADSCRT <h2 style=";text-align:left;direction:ltr"> (9) Where, F2 is the evaluation index of the severity of cement failure at the first interface of cement sheath; F3 is the evaluation index of the severity of cement failure at the second interface of cement sheath; 1CSQUADSCRT is the secondary contact stress damage value of the first interface of cement sheath; f 2CSQUADSCRT is the secondary contact stress damage value of the second interface of cement sheath; The shear failure severity assessment index F1 of the cement sheath, the bonding failure severity assessment index F2 of the first interface of the cement sheath and the bonding failure severity assessment index F3 of the second interface of the cement sheath are respectively used as the wellbore integrity failure severity assessment index F. Based on the wellbore integrity failure severity assessment index F and combined with the wellbore integrity failure severity assessment standard applicable to wellbore failures that have occurred, the severity of the wellbore integrity failure that has occurred is assessed.

10. The method for determining the risk area of ​​wellbore integrity failure during the gas injection and production phase of a gas reservoir type gas storage according to claim 9, characterized in that: The failure severity assessment criteria applicable to wellbore integrity failures that have occurred are: When the value of the wellbore integrity failure severity evaluation index F is [0, 25%], the wellbore integrity failure level is determined to be level one, and the wellbore integrity failure severity is light; When the value of the wellbore integrity failure severity assessment index F is (25%, 50%], the wellbore integrity failure level is determined to be level 2, and the wellbore integrity failure severity is moderate; When the value of the wellbore integrity failure severity evaluation index F is (50%, 75%], the wellbore integrity failure level is determined to be level three, and the wellbore integrity failure severity is relatively serious; When the value of the wellbore integrity failure severity assessment index F is (75%, 100%], the wellbore integrity failure level is determined to be level 4, and the wellbore integrity failure severity is very severe.

11. The method for determining the risk area of ​​wellbore integrity failure during the gas injection and production phase of a gas reservoir type gas storage according to claim 8, characterized in that: The wellbore integrity failure risk assessment process applicable to wellbore integrity failure that has not failed is to first divide the cement sheath into regions according to depth, and then obtain the average stress value in each region of the cement sheath based on the maximum allowable stress index of the material used for the cement sheath, and determine the cement sheath tensile failure risk assessment index or casing strength failure risk index used for wellbore integrity failure risk assessment, as shown in formula (10): Where, E is the tensile failure risk assessment index or casing strength failure risk index; f ti is the structural stress on the nodes in the cement sheath, in MPa; i is the serial number of the node in the cement ring; n is the number of vulnerable nodes; T is the maximum allowable stress index of the cement sheath structure, in MPa.

12. The method for determining the risk area of ​​wellbore integrity failure during the gas injection and production phase of a gas reservoir type gas storage according to claim 11, characterized in that: The wellbore integrity failure risk assessment criteria applicable to wellbore integrity failures that have not occurred are: When the tensile failure risk assessment index or the casing strength failure risk index is [0, 25%], the wellbore integrity failure risk level is determined to be level one, and the wellbore integrity failure risk is low; When the tensile failure risk assessment index or the casing strength failure risk index is (25%, 50%], the wellbore integrity failure risk level is determined to be level 2, and the wellbore integrity failure risk is medium; When the tensile failure risk assessment index or the casing strength failure risk index is (50%, 75%], the wellbore integrity failure risk level is determined to be level 3, and the wellbore integrity failure risk is high; When the tensile failure risk assessment index or the casing strength failure risk index is (75%, 100%], the wellbore integrity failure risk level is determined to be level 4, and the wellbore integrity failure risk is dangerous.

13. The method for determining the risk area of ​​wellbore integrity failure during the gas injection and production phase of a gas reservoir type gas storage according to claim 11, characterized in that: In step 5, the calculation formula of the wellbore integrity failure risk index is: d k =S k +F 2k +F 3k +E 1k +E 2k (11) Among them, Where, d k is the wellbore integrity failure risk index at depth k of gas reservoir type gas storage; S k F is the failure severity index of cement sheath shear damage at depth k in gas reservoir type gas storage; 2k F is the evaluation index of the severity of cement failure at the first interface of cement sheath at the depth k of gas storage reservoir; 3k E is the evaluation index of the severity of cement failure at the second interface of the cement sheath at the depth k of the gas storage reservoir; 1k E is the risk assessment index of cement sheath tensile failure at depth k in gas storage; 2k is the casing strength failure risk index at the depth k of the gas storage reservoir; It is the minimum value of the average minimum principal stress in the wellbore cement sheath shear failure area; According to the wellbore integrity failure risk index value corresponding to each depth of the gas reservoir type gas storage, the wellbore integrity failure risk level determination index value at each depth of the gas reservoir type gas storage is calculated, as shown in formula (13): Where D k is the indicator for determining the risk level of wellbore integrity failure at depth k of gas reservoir type gas storage; d max It is the maximum value of the wellbore integrity failure risk index occurring at depth k in a gas reservoir type gas storage facility.

14. The method for determining the risk area of ​​wellbore integrity failure during the gas injection and production phase of a gas reservoir type gas storage according to claim 13, characterized in that: Based on the wellbore integrity failure hazard level determination index value corresponding to each depth of the gas reservoir type gas storage, and according to the hazard area determination standard of the wellbore integrity failure of the gas reservoir type gas storage, the hazard level of each area of ​​the gas reservoir type gas storage is determined; The criteria for determining the dangerous area of ​​wellbore integrity failure in gas reservoir type gas storage are: When the wellbore integrity failure risk level determination index D at the depth k of the gas reservoir type gas storage k When the value range of is [0,25%], the danger level of the area is determined to be level one, and the danger level of the area is low; When the wellbore integrity failure risk level determination index D at the depth k of the gas reservoir type gas storage k When the value range of is (25%, 50%], the danger level of the area is determined to be level 2, and the danger level of the area is medium; When the wellbore integrity failure risk level determination index D at the depth k of the gas reservoir type gas storage k When the value range of is (50%, 75%], the danger level of the area is determined to be level 3, and the regional danger level is high; When the wellbore integrity failure risk level determination index D at the depth k of the gas reservoir type gas storage k When the value range of is (75%, 100%], the danger level of the area is determined to be level 4, and the danger level of the area is extremely high.

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