Evaluation method of wellbore collapse pressure in directional wells based on the synergistic effect of different strength criteria

Abstract

The present invention discloses a method for evaluating the collapse pressure of a directional wellbore under the synergistic effect of different strength criteria, comprising: utilizing well logging, drilling and completion, and indoor test data to determine the vertical depth of the drilled formation, the formation pore pressure, the overburden pressure, the maximum horizontal in-situ stress, the minimum horizontal in-situ stress, and the azimuth of the maximum horizontal in-situ stress, the rock cohesion, the rock internal friction angle, the rock Poisson's ratio, the rock porosity, the Biot coefficient, and the wellbore permeability; establishing a collapse pressure calculation model under different rock strength criteria; calculating the relative importance of different rock strength criteria; determining the weight coefficients of different rock strength criteria; and establishing a directional wellbore collapse pressure calculation model under the synergistic effect of different strength criteria. Due to the introduction of the weight coefficient, the present invention combines the advantages of other criteria, obtains the advantageous synergistic effect of different strength criteria, and can more accurately calculate the collapse pressure equivalent density value when a reasonable weight coefficient is given.

Description

Technical Field

[0001] The invention relates to a method for evaluating the wellbore collapse pressure of a directional well under the coordinated action of different strength criteria, and belongs to the technical field of petroleum exploration and development. Background Art

[0002] With the rapid development of my country's economy and the deepening industrialization process, the consumption of resources such as oil is increasing, and unconventional and offshore oil and gas resources are attracting increasing attention. In recent years, breakthroughs in directional, highly deviated, horizontal, and extended-reach well technologies have made unconventional and offshore oil and gas a hot area in oil and gas exploration and development. However, drilling complex well structures such as directional, highly deviated, horizontal, and extended-reach wells presents a series of engineering and technical difficulties and challenges, among which wellbore collapse is a particularly thorny issue.

[0003] From a mechanical perspective, drilling through the formation to form a wellbore disrupts the in-situ stress balance, leading to stress redistribution in the formation surrounding the wellbore. When this redistributed stress exceeds the formation strength, wellbore collapse may occur. The general approach to calculating the wellbore collapse pressure in a directional well is to calculate the wellbore stress distribution by comprehensively considering factors such as ground stress, wellbore trajectory, and wellbore pressure. The calculated stress is then applied to the rock strength criterion for judgment. The critical wellbore pressure, where the wellbore stress equals the rock strength, is the collapse pressure required to maintain wellbore stability.

[0004] Generally, wellbore stress is calculated primarily using the Bradely formula based on linear elasticity theory. However, there are many rock strength criteria to choose from, including the Mohr-Coulomb criterion, the Mogi-Coulomb criterion, the Drucker-Prager criterion, the Hoek-Brown criterion, the modified Lade criterion, the modified Wiebols-Cook criterion, and others. Different strength criteria are used in the wellbore collapse pressure assessment process primarily because rock strength criteria are not fully applicable to all rock types. This results in limitations in wellbore collapse pressure assessment methods, making it impossible to accurately calculate the collapse pressure of any type of rock or formation. This means that the collapse pressure assessment results in large errors and is only applicable to one or a few specific rock types or formations, lacking a universal wellbore collapse pressure assessment method.

[0005] To this end, the present invention integrates multiple different types of strength criteria, such as the Mohr-Coulomb criterion, the Mogi-Coulomb criterion, the Drucker-Prager criterion, the modified Lade criterion, and the modified Wiebols-Cook criterion, to give full play to the advantages and synergy of different strength criteria, thereby inventing a method for evaluating the wellbore collapse pressure of a directional well under the synergy of different strength criteria. This method can be applied to different types of rocks or formations and is a universal wellbore collapse pressure evaluation method. Summary of the Invention

[0006] In order to overcome the problems in the prior art, the present invention provides a method for evaluating the wellbore collapse pressure of a directional well under the coordinated action of different strength criteria.

[0007] The present invention provides a technical solution to solve the above technical problems: a method for evaluating the wellbore collapse pressure of a directional well under the coordinated action of different strength criteria, comprising the following steps:

[0008] S1. Using well logging, drilling and completion, and laboratory test data, determine the vertical depth of the drilled formation, formation pore pressure, overburden pressure, maximum horizontal in-situ stress, minimum horizontal in-situ stress, and azimuth of the maximum horizontal in-situ stress;

[0009] S2. Using well logging and indoor rock mechanics test data, determine the rock cohesion, rock internal friction angle, rock Poisson's ratio, rock porosity, Biot coefficient and wellbore permeability coefficient of the drilled formation;

[0010] S3. Establish a collapse pressure calculation model under different rock strength criteria;

[0011] S4. Calculate the collapse pressure of N groups of rock samples from the drilled formation under different rock strength criteria, and fit the results with the data obtained from the rock mechanics test to determine the number of rock samples that meet the different rock strength criteria. Then, calculate the corresponding ratios to obtain the relative importance of the different rock strength criteria.

[0012] S5. Based on the relative importance of different rock strength criteria, the comparison coefficient matrix A is established by using the hierarchical analysis method, the obtained weight coefficient vector is tested for consistency, and the weight coefficients of different rock strength criteria are determined;

[0013] S6. Combining the collapse pressures calculated by different strength criteria and the weight coefficient determined in step S5, a directional well collapse pressure calculation model under the synergistic effect of different strength criteria is established, and the directional wellbore collapse pressure under the synergistic effect of different strength criteria is calculated.

[0014] Further technical solution, the specific process of step S3 is:

[0015] S31, calculating the wellbore stress components of the drilled formation;

[0016] S32, calculating the effective principal stress of the wellbore of the drilled formation based on the wellbore stress components;

[0017] S33. Establishing nonlinear functions of collapse pressure under different strength criteria based on effective principal stress of wellbore;

[0018] S34. Use the dichotomy method to calculate the nonlinear function of collapse pressure under different strength criteria, and obtain the collapse pressure calculation model corresponding to different strength criteria.

[0019] According to a further technical solution, the calculation formula of the wellbore stress component is:

[0020]

[0021] in,

[0022]

[0023] Where: σ rr , σ θθ , σ zz are the radial, tangential and axial stress components of the wellbore, MPa; τ θz , τ rθ , τ rz They are the three shear stress components of the wellbore, MPa; p m is the wellbore pressure, MPa; p p is the formation pore pressure, MPa; σ v , σ H , σ h are the overlying rock pressure, maximum horizontal in-situ stress and minimum horizontal in-situ stress, respectively, in MPa; δ represents the wellbore permeability coefficient, which is dimensionless, where δ = 0 means the wellbore is completely impermeable and δ = 1 means the wellbore is completely permeable; φ is the rock porosity; ψ is the wellbore inclination angle, in degrees; Ω is the angle between the wellbore inclination and the maximum horizontal in-situ stress, in degrees; θ is the wellbore circumference angle, in degrees; v is the Poisson's ratio of the rock; K1 is the seepage effect coefficient; α is the Biot coefficient; A, B, C, D, E, F, G, H, and J are coordinate transformation coefficients.

[0024] According to a further technical solution, the calculation formula of the effective principal stress of the wellbore is:

[0025]

[0026] Where: σ1 is the maximum principal stress of the wellbore, MPa; σ2 is the intermediate principal stress of the wellbore, MPa; σ3 is the minimum principal stress of the wellbore, MPa; α is the Biot coefficient; p p is the formation pore pressure, MPa.

[0027] In a further technical solution, the nonlinear functions of collapse pressure under different strength criteria include:

[0028] Nonlinear function of well wall collapse 1:

[0029]

[0030] Where: is the collapse pressure calculated by Mohr-Coulomb criterion, MPa; c is the rock cohesion, MPa; is the internal friction angle of rock, °;

[0031] Nonlinear function of well wall collapse 2:

[0032]

[0033] in,

[0034]

[0035] Where: is the collapse pressure calculated by the Mogi-Coulomb criterion, MPa; a and b are material constants, which depend on the rock cohesion and internal friction angle;

[0036] Nonlinear function of well wall collapse 3:

[0037]

[0038] in,

[0039]

[0040] Where: is the collapse pressure calculated by the Drucker-Prager criterion, MPa; α' and k are material constants, which depend on the cohesion and internal friction angle; J1 is the average effective stress; J2 is the second invariant of the stress deviator;

[0041] Nonlinear function of well wall collapse 4:

[0042]

[0043] in,

[0044]

[0045] Where: is the collapse pressure calculated by modifying the Lade criterion, MPa; S and η are material constants, which depend on the cohesion and internal friction angle;

[0046] Nonlinear function of well wall collapse 5:

[0047]

[0048] in,

[0049]

[0050] Where: is the collapse pressure calculated by modifying the Wiebols-Cook criterion, MPa; A', B', C' are material constants, which depend on the cohesion and internal friction angle; UCS is the uniaxial strength of rock, MPa; J1 is the mean effective stress; J2 is the second invariant of the stress deviator.

[0051] Further technical solution, the specific process of step S4 is:

[0052] S41. Calculating the collapse pressure of N groups of rock samples from the drilled formation under different rock strength criteria to obtain calculated data. Then, performing a triaxial rock mechanics strength test under different confining pressures on the N groups of rock samples from the drilled formation through an indoor rock mechanics test to obtain test data. The calculated data are then fitted with the test data.

[0053] S42. Count the number of rock samples whose test results meet different rock strength criteria. If the relative error between the calculated data and the test data is within 3%, the rock samples meet the criteria.

[0054] S43. By calculating the ratio between the number of rock samples that meet different rock strength criteria, the relative importance between any two criteria is obtained.

[0055] According to a further technical solution, the different rock strength criteria include the Mohr-Coulomb criterion, the Mogi-Coulomb criterion, the Drucker-Prager criterion, the modified Lade criterion and the modified Wiebols-Cook criterion.

[0056] Further technical solution, the specific steps of step S5 are:

[0057] S51. Establishing a comparison coefficient matrix A between different strength criteria based on the relative importance of different rock strength criteria;

[0058] S52, calculating the eigenvectors of the comparison coefficient matrix A;

[0059] S53. Perform consistency check on the obtained weight coefficient vector and determine the weight coefficients for different rock strengths.

[0060] A further technical solution is that the calculation model of directional well collapse pressure under the synergistic effect of different strength criteria is:

[0061]

[0062] Where, W1 is the weight coefficient of the Mohr-Coulomb criterion; W2 is the weight coefficient of the Mogi-Coulomb criterion; W3 is the weight coefficient of the Drucker-Prager criterion; W4 is the weight coefficient of the modified Lade criterion; W5 is the weight coefficient of the modified Wiebols-Cook criterion; is the collapse pressure calculated by the Mohr-Coulomb criterion, MPa; is the collapse pressure calculated by the Mogi-Coulomb criterion, MPa; is the collapse pressure calculated by Drucker-Prager criterion, MPa; is the collapse pressure calculated by the modified Lade criterion, MPa; is the collapse pressure calculated by the modified Wiebols-Cook criterion, MPa; p c is the wellbore collapse pressure of the directional well under the synergistic effect of different strength criteria, MPa.

[0063] The present invention has the following beneficial effects: since the present invention introduces a weight coefficient, it combines the advantages of other criteria and obtains the synergistic effect of the advantages of different strength criteria. When a reasonable weight coefficient is given, the collapse pressure equivalent density value can be calculated more accurately. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Figure 1 To implement the flow chart;

[0065] Figure 2 This is a comparison chart of the collapse pressure calculation results when the well inclination is 0°;

[0066] Figure 3 This is a comparison chart of the collapse pressure calculation results when the well inclination is 15°;

[0067] Figure 4 This is a comparison chart of the collapse pressure calculation results when the well is inclined at 30°;

[0068] Figure 5 This is a comparison chart of the collapse pressure calculation results when the well is inclined at 45°;

[0069] Figure 6 This is a comparison chart of the collapse pressure calculation results when the well inclination is 60°;

[0070] Figure 7 This is a comparison chart of the collapse pressure calculation results when the well is inclined at 75°;

[0071] Figure 8This is a comparison chart of the collapse pressure calculation results when the well is inclined at 90°. DETAILED DESCRIPTION

[0072] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0073] The method for evaluating the wellbore collapse pressure of a directional well under the coordinated action of different strength criteria of the present invention comprises the following steps:

[0074] S1. Using well logging, drilling and completion, and laboratory test data, determine the vertical depth of the drilled formation, formation pore pressure, overburden pressure, maximum horizontal in-situ stress, minimum horizontal in-situ stress, and azimuth of the maximum horizontal in-situ stress;

[0075] S2. Using well logging and indoor rock mechanics test data, determine the rock cohesion, rock internal friction angle, rock Poisson's ratio, rock porosity, Biot coefficient and wellbore permeability coefficient of the drilled formation;

[0076] S3. Establishing a collapse pressure calculation model under different rock strength criteria, specifically including the following steps:

[0077] S31, calculating the wellbore stress components of the drilled formation;

[0078]

[0079] in,

[0080]

[0081] Where: σ rr , σ θθ , σ zz are the radial, tangential and axial stress components of the wellbore, MPa; τ θz , τ rθ , τ rz They are the three shear stress components of the wellbore, MPa; p m is the wellbore pressure, MPa; p p is the formation pore pressure, MPa; σ v , σ H , σ hare the overburden rock pressure, maximum horizontal in-situ stress, and minimum horizontal in-situ stress, respectively, in MPa; δ represents the wellbore permeability coefficient, dimensionless, where δ = 0 means the wellbore is completely impermeable and δ = 1 means the wellbore is completely permeable; φ is the rock porosity; ψ is the wellbore inclination angle, in degrees; Ω is the angle between the wellbore inclination and the maximum horizontal in-situ stress, in degrees; θ is the wellbore circumference angle, in degrees; v is the rock Poisson's ratio; K1 is the seepage effect coefficient; α is the Biot coefficient; A, B, C, D, E, F, G, H, and J are coordinate transformation coefficients;

[0082] S32, calculating the effective principal stress of the wellbore of the drilled formation based on the wellbore stress components;

[0083]

[0084] Where, σ1 is the maximum principal stress of the wellbore, MPa; σ2 is the intermediate principal stress of the wellbore, MPa; σ3 is the minimum principal stress of the wellbore, MPa; α is the Biot coefficient; p p is the formation pore pressure, MPa;

[0085] S33. Establishing nonlinear functions of collapse pressure under different strength criteria based on effective principal stress of wellbore;

[0086] (1) Substituting the effective principal stress of the borehole wall into the Mohr-Coulomb criterion, the nonlinear function 1 for solving the borehole wall collapse is obtained;

[0087]

[0088] Where: is the collapse pressure calculated by Mohr-Coulomb criterion, MPa; c is the rock cohesion, MPa; is the internal friction angle of rock, °;

[0089] (2) Substituting the effective principal stress of the borehole wall into the Mogi-Coulomb criterion, the nonlinear function 2 for solving the borehole wall collapse is obtained;

[0090]

[0091] in,

[0092]

[0093] Where: is the collapse pressure calculated by the Mogi-Coulomb criterion, MPa; a and b are material constants, which depend on the rock cohesion and internal friction angle;

[0094] (3) Substituting the effective principal stress of the wellbore into the Drucker-Prager criterion, we can obtain the nonlinear function 3 for solving the wellbore collapse;

[0095]

[0096] in,

[0097]

[0098] Where: is the collapse pressure calculated by the Drucker-Prager criterion, MPa; α' and k are material constants, which depend on the cohesion and internal friction angle; J1 is the average effective stress; J2 is the second invariant of the stress deviator;

[0099] (4) Substituting the effective principal stress of the wellbore into the modified Lade criterion, the nonlinear function 4 for solving the wellbore collapse is obtained;

[0100]

[0101] in,

[0102]

[0103] Where: is the collapse pressure calculated by modifying the Lade criterion, MPa; S and η are material constants, which depend on the cohesion and internal friction angle;

[0104] (5) Substituting the effective principal stress of the borehole wall into the modified Wiebols-Cook criterion, the nonlinear function 5 for solving the borehole wall collapse is obtained;

[0105]

[0106] in,

[0107]

[0108] Where: is the collapse pressure calculated by modifying the Wiebols-Cook criterion, MPa; A', B', C' are material constants, which depend on the cohesion and internal friction angle; UCS is the uniaxial strength of rock, MPa; J1 is the mean effective stress; J2 is the second invariant of stress deviator;

[0109] S34, using a dichotomy method to calculate the nonlinear function of collapse pressure under different strength criteria, and obtaining a collapse pressure calculation model corresponding to different strength criteria;

[0110] S4. Calculate the collapse pressure of N groups of rock samples from the drilled formation under different rock strength criteria, and fit the results with the data obtained from the rock mechanics test to determine the number of rock samples that meet the different rock strength criteria. Then, calculate the corresponding ratios to obtain the relative importance of the different rock strength criteria.

[0111] S41. Conduct triaxial rock mechanics strength tests on N groups of rock samples from the drilled formation under different confining pressures through indoor rock mechanics tests. Then, calculate the collapse pressure of the N groups of rock samples from the drilled formation using the Mohr-Coulomb criterion, the Mogi-Coulomb criterion, the Drucker-Prager criterion, the modified Lade criterion, and the modified Wiebols-Cook criterion, respectively. Fit the test results to the calculated results.

[0112] S42. Count the number of rock samples whose test results meet the Mohr-Coulomb criterion and mark it as n1; use the same method to count the number of rock samples whose test results meet the Mogi-Coulomb criterion, Drucker-Prager criterion, modified Lade criterion and modified Wiebols-Cook criterion and mark them as n2, n3, n4 and n5 respectively;

[0113] Among them, the relative error between the test results and the calculated results is within 3%, which is the standard for good agreement between the test data and the strength criterion;

[0114] S43, by calculating the ratio between the number of rock samples n1, n2, n3, n4 and n5 that meet the rock strength criteria Get the relative importance a between the two criteria ij ;

[0115] a ij The comparison result of the importance of criteria i and j is given by the experts based on The value of is given by means of a proportional scale table, and:

[0116] Table 1 Ratio scale table

[0117] Factor i vs. factor j Quantized value Equally important 1 Slightly important 3 Strong and important 5 Strongly important 7 Extremely important 9 The middle value of two adjacent judgments 2，4，6，8

[0118] S5. Based on the relative importance of different rock strength criteria, the comparison coefficient matrix A is established by using the hierarchical analysis method, the obtained weight coefficient vector is tested for consistency, and the weight coefficients of different rock strength criteria are determined;

[0119] S51, establishing a comparison coefficient matrix A between different strength criteria;

[0120]

[0121] Among them, a ij is the relative importance of the pairwise criteria obtained in step S43;

[0122] S52, calculating the eigenvectors of the comparison coefficient matrix A;

[0123] First, normalize each column of the matrix:

[0124]

[0125] Secondly, the normalized matrix is ​​summed row by row to obtain the column vector;

[0126]

[0127] Then, the column vector obtained by summing is normalized to obtain the eigenvector;

[0128]

[0129] S53, performing consistency check on the weight coefficient;

[0130] In order to verify the validity of the weight coefficient, the consistency ratio (CR) is calculated, which is the ratio of the consistency index (CI) to the random index (RI). The consistency ratio is defined as:

[0131]

[0132] in,

[0133]

[0134]

[0135]

[0136] Where CR is the consistency ratio; CI is the consistency index; RI is the random consistency index; λ max is the largest characteristic root of matrix A; (AW) i is the i-th component of AW; W i is the weight coefficient;

[0137] The random consistency index RI is related to the order of the comparison coefficient matrix. Generally, the larger the matrix order, the greater the possibility of random deviation from the consistency. The corresponding relationship is shown in Table 2.

[0138] Table 2 Standard values ​​of random consistency index RI

[0139] Matrix order 1 2 3 4 5 6 7 8 9 10 RI 0.00 0.00 0.58 0.90 1.12 1.24 1.32 1.41 1.45 1.49

[0140] When the consistency ratio CR<0.1, it is considered that the inconsistency of the comparison coefficient matrix A is within the allowable range and has satisfactory consistency. After passing the consistency test, its normalized eigenvector W can be used as the weight coefficient vector. Otherwise, the comparison coefficient matrix A must be reconstructed. ij to adjust;

[0141] S6. Combining the collapse pressures calculated by different strength criteria and the weight coefficient determined in step S5, a directional well collapse pressure calculation model under the coordinated action of different strength criteria is established, and the wellbore collapse pressure of the directional well under the coordinated action of different strength criteria is calculated;

[0142]

[0143] Where: W1 is the weight coefficient of the Mohr-Coulomb criterion; W2 is the weight coefficient of the Mogi-Coulomb criterion; W3 is the weight coefficient of the Drucker-Prager criterion; W4 is the weight coefficient of the modified Lade criterion; W5 is the weight coefficient of the modified Wiebols-Cook criterion; is the collapse pressure calculated by the Mohr-Coulomb criterion, MPa; is the collapse pressure calculated by the Mogi-Coulomb criterion, MPa; is the collapse pressure calculated by Drucker-Prager criterion, MPa; is the collapse pressure calculated by the modified Lade criterion, MPa; is the collapse pressure calculated by the modified Wiebols-Cook criterion, MPa; p c is the wellbore collapse pressure of the directional well under the synergistic effect of different strength criteria, MPa.

[0144] Example 1

[0145] The present invention provides a method for evaluating the wellbore collapse pressure of a directional well under the coordinated action of different strength criteria, comprising:

[0146] S1. Using well logging, drilling and completion, and laboratory test data, it was determined that the vertical depth of the drilled formation was 3000 m, the formation pore pressure was 42 MPa, the overburden pressure was 90 MPa, the maximum horizontal in-situ stress was 80 MPa, the minimum horizontal in-situ stress was 60 MPa, and the azimuth of the maximum horizontal in-situ stress was 0°.

[0147] S2. Using well logging and indoor rock mechanics test data, it was determined that the rock cohesion of the drilled formation was 25 MPa, the rock internal friction angle was 35°, the rock Poisson's ratio was 0.25, the rock porosity was 0.1, the Biot coefficient was 0.8, and the wellbore permeability coefficient was 0;

[0148] S3. Based on the basic parameters determined in steps S1 and S2, a collapse pressure calculation model under different rock strength criteria is established, and the nonlinear function of the collapse pressure under different strength criteria is calculated using the dichotomy method to obtain the collapse pressure calculation model corresponding to different strength criteria. Convert the collapse pressure to equivalent density, and the calculation result is as follows: Figures 2 to 8 As shown;

[0149] S4. Conduct indoor rock mechanics tests to determine the number of rock samples n1, n2, n3, n4, and n5 that meet the rock strength criteria, and calculate the relative importance of different criteria by calculating the corresponding ratios;

[0150] S5. Using the hierarchical analysis method, a comparison coefficient matrix A is established, consistency test is performed on the obtained weight coefficient vector, and the weight coefficient is determined;

[0151] First, the comparison coefficient matrix A between different strength criteria is established;

[0152]

[0153] Secondly, normalize each column of matrix A to obtain:

[0154]

[0155] Then sum the normalized matrix row by row to get the column vector;

[0156]

[0157] Then normalize the summed column vector to get the eigenvector:

[0158] W=[0.22 0.48 0.04 0.06 0.20] T

[0159] In order to verify the validity of the weight coefficient, the consistency is tested by calculating the consistency ratio (CR), which is the ratio of the consistency index (CI) to the random index (RI):

[0160]

[0161]

[0162]

[0163] After verification, it was found that the consistency ratio CR was less than 0.1, passing the consistency test; therefore, the weight coefficients were W1 = 0.22, W2 = 0.48, W3 = 0.04, W4 = 0.06, and W5 = 0.20;

[0164] S6. Combining the collapse pressures calculated by different strength criteria and the weight coefficient determined in step S5, a directional well collapse pressure calculation model under the coordinated action of different strength criteria is established, and the wellbore collapse pressure of the directional well under the coordinated action of different strength criteria is calculated;

[0165]

[0166] Therefore, by substituting the results calculated using the Mohr-Coulomb criterion, Mogi-Coulomb criterion, Drucker-Prager criterion, modified Lade criterion, and modified Wiebols-Cook criterion into the above formula, the collapse pressure p under the synergistic effect of different strength criteria can be obtained. c , convert the collapse pressure into equivalent density, and the calculation result is as follows Figures 2 to 8 shown.

[0167] Depend on Figures 2 to 8 It can be seen that: (1) As the well inclination angle increases, the collapse pressure equivalent density also increases. At different azimuth angles, the collapse pressure equivalent density calculated by each criterion is different. Among them, the Mohr-Coulomb criterion ignores the influence of the intermediate principal stress on rock failure, so the collapse pressure calculated by it is significantly higher than that of other calculation models. Then comes the new model, Mogi-Coulomb criterion, modified Lade criterion and modified Wiebols-Cook criterion, while the Drucker-Prager criterion calculates the collapse pressure significantly too low in all cases. Due to the introduction of the weight coefficient, the new model combines the advantages of other criteria and obtains the synergistic effect of the advantages of different strength criteria. As long as the weight coefficient is reasonable, a more accurate collapse pressure equivalent density value can be calculated.

[0168] The above description does not limit the present invention in any form. Although the present invention has been disclosed through the above embodiments, it is not intended to limit the present invention. Any technician familiar with the profession can use the technical content disclosed above to make some changes or modifications to equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for evaluating the wellbore collapse pressure of a directional well under the synergistic effect of different strength criteria, characterized in that: The following steps are involved: S1. Using well logging, drilling and completion, and laboratory test data, determine the vertical depth of the drilled formation, formation pore pressure, overburden pressure, maximum horizontal in-situ stress, minimum horizontal in-situ stress, and azimuth of the maximum horizontal in-situ stress; S2. Using well logging and indoor rock mechanics test data, determine the rock cohesion, rock internal friction angle, rock Poisson's ratio, rock porosity, Biot coefficient and wellbore permeability coefficient of the drilled formation; S3. Establish a collapse pressure calculation model under different rock strength criteria; S31, calculating the wellbore stress components of the drilled formation; in, Where: σ rr , σ θθ , σ zz are the radial, tangential and axial stress components of the wellbore, MPa; τ θz , τ rθ , τ rz They are the three shear stress components of the wellbore, MPa; p m is the wellbore pressure, MPa; p p is the formation pore pressure, MPa; σ v , σ H , σ h are the overburden rock pressure, maximum horizontal in-situ stress, and minimum horizontal in-situ stress, respectively, in MPa; δ represents the wellbore permeability coefficient, dimensionless, where δ = 0 means the wellbore is completely impermeable and δ = 1 means the wellbore is completely permeable; φ is the rock porosity; ψ is the wellbore inclination angle, in degrees; Ω is the angle between the wellbore inclination and the maximum horizontal in-situ stress, in degrees; θ is the wellbore circumference angle, in degrees; v is the rock Poisson's ratio; K1 is the seepage effect coefficient; α is the Biot coefficient; A, B, C, D, E, F, G, H, and J are coordinate transformation coefficients; S32, calculating the effective principal stress of the wellbore of the drilled formation based on the wellbore stress components; σ3=(1-δφ)p m +δφp p -αp p Where: σ1 is the maximum principal stress of the wellbore, MPa; σ2 is the intermediate principal stress of the wellbore, MPa; σ3 is the minimum principal stress of the wellbore, MPa; α is the Biot coefficient; p p is the formation pore pressure, MPa; S33. Establishing nonlinear functions of collapse pressure under different strength criteria based on effective principal stress of wellbore; The different rock strength criteria include the Mohr-Coulomb criterion, the Mogi-Coulomb criterion, the Drucker-Prager criterion, the modified Lade criterion and the modified Wiebols-Cook criterion; S34, using a dichotomy method to calculate the nonlinear function of collapse pressure under different strength criteria, and obtaining a collapse pressure calculation model corresponding to different strength criteria; S4. Calculate the collapse pressure of N groups of rock samples from the drilled formation under different rock strength criteria, and fit the results with the data obtained from the rock mechanics test to determine the number of rock samples that meet the different rock strength criteria. Then, calculate the corresponding ratios to obtain the relative importance of the different rock strength criteria. S41. Calculating the collapse pressure of N groups of rock samples from the drilled formation under different rock strength criteria to obtain calculated data. Then, performing a triaxial rock mechanics strength test under different confining pressures on the N groups of rock samples from the drilled formation through an indoor rock mechanics test to obtain test data. The calculated data are then fitted with the test data. S42. Count the number of rock samples whose test results meet different rock strength criteria. If the relative error between the calculated data and the test data is within 3%, the rock samples meet the criteria. S43, by calculating the ratio between the number of rock samples that meet different rock strength criteria, the relative importance between each criterion is obtained; S5. Based on the relative importance of different rock strength criteria, the comparison coefficient matrix A is established by using the hierarchical analysis method, the obtained weight coefficient vector is tested for consistency, and the weight coefficients of different rock strength criteria are determined; S51. Establishing a comparison coefficient matrix A between different strength criteria based on the relative importance of different rock strength criteria; S52, calculating the eigenvectors of the comparison coefficient matrix A; S53, performing consistency check on the obtained weight coefficient vector, and determining the weight coefficients of different rock strength standards; S6. Combining the collapse pressures calculated by different strength criteria and the weight coefficient determined in step S5, a directional well collapse pressure calculation model under the coordinated action of different strength criteria is established, and the wellbore collapse pressure of the directional well under the coordinated action of different strength criteria is calculated; Where, W1 is the weight coefficient of the Mohr-Coulomb criterion; W2 is the weight coefficient of the Mogi-Coulomb criterion; W3 is the weight coefficient of the Drucker-Prager criterion; W4 is the weight coefficient of the modified Lade criterion; W5 is the weight coefficient of the modified Wiebols-Cook criterion; is the collapse pressure calculated by the Mohr-Coulomb criterion, MPa; is the collapse pressure calculated by the Mogi-Coulomb criterion, MPa; is the collapse pressure calculated by Drucker-Prager criterion, MPa; is the collapse pressure calculated by the modified Lade criterion, MPa; is the collapse pressure calculated by the modified Wiebols-Cook criterion, MPa; p c is the wellbore collapse pressure of the directional well under the synergistic effect of different strength criteria, MPa.

2. The method for evaluating the wellbore collapse pressure of a directional well under the synergistic effect of different strength criteria according to claim 1 is characterized in that: The nonlinear functions of collapse pressure under different strength criteria include: Nonlinear function of well wall collapse 1: Where: is the collapse pressure calculated by Mohr-Coulomb criterion, MPa; c is the rock cohesion, MPa; is the internal friction angle of rock, °; Nonlinear function of well wall collapse 2: in, Where: is the collapse pressure calculated by the Mogi-Coulomb criterion, MPa; a and b are material constants, which depend on the rock cohesion and internal friction angle; Nonlinear function of well wall collapse 3: in, Where: is the collapse pressure calculated by the Drucker-Prager criterion, MPa; α' and k are material constants, which depend on the cohesion and internal friction angle; J1 is the average effective stress; J2 is the second invariant of the stress deviator; Nonlinear function of well wall collapse 4: in, Where: is the collapse pressure calculated by modifying the Lade criterion, MPa; S and η are material constants, which depend on the cohesion and internal friction angle; Nonlinear function of well wall collapse 5: in, Where: is the collapse pressure calculated by modifying the Wiebols-Cook criterion, MPa; A', B', C' are material constants, which depend on the cohesion and internal friction angle; UCS is the uniaxial strength of rock, MPa; J1 is the mean effective stress; J2 is the second invariant of the stress deviator.

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