Method and system for predicting leakage pressure of structural plane development stratum

Abstract

The invention relates to a leakage pressure prediction method and system for a structural plane development stratum, and belongs to the field of oil-gas exploration and development. The method comprises the following steps: performing borehole coordinate conversion based on formation stress state distribution to obtain well periphery stress distribution under any borehole trajectory; based on the well circumference stress distribution under any well track, the three-direction principal stress of the well wall is obtained; based on the three-direction principal stress of the well wall, the dip angle and the trend of the structural surface, the tensile strength of a base body, the tensile strength of bedding, the fracture toughness at different bedding angles, the shear failure strength of the base body and the shear failure strength of bedding; and obtaining the leakage pressure of matrix tensile failure, the leakage pressure of tensile failure along the bedding surface, the leakage pressure of shear failure along the matrix, the leakage pressure of shear failure along the bedding surface and the leakage pressure of expansion along the crack surface. According to the method, the overall calculation method is reliable, consideration factors are comprehensive, and high practicability is achieved.

Description

Technical Field

[0001] The present invention belongs to the field of oil and gas exploration and development, and in particular relates to a method and system for predicting the leakage pressure of a structure-developed formation. Background Art

[0002] Formations with developed structural planes, such as fractured carbonates and layered shales, are common geological formations encountered during oil drilling. These formations are also typical examples of formations prone to wellbore instability. Drilling experience in multiple blocks domestically and internationally has shown that drilling these formations frequently leads to complex downhole conditions (especially significant drilling fluid loss), long drilling cycles, and high drilling costs, severely hindering the efficient development of oil and gas in these reservoirs.

[0003] Bedding and natural fractures, as typical weak structural planes, are the main controlling factors for leakage in formations with structural plane development. Compared with homogeneous formations, the rock strength of formations with structural plane development is relatively low, and the structural plane provides better seepage channels, resulting in a significant decrease in the leakage pressure of the formation, a decrease in the orientation of safe wellbore trajectories, and an increase in drilling difficulty. In order to effectively control formation leakage, it is necessary to first determine the accurate distribution of formation leakage pressure, and then formulate reasonable drilling engineering parameters such as drilling fluid density, wellbore trajectory, and wellbore structure design. To this end, based on indoor mechanical experiments and considering the development characteristics of formation structural planes, the present invention integrates five types of leakage mechanisms, namely, tensile failure along the matrix, shear failure along the matrix, tensile fracture along the bedding, shear fracture along the bedding, and expansion along fractures, to construct a new leakage pressure prediction method suitable for formations with structural plane development. Summary of the Invention

[0004] In response to the above problems, the present invention provides a method and system for predicting the lost circulation pressure of a structure-developed formation.

[0005] The first object of the present invention is to provide a method for predicting lost circulation pressure in a surface-developed formation, comprising:

[0006] Based on the experimental tests on rock samples with different bedding angles, the matrix tensile strength, bedding tensile strength, fracture toughness at different bedding angles, matrix shear failure strength and bedding shear failure strength were obtained;

[0007] Based on the wellbore coordinate transformation of the formation stress state distribution, the stress distribution around the wellbore under any wellbore trajectory is obtained;

[0008] Based on the stress distribution around the wellbore under any wellbore trajectory, the three-dimensional principal stress of the wellbore wall is obtained;

[0009] Based on the three-dimensional principal stress of the wellbore, the inclination and strike of the structural surface, the matrix tensile strength, the bedding tensile strength, the fracture toughness at different bedding angles, the matrix shear failure strength and the bedding shear failure strength, the leakage pressure of matrix tensile failure, the leakage pressure of tensile fracture along the bedding surface, the leakage pressure along the matrix shear fracture, the leakage pressure of shear fracture along the bedding surface and the leakage pressure of expansion along the fracture surface are obtained, wherein the inclination and strike of the structural surface include the inclination and strike of the bedding surface and the inclination and strike of the natural fracture surface;

[0010] Based on the comparison of the leakage pressure caused by matrix tensile failure, the leakage pressure caused by tensile fracture along bedding plane, the leakage pressure caused by matrix shear fracture, the leakage pressure caused by shear fracture along bedding plane and the leakage pressure caused by expansion along fracture plane, the minimum value is determined to be the formation leakage pressure.

[0011] In an embodiment of the present invention, the rock samples with different bedding angles are obtained by drilling cores along different bedding angles.

[0012] In an embodiment of the present invention, the matrix tensile strength and bedding tensile strength are obtained by Brazilian splitting tests on rock samples with different bedding angles, and the fracture toughness at different bedding angles is obtained by center groove semi-disk tests on rock samples with different bedding angles; the matrix shear failure strength and bedding shear failure strength are obtained by testing rock samples with different bedding angles using a triaxial compression tester.

[0013] In an embodiment of the present invention, the distribution of formation stress state is obtained based on drilling and geological data statistics of the target block.

[0014] In an embodiment of the present invention, the three-dimensional principal stress of the wellbore wall is obtained based on the wellbore stress distribution under an arbitrary wellbore trajectory, including:

[0015] Based on the stress distribution around the wellbore under any wellbore trajectory, the principal stress of the wellbore wall is calculated;

[0016] Based on the comparison of the magnitude of the main stress of the wellbore wall, the maximum, intermediate and minimum main stresses at the wellbore wall are determined; among them, the maximum, intermediate and minimum main stresses are the three-dimensional main stresses of the wellbore wall.

[0017] In an embodiment of the present invention, the dip angle and strike of the structural surface are obtained by statistically analyzing imaging logging data in the work area.

[0018] In an embodiment of the present invention, the leakage pressure of matrix tensile failure, the leakage pressure of tensile fracture along bedding plane, the leakage pressure along matrix shear fracture, the leakage pressure along bedding plane shear fracture, and the leakage pressure along fracture plane expansion are obtained based on the three-dimensional principal stress of the wellbore, the inclination and strike of the structural surface, the matrix tensile strength, the bedding tensile strength, the fracture toughness at different bedding angles, the matrix shear failure strength, and the bedding shear failure strength, including:

[0019] Based on the three-dimensional principal stress of the wellbore and the dip and strike of the bedding plane, the angle between the three-dimensional principal stress of the wellbore and the normal direction of the bedding plane is calculated;

[0020] Based on the three-dimensional principal stress of the wellbore and the inclination and strike of the natural fracture surface, the angle between the three-dimensional principal stress of the wellbore and the normal direction of the fracture surface is calculated;

[0021] Based on the three principal stresses of the wellbore, the angle between the three principal stresses of the wellbore and the normal direction of the bedding plane, the tensile strength of the matrix, the tensile strength of the layer, and the maximum tensile stress criterion, the leakage pressure along the tensile failure of the matrix and the leakage pressure along the tensile failure of the bedding plane are obtained;

[0022] Based on the three principal stresses of the wellbore, the angle between the three principal stresses of the wellbore and the normal direction of the bedding plane, the tensile strength of the matrix, the shear failure strength of the matrix, the shear failure strength of the bedding, and the shear failure criterion, the loss pressure along the shear failure of the matrix and the loss pressure along the shear failure of the bedding plane are obtained;

[0023] Based on the three principal stresses of the wellbore, the dip and strike of the wellbore and bedding plane, the angle between the three principal stresses of the wellbore and the normal of the fracture plane, the fracture toughness at different bedding angles, and the approximate fracture toughness criterion, the leakage pressure along the fracture plane is obtained.

[0024] A second object of the present invention is to provide a system for predicting lost circulation pressure in a faceted formation, comprising:

[0025] The experimental testing module is used to test rock samples with different bedding angles to obtain matrix tensile strength, bedding tensile strength, fracture toughness at different bedding angles, matrix shear failure strength, and bedding shear failure strength;

[0026] The stress distribution module is used to convert the wellbore coordinates based on the formation stress state distribution to obtain the wellbore circumferential stress distribution under any wellbore trajectory;

[0027] The three-dimensional principal stress module is used to obtain the three-dimensional principal stress of the wellbore wall based on the stress distribution around the wellbore under any wellbore trajectory;

[0028] The calculation module is used to obtain the leakage pressure of matrix tensile failure, the leakage pressure of tensile fracture along bedding plane, the leakage pressure along matrix shear fracture, the leakage pressure along bedding plane shear fracture and the leakage pressure along fracture plane expansion based on the three-dimensional principal stress of the wellbore, the inclination and strike of the structural plane, the matrix tensile strength, the bedding tensile strength, the fracture toughness at different bedding angles, the matrix shear failure strength and the bedding shear failure strength, wherein the inclination and strike of the structural plane include the inclination and strike of the bedding plane and the inclination and strike of the natural fracture plane;

[0029] The determination module is used to compare the values ​​of the leakage pressure caused by matrix tensile damage, the leakage pressure caused by tensile fracture along the bedding plane, the leakage pressure caused by matrix shear fracture, the leakage pressure caused by shear fracture along the bedding plane and the leakage pressure caused by expansion along the fracture plane, and determine the minimum value as the formation leakage pressure.

[0030] In an embodiment of the present invention, the three-dimensional principal stress module includes a wellbore principal stress submodule and a comparison submodule;

[0031] The wellbore principal stress submodule is used to calculate the wellbore principal stress based on the wellbore circumferential stress distribution under any wellbore trajectory;

[0032] The comparison submodule is used to determine the maximum, middle and minimum principal stresses at the wellbore position based on the comparison of the magnitudes of the wellbore principal stresses; wherein the maximum, middle and minimum principal stresses are the three-dimensional principal stresses of the wellbore.

[0033] In an embodiment of the present invention, the calculation module includes a first calculation submodule, a second calculation submodule, a third calculation submodule, a fourth calculation submodule and a fifth calculation submodule;

[0034] The first calculation submodule is used to calculate the angle between the three-dimensional principal stress of the wellbore and the normal direction of the bedding surface based on the three-dimensional principal stress of the wellbore and the dip and strike of the bedding surface;

[0035] The second calculation submodule is used to calculate the angle between the three-dimensional principal stress of the wellbore and the normal direction of the fracture surface based on the three-dimensional principal stress of the wellbore and the inclination and strike of the natural fracture surface;

[0036] The third calculation submodule is used to obtain the leakage pressure along the tensile failure of the matrix and the leakage pressure along the tensile fracture of the bedding plane based on the three principal stresses of the wellbore, the angle between the three principal stresses of the wellbore and the normal direction of the bedding plane, the tensile strength of the matrix, the tensile strength of the layer, and the maximum tensile stress criterion;

[0037] The fourth calculation submodule is used to obtain the leakage pressure along the shear fracture of the matrix and the leakage pressure along the shear fracture of the bedding plane based on the three-dimensional principal stress of the wellbore, the angle between the three-dimensional principal stress of the wellbore and the normal direction of the bedding plane, the tensile strength of the matrix, the shear failure strength of the matrix, the shear failure strength of the bedding, and the shear failure criterion;

[0038] The fifth calculation submodule is used to obtain the leakage pressure extending along the fracture surface based on the three-dimensional principal stress of the wellbore, the three-dimensional principal stress of the wellbore and the inclination and strike of the bedding surface, the angle between the three-dimensional principal stress of the wellbore and the normal of the fracture surface, the fracture toughness at different bedding angles, and the approximate fracture toughness criterion.

[0039] Beneficial effects of the present invention:

[0040] The present invention provides a method and system for predicting the loss pressure of a structural surface-developed formation. The method utilizes the mechanical parameters of the matrix, bedding, and fractures (including matrix tensile strength, bedding tensile strength, fracture toughness at different bedding angles, matrix shear failure strength, and bedding shear failure strength), the three-dimensional principal stress of the wellbore, and the spatial distribution of the bedding plane and the fracture plane (characterized by the angle between the three-dimensional principal stress of the wellbore and the normal to the bedding plane; the angle between the three-dimensional principal stress of the wellbore and the normal to the fracture plane) to obtain the loss pressure of matrix tensile failure, the loss pressure of tensile fracture along the bedding plane, the loss pressure of matrix shear fracture, the loss pressure of shear fracture along the bedding plane, and the extended loss pressure along the fracture plane. The method also predicts the loss pressure of the structural surface formation by comparing the loss pressure of matrix tensile failure, the loss pressure of tensile fracture along the bedding plane, the loss pressure of matrix shear fracture, the loss pressure of shear fracture along the bedding plane, and the extended loss pressure along the fracture plane.

[0041] In the above process, the present invention takes into account the defects of the existing structural surface formation loss pressure prediction method, integrates five types of loss mechanisms: tensile failure along the matrix, shear failure along the matrix, tensile fracture along the bedding, shear fracture along the bedding, and expansion along the cracks, and forms a new structural surface formation loss pressure prediction method. The overall calculation method is reliable, takes into account comprehensive factors, and has strong practicality.

[0042] Other features and advantages of the present invention will be described in the following description, and in part will become apparent from the description, or will be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0044] Figure 1 A schematic flow chart of a method for predicting lost circulation pressure in a faceted formation according to an embodiment of the present invention is shown;

[0045] Figure 2 A schematic diagram showing matrix tensile strength and bedding tensile strength, shear failure strength and bedding shear failure strength obtained according to a Brazilian splitting test and a triaxial compression test in an embodiment of the present invention, respectively;

[0046] Figure 3 A schematic diagram showing the fracture toughness at different bedding angles tested using the center-notched half-disk method according to an embodiment of the present invention is shown;

[0047] Figure 4 A comparison diagram of the lost circulation pressure, the actual lost circulation volume, and the practical drilling fluid density in the lost circulation pressure prediction at the lost circulation location according to an embodiment of the present invention is shown;

[0048] Figure 5 A schematic diagram of a framework of a system for predicting lost circulation pressure in a faceted formation according to an embodiment of the present invention is shown;

[0049] In the figure: experimental test module 1; stress distribution module 2; three-direction principal stress module 3; calculation module 4. DETAILED DESCRIPTION

[0050] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0051] like Figure 1 As shown, a method for predicting lost circulation pressure in a faceted formation according to an embodiment of the present invention includes:

[0052] S1. Based on the experimental testing of rock samples with different bedding angles, the matrix tensile strength, bedding tensile strength, fracture toughness at different bedding angles, matrix shear failure strength and bedding shear failure strength are obtained;

[0053] S2. Based on the formation stress state distribution, the wellbore coordinate transformation is performed to obtain the stress distribution around the wellbore under any wellbore trajectory;

[0054] S3. Based on the stress distribution around the wellbore under any wellbore trajectory, the three-dimensional principal stress of the wellbore wall is obtained;

[0055] S4. Based on the three principal stresses of the wellbore, the inclination and strike of the structural surface, the matrix tensile strength, the bedding tensile strength, the fracture toughness at different bedding angles, the matrix shear failure strength, and the bedding shear failure strength, the leakage pressure due to matrix tensile failure, the leakage pressure due to tensile fracture along the bedding surface, the leakage pressure due to matrix shear fracture, the leakage pressure due to shear fracture along the bedding surface, and the leakage pressure due to expansion along the fracture surface are obtained. The inclination and strike of the structural surface include the inclination and strike of the bedding surface and the inclination and strike of the natural fracture surface.

[0056] S5. Based on the comparison of the leakage pressure due to matrix tensile damage, the leakage pressure due to tensile fracture along the bedding plane, the leakage pressure due to shear fracture along the matrix, the leakage pressure due to shear fracture along the bedding plane and the leakage pressure due to expansion along the fracture plane, the minimum value is determined as the formation leakage pressure.

[0057] In step S1, the rock samples with different bedding angles are obtained by drilling cores along different bedding angles;

[0058] In the embodiment of the present invention, field outcrops or downhole rock samples are used as objects, and cores (short cylindrical cores, 25 mm in diameter, 25 mm in length) are drilled along different bedding angles using an indoor drilling rig to serve as rock samples with different bedding angles.

[0059] The Brazilian splitting test and triaxial compression test were used to obtain the matrix tensile strength, bedding tensile strength, shear failure strength and bedding shear failure strength respectively. Figure 2 As shown. The test results show that the tensile strength of the matrix S tm About 5.5MPa, shear failure strength T tm is 66.3MPa; bedding tensile strength S tb About 4.2MPa, bedding shear failure strength T tb The fracture toughness at different bedding angles was tested using the center-notched half-disk method. Figure 3 As the bedding angle increases, the fracture toughness decreases, as shown in formula (1):

[0060] K IC (θ b )=-0.0051θ b +1.2725 (1)

[0061] In formula (1), K IC (θ b )—Fracture toughness at different bedding angles.

[0062] It can be seen that the purpose of step S1 is to obtain the mechanical parameters of the matrix, bedding and cracks including matrix tensile strength, bedding tensile strength, fracture toughness at different bedding angles, matrix shear failure strength and bedding shear failure strength.

[0063] In step S2, the formation stress state distribution is obtained based on drilling and geological data statistics of the target block. The formation stress state distribution includes vertical ground stress, horizontal ground stress and pore pressure, as shown in Table 1.

[0064] Table 1

[0065] stress Numerical Vertical geostress 77.01MPa~83.98MPa Maximum horizontal ground stress 69.26MPa~78.06MPa Minimum horizontal ground stress 62.04MPa~70.25MPa Pore ​​pressure 42.05MPa~61.21MPa

[0066] According to the above stress distribution characteristics, the wellbore coordinate transformation is used to obtain the wellbore stress (σ r , σ θ , σ z , σ θz , σ rθ , σ rz ), as shown in formula (2):

[0067]

[0068] In formula (2): r , σ θ , σ z — radial, circumferential and axial normal stresses in cylindrical coordinate system, MPa; σ θz , σ rθ , σ rz Distribution is the shear stress in the θZ, rθ, and rz planes in cylindrical coordinates, MPa; σ xx , σ yy , σ zz Distribution is the stress component in the X, Y, and Z directions in rectangular coordinates, MPa; σ xy , σ xz , σ yz are the components of ground stress in the XY, XZ, and YZ planes in the rectangular coordinate system, MPa; ψ is the wellbore angle, °; v is the Poisson's ratio; p w is the liquid column pressure, MPa.

[0069] In step S2, the three-dimensional principal stress of the wellbore wall is obtained based on the stress distribution around the wellbore under any wellbore trajectory, including:

[0070] A1. Calculate the principal stress of the wellbore based on the stress distribution around the wellbore under any wellbore trajectory;

[0071] A2. Based on the comparison of the magnitude of the main stress of the wellbore wall, the maximum, intermediate and minimum main stresses at the wellbore wall are determined; among them, the maximum, intermediate and minimum main stresses are the three-dimensional main stresses of the wellbore wall.

[0072] In step A1, the main stress of the wellbore (σ i , σ j , σ k ) (solved using formula (3)), as shown in formula (3), the method of obtaining the main stress of the wellbore wall according to the obtained wellbore wall stress distribution is common knowledge in the technical field, and the present invention does not limit the specific obtaining process;

[0073]

[0074] In formula (3): i, σ j , σ k —Triaxial principal stress at the wellbore wall, MPa.

[0075] In step A2, the maximum, intermediate, and minimum principal stresses (σ1, σ2, σ3) at the wellbore are determined by comparing the three principal stresses.

[0076] In step S3, the dip angle Dp and strike Az of the structural surface are obtained by statistically analyzing imaging logging data in the work area;

[0077] Since the structural plane is divided into two categories, bedding plane and fracture plane, the dip angle Dp and strike Az of the structural plane include the dip angle Dp1 and strike Az1 of the bedding plane, and the dip angle Dp2 and strike Az2 of the natural fracture plane;

[0078] The obtained bedding plane dip angle Dp1 is 32°, and the dip Az1 is 65°; the fracture plane dip angle Dp2 is 14°, and the dip Az2 is 75°;

[0079] And calculate the direction vector of the normal line of the structural surface (fracture surface and bedding surface) as shown in formula (4);

[0080] Based on the stress distribution of the wellbore and the spatial coordinate relationship, the direction vector of the normal line of the structural surface (fracture surface, bedding surface) is as follows:

[0081]

[0082] In formula (4), n1 is the normal vector of the structural surface; Dp is the inclination angle of the structural surface, in degrees. Dp1 is used when the structural surface is a bedding plane, and Dp2 is used when the structural surface is a fracture plane; Az is the strike of the structural surface, in degrees. Az2 is used when the structural surface is a bedding plane, and Az2 is used when the structural surface is a fracture plane.

[0083] Step S4, based on the three principal stresses of the wellbore, the inclination and strike of the structural surface, the matrix tensile strength, the bedding tensile strength, the fracture toughness at different bedding angles, the matrix shear failure strength, and the bedding shear failure strength, obtains the leakage pressure due to matrix tensile failure, the leakage pressure due to tensile fracture along the bedding plane, the leakage pressure due to matrix shear fracture, the leakage pressure due to shear fracture along the bedding plane, and the leakage pressure due to expansion along the fracture plane, including:

[0084] B1. Based on the three principal stresses of the wellbore and the dip and strike of the bedding plane, calculate the angle between the three principal stresses of the wellbore and the normal direction of the bedding plane;

[0085] B2. Based on the three-dimensional principal stress of the wellbore and the inclination and strike of the natural fracture surface, calculate the angle between the three-dimensional principal stress of the wellbore and the normal direction of the fracture surface;

[0086] B3. Based on the three principal stresses of the wellbore, the angle between the three principal stresses of the wellbore and the normal direction of the bedding plane, the tensile strength of the matrix, the tensile strength of the interlayer, and the maximum tensile stress criterion, the loss pressure along the tensile failure of the matrix and the loss pressure along the tensile failure of the bedding plane are obtained;

[0087] B4. Based on the three principal stresses of the wellbore, the angle between the three principal stresses of the wellbore and the normal direction of the bedding plane, the matrix tensile strength, the matrix shear failure strength, the bedding shear failure strength, and the shear failure criterion, the loss pressure along the matrix shear failure and the loss pressure along the bedding plane shear failure are obtained;

[0088] B5. Based on the three principal stresses of the wellbore, the dip and strike of the wellbore and bedding plane, the angle between the three principal stresses of the wellbore and the normal of the fracture plane, the fracture toughness at different bedding angles, and the approximate fracture toughness criterion, the leakage pressure along the fracture plane is obtained.

[0089] In step B1 and step B2, the angle between the three principal stresses of the wellbore and the normal direction of the bedding plane is calculated based on the three principal stresses of the wellbore and the dip and strike of the bedding plane; the angle between the three principal stresses of the wellbore and the normal direction of the fracture plane is calculated based on the three principal stresses of the wellbore and the dip and strike of the natural fracture plane;

[0090] Taking the maximum principal stress as an example, the angle between the maximum principal stress of the wellbore and the normal to the bedding plane is calculated. First, the maximum principal stress direction vector n2(σ1) of any point on the wellbore is calculated by coordinate transformation, combining the well inclination angle α, the azimuth angle β, and the well circumference angle ψ. Secondly, the direction vector of the normal to the structural surface (fracture surface, bedding surface) and the maximum principal stress direction vector n2(σ1) are used to calculate the angle between the two direction vectors, thereby obtaining the angle between the three-dimensional principal stress of the wellbore and the normal to the bedding plane. Similarly, the angle between the remaining three-dimensional principal stress of the wellbore and the normal to the bedding plane, as well as the angle between the three-dimensional principal stress of the wellbore and the normal to the fracture plane, are obtained.

[0091] Taking the maximum principal stress as an example, the specific calculation process is as follows:

[0092] The maximum principal stress at the wellbore position and the vertical angle are shown in formula (5):

[0093]

[0094] For any point on the wellbore wall, the maximum principal stress direction vector n2(σ1) can be expressed in the coordinate system as formula (6):

[0095]

[0096] In formula (6), α and β are the well inclination and azimuth, respectively, in degrees. ψ is the well circumference angle, in degrees.

[0097] Based on the same spatial transformation principle, the distribution of the direction vectors n2(σ1) and n2(σ3) of the intermediate principal stress (σ2) and the minimum principal stress (σ3) can be obtained. On this basis, the angle between the normal direction of the structural plane (bedding plane and fracture plane) and the three principal stresses is shown in Equation (7).

[0098]

[0099] In formula (7): β i (i=1,2,3) is the angle between the bedding plane normal and σ1, σ2, σ3, in degrees. β i f (i=1,2,3) is the angle between the normal of the crack surface and σ1, σ2, σ3, °.

[0100] In step B3, based on the three principal stresses of the wellbore, the angle between the three principal stresses of the wellbore and the normal direction of the bedding plane, the tensile strength of the matrix, the tensile strength of the layer, and the maximum tensile stress criterion, the loss pressure along the tensile failure of the matrix and the loss pressure along the tensile failure of the bedding plane are obtained;

[0101] The details are as follows:

[0102] According to the maximum tensile stress criterion (specific expression is shown in formula (8)), the leakage pressure P along the matrix shear fracture is mf , the leakage pressure P due to shear fracture along the bedding plane bf The calculation expression of is shown in formula (8);

[0103]

[0104] In formula (8): S tm 、S tb — are matrix tensile strength and bedding tensile strength, MPa; δ—biot coefficient.

[0105] In step B4, based on the three principal stresses of the wellbore, the angle between the three principal stresses of the wellbore and the normal direction of the bedding plane, the matrix tensile strength, the matrix shear failure strength, the bedding shear failure strength, and the shear failure criterion, the leakage pressure P along the matrix shear failure is obtained. mf , the leakage pressure P due to shear failure along the bedding plane bf ;

[0106] The details are as follows:

[0107] According to the shear failure criterion (the specific expression is shown in formula (9)), the leakage pressure along the matrix shear fracture (P mtf ), the leakage pressure due to shear fracture along the bedding plane (P btf ).

[0108]

[0109] Where: T tm 、T tb —are the matrix shear failure strength and bedding shear failure strength, MPa.

[0110] In B5, the leakage pressure along the fracture surface is obtained based on the three principal stresses of the wellbore, the dip and strike of the bedding plane, the angle between the three principal stresses of the wellbore and the normal of the fracture surface, the fracture toughness at different bedding angles, and the approximate fracture toughness criterion;

[0111] The details are as follows:

[0112] According to the approximate fracture toughness criterion (the specific expression is shown in formula (10)), the leakage pressure P along the crack surface is l The calculation expression of is shown in formula (10);

[0113]

[0114] In formula (10): —Angle between the normal direction of the crack surface and the maximum principal stress, °; β3—Angle between the normal direction of the bedding surface and the minimum principal stress, °; l a —fracture half-length, m; obtained by imaging logging in the target work area, taking 0.3 m; K IC (β3)—Fracture toughness at bedding angle β3, MPa.

[0115] Among them, the fracture toughness values ​​at different angles are obtained from previous experiments and can be calculated according to formula (1).

[0116] In step S5, based on the comparison of the values ​​of the leakage pressure due to matrix tensile failure, the leakage pressure due to tensile fracture along bedding plane, the leakage pressure due to matrix shear fracture, the leakage pressure due to shear fracture along bedding plane, and the leakage pressure due to expansion along fracture plane, the minimum value is determined as the formation leakage pressure;

[0117] Specifically:

[0118] Under the same stress state, by comparing the leakage pressure P along the tensile failure of the matrix mf , leakage pressure P along matrix shear failure mtf , leakage pressure P of tensile fracture along bedding plane bf , the leakage pressure P due to shear fracture along the bedding plane btf , leakage pressure along the fracture surface P l , where the minimum value is the final formation loss pressure, and the expression is shown in formula (12).

[0119] P perf =min(P l ,P bf ,Pmf ,P btf ,P mtf ) (12)

[0120] Based on the above method, the geomechanical characteristics and structural surface development of the leakage location in a certain work area were used to predict the leakage pressure at the leakage location, and compared with the actual leakage volume and practical drilling fluid density, such as Figure 4 As shown. Figure 4 It can be seen that at the leakage location, the drilling fluid density is greater than the formation leakage pressure. Furthermore, the greater the difference between the drilling fluid density and the leakage pressure, the more obvious the leakage phenomenon and the greater the leakage volume. This indicates that the leakage pressure distribution predicted by the present invention is consistent with the actual leakage phenomenon, demonstrating the applicability of the model.

[0121] like Figure 5 As shown, a system for predicting lost circulation pressure in a faceted formation according to an embodiment of the present invention includes:

[0122] The experimental testing module is used to test rock samples with different bedding angles to obtain matrix tensile strength, bedding tensile strength, fracture toughness at different bedding angles, matrix shear failure strength, and bedding shear failure strength;

[0123] The stress distribution module is used to convert the wellbore coordinates based on the formation stress state distribution to obtain the wellbore circumferential stress distribution under any wellbore trajectory;

[0124] The three-dimensional principal stress module is used to obtain the three-dimensional principal stress of the wellbore wall based on the stress distribution around the wellbore under any wellbore trajectory;

[0125] The calculation module is used to obtain the leakage pressure of matrix tensile failure, the leakage pressure of tensile fracture along bedding plane, the leakage pressure along matrix shear fracture, the leakage pressure along bedding plane shear fracture and the leakage pressure along fracture plane expansion based on the three-dimensional principal stress of the wellbore, the inclination and strike of the structural plane, the matrix tensile strength, the bedding tensile strength, the fracture toughness at different bedding angles, the matrix shear failure strength and the bedding shear failure strength, wherein the inclination and strike of the structural plane include the inclination and strike of the bedding plane and the inclination and strike of the natural fracture plane;

[0126] The determination module is used to compare the values ​​of the leakage pressure caused by matrix tensile damage, the leakage pressure caused by tensile fracture along the bedding plane, the leakage pressure caused by matrix shear fracture, the leakage pressure caused by shear fracture along the bedding plane and the leakage pressure caused by expansion along the fracture plane, and determine the minimum value as the formation leakage pressure.

[0127] In an embodiment of the present invention, the three-dimensional principal stress module includes a wellbore principal stress submodule and a comparison submodule;

[0128] The wellbore principal stress submodule is used to calculate the wellbore principal stress based on the wellbore circumferential stress distribution under any wellbore trajectory;

[0129] The comparison submodule is used to determine the maximum, middle and minimum principal stresses at the wellbore position based on the comparison of the magnitudes of the wellbore principal stresses; wherein the maximum, middle and minimum principal stresses are the three-dimensional principal stresses of the wellbore.

[0130] In an embodiment of the present invention, the calculation module includes a first calculation submodule, a second calculation submodule, a third calculation submodule, a fourth calculation submodule and a fifth calculation submodule;

[0131] The first calculation submodule is used to calculate the angle between the three-dimensional principal stress of the wellbore and the normal direction of the bedding surface based on the three-dimensional principal stress of the wellbore and the dip and strike of the bedding surface;

[0132] The second calculation submodule is used to calculate the angle between the three-dimensional principal stress of the wellbore and the normal direction of the fracture surface based on the three-dimensional principal stress of the wellbore and the inclination and strike of the natural fracture surface;

[0133] The third calculation submodule is used to obtain the leakage pressure along the tensile failure of the matrix and the leakage pressure along the tensile fracture of the bedding plane based on the three principal stresses of the wellbore, the angle between the three principal stresses of the wellbore and the normal direction of the bedding plane, the tensile strength of the matrix, the tensile strength of the layer, and the maximum tensile stress criterion;

[0134] The fourth calculation submodule is used to obtain the leakage pressure along the shear fracture of the matrix and the leakage pressure along the shear fracture of the bedding plane based on the three-dimensional principal stress of the wellbore, the angle between the three-dimensional principal stress of the wellbore and the normal direction of the bedding plane, the tensile strength of the matrix, the shear failure strength of the matrix, the shear failure strength of the bedding, and the shear failure criterion;

[0135] The fifth calculation submodule is used to obtain the leakage pressure extending along the fracture surface based on the three-dimensional principal stress of the wellbore, the three-dimensional principal stress of the wellbore and the inclination and strike of the bedding surface, the angle between the three-dimensional principal stress of the wellbore and the normal of the fracture surface, the fracture toughness at different bedding angles, and the approximate fracture toughness criterion.

[0136] Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for predicting lost circulation pressure in a surface-developed formation, characterized in that: include: Based on the experimental tests on rock samples with different bedding angles, the matrix tensile strength, bedding tensile strength, fracture toughness at different bedding angles, matrix shear failure strength and bedding shear failure strength were obtained; Based on the wellbore coordinate transformation of the formation stress state distribution, the stress distribution around the wellbore under any wellbore trajectory is obtained; Based on the stress distribution around the wellbore under any wellbore trajectory, the three-dimensional principal stress of the wellbore wall is obtained; Based on the three-dimensional principal stress of the wellbore, the inclination and strike of the structural surface, the matrix tensile strength, the bedding tensile strength, the fracture toughness at different bedding angles, the matrix shear failure strength and the bedding shear failure strength, the leakage pressure of matrix tensile failure, the leakage pressure of tensile fracture along the bedding surface, the leakage pressure along the matrix shear fracture, the leakage pressure of shear fracture along the bedding surface and the leakage pressure of expansion along the fracture surface are obtained, wherein the inclination and strike of the structural surface include the inclination and strike of the bedding surface and the inclination and strike of the natural fracture surface; Based on the comparison of the leakage pressure caused by matrix tensile failure, the leakage pressure caused by tensile fracture along bedding plane, the leakage pressure caused by matrix shear fracture, the leakage pressure caused by shear fracture along bedding plane and the leakage pressure caused by expansion along fracture plane, the minimum value is determined to be the formation leakage pressure.

2. The method for predicting lost circulation pressure in a faceted formation according to claim 1, wherein: The rock samples with different bedding angles are obtained by drilling cores along different bedding angles.

3. The method for predicting lost circulation pressure in a faceted formation according to claim 1, wherein: The matrix tensile strength and bedding tensile strength are obtained through Brazilian splitting tests on rock samples with different bedding angles, and the fracture toughness at different bedding angles is obtained through center groove semi-disk tests on rock samples with different bedding angles; the matrix shear failure strength and bedding shear failure strength are obtained through testing rock samples with different bedding angles using a triaxial compression tester.

4. The method for predicting lost circulation pressure in a faceted formation according to claim 1, wherein: The distribution of formation stress state is obtained based on drilling and geological data statistics of the target block.

5. The method for predicting lost circulation pressure in a faceted formation according to claim 1, wherein: The three-dimensional principal stress of the wellbore wall is obtained based on the stress distribution around the wellbore under any wellbore trajectory, including: Based on the stress distribution around the wellbore under any wellbore trajectory, the principal stress of the wellbore wall is calculated; Based on the comparison of the magnitude of the main stress of the wellbore wall, the maximum, intermediate and minimum main stresses at the wellbore wall are determined; among them, the maximum, intermediate and minimum main stresses are the three-dimensional main stresses of the wellbore wall.

6. The method for predicting lost circulation pressure in a faceted formation according to claim 1, wherein: The dip and strike of the structural surface are obtained by statistically analyzing imaging logging data in the work area.

7. A method for predicting lost circulation pressure in a faceted formation according to any one of claims 1 to 6, characterized in that: The leakage pressure due to matrix tensile failure, the leakage pressure due to tensile fracture along bedding plane, the leakage pressure due to matrix shear fracture, the leakage pressure due to shear fracture along bedding plane, and the leakage pressure due to expansion along fracture plane are obtained based on the three principal stresses of the wellbore, the inclination and strike of the structural plane, the matrix tensile strength, the bedding tensile strength, the fracture toughness at different bedding angles, the matrix shear failure strength, and the bedding shear failure strength, including: Based on the three-dimensional principal stress of the wellbore and the dip and strike of the bedding plane, the angle between the three-dimensional principal stress of the wellbore and the normal direction of the bedding plane is calculated; Based on the three-dimensional principal stress of the wellbore and the inclination and strike of the natural fracture surface, the angle between the three-dimensional principal stress of the wellbore and the normal direction of the fracture surface is calculated; Based on the three principal stresses of the wellbore, the angle between the three principal stresses of the wellbore and the normal direction of the bedding plane, the tensile strength of the matrix, the tensile strength of the layer, and the maximum tensile stress criterion, the leakage pressure along the tensile failure of the matrix and the leakage pressure along the tensile failure of the bedding plane are obtained; Based on the three principal stresses of the wellbore, the angle between the three principal stresses of the wellbore and the normal direction of the bedding plane, the tensile strength of the matrix, the shear failure strength of the matrix, the shear failure strength of the bedding, and the shear failure criterion, the loss pressure along the shear failure of the matrix and the loss pressure along the shear failure of the bedding plane are obtained; Based on the three principal stresses of the wellbore, the dip and strike of the wellbore and bedding plane, the angle between the three principal stresses of the wellbore and the normal of the fracture plane, the fracture toughness at different bedding angles, and the approximate fracture toughness criterion, the leakage pressure along the fracture plane is obtained.

8. A system for predicting lost pressure in a surface-developed formation, characterized in that: include: The experimental testing module is used to test rock samples with different bedding angles to obtain matrix tensile strength, bedding tensile strength, fracture toughness at different bedding angles, matrix shear failure strength, and bedding shear failure strength; The stress distribution module is used to convert the wellbore coordinates based on the formation stress state distribution to obtain the wellbore circumferential stress distribution under any wellbore trajectory; The three-dimensional principal stress module is used to obtain the three-dimensional principal stress of the wellbore wall based on the stress distribution around the wellbore under any wellbore trajectory; The calculation module is used to obtain the leakage pressure of matrix tensile failure, the leakage pressure of tensile fracture along bedding plane, the leakage pressure along matrix shear fracture, the leakage pressure along bedding plane shear fracture and the leakage pressure along fracture plane expansion based on the three-dimensional principal stress of the wellbore, the inclination and strike of the structural plane, the matrix tensile strength, the bedding tensile strength, the fracture toughness at different bedding angles, the matrix shear failure strength and the bedding shear failure strength, wherein the inclination and strike of the structural plane include the inclination and strike of the bedding plane and the inclination and strike of the natural fracture plane; The determination module is used to compare the values ​​of the leakage pressure caused by matrix tensile damage, the leakage pressure caused by tensile fracture along the bedding plane, the leakage pressure caused by matrix shear fracture, the leakage pressure caused by shear fracture along the bedding plane and the leakage pressure caused by expansion along the fracture plane, and determine the minimum value as the formation leakage pressure.

9. A system for predicting lost circulation pressure in a faceted formation according to claim 8, characterized in that: The three-dimensional principal stress module includes a wellbore principal stress submodule and a comparison submodule; The wellbore principal stress submodule is used to calculate the wellbore principal stress based on the wellbore circumferential stress distribution under any wellbore trajectory; The comparison submodule is used to determine the maximum, middle and minimum principal stresses at the wellbore position based on the comparison of the magnitudes of the wellbore principal stresses; wherein the maximum, middle and minimum principal stresses are the three-dimensional principal stresses of the wellbore.

10. A system for predicting lost circulation pressure in a faceted formation according to claim 8 or 9, characterized in that: The calculation module includes a first calculation submodule, a second calculation submodule, a third calculation submodule, a fourth calculation submodule and a fifth calculation submodule; The first calculation submodule is used to calculate the angle between the three-dimensional principal stress of the wellbore and the normal direction of the bedding surface based on the three-dimensional principal stress of the wellbore and the dip and strike of the bedding surface; The second calculation submodule is used to calculate the angle between the three-dimensional principal stress of the wellbore and the normal direction of the fracture surface based on the three-dimensional principal stress of the wellbore and the inclination and strike of the natural fracture surface; The third calculation submodule is used to obtain the leakage pressure along the tensile failure of the matrix and the leakage pressure along the tensile fracture of the bedding plane based on the three principal stresses of the wellbore, the angle between the three principal stresses of the wellbore and the normal direction of the bedding plane, the tensile strength of the matrix, the tensile strength of the layer, and the maximum tensile stress criterion; The fourth calculation submodule is used to obtain the leakage pressure along the shear fracture of the matrix and the leakage pressure along the shear fracture of the bedding plane based on the three-dimensional principal stress of the wellbore, the angle between the three-dimensional principal stress of the wellbore and the normal direction of the bedding plane, the tensile strength of the matrix, the shear failure strength of the matrix, the shear failure strength of the bedding, and the shear failure criterion; The fifth calculation submodule is used to obtain the leakage pressure extending along the fracture surface based on the three-dimensional principal stress of the wellbore, the three-dimensional principal stress of the wellbore and the inclination and strike of the bedding surface, the angle between the three-dimensional principal stress of the wellbore and the normal of the fracture surface, the fracture toughness at different bedding angles, and the approximate fracture toughness criterion.

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