A method for estimating parameters of fractures in a wellbore in a rock containing inclined fractures based on inversion-assisted modeling

Abstract

This invention relates to a method for estimating fracture parameters in wells containing inclined fractures based on inversion-assisted modeling, belonging to the field of geophysics. First, an isotropic background framework containing both soft and hard pores is constructed using inclusion theory. Second, based on an improved Hudson and Schoenberg fracture model and Bond transform, the stiffness coefficient perturbation caused by inclined fractures is established and introduced into the background medium to establish a rock physics model of the TTI medium containing inclined fractures. Then, a step-by-step inversion strategy is adopted. First, the clay content is inverted using density and P-wave and S-wave velocities as known quantities. Then, the inclusion content, fracture density, and fracture dip angle are inverted using P-wave and S-wave velocities as constraints. Finally, the inverted parameters are used to correct the model, and the fracture normal and tangential weaknesses are estimated. This invention, through the combination of refined modeling and step-by-step inversion, provides a new method for estimating fracture parameters and fracture elastic parameters in wells, laying a data foundation for subsequent fracture seismic prediction.

Description

Technical Field

[0001] This invention belongs to the field of geophysics, specifically relating to a method for estimating fracture parameters in wells with inclined fractured rocks based on inversion-assisted modeling. Background Technology

[0002] Rocks containing naturally inclined fractures are widely found in unconventional reservoirs such as carbonate rocks and shale. These rocks exhibit inclined, transversely isotropic medium characteristics due to the inclined distribution of fractures. As a key channel for oil and gas accumulation and migration, the accurate characterization of fracture parameters and filling fluid properties directly determines the accuracy of reservoir "sweet spot" prediction and development efficiency. To extract these fracture characteristic parameters from seismic data, it is necessary to construct corresponding rock physics models. These models can establish a relationship between fracture parameters and rock elastic parameters (such as P-wave velocity, S-wave velocity, impedance, etc.) obtained through seismic methods. Bristow (1960) first presented a method for calculating the elastic modulus of fractured media based on the method for calculating the effective elastic modulus of ellipsoids; Walsh (1965) first studied the influence of dry fractures on the effective elasticity of rocks; based on the long-wavelength first-order scattering theory; Hudson (1980) proposed a theoretical model based on thin coin-shaped fractures based on random scattering theory. This theoretical model calculates the influence of fractures on the background medium as a second-order correction quantity of the background, breaking through the previous assumption of isotropy. Based on Backus theory, Schoenberg (1980) proposed a linear smoothness theory model based on the Hudson model to simulate infinitely long and thin planar cracks. Based on the theoretical foundation of various equivalent models, Zhang Guangzhi et al. (2013) constructed a rock physics model of fractured carbonate rocks using the Hudson and Schoenberg models and analyzed the influence of fracture density and filling fluid on rock elastic parameters. Chen Huaizhen et al. (2014) constructed an equivalent rock physics model and inverted the rock physics parameters of fractured rocks based on azimuth anisotropic elastic impedance, reducing the uncertainty of fracture parameter prediction. Guo Junxin et al. (2018) established an inclined fracture model considering the background anisotropy of fractured rocks and analyzed the influence of background anisotropy on rock elastic parameters. Based on the anisotropic Gassmann equation, Pan Xinpeng et al. (2019) used the Schoenberg linear slip model to establish the relationship between the P-wave reflection characteristics of fractured gas-bearing reservoirs and fluid and fracture parameters. Ba et al. (2023) introduced vertical fractures with different orientations into an isotropic matrix, simulated the response of azimuth seismic reflection based on plane reflection and transmission, and analyzed the influence of parameters such as fracture density, aspect ratio, and fluid on seismic reflection.

[0003] Current research has focused on rock physical modeling of rocks containing vertical and inclined fractures, and has discussed the AVAZ inversion of fracture weakness parameters. However, in practical applications, well logging data often lacks fracture elastic parameters, and fracture dip angle information is also limited. Currently, there is no specific research proposing how to accurately estimate fracture parameters in wells, including fracture density, fracture dip angle, and fracture weakness. The lack of these parameters directly affects the subsequent seismic inversion. Summary of the Invention

[0004] This invention addresses the problems of existing technologies by providing a method for estimating fracture parameters in wells with inclined fractures based on inversion-assisted modeling. It simultaneously considers the influence of both soft and hard porosity in an isotropic background medium to improve the accuracy of background modulus estimation. Furthermore, it introduces inclined fractures into the dual-porosity isotropic background to establish a rock physics model containing inclined fractures. To further improve the estimation accuracy of fracture parameters and fracture elastic parameters in the well, this invention employs a step-by-step inversion-assisted modeling process, thereby improving the reliability of predicting fracture density, dip angle, and fracture weakness.

[0005] To address the above technical problems, this invention provides the following technical solution: a method for estimating fracture parameters in a well with inclined fractures based on inversion-assisted modeling, comprising the following steps:

[0006] Step 1: Calculate the background matrix modulus of mixed minerals based on the VRH average model;

[0007] Step 2: Construct a medium containing soft pores and a main phase medium containing hard pores using a DEM model. Add the inclusions to the main phase medium to construct a background medium with dual pores.

[0008] Step 3: Perform fluid substitution using the Gassmann equation to form an isotropic background skeleton for the saturated fluid;

[0009] Step 4: Based on the improved Hudson and Schoenberg crack model, form the vertical crack stiffness matrix for saturated fluid;

[0010] Step 5: Perform spatial rotation using the Bond transformation matrix to add the inclined crack to the isotropic background medium, ultimately forming the stiffness matrix of the saturated fluid inclined crack rock TTI medium. Calculate the P-wave velocity and S-wave velocity of the saturated fluid inclined crack rock TTI medium using the stiffness matrix.

[0011] Step 6: Establish initial values ​​for physical property parameters, including clay content, inclusion content, fracture density, and fracture dip angle; establish the objective function from the first step to invert clay content; and correct the initially estimated clay content.

[0012] Step 7: Using the corrected clay content as a known parameter, establish the objective function for the second inversion step, and invert the inclusion content, fracture density, and fracture dip angle with P-wave velocity and S-wave velocity as constraints.

[0013] Step 8: After obtaining the inversion results of clay content, inclusion content, fracture density, and fracture dip angle, the established rock physics model is modified to better reflect the actual formation conditions. Based on the modified rock physics model, the fracture elastic parameters are estimated: normal fracture weakness δ. N Tangential crack weakness δ T .

[0014] Furthermore, in step 1 above, for a rock background matrix containing multiple mineral components, the Voigt-Reuss-Hill average model is used to fuse the elastic moduli of each individual mineral to obtain the matrix modulus:

[0015] ,

[0016] Among them, M mat M is the elastic modulus of the rock matrix. v M represents the elastic modulus of the rock matrix obtained using the Voigt modulus. R This represents the elastic modulus of the rock matrix obtained using the Reuss model.

[0017] Furthermore, step 2 described above includes the following sub-steps:

[0018] Step 2.1: Using the DEM method, construct inclusion media containing soft pores, as shown in the following formula:

[0019] ,

[0020] ,

[0021] , ,

[0022] in, and These are the initial bulk modulus and initial shear modulus of the spherical inclusion; K sp and μ sp The bulk modulus and shear modulus of the soft hole are gradually added. This represents the initial value of soft pore porosity. and The equivalent bulk modulus and equivalent shear modulus of a spherical inclusion containing a soft cavity; and It refers to the geometric factor of soft porosity in the equivalent medium;

[0023] Step 2.2: Using the DEM method, hard pores are added to the main phase of the background medium.

[0024] ,

[0025] ,

[0026] , ,

[0027] in, and These are the initial bulk modulus and initial shear modulus of the main phase medium; K p and μ p For gradually added hard hole bulk modulus and shear modulus, This represents the initial value of hard pore porosity. and The equivalent bulk modulus and equivalent shear modulus of the main phase medium containing hard pores; and It refers to the geometric factor of hard pores in the equivalent medium;

[0028] Step 2.3: Using the DEM method, the inclusions were added to the main phase medium to construct the rock dry framework modulus as follows:

[0029] ,

[0030] ,

[0031] , ,

[0032] in, and K represents the initial bulk modulus and initial shear modulus of the hard-pore main phase medium; inc and μ inc The bulk modulus and shear modulus of the gradually added soft-pore inclusions, and The equivalent bulk modulus and equivalent shear modulus of the formed rock skeleton; and It refers to the geometric factor of spherical inclusions with soft pores in the equivalent medium.

[0033] Furthermore, in step 3 above, fluid substitution is achieved through the Gassmann equation, forming an isotropic background skeleton for the saturated fluid, the modulus of which is expressed as follows:

[0034] , ,

[0035] Among them, Ksat K0 is the effective bulk modulus of saturated rock, and K0 is the bulk modulus of the minerals that make up the rock. f The effective bulk modulus of pore fluids. It is porosity, μ sat It is the effective shear modulus of saturated rock.

[0036] Furthermore, step 4 described above includes the following sub-steps:

[0037] Step 4.1: Based on the improved Hudson crack model, obtain the crack elastic parameters characterized by crack parameters and crack fluid parameters:

[0038] , ,

[0039] in, and As an intermediate variable, the calculation formula is as follows:

[0040] ,

[0041] In the formula, e is the crack density. Water saturation of the cracks The viscosity of the fluid filling the fracture is given by α, the aspect ratio of the fracture is given by ω, and the angular frequency is given by δ. N For the normal crack weakness, δ T For tangential crack weakness, g = µ / (λ + 2μ), where λ is the Lamé constant of the homogeneous isotropic background medium and μ is the shear modulus of the homogeneous isotropic background medium.

[0042] Step 4.2: Based on the crack elastic parameters, the HTI medium stiffness matrix of the rock with vertical cracks is given as follows:

[0043] ,

[0044] Step 4.3: The longitudinal wave velocity of the isotropic background medium transverse wave velocity Substituting the mathematical relationships between density ρ, Lamé constant λ, and shear modulus μ into the HTI medium stiffness matrix of vertically fractured rock, we obtain the following form, expressed by the P-wave velocity, S-wave velocity, and density of the background medium:

[0045] ,

[0046] In the formula, , , , ; and It is an intermediate variable.

[0047] Furthermore, step 5 mentioned above includes the following sub-steps:

[0048] Step 5.1: Obtain the TTI stiffness matrix C TTI The TTI stiffness matrix C TTI The stiffness matrix C of the corresponding VTI medium VTI Obtained by rotation, the expression is as follows:

[0049] ,

[0050] In the formula, The angle of the crack. The Bond transformation matrix has the following specific form:

[0051] ;

[0052] Step 5.2: The stiffness matrix of the horizontally fractured rock... The stiffness matrix of the rock with vertical cracks was calculated. :

[0053] ,

[0054] in, This is the Bond matrix when the crack dip angle is 90°.

[0055] Step 5.3: The stiffness matrix of the rock with vertical cracks... Obtain the stiffness matrix of the TTI medium :

[0056] ,

[0057] Step 5.4: Calculate the stiffness matrix of the TTI medium. The specific format is as follows:

[0058] ,

[0059] In the formula, c represents the matrix element of the stiffness matrix, which is a function of the background medium parameters and the crack weakness, and its specific expression is as follows:

[0060] ,

[0061] ,

[0062] ,

[0063] ,

[0064] , ,

[0065] ,

[0066] ,

[0067] ,

[0068] , ,

[0069] ,

[0070] ,

[0071] Step 5.4: Based on the stiffness matrix results of the TTI medium, calculate the P-wave velocity of the TTI medium in the inclined fractured rock using the following formula. and transverse wave velocity :

[0072] ,

[0073] .

[0074] Furthermore, step 6 described above includes the following sub-steps:

[0075] Step 6.1: Establish initial values ​​for the inversion parameters, including clay content, inclusion content, fracture density, and fracture dip angle. The initial parameter values ​​are set as follows:

[0076] ,

[0077] Calculate the initial clay content using gamma curves:

[0078] , ,

[0079] Among them, I Gr It is the clay content index, Gr is the gamma curve, Gr min and Gr max These are the minimum and maximum values ​​of the gamma curve, V. sh It represents the clay content, and β is the Hirsch index;

[0080] Step 6.2: Calculate the initial inclusion content using the initial clay content, as shown in the following formula:

[0081] ,

[0082] In the formula, A1 is an adjustment factor, obtained from empirical values;

[0083] Step 6.3: The initial values ​​for crack density and crack dip angle are set as follows: =0.1, =80°,

[0084] Establish the objective function for the first step of inversion of mud content In the following form:

[0085] ,

[0086] In the formula, The weights of the density data items retrieved in the first step of the inversion; The weights of the P-wave velocity data items retrieved in the first step; The weights of the shear wave velocity data items retrieved in the first step are as follows:

[0087] , , , ,

[0088] In the formula, ρ pre The density estimated for building the model, ρ obs This is the measured density; The longitudinal wave velocity of the TTI medium estimated for the established model. The predicted shear wave velocity from the established model; The actual P-wave velocity curve in the well. The actual shear wave velocity curve in the well. This represents the average actual P-wave velocity in the well. This represents the average actual shear wave velocity in the well.

[0089] Step 6.4: Update the mud content using an iterative method. Establish an objective function to minimize the error. When the error is minimized, output the mud content inversion result. .

[0090] Furthermore, the density ρ estimated by the aforementioned model... pre The calculation formula is as follows:

[0091] ,

[0092] Where, ρ s ρ is the density of sandstone. sh This represents the density of the mudstone.

[0093] Furthermore, step 7 mentioned above includes the following sub-steps:

[0094] Step 7.1: Using P-wave and S-wave velocities as constraints, invert the inclusion content, fracture density, and fracture dip angle, and then adjust the corrected clay content. As known input parameters, the initial values ​​of the inversion parameters in the second step are set as follows:

[0095] ,

[0096] The initial value of the inclusion content is calculated using the following formula:

[0097] ,

[0098] In the formula, A2 is an adjustment factor, which is obtained from empirical values.

[0099] Step 7.2: The initial values ​​for crack density and crack dip angle are set as follows: =0.1, =80°.

[0100] Using P-wave velocity and S-wave velocity as constraints, an objective function is established for the second step of inversion to retrieve inclusion content, fracture density, and fracture dip angle. as follows:

[0101] In the formula, The weights for the P-wave velocity data terms retrieved in the second step; The weights for the shear wave velocity data terms retrieved in the second step are determined by the following mathematical relationship:

[0102] , , ,

[0103] Step 7.3: Establish the objective function to minimize the error and update the inclusion content. Crack density and crack dip angle When the error is below the threshold, the inversion result is output: e inv and .

[0104] Furthermore, in step 8 above, four parameters V are obtained. sh V inc , e and inversion results Subsequently, the established rock physics model was modified to better reflect the actual formation conditions. Based on the modified rock physics model, the final fracture elastic parameters were estimated: the normal fracture weakness δ. N Tangential crack weakness δ T .

[0105] Compared with the prior art, the beneficial technical effects of the present invention using the above technical solution are as follows:

[0106] This invention constructs a dual-pore isotropic background framework that simultaneously contains soft pores (inclusions) and hard pores (main phase), and uses the VRH averaging model, DEM model and Gassmann equation for accurate modulus calculation, thereby improving the estimation accuracy of the elastic parameters of the background medium. By combining the improved Hudson and Schoenberg fracture model with Bond space rotation transformation, a rock physics model of TTI medium containing inclined fractures is established, realizing the effective characterization of the elastic properties of inclined fractured rocks.

[0107] Furthermore, this invention employs a step-by-step inversion strategy. First, it uses density and P-wave and S-wave velocities as joint constraints to invert and correct the clay content, which is sensitive to elastic parameters. Then, using the inverted clay content as known input, it uses P-wave and S-wave velocities to constrain the inversion of inclusion content, fracture density, and fracture dip angle. This process effectively reduces the uncertainty of simultaneous multi-parameter inversion and significantly improves the estimation accuracy and reliability of key parameters such as fracture density and dip angle. Based on the high-precision inversion results of clay content, inclusion content, fracture density, and fracture dip angle, the initial rock physics model is modified with depth, and finally, the normal and tangential fracture weakness in the well is predicted. This method fills the gap in well logging data where such parameters are usually lacking and can provide an important in-well data foundation for subsequent fracture seismic prediction and inversion.

[0108] Application examples show that, compared with the traditional modeling method that estimates clay content based on gamma curves and uses empirical parameter values, the P-wave velocity and S-wave velocity predicted by the present invention through the inversion-assisted modeling process have the highest agreement with the measured data and the smallest error. This fully demonstrates the effectiveness, stability and superiority of the method under real complex formation conditions, and provides more reliable support for in-well fracture parameters for the efficient development of oil and gas reservoirs. Attached Figure Description

[0109] Figure 1 Modeling process for rock physics models containing inclined cracks.

[0110] Figure 2 To assist in the inversion modeling process.

[0111] Figure 3 This is data from a test well.

[0112] Figure 4 The results are based on rock physical modeling predictions of mud content estimated using gamma curves, while other important parameters are set using empirical values.

[0113] Figure 5(a) is a schematic diagram of the elastic parameter results predicted by the mud content inversion in the first step in the embodiment.

[0114] Figure 5(b) is a schematic diagram of the elastic parameters and crack weakness results predicted by the inclusion content, crack density and crack dip angle in the second step of the embodiment. Detailed Implementation

[0115] To better understand the technical content of the present invention, specific embodiments are described below in conjunction with the accompanying drawings.

[0116] In this invention, various aspects of the invention are described with reference to the accompanying drawings, in which numerous illustrative embodiments are shown. Embodiments of the invention are not limited to those depicted in the drawings. It should be understood that the invention is implemented through any of the various concepts and embodiments described above, as well as the concepts and embodiments described in detail below, because the concepts and embodiments disclosed herein are not limited to any particular implementation. Furthermore, some aspects of the invention disclosed may be used alone or in any suitable combination with other aspects of the invention disclosed.

[0117] like Figure 1 As shown in the embodiment, a method for estimating fracture parameters in a rock well with inclined fractures based on inversion-assisted modeling is provided. The steps are as follows:

[0118] Step 1: Calculate the background matrix modulus of mixed minerals based on the VRH average model;

[0119] Step 2: Construct a medium containing soft pores and a main phase medium containing hard pores using a DEM model. Add the inclusions to the main phase medium to construct a background medium with dual pores.

[0120] Step 3: Perform fluid substitution using the Gassmann equation to form an isotropic background skeleton for the saturated fluid;

[0121] Step 4: Based on the improved Hudson and Schoenberg crack model, form the vertical crack stiffness matrix for saturated fluid;

[0122] Step 5: Perform spatial rotation using the Bond transformation matrix to add the inclined crack to the isotropic background medium, ultimately forming the stiffness matrix of the saturated fluid inclined crack rock TTI medium. Calculate the P-wave velocity and S-wave velocity of the saturated fluid inclined crack rock TTI medium using the stiffness matrix.

[0123] Step 6: Establish initial values ​​for physical property parameters, including clay content, inclusion content, fracture density, and fracture dip angle; establish the objective function from the first step to invert clay content; and correct the initially estimated clay content.

[0124] Step 7: Using the corrected clay content as a known parameter, establish the objective function for the second inversion step, and invert the inclusion content, fracture density, and fracture dip angle with P-wave velocity and S-wave velocity as constraints.

[0125] Step 8: After obtaining the inversion results of clay content, inclusion content, fracture density, and fracture dip angle, the established rock physics model is modified to better reflect the actual formation conditions. Based on the modified rock physics model, the fracture elastic parameters are estimated: normal fracture weakness δ. N Tangential crack weakness δ T .

[0126] In a preferred embodiment, in step 1, for a rock background matrix containing multiple mineral components, the Voigt-Reuss-Hill (VRH) averaging model is used to fuse the elastic moduli of each individual mineral to obtain the matrix modulus:

[0127] ,

[0128] Among them, M mat M is the elastic modulus of the rock matrix. v M represents the elastic modulus of the rock matrix obtained using the Voigt modulus. R This represents the elastic modulus of the rock matrix obtained using the Reuss model.

[0129] In a preferred embodiment, step 2 includes the following sub-steps:

[0130] Step 2.1: Construct inclusions containing soft pores using the isotropic DEM method, as shown in the following formula:

[0131] ,

[0132] ,

[0133] , ,

[0134] in, and These are the initial bulk modulus and initial shear modulus of the spherical inclusion; K sp and μ sp The bulk modulus and shear modulus of the soft hole are gradually added. This represents the initial value of soft pore porosity. and The equivalent bulk modulus and equivalent shear modulus of a spherical inclusion containing a soft cavity; and It refers to the geometric factor of soft porosity in the equivalent medium;

[0135] Step 2.2: Using the DEM method, hard pores are added to the main phase of the background medium.

[0136] ,

[0137] ,

[0138] , ,

[0139] in, and These are the initial bulk modulus and initial shear modulus of the main phase medium; K p and μ p For gradually added hard hole bulk modulus and shear modulus, This represents the initial value of hard pore porosity. and The equivalent bulk modulus and equivalent shear modulus of the main phase medium containing hard pores; and It refers to the geometric factor of hard pores in the equivalent medium;

[0140] Step 2.3: Using the DEM method, inclusions were added to the main phase to construct the rock skeleton modulus as follows:

[0141] ,

[0142] ,

[0143] , ,

[0144] in, and K represents the initial bulk modulus and initial shear modulus of the hard-pore main phase medium; inc and μ inc The bulk modulus and shear modulus of the gradually added soft-pore inclusions, and The equivalent bulk modulus and equivalent shear modulus of the formed rock skeleton; and It refers to the geometric factor of spherical inclusions with soft pores in the equivalent medium.

[0145] In a preferred embodiment, in step 3, fluid replacement is achieved through the Gassmann equation to form an isotropic background skeleton of saturated fluid, the modulus of which is expressed as follows:

[0146] , ,

[0147] Among them, Ksat K0 is the effective bulk modulus of saturated rock, and K0 is the bulk modulus of the minerals that make up the rock. f The effective bulk modulus of pore fluids. It is porosity, μ sat It is the effective shear modulus of saturated rock.

[0148] In a preferred embodiment, step 4 includes the following sub-steps:

[0149] Step 4.1: Based on the improved Hudson crack model, obtain the crack elastic parameters characterized by crack parameters and crack fluid parameters:

[0150] , ,

[0151] in, and As an intermediate variable, the calculation formula is as follows:

[0152] ,

[0153] In the formula, e is the crack density. Water saturation of the cracks The viscosity of the fluid filling the fracture is given by α, the aspect ratio of the fracture is given by ω, and the angular frequency is given by δ. N For the normal crack weakness, δ T For tangential crack weakness, g = µ / (λ + 2μ), where λ is the Lamé constant of the homogeneous isotropic background medium and μ is the shear modulus of the homogeneous isotropic background medium.

[0154] Step 4.2: Based on the crack elastic parameters, the HTI medium stiffness matrix of the rock with vertical cracks is given as follows:

[0155] ,

[0156] Step 4.3: The longitudinal wave velocity of the isotropic background medium transverse wave velocity Substituting the mathematical relationships between density ρ, Lamé constant λ, and shear modulus μ into the HTI medium stiffness matrix of vertically fractured rock, we obtain the following form, expressed by the P-wave velocity, S-wave velocity, and density of the background medium:

[0157] ,

[0158] In the formula, , , , ,

[0159] It is an intermediate variable.

[0160] In a preferred embodiment, step 5 includes the following sub-steps:

[0161] Step 5.1: Obtain the TTI stiffness matrix C TTI The TTI stiffness matrix C TTI The stiffness matrix C of the corresponding VTI medium VTI Obtained by rotation, the expression is as follows:

[0162] ,

[0163] In the formula, The angle of the crack. The Bond transformation matrix has the following specific form:

[0164] ;

[0165] Step 5.2: The stiffness matrix of the horizontally fractured rock... The stiffness matrix of the rock with vertical cracks was calculated. :

[0166]

[0167] in, This is the Bond matrix when the crack dip angle is 90°.

[0168] Step 5.3: The stiffness matrix of the rock with vertical cracks... Obtain the stiffness matrix of the TTI medium :

[0169]

[0170] Step 5.4: Calculate the stiffness matrix of the TTI medium. The specific format is as follows:

[0171] ,

[0172] In the formula, c is a matrix element of the stiffness matrix, which is a parameter of the background medium (background medium longitudinal wave velocity). Background medium shear wave velocity and density ρ) and crack weakness (normal crack weakness δ) N and tangential crack weakness δ T The function is defined as follows:

[0173]

[0174]

[0175]

[0176]

[0177] ,

[0178]

[0179]

[0180]

[0181] ,

[0182]

[0183]

[0184] Step 5.4: Based on the stiffness matrix results of the TTI medium, calculate the P-wave velocity of the TTI medium in the inclined fractured rock using the following formula. and transverse wave velocity :

[0185] ,

[0186] .

[0187] In a preferred embodiment, step 6 includes the following sub-steps:

[0188] Step 6.1: Establish initial values ​​for the inversion parameters, including clay content, inclusion content, fracture density, and fracture dip angle. The initial parameter values ​​are set as follows:

[0189] ,

[0190] Calculate the initial clay content using gamma curves:

[0191] , ,

[0192] Among them, I Gr It is the clay content index, Gr is the gamma curve, Gr min and Gr max These are the minimum and maximum values ​​of the gamma curve, V. sh It represents the clay content, and β is the Hirsch index.

[0193] Step 6.2: Calculate the initial inclusion content using the initial clay content, as shown in the following formula:

[0194] ,

[0195] In the formula, A1 is an adjustment factor, obtained from empirical values;

[0196] Step 6.3: The initial values ​​for crack density and crack dip angle are set as follows: =0.1, =80°,

[0197] Establish the objective function for the first step of inversion of mud content In the following form:

[0198] ,

[0199] In the formula, The weights of the density data items retrieved in the first step of the inversion; The weights of the P-wave velocity data items retrieved in the first step; The weights of the shear wave velocity data items retrieved in the first step are as follows:

[0200] , , , ,

[0201] In the formula, ρ pre The density estimated for building the model, ρ obs This is the measured density; The longitudinal wave velocity of the TTI medium estimated for the established model. The predicted shear wave velocity from the established model; The actual P-wave velocity curve in the well. The actual shear wave velocity curve in the well. This represents the average actual P-wave velocity in the well. This represents the average actual shear wave velocity in the well. ρ pre The calculation formula is as follows:

[0202] ,

[0203] Where, ρ s ρ is the density of sandstone. sh This represents the density of the mudstone.

[0204] Step 6.4: Update the mud content using an iterative method. Establish an objective function to minimize the error. When the error is minimized, output the mud content inversion result. .

[0205] In a preferred embodiment, step 7 includes the following sub-steps:

[0206] Step 7.1: Using P-wave and S-wave velocities as constraints, invert the inclusion content, fracture density, and fracture dip angle, and then adjust the corrected clay content. As known input parameters, the initial values ​​of the inversion parameters in the second step are set as follows:

[0207] ,

[0208] The initial value of the inclusion content is calculated using the following formula:

[0209] ,

[0210] In the formula, A2 is an adjustment factor, which is obtained from empirical values.

[0211] Step 7.2: The initial values ​​for crack density and crack dip angle are set as follows: =0.1, =80°.

[0212] Using P-wave velocity and S-wave velocity as constraints, an objective function is established for the second step of inversion to retrieve inclusion content, fracture density, and fracture dip angle. as follows:

[0213] ,

[0214] In the formula, The weights for the P-wave velocity data terms retrieved in the second step; The weights for the shear wave velocity data terms retrieved in the second step are determined by the following mathematical relationship:

[0215] , , ,

[0216] Step 7.3: Establish the objective function to minimize the error and update the inclusion content. Crack density and crack dip angle When the error is below the threshold, the inversion result is output: e inv and .

[0217] As a preferred embodiment, four parameters V are obtained. sh V inc , e and inversion results Subsequently, the established rock physics model was modified to better reflect the actual formation conditions. Based on the modified rock physics model, the final fracture elastic parameters were estimated: the normal fracture weakness δ. N Tangential crack weakness δ T .

[0218] Finally, to verify the effectiveness of the present invention, the method proposed in this invention was applied to actual well logging data to demonstrate the effect of the inversion-assisted modeling method for estimating fracture parameters in wells with inclined fractures.

[0219] Well data used for testing, such as Figure 3 As shown, the data includes measured P-wave velocity, S-wave velocity, density, porosity, water saturation, and gamma curves. Figure 2 The flowchart of inversion-assisted rock physical modeling is shown, based on Figure 2 The modeling methods presented were compared using the following inversion tests:

[0220] (1) In rock physics modeling, gamma curves are used to estimate clay content, and other important parameters are fixed or empirical values ​​(such as fracture density, fracture dip angle, and the proportion of pore types in the background medium), and the elastic parameters are predicted.

[0221] (2) The clay content is obtained by inversion based on rock physics modeling, and other important parameters are fixed or empirical values ​​(such as fracture density, fracture dip angle, and the proportion of pore types in the background medium). Elastic parameters are predicted by rock physics modeling.

[0222] (3) The inclusion content, fracture density and fracture dip angle are obtained by inversion based on rock physics modeling, and the rock physics model is corrected by inverting the clay content, inclusion content, fracture density and fracture dip angle to model and predict elastic parameters and fracture weakness.

[0223] The results are as follows Figure 4 , Figure 5a and Figure 5bAs shown in the figure. The black solid line represents the measured data, including P-wave velocity, S-wave velocity, and density; the green dashed line represents the clay content estimated using gamma curves; the blue dashed line represents the parameters obtained from inversion, including clay content, inclusion content, fracture density, and fracture dip angle; the red dashed line represents the elastic parameters estimated using the rock physics model, including P-wave and S-wave velocities, density, and two fracture weaknesses. It can be seen that: when estimating clay content using gamma curves with other important parameters fixed (Test 1), the prediction error is the largest, even the density prediction result is not ideal, indicating that the initial estimation of clay content is inaccurate; while when using inverted clay content with other important parameters fixed or empirical values ​​(Test 2), the prediction error is reduced, with the density prediction result showing the most significant improvement, indicating that the clay content estimation result is reliable, but the prediction errors of P-wave velocity and S-wave velocity are still large; the rock physics model corrected by inverted clay content, inclusion content, fracture density, and fracture dip angle parameters (Test 3) has higher prediction accuracy, and the predicted P-wave velocity and S-wave velocity have the highest consistency with the actual values, demonstrating the effectiveness of this method. The tests demonstrate that important parameters in inclined fractured rocks, such as clay content, fracture density, fracture dip angle, and the proportion of pore types in the background medium, should be considered in relation to depth. This indicates that the modeling method proposed in this paper can effectively simulate the characteristics of shale rocks and obtain relatively reliable simulation results of elastic parameters.

[0224] While the present invention has been described above with reference to preferred embodiments, it is not intended to limit the invention. Those skilled in the art can make various modifications and refinements without departing from the spirit and scope of the invention. Therefore, the scope of protection of the present invention shall be determined by the claims.

Claims

1. A method for estimating fracture parameters in a well containing inclined fractured rock based on inversion-assisted modeling, characterized in that, Includes the following steps: Step 1: Calculate the background matrix modulus of mixed minerals based on the VRH average model; Step 2: Construct a medium containing soft pores and a main phase medium containing hard pores using a DEM model. Add the inclusions to the main phase medium to construct a background medium with dual pores. Step 3: Perform fluid substitution using the Gassmann equation to form an isotropic background skeleton for the saturated fluid; Step 4: Based on the improved Hudson and Schoenberg crack model, form the vertical crack stiffness matrix for saturated fluid; Step 5: Perform spatial rotation using the Bond transformation matrix to add the inclined crack to the isotropic background medium, ultimately forming the stiffness matrix of the saturated fluid inclined crack rock TTI medium. Calculate the P-wave velocity and S-wave velocity of the saturated fluid inclined crack rock TTI medium using the stiffness matrix. Step 6: Establish initial values ​​for physical property parameters, including clay content, inclusion content, fracture density, and fracture dip angle; establish the objective function from the first step to invert clay content; and correct the initially estimated clay content. Step 7: Using the corrected clay content as a known parameter, establish the objective function for the second inversion step, and invert the inclusion content, fracture density, and fracture dip angle with P-wave velocity and S-wave velocity as constraints. Step 8: After obtaining the inversion results of clay content, inclusion content, fracture density, and fracture dip angle, the established rock physics model is modified to better reflect the actual formation conditions. Based on the modified rock physics model, the fracture elastic parameters are estimated: normal fracture weakness δ. N Tangential crack weakness δ T .

2. The method for estimating fracture parameters in inclined fractured rock wells based on inversion-assisted modeling according to claim 1, characterized in that, In step 1, for a rock background matrix containing multiple mineral components, the Voigt-Reuss-Hill average model is used to fuse the elastic moduli of each individual mineral to obtain the matrix modulus: ， Among them, M mat M is the elastic modulus of the rock matrix. v M represents the elastic modulus of the rock matrix obtained using the Voigt modulus. R This represents the elastic modulus of the rock matrix obtained using the Reuss model.

3. The method for estimating fracture parameters in wells with inclined fractures based on inversion-assisted modeling as described in claim 1, characterized in that, Step 2 includes the following sub-steps: Step 2.1: Using the DEM method, construct inclusion media containing soft pores, as shown in the following formula: ， ， ， ， in, and These are the initial bulk modulus and initial shear modulus of the spherical inclusion; K sp and μ sp The bulk modulus and shear modulus of the soft hole are gradually added. This represents the initial value of soft pore porosity. and The equivalent bulk modulus and equivalent shear modulus of a spherical inclusion containing a soft cavity; and It refers to the geometric factor of soft porosity in the equivalent medium; Step 2.2: Using the DEM method, hard pores are added to the main phase of the background medium. ， ， ， ， in, and These are the initial bulk modulus and initial shear modulus of the main phase medium; K p and μ p For gradually added hard hole bulk modulus and shear modulus, This represents the initial value of hard pore porosity. and The equivalent bulk modulus and equivalent shear modulus of the main phase medium containing hard pores; and It refers to the geometric factor of hard pores in the equivalent medium; Step 2.3: Using the DEM method, the inclusions were added to the main phase medium to construct the rock dry framework modulus as follows: ， ， ， ， in, and K represents the initial bulk modulus and initial shear modulus of the hard-pore main phase medium; inc and μ inc The bulk modulus and shear modulus of the gradually added soft-pore inclusions, and The equivalent bulk modulus and equivalent shear modulus of the formed rock skeleton; and It refers to the geometric factor of spherical inclusions with soft pores in the equivalent medium.

4. The method for estimating fracture parameters in inclined fractured rock wells based on inversion-assisted modeling according to claim 3, characterized in that, In step 3, fluid substitution is achieved through the Gassmann equation, forming an isotropic background skeleton for the saturated fluid, the modulus of which is expressed as follows: , ， Among them, K sat K0 is the effective bulk modulus of saturated rock, and K0 is the bulk modulus of the minerals that make up the rock. f The effective bulk modulus of pore fluids. It is porosity, μ sat It is the effective shear modulus of saturated rock.

5. The method for estimating fracture parameters in wells with inclined fractures based on inversion-assisted modeling according to claim 1, characterized in that, Step 4 includes the following sub-steps: Step 4.1: Based on the improved Hudson crack model, obtain the crack elastic parameters characterized by crack parameters and crack fluid parameters: ， ， in, and As an intermediate variable, the calculation formula is as follows: ， ， In the formula, e is the crack density. Water saturation of the cracks The viscosity of the fluid filling the fracture is given by α, the aspect ratio of the fracture is given by ω, and the angular frequency is given by δ. N For the normal crack weakness, δ T For tangential crack weakness, g = µ / (λ + 2μ), where λ is the Lamé constant of the homogeneous isotropic background medium and μ is the shear modulus of the homogeneous isotropic background medium. Step 4.2: Based on the crack elastic parameters, the HTI medium stiffness matrix of the rock with vertical cracks is given as follows: ， Step 4.3: The longitudinal wave velocity of the isotropic background medium transverse wave velocity Substituting the mathematical relationships between density ρ, Lamé constant λ, and shear modulus μ into the HTI medium stiffness matrix of vertically fractured rock, we obtain the following form, expressed by the P-wave velocity, S-wave velocity, and density of the background medium: ， In the formula, , , , ; and It is an intermediate variable.

6. The method for estimating fracture parameters in wells with inclined fractures based on inversion-assisted modeling according to claim 1, characterized in that, Step 5 includes the following sub-steps: Step 5.1: Obtain the TTI stiffness matrix C TTI The TTI stiffness matrix C TTI The stiffness matrix C of the corresponding VTI medium VTI Obtained by rotation, the expression is as follows: ， In the formula, The angle of the crack. The Bond transformation matrix has the following specific form: ； Step 5.2: The stiffness matrix of the horizontally fractured rock... The stiffness matrix of the rock with vertical cracks was calculated. : ， in, This is the Bond matrix when the crack dip angle is 90°. Step 5.3: The stiffness matrix of the rock with vertical cracks... Obtain the stiffness matrix of the TTI medium : ， Step 5.4: Calculate the stiffness matrix of the TTI medium. The specific format is as follows: ， In the formula, c represents the matrix element of the stiffness matrix, which is a function of the background medium parameters and the crack weakness, and its specific expression is as follows: ， ， ， ， ， ， ， ， ， ， ， ， ， Step 5.4: Based on the stiffness matrix results of the TTI medium, calculate the P-wave velocity of the TTI medium in the inclined fractured rock using the following formula. and transverse wave velocity : ， 。 7. The method for estimating fracture parameters in inclined fractured rock wells based on inversion-assisted modeling according to claim 6, characterized in that, Step 6 includes the following sub-steps: Step 6.1: Establish initial values ​​for the inversion parameters, including clay content, inclusion content, fracture density, and fracture dip angle. The initial parameter values ​​are set as follows: ， Calculate the initial clay content using gamma curves: ， ， Among them, I Gr It is the clay content index, Gr is the gamma curve, Gr min and Gr max These are the minimum and maximum values ​​of the gamma curve, V. sh It represents the clay content, and β is the Hirsch index; Step 6.2: Calculate the initial inclusion content using the initial clay content, as shown in the following formula: ， In the formula, A1 is an adjustment factor, obtained from empirical values; Step 6.3: The initial values ​​for crack density and crack dip angle are set as follows: =0.1, =80°, Establish the objective function for the first step of inversion of mud content In the following form: ， In the formula, The weights of the density data items retrieved in the first step of the inversion; The weights of the P-wave velocity data items retrieved in the first step; The weights of the shear wave velocity data items retrieved in the first step are as follows: ， ， ， ， ， In the formula, ρ pre The density estimated for building the model, ρ obs This is the measured density; The longitudinal wave velocity of the TTI medium estimated for the established model. The predicted shear wave velocity from the established model; The actual P-wave velocity curve in the well. The actual shear wave velocity curve in the well. This represents the average actual P-wave velocity in the well. This represents the average actual shear wave velocity in the well. Step 6.4: Update the mud content using an iterative method. Establish an objective function to minimize the error. When the error is minimized, output the mud content inversion result. .

8. The method for estimating fracture parameters in a well with inclined fractures based on inversion-assisted modeling as described in claim 7, characterized in that, The density ρ estimated by the model pre The calculation formula is as follows: ， Where, ρ s ρ is the density of sandstone. sh This represents the density of the mudstone.

9. The method for estimating fracture parameters in inclined fractured rock wells based on inversion-assisted modeling according to claim 1, characterized in that, Step 7 includes the following sub-steps: Step 7.1: Using P-wave and S-wave velocities as constraints, invert the inclusion content, fracture density, and fracture dip angle, and then adjust the corrected clay content. As known input parameters, the initial values ​​of the inversion parameters in the second step are set as follows: ， The initial value of the inclusion content is calculated using the following formula: ， In the formula, A2 is an adjustment factor, obtained from empirical values; Step 7.2: The initial values ​​for crack density and crack dip angle are set as follows: =0.1, =80°; Using P-wave velocity and S-wave velocity as constraints, an objective function is established for the second step of inversion to retrieve inclusion content, fracture density, and fracture dip angle. as follows: ， In the formula, The weights for the P-wave velocity data terms retrieved in the second step; The weights for the shear wave velocity data terms retrieved in the second step are determined by the following mathematical relationship: ， ， ， ； Step 7.3: Establish the objective function to minimize the error and update the inclusion content. Crack density and crack dip angle When the error is below the threshold, the inversion result is output: e inv and .

10. The method for estimating fracture parameters in a well with inclined fractures based on inversion-assisted modeling according to claim 1, characterized in that, In step 8, four parameters V are obtained. sh V inc , e and inversion results Subsequently, the established rock physics model was modified to better reflect the actual formation conditions. Based on the modified rock physics model, the final fracture elastic parameters were estimated: the normal fracture weakness δ. N Tangential crack weakness δ T .

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