CN-121997635-A - Complex reservoir rock electrocardio evaluation method and system based on orthotropic electrical theory

CN121997635ACN 121997635 ACN121997635 ACN 121997635ACN-121997635-A

Abstract

The invention discloses a complex reservoir rock core electrical property evaluation method and system based on an orthotropic electrical theory, and relates to the technical field of oil and gas reservoir exploration theory and application. In the invention, an electrical theoretical model based on orthotropic conductivity tensor is constructed, a tensor expression form comprising transverse conductivity and longitudinal conductivity is established, a corresponding resistivity tensor is deduced, a control equation of a steady current field in an anisotropic medium is established through a Maxwell equation set and a generalized Laplace equation, the system description of the conduction rule of current in the orthotropic medium is realized, the limitation that the traditional method depends on an isotropy assumption is overcome from a theoretical source, and a strict mathematical physical foundation is laid for the accurate characterization of the complex reservoir rock electrocardiographic anisotropy.

Inventors

LI ZELIN
CHEN HUI
ZHANG XIAOFENG
LI HAILIN
LI JINSONG

Assignees

东华理工大学

Dates

Publication Date: 20260508
Application Date: 20251226

Claims (10)

1. The complex reservoir rock electrocardio evaluation method based on the orthotropic electrical theory is characterized by comprising the following steps of: S1, constructing a complex reservoir rock core orthotropic electrical basic model, and determining orthotropic expression forms of conductivity and resistivity tensors; S2, deducing electric field distribution and potential analysis solutions of the anisotropic medium after current is injected into the array electrode based on a Maxwell equation set and a generalized Laplace equation; s3, establishing a core analytic calculation formula of longitudinal resistivity, transverse resistivity and anisotropic coefficient, and introducing a multidimensional error correction model of limited length core, temperature-pressure coupling and polarization effect; s4, verifying the accuracy of a theoretical model through finite element numerical simulation, and optimizing electrode layout and measurement parameters; S5, substituting the actual measurement data into the corrected theoretical formula to realize quantitative evaluation and characterization of the rock core anisotropy of the complex reservoir.
2. The complex reservoir litho-electrical evaluation method based on orthotropic electrical theory according to claim 1, wherein in S1, the orthotropic electrical basic model comprises: s11, the rock core is a uniform orthotropic medium and is provided with three mutually perpendicular symmetry axes, namely an axial direction and two mutually perpendicular radial directions; s12, in two radial directions, the electrical properties are consistent, and the same transverse conductivity and transverse resistivity are expressed; S13, in the axial direction, the electrical properties are different from the radial direction, and the longitudinal conductivity and the longitudinal resistivity are different; And S14, the conductivity tensor is an orthogonal diagonal matrix, diagonal elements of the conductivity tensor comprise two identical transverse conductivity components and one different longitudinal conductivity component, and the resistivity tensor is an inverse matrix of the conductivity tensor, and diagonal elements of the conductivity tensor comprise two identical transverse resistivity components and one different longitudinal resistivity component.
3. The complex reservoir geotechnical property evaluation method based on the orthotropic electrical theory according to claim 1, wherein in S2, deriving the electric field distribution and the potential analysis solution after the current is injected into the array electrode in the anisotropic medium comprises the following steps: S21, aiming at an axial array electrode, assuming that a rock core is an infinitely long cylindrical medium, and obtaining axial potential distribution by solving an axial injection current meeting a generalized Laplacian equation through a separation variable method; S22, solving a generalized Laplace equation under a cylindrical coordinate system to obtain radial potential distribution when current is radially injected to the annular array electrode.
4. The complex reservoir geotechnical property evaluation method based on the orthotropic electrical theory according to claim 1, wherein in S3, a core analytic calculation formula of a longitudinal resistivity, a transverse resistivity and an anisotropic coefficient is established, comprising: S31, based on axial potential distribution, establishing a longitudinal resistivity calculation formula; S32, establishing a transverse resistivity calculation formula based on radial potential distribution; and S33, establishing an anisotropic coefficient calculation formula based on the longitudinal resistivity and the transverse resistivity.
5. The complex reservoir electrocardiographic evaluation method based on orthotropic electrical theory according to claim 1, wherein in S4, the finite element numerical simulation verification theoretical model comprises the steps of: s41, establishing an orthotropic core geometric model, defining material properties as conductivity tensors, and setting electrode injection current boundary conditions and zero potential boundary conditions; S42, splitting the model by adopting a tetrahedral grid, and carrying out grid encryption on the vicinity of the electrode and the core boundary area; S43, solving electric field distribution and potential values based on a finite element method, comparing a simulation result with a theoretical analysis solution, and verifying that the error of a theoretical model is smaller than a set threshold; s44, simulating the influence of the number of electrodes, the electrode spacing and the excitation frequency on the measurement accuracy by a control variable method, and optimizing to obtain the optimal measurement parameter combination.
6. The complex reservoir rock electrical property evaluation method based on the orthotropic electrical theory according to claim 1, wherein in S5, the quantitative evaluation and characterization of the complex reservoir rock anisotropy comprises: s51, substituting the actual measurement data into the corrected longitudinal resistivity formula and the corrected transverse resistivity formula to respectively calculate corrected longitudinal resistivity and corrected transverse resistivity; S52, calculating the anisotropic coefficient of the complex reservoir core based on the corrected longitudinal resistivity and transverse resistivity; And S53, comparing the anisotropy coefficient with a preset anisotropy grade threshold value, and determining the anisotropy grade of the core.
7. The complex reservoir litho-electrical evaluation method based on orthotropic electrical theory of claim 6, wherein the anisotropy grade comprises: s531, if the coefficient is smaller than a first threshold value, judging that the anisotropic reservoir is weak; S532, if the coefficient is larger than or equal to a first threshold value and smaller than a second threshold value, judging that the anisotropic reservoir is medium; And S533, if the coefficient is greater than or equal to a second threshold value, judging that the reservoir is a strong anisotropic reservoir.
8. The complex reservoir electrocardiographic evaluation method based on orthotropic electrical theory according to claim 1, wherein in S3, the multidimensional error correction model of finite length core, thermo-compression coupling and polarization effect comprises: S34, introducing a limited length core correction model, namely introducing a length correction coefficient related to the length and the diameter of the core, and correcting the calculated resistivity; S35, carrying out exponential relation correction on the resistivity under the actual temperature and pressure conditions based on the resistivity under the standard temperature and combined with the temperature coefficient and the confining pressure coefficient by using a temperature and pressure coupling correction model; And S36, correcting the polarization effect correction model by adopting a complex resistivity model aiming at the electrochemical polarization effect under the alternating current excitation signal, and taking the real part as the effective resistivity.
9. The complex reservoir electrocardiographic evaluation method based on orthotropic electrical theory of claim 7 wherein the application sequence of the multi-dimensional error correction model in S3 is that the longitudinal resistivity and the transverse resistivity which are originally calculated are corrected by adopting a finite length core correction model, And then, carrying out temperature and pressure condition correction on the resistivity after the length correction by adopting a temperature and pressure coupling correction model, and finally, carrying out frequency dependency correction on the resistivity after the temperature and pressure correction by adopting a polarization effect correction model to obtain the effective resistivity finally used for quantitative evaluation.
10. Complex reservoir petrophysical property evaluation system based on orthotropic electrical theory, the complex reservoir petrophysical property evaluation method based on orthotropic electrical theory according to any of claims 1 to 9, comprising: the measuring unit is used for applying axial and radial array electrode current excitation to the complex reservoir core and collecting corresponding axial and radial voltage response signals; The construction unit is used for constructing an orthotropic electrical basic model of the core and determining conductivity and resistivity tensor forms; the analysis unit is used for calculating electric field distribution and potential analysis solutions in the anisotropic medium based on the Maxwell equation set and the generalized Laplace equation; The correction unit is used for establishing a core calculation formula of longitudinal resistivity, transverse resistivity and anisotropic coefficient, and calling a multidimensional error correction model of finite length core, temperature-pressure coupling and polarization effect to correct a calculation result; The verification unit is used for verifying the accuracy of the theoretical model through a finite element numerical simulation engine and optimizing the electrode layout and the measurement parameters; and the evaluation unit is used for substituting the actual measurement data into the corrected theoretical formula, calculating to obtain the anisotropic coefficient of the core, and outputting the anisotropic grade evaluation of the core according to a preset threshold value.

Description

Complex reservoir rock electrocardio evaluation method and system based on orthotropic electrical theory Technical Field The invention relates to the technical field of oil and gas reservoir exploration theory and application, in particular to a complex reservoir rock electrocardio evaluation method and system based on an orthotropic electrical theory. Background Electrical anisotropy of complex reservoirs (e.g., fractured, bedding and developing, heterogeneous sandstone reservoirs) is a key geologic feature affecting the exploration and development of oil and gas, essentially due to the significant differences in the reservoir's microscopic pore structure, mineral composition and fluid distribution in the longitudinal and transverse directions, resulting in the resistivity exhibiting significant directional dependence. The anisotropic characteristic is accurately represented, and the anisotropic characteristic is a core precondition for improving logging interpretation accuracy, optimizing reserve evaluation schemes and reducing development risks. At present, the traditional method is mostly based on an isotropic model, cannot accurately describe the current conduction rule of an orthotropic medium, and the existing calculation formula depends on infinite medium assumption, and does not consider the actual size of a rock core, the underground temperature and pressure environment and the electrode polarization effect, so that the deviation between a calculation result and the actual working condition is remarkable, and the logging interpretation precision and the reliability of reserve evaluation are restricted. Therefore, a complex reservoir geotechnical property evaluation method and system based on orthotropic electrical theory are now proposed to solve the above problems. Disclosure of Invention The invention mainly aims to provide a complex reservoir litho-electrical evaluation method and system based on orthotropic electrical theory, so as to solve the problems in the background. In order to achieve the purpose, the technical scheme adopted by the invention is that the complex reservoir rock electrocardio evaluation method based on the orthotropic electricity theory comprises the following steps: S1, constructing a complex reservoir rock core orthotropic electrical basic model, and determining orthotropic expression forms of conductivity and resistivity tensors; S2, deducing electric field distribution and potential analysis solutions of the anisotropic medium after current is injected into the array electrode based on a Maxwell equation set and a generalized Laplace equation; s3, establishing a core analytic calculation formula of longitudinal resistivity, transverse resistivity and anisotropic coefficient, and introducing a multidimensional error correction model of limited length core, temperature-pressure coupling and polarization effect; s4, verifying the accuracy of a theoretical model through finite element numerical simulation, and optimizing electrode layout and measurement parameters; S5, substituting the actual measurement data into the corrected theoretical formula to realize quantitative evaluation and characterization of the rock core anisotropy of the complex reservoir. Preferably, in the S1, the orthotropic electrical basic model includes: s11, the rock core is a uniform orthotropic medium and is provided with three mutually perpendicular symmetry axes, namely an axial direction and two mutually perpendicular radial directions; s12, in two radial directions, the electrical properties are consistent, and the same transverse conductivity and transverse resistivity are expressed; S13, in the axial direction, the electrical properties are different from the radial direction, and the longitudinal conductivity and the longitudinal resistivity are different; And S14, the conductivity tensor is an orthogonal diagonal matrix, diagonal elements of the conductivity tensor comprise two identical transverse conductivity components and one different longitudinal conductivity component, and the resistivity tensor is an inverse matrix of the conductivity tensor, and diagonal elements of the conductivity tensor comprise two identical transverse resistivity components and one different longitudinal resistivity component. Preferably, in the step S2, deriving the electric field distribution and the potential analysis solution after the current is injected into the array electrode in the anisotropic medium includes the following steps: S21, aiming at an axial array electrode, assuming that a rock core is an infinitely long cylindrical medium, and obtaining axial potential distribution by solving an axial injection current meeting a generalized Laplacian equation through a separation variable method; S22, solving a generalized Laplace equation under a cylindrical coordinate system to obtain radial potential distribution when current is radially injected to the annular array electrode. Preferably, in the ste