Complex reservoir core electrical property evaluation method and system based on orthotropic electrical theory

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 theories and application, and the method comprises the following steps: constructing a complex reservoir rock core orthotropic electrical basic model, and determining the orthotropic expression form of conductivity and resistivity tensor; according to the method, an electrical theoretical model based on orthotropic conductivity tensor is constructed, a tensor expression form containing transverse conductivity and longitudinal conductivity is established, a corresponding resistivity tensor is derived, and the electrical resistivity of the current transformer is calculated through a Maxwell equation set and a generalized Laplacian equation. A control equation of a stable current field in the anisotropic medium is established, systematic description of the conduction rule of the current in the orthotropic medium is achieved, the limitation that a traditional method depends on isotropic hypothesis is overcome from the theoretical root, and a rigorous mathematical physical foundation is laid for accurate characterization of the electrical anisotropy of a complex reservoir core.

Description

Technical Field

[0001] This invention relates to the field of oil and gas reservoir exploration theory and application technology, and in particular to a method and system for evaluating the electrical properties of complex reservoir cores based on orthogonal anisotropic electrical theory. Background Technology

[0002] The electrical anisotropy of complex reservoirs (such as fractured, bedding-rich, and heterogeneous sandstone reservoirs) is a key geological feature affecting oil and gas exploration and development. This anisotropy stems from significant differences in microstructure, mineral composition, and fluid distribution along the vertical and horizontal directions, resulting in a pronounced directional dependence of resistivity. Accurately characterizing this anisotropy is a crucial prerequisite for improving well logging interpretation accuracy, optimizing reserve assessment schemes, and reducing development risks.

[0003] Currently, traditional methods are mostly based on isotropic models, which cannot accurately describe the current conduction law in orthotropic media. Existing calculation formulas rely on the assumption of an infinite medium and do not consider the actual size of the core, the underground temperature and pressure environment, and the electrode polarization effect, resulting in significant deviations between the calculation results and actual working conditions, which restricts the accuracy of well logging interpretation and the reliability of reserve assessment.

[0004] Therefore, a method for evaluating the electrical properties of core samples from complex reservoirs based on orthogonal anisotropic electrical theory is proposed, along with a systematic solution to the aforementioned problems. Summary of the Invention

[0005] The main objective of this invention is to provide a method and system for evaluating the electrical properties of complex reservoir cores based on orthogonal anisotropic electrical theory, in order to solve the problems mentioned in the background above.

[0006] To achieve the above objectives, the technical solution adopted by this invention is: a method for evaluating the electrical properties of complex reservoir cores based on orthogonal anisotropic electrical theory, comprising the following steps:

[0007] S1: Construct a basic orthogonal anisotropic electrical model of complex reservoir cores and clarify the orthogonal anisotropic expression of conductivity and resistivity tensors;

[0008] S2: Based on Maxwell's equations and the generalized Laplace equation, the electric field distribution and potential analytical solution after current is injected into an array of electrodes in an anisotropic medium are derived.

[0009] S3: Establish the core analytical calculation formulas for longitudinal resistivity, transverse resistivity and anisotropy coefficient, and introduce a multi-dimensional error correction model for finite-length cores, temperature-pressure coupling and polarization effects.

[0010] S4: Verify the accuracy of the theoretical model through finite element numerical simulation, and optimize the electrode layout and measurement parameters;

[0011] S5: Substitute actual measurement data into the corrected theoretical formula to achieve quantitative evaluation and characterization of anisotropy in complex reservoir cores.

[0012] Preferably, in S1, the orthogonal anisotropic electrical basic model includes:

[0013] S11: The core is a homogeneous orthotropic anisotropic medium with three mutually perpendicular axes of symmetry: the axial axis and two mutually perpendicular radial axes.

[0014] S12: The electrical properties are consistent in both radial directions, exhibiting the same transverse conductivity and transverse resistivity;

[0015] S13: In the axial direction, the electrical properties are different from those in the radial direction, exhibiting different longitudinal conductivity and longitudinal resistivity;

[0016] S14: The conductivity tensor is an orthogonal diagonal matrix, whose diagonal elements include two identical horizontal conductivity components and one different vertical conductivity component; the resistivity tensor is the inverse matrix of the conductivity tensor, whose diagonal elements include two identical horizontal resistivity components and one different vertical resistivity component.

[0017] Preferably, in step S2, deriving the analytical solution of the electric field distribution and potential after injecting current into the array electrodes in the anisotropic medium includes the following steps:

[0018] S21: For axial array electrodes, assuming the core is an infinitely long cylindrical medium, the axial injected current satisfies the generalized Laplace equation, and the axial potential distribution is obtained by solving the method of separation of variables.

[0019] S22: For a ring array electrode, when a current is injected radially, the radial potential distribution is obtained by solving the generalized Laplace equation in cylindrical coordinates.

[0020] Preferably, in step S3, the core analytical calculation formulas for longitudinal resistivity, transverse resistivity, and anisotropy coefficient are established, including:

[0021] S31: Based on the axial potential distribution, establish the formula for calculating longitudinal resistivity;

[0022] S32: Based on the radial potential distribution, establish the formula for calculating transverse resistivity;

[0023] S33: Based on the longitudinal resistivity and transverse resistivity, establish a formula for calculating the anisotropy coefficient.

[0024] Preferably, in step S4, the finite element numerical simulation verification of the theoretical model includes the following steps:

[0025] S41: Establish an orthogonal anisotropic core geometric model, define the material property as the electrical conductivity tensor, and set electrode injection current boundary conditions and zero potential boundary conditions.

[0026] S42: Tetrahedral meshes are used to divide the model, and the mesh is refined near the electrode and at the boundary with the core.

[0027] S43: Solve the electric field distribution and potential value based on the finite element method, compare the simulation results with the theoretical analytical solution, and verify that the error of the theoretical model is less than the set threshold.

[0028] S44: The effects of the number of electrodes, electrode spacing, and excitation frequency on measurement accuracy are simulated by controlling the variable method, and the optimal combination of measurement parameters is obtained.

[0029] Preferably, in step S5, the quantitative evaluation and characterization of anisotropy in complex reservoir cores includes:

[0030] S51: Substitute the actual measured data into the corrected longitudinal resistivity formula and transverse resistivity formula to calculate the corrected longitudinal resistivity and transverse resistivity respectively.

[0031] S52: Based on the corrected longitudinal resistivity and transverse resistivity, calculate the anisotropy coefficient of the complex reservoir core.

[0032] S53: Compare the anisotropy coefficient with a preset anisotropy level threshold to determine the anisotropy level to which the core belongs.

[0033] Preferably, the anisotropy level includes:

[0034] S531: If the coefficient is less than the first threshold, it is determined to be a weakly anisotropic reservoir;

[0035] S532: If the coefficient is greater than or equal to the first threshold and less than the second threshold, it is determined to be a medium anisotropic reservoir.

[0036] S533: If the coefficient is greater than or equal to the second threshold, it is determined to be a strongly anisotropic reservoir.

[0037] Preferably, in S3, the multi-dimensional error correction model for finite-length core, temperature-pressure coupling, and polarization effects includes:

[0038] S34: Finite-length core correction model: Introduces a length correction coefficient related to the core length and diameter to correct the calculated resistivity;

[0039] S35: Temperature-pressure coupling correction model: Based on the resistivity under standard temperature and pressure, combined with the temperature coefficient and confining pressure coefficient, the resistivity under actual temperature and pressure conditions is corrected exponentially.

[0040] S36: Polarization effect correction model: For the electrochemical polarization effect under AC excitation signal, a complex resistivity model is used for correction, and the real part is taken as the effective resistivity.

[0041] Preferably, the application sequence of the multi-dimensional error correction model in S3 is as follows: first, the finite-length core correction model is used to correct the original calculated longitudinal and transverse resistivity; then, the temperature-pressure coupling correction model is used to correct the temperature-pressure condition of the resistivity after length correction; finally, the polarization effect correction model is used to correct the frequency dependence of the resistivity after temperature-pressure correction, so as to obtain the final effective resistivity for quantitative evaluation.

[0042] A complex reservoir core electrical property evaluation system based on orthogonal anisotropic electrical theory includes:

[0043] Measurement unit: used to apply axial and radial array electrode current excitation to complex reservoir cores and acquire the corresponding axial and radial voltage response signals;

[0044] Construction Unit: Construct the orthogonal anisotropic electrical basic model of the core and determine the form of the conductivity and resistivity tensors;

[0045] Analytical Unit: Based on Maxwell's equations and the generalized Laplace equation, calculate the electric field distribution and potential analytical solutions in anisotropic media;

[0046] Correction Unit: Establish the core calculation formulas for longitudinal resistivity, transverse resistivity and anisotropy coefficient, and call the multi-dimensional error correction model of finite length core, temperature and pressure coupling and polarization effect to correct the calculation results;

[0047] Verification Unit: Verify the accuracy of the theoretical model using a finite element numerical simulation engine, and optimize the electrode layout and measurement parameters;

[0048] Evaluation Unit: Substitutes the actual measurement data into the corrected theoretical formula to calculate the anisotropy coefficient of the core, and outputs the core anisotropy level evaluation according to the preset threshold.

[0049] The present invention has the following beneficial effects:

[0050] 1. In this invention, an electrical theoretical model based on orthogonal anisotropic conductivity tensors is constructed. A tensor expression containing transverse and longitudinal conductivity is established, and the corresponding resistivity tensor is derived. Furthermore, through Maxwell's equations and the generalized Laplace equation, the governing equations of the steady current field in anisotropic media are established, realizing a systematic description of the current conduction law in orthogonal anisotropic media. This overcomes the limitations of traditional methods that rely on the isotropic assumption from a theoretical perspective, laying a rigorous mathematical and physical foundation for the accurate characterization of the electrical anisotropy of complex reservoir cores.

[0051] 2. This invention integrates geometric correction of finite-length cores, temperature-pressure coupling correction based on the Arrhenius equation, and polarization effect correction based on the complex resistivity model. By establishing a quantitative relationship between the correction coefficient function and physical property parameters, the systematic errors of the theoretical formula in practical applications are eliminated layer by layer, which significantly improves the engineering reliability and working condition adaptability of the resistivity and anisotropy coefficient calculation results, and makes the theoretical model better fit the actual underground reservoir environment.

[0052] 3. This invention employs a closed-loop verification and optimization system combining theoretical analysis, numerical simulation, and experimental measurement. An orthogonal anisotropic rock core electrical model is constructed using the finite element method. The accuracy of the theoretical model is systematically verified by comparing the numerical solutions of potential distribution and electric field intensity with the theoretical analytical solutions. Furthermore, the controlled variable method is used to simulate and optimize key measurement parameters such as electrode layout and excitation frequency, resulting in a parameter combination scheme with theoretical guidance. This system not only enhances the scientific rigor and reliability of the method. Attached Figure Description

[0053] Figure 1 This is a flowchart of the method for evaluating the electrical properties of complex reservoir cores based on orthogonal anisotropic electrical theory, as described in this invention.

[0054] Figure 2 This is a schematic diagram of the principal axis coordinate system and resistivity tensor of the orthogonal anisotropic medium of the present invention;

[0055] Figure 3 This is a comparison chart of the theoretical solution and numerical simulation results of the axial array electrode potential distribution of this invention;

[0056] Figure 4 This is a comparison chart of the theoretical solution and numerical simulation results of the radial array electrode potential distribution of this invention;

[0057] Figure 5 This invention illustrates the variation of the anisotropy coefficient with temperature and pressure.

[0058] Figure 6 This is a schematic diagram of the potential distribution of the core cross section according to the present invention. Detailed Implementation

[0059] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0060] Please see Figure 1 and Figure 2 This invention provides a technical solution: a method for evaluating the electrical properties of complex reservoir cores based on orthogonal anisotropic electrical theory, comprising the following steps:

[0061] S1: Construct a basic orthogonal anisotropic electrical model of complex reservoir cores and clarify the orthogonal anisotropic expression of conductivity and resistivity tensors;

[0062] S2: Based on Maxwell's equations and the generalized Laplace equation, the electric field distribution and potential analytical solution after current is injected into an array of electrodes in an anisotropic medium are derived.

[0063] S3: Establish the core analytical calculation formulas for longitudinal resistivity, transverse resistivity and anisotropy coefficient, and introduce a multi-dimensional error correction model for finite-length cores, temperature-pressure coupling and polarization effects.

[0064] S4: Verify the accuracy of the theoretical model through finite element numerical simulation, and optimize the electrode layout and measurement parameters;

[0065] S5: Substitute actual measurement data into the corrected theoretical formula to achieve quantitative evaluation and characterization of anisotropy in complex reservoir cores.

[0066] This method is based on the following basic assumptions and applicable premises;

[0067] The measurement uses a sinusoidal AC excitation signal, and the core is in the linear electrical response range, so the nonlinear conductivity effect is ignored.

[0068] The electrode made good contact with the core, and the contact resistance could be eliminated through subsequent error correction. There was no obvious electrochemical corrosion during the measurement process.

[0069] Electromagnetic interference in the measurement environment has been suppressed through effective shielding and filtering to ensure that it does not affect the distribution of electric field and potential.

[0070] In deriving the analytical solution for the potential under the array electrodes, the following reasonable simplification was adopted to obtain a concise analytical expression:

[0071] For axial array electrodes (longitudinal measurement): Assuming the voltage electrode spacing is much smaller than the core radius, the radial electric field component can be ignored under this condition, and the three-dimensional problem can be simplified into a one-dimensional problem mainly along the axial direction.

[0072] For ring array electrodes (lateral measurement): Based on the axisymmetry of the ring electrodes, it is assumed that the potential distribution is independent of the circumferential angle and axial distance, and only varies with the radial distance, thus simplifying the governing equation to a radial one-dimensional form;

[0073] In S1, the basic model of orthogonal anisotropic electricity includes:

[0074] S11: The core is a homogeneous orthotropic anisotropic medium with three mutually perpendicular axes of symmetry: the axial axis and two mutually perpendicular radial axes.

[0075] S12: The electrical properties are consistent in both radial directions, exhibiting the same transverse conductivity and transverse resistivity;

[0076] S13: In the axial direction, the electrical properties are different from those in the radial direction, exhibiting different longitudinal conductivity and longitudinal resistivity;

[0077] S14: The conductivity tensor is an orthogonal diagonal matrix, whose diagonal elements include two identical transverse conductivity components and one distinct longitudinal conductivity component; the resistivity tensor is the inverse matrix of the conductivity tensor, whose diagonal elements include two identical transverse resistivity components and one distinct longitudinal resistivity component.

[0078] Based on the above assumptions and premises:

[0079] Based on the electrical properties of orthotropic media, the current density vector... With electric field intensity vector Satisfies linear conduction relationship:

[0080] ;

[0081] In the formula, It is the second-order conductivity tensor;

[0082] conductivity tensor In the principal axis coordinate system, it is a diagonal matrix:

[0083] ;

[0084] in, Transverse conductivity, Longitudinal conductivity;

[0085] resistivity tensor The inverse matrix of the conductivity tensor:

[0086] ;

[0087] In the formula, Transverse resistivity, Longitudinal resistivity;

[0088] Simultaneously, the electric field intensity vector is introduced. With potential Potential satisfy And substitute the current density vector With electric field intensity vector Given a linear conduction relationship, the relationship between current density and potential gradient can be obtained:

[0089] ;

[0090] In a steady current field, the current continuity equation satisfies Substituting this into the relationship between current density and potential gradient, we obtain the generalized Laplace equation for a steady current field in an orthogonal anisotropic medium:

[0091] .

[0092] In S2, the derivation of the analytical solution for the electric field distribution and potential after current injection into the array electrodes in an anisotropic medium includes the following steps:

[0093] S21: For axial array electrodes, assuming the core is an infinitely long cylindrical medium, the axial injected current satisfies the generalized Laplace equation, and the axial potential distribution is obtained by solving the method of separation of variables.

[0094] Specifically, the formula for calculating axial potential distribution is as follows:

[0095] ;

[0096] In the formula, Represents axial injection current. This represents the potential distribution under axial current excitation.

[0097] S22: For a ring array electrode, when a current is injected radially, the radial potential distribution is obtained by solving the generalized Laplace equation in cylindrical coordinates.

[0098] Specifically, the formula for calculating radial potential distribution is:

[0099]

[0100] In the formula, r is the radial distance and z is the axial distance. Where L is the circumferential angle, L is the length of the annular electrode, and R is the radius of the core sample. This represents the potential distribution under radial current excitation. Represents radial injection current;

[0101] In S3, the core analytical calculation formulas for longitudinal resistivity, transverse resistivity, and anisotropy coefficient are established, including:

[0102] S31: Based on the axial potential distribution, establish the formula for calculating longitudinal resistivity;

[0103] Specifically, the formula for calculating longitudinal resistivity is:

[0104] ;

[0105] In the formula, Represents the axial voltage difference. Represents axial injection current. Represents the core radius;

[0106] S32: Based on the radial potential distribution, establish the formula for calculating transverse resistivity;

[0107] Specifically, the formula for calculating transverse resistivity is:

[0108] ;

[0109] In the formula, Represents the axial length of the ring electrode. Represents radial voltage difference. Represents radial injection current. and This represents the distance of the radial voltage electrode from the core axis, and Less than ;

[0110] S33: Based on longitudinal resistivity and transverse resistivity, establish the formula for calculating the anisotropy coefficient;

[0111] Specifically, the formula for calculating the anisotropy coefficient is as follows:

[0112] ;

[0113] In the formula, Represents the anisotropy coefficient, which is dimensionless;

[0114] In S4, the finite element numerical simulation verification of the theoretical model includes the following steps:

[0115] S41: Establish an orthogonal anisotropic core geometric model, define the material property as the electrical conductivity tensor, and set electrode injection current boundary conditions and zero potential boundary conditions.

[0116] S42: Tetrahedral meshes are used to divide the model, and the mesh is refined near the electrode and at the boundary with the core.

[0117] S43: Solve the electric field distribution and potential value based on the finite element method, compare the simulation results with the theoretical analytical solution, and verify that the error of the theoretical model is less than the set threshold.

[0118] S44: The effects of the number of electrodes, electrode spacing, and excitation frequency on measurement accuracy are simulated by controlling the variable method, and the optimal combination of measurement parameters is obtained.

[0119] In S5, the quantitative evaluation and characterization of anisotropy in complex reservoir cores includes:

[0120] S51: Substitute the actual measured data into the corrected longitudinal resistivity formula and transverse resistivity formula to calculate the corrected longitudinal resistivity and transverse resistivity respectively.

[0121] S52: Calculate the anisotropy coefficient of complex reservoir cores based on the corrected longitudinal and transverse resistivity.

[0122] S53: Compare the anisotropy coefficient with the preset anisotropy level threshold to determine the anisotropy level of the core.

[0123] Anisotropy levels include:

[0124] S531: If the coefficient is less than the first threshold, it is determined to be a weakly anisotropic reservoir;

[0125] S532: If the coefficient is greater than or equal to the first threshold and less than the second threshold, it is determined to be a medium anisotropic reservoir.

[0126] S533: If the coefficient is greater than or equal to the second threshold, it is determined to be a strongly anisotropic reservoir.

[0127] Specifically, the first threshold and the second threshold are based on The anisotropy level classification standard is established, and it is calibrated by combining theoretical derivation and engineering practice. For example, the first threshold is 1.2 and the second threshold is 2.0.

[0128] In S3, the multi-dimensional error correction model for finite-length cores, temperature-pressure coupling, and polarization effects includes:

[0129] S34: Finite-length core correction model: Introduces a length correction coefficient related to the core length and diameter to correct the calculated resistivity;

[0130] Specifically, the finite-length core correction model is as follows:

[0131] ;

[0132] In the formula, The length of the core sample. The diameter of the rock core. Represents the length correction factor. Let be a function determined theoretically or experimentally, and greater than 1; then the corrected longitudinal and transverse resistivity are . , ;

[0133] S35: Temperature-pressure coupling correction model: Based on the resistivity under standard temperature and pressure, combined with the temperature coefficient and confining pressure coefficient, the resistivity under actual temperature and pressure conditions is corrected exponentially.

[0134] Specifically, the temperature-pressure coupling correction model is as follows:

[0135] ;

[0136] In the formula, Standard temperature and pressure The resistivity is given by , where a is the temperature coefficient and b is the confining pressure coefficient.

[0137] S36: Polarization effect correction model: For the electrochemical polarization effect under AC excitation signal, a complex resistivity model is used for correction, and the real part is taken as the effective resistivity.

[0138] Specifically, by introducing polarization resistors With polarization capacitor The complex resistivity model is:

[0139] ;

[0140] In the formula, where To the angular frequency of the excitation signal, is the polarization time constant. In the formula, This is the axial voltage difference. For axial current injection, This refers to the position of the axial voltage electrode. Radial voltage difference, For radial injection current, Radial electrode distance;

[0141] The application sequence of the multi-dimensional error correction model in S3 is as follows: First, the finite-length core correction model is used to correct the original calculated longitudinal and transverse resistivity. Then, the temperature-pressure coupling correction model is used to correct the temperature-pressure condition of the resistivity after length correction. Finally, the polarization effect correction model is used to correct the frequency dependence of the resistivity after temperature-pressure correction, so as to obtain the final effective resistivity for quantitative evaluation.

[0142] A complex reservoir core electrical property evaluation system based on orthogonal anisotropic electrical theory includes:

[0143] Measurement unit: used to apply axial and radial array electrode current excitation to complex reservoir cores and acquire the corresponding axial and radial voltage response signals;

[0144] Building Unit: Construct the basic orthogonal anisotropic electrical model of the core and determine the forms of the conductivity and resistivity tensors;

[0145] Analytical Unit: Based on Maxwell's equations and the generalized Laplace equation, calculate the electric field distribution and potential analytical solutions in anisotropic media;

[0146] Correction Unit: Establish the core calculation formulas for longitudinal resistivity, transverse resistivity and anisotropy coefficient, and call the multi-dimensional error correction model of finite length core, temperature and pressure coupling and polarization effect to correct the calculation results;

[0147] Verification Unit: Verify the accuracy of the theoretical model using a finite element numerical simulation engine, and optimize the electrode layout and measurement parameters;

[0148] Evaluation Unit: Substitutes the actual measurement data into the corrected theoretical formula to calculate the anisotropy coefficient of the core, and outputs the core anisotropy level evaluation according to the preset threshold.

[0149] Practical application verification:

[0150] 1. Select a core sample from a fractured sandstone reservoir and test it under simulated temperature and pressure conditions. , Electrical measurements were performed to obtain the axial current. Voltage difference radial current Voltage difference ;

[0151] 2. Substitute system parameters The original formula is used to calculate the original... ;

[0152] 3. Introduce error correction: Finite-length correction coefficient Temperature and pressure correction factor The polarization correction factor is 0.99. ;

[0153] 4. Evaluation results: The reservoir core is moderately anisotropic, and the consistency with the actual logging data is >92%, which verifies the practicality of the theoretical method.

[0154] in, Figure 2The differences in electrical parameters along the axial (z) and radial (x / y) axes clearly demonstrate the orthogonal anisotropic electrical nature of complex reservoir cores: the resistivity (ρ) of the medium in the X and Y radial (lateral) axes... h While the resistivity (ρᵥ = 5.0 Ω·m) is consistent along the Z-axis (longitudinal direction), it differs along the Z-axis (longitudinal direction), exhibiting orthogonal anisotropy characteristics of "transverse isotropy and longitudinal anisotropy." Simultaneously, the principal axis coordinate system of the anisotropic medium is clearly defined, delineating the spatial boundaries of the transverse and longitudinal directions. This provides a clear spatial reference for the separate derivation of the axial and radial electric fields.

[0155] Figure 3 The horizontal axis represents axial distance, and the vertical axis represents potential value, with theoretical curves and simulated data points marked. This illustrates the decay law of internal potential in the core with axial distance under axial current excitation: the potential is inversely proportional to the square root of the axial distance, and shows a smooth decay trend as the axial distance increases. It also shows that the theoretical analytical solution and numerical simulation results are in extremely high agreement, with only a small error (within about 2%).

[0156] Figure 4 In the figure, the horizontal axis represents the radial distance, and the vertical axis represents the potential value, with the theoretical curve and simulation data points marked. This illustrates the logarithmic variation of the potential inside the core with the radial distance under radial current excitation: the potential is proportional to the logarithm of the radial distance and increases slowly with the increase of the radial distance. It also shows that the theoretical analytical solution and the numerical simulation results with noise are in high agreement, with the relative error controlled within 2%.

[0157] Figure 5 In the figure, the horizontal axis represents temperature, the left vertical axis represents the anisotropy coefficient, and the right vertical axis represents the confining pressure. This illustrates the variation of the anisotropy coefficient under the coupling effect of temperature and pressure: as temperature increases (25℃→150℃) and confining pressure increases (0MPa→100MPa), the anisotropy coefficient shows a slow decreasing trend, but always remains greater than 1 (in the weak to medium anisotropy range). It also clarifies the coupled influence of temperature and confining pressure on electrical parameters (increased temperature decreases resistivity, and increased confining pressure increases resistivity).

[0158] Figure 6 The diagram illustrates the spatial distribution characteristics of potential in the axial and radial directions. It visually demonstrates the spatial distribution characteristics of potential under axial current excitation inside the core: the potential is high near the current electrode, decays towards both ends along the axial direction, and is symmetrically distributed in the radial direction. It also clearly shows the positional correspondence between the voltage electrode and the current electrode, as well as the spatial distribution law of the potential gradient.

[0159] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus.

[0160] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for evaluating the electrical properties of core samples from complex reservoirs based on orthogonal anisotropic electrical theory, characterized in that, Includes the following steps: S1: Construct a basic orthogonal anisotropic electrical model of complex reservoir cores and clarify the orthogonal anisotropic expression of conductivity and resistivity tensors; S2: Based on Maxwell's equations and the generalized Laplace equation, the electric field distribution and potential analytical solution after current is injected into an array of electrodes in an anisotropic medium are derived. S3: Establish the core analytical calculation formulas for longitudinal resistivity, transverse resistivity and anisotropy coefficient, and introduce a multi-dimensional error correction model for finite-length cores, temperature-pressure coupling and polarization effects. S4: Verify the accuracy of the theoretical model through finite element numerical simulation, and optimize the electrode layout and measurement parameters; S5: Substitute actual measurement data into the corrected theoretical formula to achieve quantitative evaluation and characterization of anisotropy in complex reservoir cores.

2. The method for evaluating the electrical properties of complex reservoir cores based on orthogonal anisotropic electrical theory according to claim 1, characterized in that, In S1, the basic orthogonal anisotropic electrical model includes: S11: The core is a homogeneous orthotropic anisotropic medium with three mutually perpendicular axes of symmetry: the axial axis and two mutually perpendicular radial axes. S12: The electrical properties are consistent in both radial directions, exhibiting the same transverse conductivity and transverse resistivity; S13: In the axial direction, the electrical properties are different from those in the radial direction, exhibiting different longitudinal conductivity and longitudinal resistivity; S14: The conductivity tensor is an orthogonal diagonal matrix, whose diagonal elements include two identical horizontal conductivity components and one different vertical conductivity component; the resistivity tensor is the inverse matrix of the conductivity tensor, whose diagonal elements include two identical horizontal resistivity components and one different vertical resistivity component.

3. The method for evaluating the electrical properties of complex reservoir cores based on orthogonal anisotropic electrical theory according to claim 1, characterized in that, In step S2, deriving the analytical solution of the electric field distribution and potential after injecting current into the array electrodes in the anisotropic medium includes the following steps: S21: For axial array electrodes, assuming the core is an infinitely long cylindrical medium, the axial injected current satisfies the generalized Laplace equation, and the axial potential distribution is obtained by solving the method of separation of variables. S22: For a ring array electrode, when a current is injected radially, the radial potential distribution is obtained by solving the generalized Laplace equation in cylindrical coordinates.

4. The method for evaluating the electrical properties of complex reservoir cores based on orthogonal anisotropic electrical theory according to claim 1, characterized in that, In S3, the core analytical calculation formulas for longitudinal resistivity, transverse resistivity, and anisotropy coefficient are established, including: S31: Based on the axial potential distribution, establish the formula for calculating longitudinal resistivity; S32: Based on the radial potential distribution, establish the formula for calculating transverse resistivity; S33: Based on the longitudinal resistivity and transverse resistivity, establish a formula for calculating the anisotropy coefficient.

5. The method for evaluating the electrical properties of complex reservoir cores based on orthogonal anisotropic electrical theory according to claim 1, characterized in that, In step S4, the finite element numerical simulation verification of the theoretical model includes the following steps: S41: Establish an orthogonal anisotropic core geometric model, define the material property as the electrical conductivity tensor, and set electrode injection current boundary conditions and zero potential boundary conditions. S42: Tetrahedral meshes are used to divide the model, and the mesh is refined near the electrode and at the boundary with the core. S43: Solve the electric field distribution and potential value based on the finite element method, compare the simulation results with the theoretical analytical solution, and verify that the error of the theoretical model is less than the set threshold. S44: The effects of the number of electrodes, electrode spacing, and excitation frequency on measurement accuracy are simulated by controlling the variable method, and the optimal combination of measurement parameters is obtained.

6. The method for evaluating the electrical properties of complex reservoir cores based on orthogonal anisotropic electrical theory according to claim 1, characterized in that, In S5, the quantitative evaluation and characterization of anisotropy in complex reservoir cores includes: S51: Substitute the actual measured data into the corrected longitudinal resistivity formula and transverse resistivity formula to calculate the corrected longitudinal resistivity and transverse resistivity respectively. S52: Based on the corrected longitudinal resistivity and transverse resistivity, calculate the anisotropy coefficient of the complex reservoir core. S53: Compare the anisotropy coefficient with a preset anisotropy level threshold to determine the anisotropy level to which the core belongs.

7. The method for evaluating the electrical properties of complex reservoir cores based on orthogonal anisotropic electrical theory according to claim 6, characterized in that, The anisotropy levels include: S531: If the coefficient is less than the first threshold, it is determined to be a weakly anisotropic reservoir; S532: If the coefficient is greater than or equal to the first threshold and less than the second threshold, it is determined to be a medium anisotropic reservoir. S533: If the coefficient is greater than or equal to the second threshold, it is determined to be a strongly anisotropic reservoir.

8. The method for evaluating the electrical properties of complex reservoir cores based on orthogonal anisotropic electrical theory according to claim 1, characterized in that, The multi-dimensional error correction model for finite-length cores, temperature-pressure coupling, and polarization effects in S3 includes: S34: Finite-length core correction model: Introduces a length correction coefficient related to the core length and diameter to correct the calculated resistivity; S35: Temperature-pressure coupling correction model: Based on the resistivity under standard temperature and pressure, combined with the temperature coefficient and confining pressure coefficient, the resistivity under actual temperature and pressure conditions is corrected exponentially. S36: Polarization effect correction model: For the electrochemical polarization effect under AC excitation signal, a complex resistivity model is used for correction, and the real part is taken as the effective resistivity.

9. The method for evaluating the electrical properties of complex reservoir cores based on orthogonal anisotropic electrical theory according to claim 7, characterized in that, The application sequence of the multi-dimensional error correction model in S3 is as follows: First, the finite-length core correction model is used to correct the original calculated longitudinal and transverse resistivity. Next, a temperature-pressure coupling correction model is used to correct the temperature-pressure condition of the resistivity after length correction. Finally, a polarization effect correction model is used to correct the frequency dependence of the resistivity after temperature-pressure correction, so as to obtain the final effective resistivity for quantitative evaluation.

10. A system for evaluating the electrical properties of complex reservoir cores based on orthogonal anisotropic electrical theory, comprising the method for evaluating the electrical properties of complex reservoir cores based on orthogonal anisotropic electrical theory as described in any one of claims 1-9, characterized in that... include: Measurement unit: used to apply axial and radial array electrode current excitation to complex reservoir cores and acquire the corresponding axial and radial voltage response signals; Construction Unit: Construct the orthogonal anisotropic electrical basic model of the core and determine the form of the conductivity and resistivity tensors; Analytical Unit: Based on Maxwell's equations and the generalized Laplace equation, calculate the electric field distribution and potential analytical solutions in anisotropic media; Correction Unit: Establish the core calculation formulas for longitudinal resistivity, transverse resistivity and anisotropy coefficient, and call the multi-dimensional error correction model of finite length core, temperature and pressure coupling and polarization effect to correct the calculation results; Verification Unit: Verify the accuracy of the theoretical model using a finite element numerical simulation engine, and optimize the electrode layout and measurement parameters; Evaluation Unit: Substitutes the actual measurement data into the corrected theoretical formula to calculate the anisotropy coefficient of the core, and outputs the core anisotropy level evaluation according to the preset threshold.

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