A dynamic propagation model analysis method for porous media waves at different frequencies for complex geological exploration

Abstract

This invention discloses a dynamic propagation model analysis method for porous media waves at different frequencies for complex geological exploration. The method comprises the following steps: obtaining the porous media waves to be analyzed; inputting the porous media waves to be analyzed into a dynamic propagation model to obtain analysis results. The dynamic propagation model is constructed by combining a time-varying viscoelastic constitutive model with a Biot model. This method is effectively applicable to wave propagation in porous media at different frequencies and offers valuable insights for complex geological exploration and deep reservoir parameter inversion analysis. It can provide a theoretical basis for the exploration of mineral, oil, and gas resources in my country, offering significant results and facilitating widespread adoption.

Description

Technical Field

[0001] The present invention belongs to the technical field of oil and gas reservoir exploration, and in particular relates to a dynamic propagation model analysis method of porous medium material waves at different frequencies for complex geological exploration. Background Art

[0002] The primary task before mining mineral and oil and gas resources is to quantitatively and qualitatively determine the parameters and structural information of the strata in which the resources are located. Typically, the rock and soil carrier of a resource reservoir is a multi-field, multi-phase mixture composed of mineral particles, mineral skeletons, groundwater, and various fluids (such as oil and gas), which is considered a fluid-containing granular material system. In stark contrast to shallow strata, the rock and soil of deep reservoir geology is characterized by "three highs and one disturbance": high geothermal temperature, high water pressure, high geostress, and susceptibility to disturbance. This makes the fluid-containing rock and soil granular material in deep areas highly susceptible to forming a unique composite geological body.

[0003] At present, seismic exploration technology is widely used in oil and gas exploration and solid resource geological prospecting. Its essence is to obtain underground reservoir parameter information by inverting the propagation information of dynamic waves in rock and soil. However, as a discrete porous medium containing fluid-containing granular materials, the reservoir is equivalent to a single-phase continuous medium through the large-scale geological structure inversion method, which cannot explain the action mechanism of the fluid inside the rock. Therefore, it is urgent to carry out mathematical and physical modeling research on unconventional oil and gas reservoirs and design a suitable porous medium wave propagation model to characterize the dispersion and attenuation laws of seismic waves in the reservoir. Existing technologies have carried out a lot of research on the propagation and dissipation of dynamic waves in underground reservoir rock and soil from many aspects and angles. However, most studies still imitate the large-scale geological structure inversion method to analyze the underground reservoir as a single-phase continuous medium, which has certain defects and shortcomings for discrete systems composed of particles and fluids. Given that the original intention of developing oil and gas reservoir theory is to more effectively identify underground oil and gas enrichment areas, there is an urgent need to develop corresponding discrete porous media analysis methods and study the propagation and dissipation mechanisms of dynamic waves of fluid-containing granular materials in underground resource reservoirs. Summary of the Invention

[0004] To solve the above technical problems, the present invention proposes a dynamic propagation model analysis method for porous medium material waves at different frequencies for complex geological exploration. The method can be effectively applied to the wave propagation of porous medium materials under different frequency conditions of high frequency and low frequency, and has a good reference value for complex geological exploration and deep reservoir parameter inversion analysis.

[0005] The present invention provides a dynamic propagation model analysis method for porous medium material waves at different frequencies for complex geological exploration, comprising:

[0006] Obtaining the material wave of the porous medium to be analyzed;

[0007] The porous medium material wave to be analyzed is input into a dynamic propagation model to obtain an analysis result, wherein the dynamic propagation model is constructed by combining a time-varying dependent viscoelastic constitutive model with a Biot model.

[0008] Optionally, constructing the dynamic propagation model includes:

[0009] The time-dependent state variables are introduced to modify the viscoelastic model of porous media and obtain the time-dependent viscoelastic constitutive equation.

[0010] The ideal elastic constitutive equation is replaced by the time-varying viscoelastic constitutive equation, and the stress-strain equation of the rock solid is re-characterized;

[0011] The stress-strain equation is combined with the poroelastic Biot model to obtain the wave propagation equation.

[0012] Optionally, obtaining the time-varying viscoelastic constitutive equation includes:

[0013]

[0014] Where σ is stress, ε is strain, η is fluid viscosity, s is the time-varying relaxation state variable, and E1 and E2 are the elastic moduli of the two spring elements in the viscoelastic model.

[0015] Optionally, the stress-strain equations for the rock solid can be reformulated to include:

[0016]

[0017] Where R1 and R2 are relaxation functions, u is the solid displacement tensor, T is the transpose sign, t is the relaxation time, e and γ are the volume strains of the solid skeleton and fluid, respectively, and β and are the Biot-Willis coefficient and fluid storage coefficient respectively, and I is the unit tensor.

[0018] Optionally, the wave propagation equation is analyzed using the Helmholtz quantitative analysis wave propagation equation to obtain a P-wave equivalent equation and an S-wave equivalent equation, and the formation parameters are analyzed based on the P-wave equivalent equation and the S-wave equivalent equation.

[0019] Optionally, the P-wave equivalent equation is:

[0020]

[0021] Among them, ψ s and ψ f is the scalar potential function, ψ s and ψ f is the vector potential function.

[0022] Optionally, the S-wave equivalent equation is:

[0023]

[0024] Among them, ψ s and ψ f is the scalar potential function, ψ s and ψ f is the vector potential function, ρ 11 ,ρ 12 ,ρ 22 is the mass density coefficient of the saturated porous medium material system, and κ is the permeability.

[0025] Compared with the prior art, the present invention has the following advantages and technical effects:

[0026] The method of the present invention has simple steps, a reasonable design, and is easy to implement. By preparing several types of typical rock samples containing porous media materials and conducting mechanical strength and wave velocity tests, the test results are calculated and analyzed to establish a time-varying constitutive relationship and wave propagation model for the porous media materials. The model is reasonable and effective, and can be effectively applied to the wave propagation of porous media materials under different high-frequency and low-frequency conditions. It has a good reference value for complex geological exploration and deep reservoir parameter inversion analysis, and can provide a theoretical reference basis for the exploration of mineral resources, oil and gas, etc. in my country. It has significant effects and is easy to promote. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of this application. The exemplary embodiments and descriptions of this application are intended to explain this application and do not constitute an improper limitation on this application. In the accompanying drawings:

[0028] Figure 1 This is a flow chart of a method for analyzing a dynamic propagation model of porous medium material waves at different frequencies for complex geological exploration according to an embodiment of the present invention;

[0029] Figure 2 is a schematic diagram of a testing tool and a rock sample according to an embodiment of the present invention;

[0030] Figure 3 1 and 12 are dynamic propagation curves of waves in porous media materials at different frequencies according to an embodiment of the present invention, wherein (a) is a P-wave dynamic propagation curve, and (b) is a S-wave dynamic propagation curve. DETAILED DESCRIPTION

[0031] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0032] It should be noted that the steps shown in the flowcharts of the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and that, although a logical order is shown in the flowcharts, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0033] This embodiment proposes a dynamic propagation model analysis method for porous media material waves at different frequencies for complex geological exploration, such as Figure 1 As shown, the specific steps include:

[0034] Obtaining the material wave of the porous medium to be analyzed;

[0035] The wave of the porous medium material to be analyzed is input into the dynamic propagation model to obtain the analysis results. The dynamic propagation model is constructed by combining the time-varying viscoelastic constitutive model with the Biot model.

[0036] Specifically, by preparing several types of typical rock samples containing porous media materials and conducting mechanical strength and wave velocity tests, the test results are calculated and analyzed, and the time-varying constitutive relationship of porous media materials and the wave propagation model are established. The model is reasonable and effective, and can be effectively applied to the wave propagation of porous media materials under high and low frequency conditions. It has a good reference value for complex geological exploration and deep reservoir parameter inversion analysis, and can provide a theoretical reference basis for the exploration of mineral, oil and gas resources in my country. The effect is significant and easy to promote.

[0037] In this embodiment, the specific process of step 1, preparing the porous medium material, includes: selecting representative Longmaxi shale to ensure that it has uniform texture and no obvious cracks and defects; using a professional rock cutter to cut the large rock into standard rock samples with a diameter of 50 mm and a height of 100 mm, ensuring that the cutting surface is flat during the cutting process, and using a grinder to finely grind the two end faces of the rock sample to ensure that the end faces are perpendicular to the axis of the rock sample to ensure the accuracy of the test results; and saturating it with oil after completing the test preparation.

[0038] Step 2: The specific process of the weight, diameter and height of the porous medium material rock sample includes: weighing the rock sample with an electronic scale with an accuracy of 0.01g, and measuring the diameter and height of the rock sample with a ruler with an accuracy of 0.1mm.

[0039] Step 3: The specific process of mechanical strength test and wave velocity test on porous medium material rock samples includes: Figure 2As shown in the figure, a rock dynamic servo triaxial apparatus with a maximum load capacity of 1000kN equipped with an ultrasonic tester was used to test the rock samples in a stress control mode with sinusoidal periodic cyclic loads applied at 0.1Hz, 0.2Hz, 0.5Hz, 1Hz, 2Hz, 5Hz and 10Hz. The wave velocity changes of the rock samples during the loading process were recorded, and the rock samples were tested 5 times.

[0040] Step 4. The specific process of calculating and analyzing the wave velocity propagation test results of the rock sample includes: among the results of 5 tests, eliminating the sample data with the largest and smallest test wave velocities, retaining the 3 test data with intermediate intensities, and calculating the average value of the retained 3 test data.

[0041] Specifically, the calculation results of the P-wave and S-wave velocities of the Longmaxi shale in 7 low-frequency ranges of 0.1 Hz, 0.2 Hz, 0.5 Hz, 1 Hz, 2 Hz, 5 Hz and 10 Hz are shown in Tables 1 and 2.

[0042] Table 1

[0043]

[0044] Table 2

[0045]

[0046] As can be seen from Tables 1 and 2, the velocity dispersion of the Longmaxi shale increases with increasing frequency, particularly at 0.5 Hz, where velocity dispersion first appears in the shale's P and S waves. In terms of the absolute value of velocity dispersion, the P-wave velocity increases from 4549.6 m / s to 4697.5 m / s, while the S-wave velocity increases from 2577.3 m / s to 2651.5 m / s. This data indicates that the P-wave dispersion is significantly higher than that of the S-wave, reflecting the P-wave's greater sensitivity to changes in medium properties at high frequencies. Furthermore, the P-wave dispersion characteristics are of great significance in practical engineering applications because they can affect the velocity and attenuation characteristics of seismic wave propagation, thereby affecting the detection and assessment of underground structures.

[0047] Furthermore, the porous medium material wave to be analyzed is input into the dynamic propagation model to obtain the analysis results:

[0048] The time-dependent state variables are introduced to modify the viscoelastic model of porous media and obtain the time-dependent viscoelastic constitutive equation.

[0049] The ideal elastic constitutive equation is replaced by the time-varying viscoelastic constitutive equation, and the stress-strain equation of the rock solid is re-characterized;

[0050] Combine the stress-strain equation with the poroelastic Biot model to obtain the wave propagation equation;

[0051] The wave propagation equation is analyzed using the Helmholtz quantitative analysis method to obtain an equivalent equation.

[0052] Specifically, step five: establish the time-varying constitutive relationship of porous media materials and the wave propagation model:

[0053] Step 501: introduce time-dependent state variables to modify the viscoelastic model of the porous medium and establish a time-dependent constitutive equation:

[0054]

[0055] Where σ is stress, ε is strain, η is fluid viscosity, s is the time-varying relaxation state variable, and E1 and E2 are the elastic moduli of the two spring elements in the Zener model.

[0056] Step 502: In this step, as an additional embodiment, the generalized forces of solids and fluids are re-expressed using the divergence of tensors:

[0057]

[0058] Where A represents the fourth-order elastic tensor of the solid skeleton, I is the unit tensor, e and γ represent the volume strain of the solid skeleton and the fluid, respectively, and β and are the Biot-Willis coefficient and the fluid storage coefficient, respectively.

[0059] Step 503: Use the time-varying viscoelastic constitutive model to replace the ideal elastic constitutive model and re-describe the stress-strain relationship of the rock solid:

[0060]

[0061] Where R1 and R2 are relaxation functions, u is the solid displacement tensor, T is the transpose sign, t is the relaxation time, e and γ are the volume strains of the solid skeleton and fluid, respectively, and β and are the Biot-Willis coefficient and fluid storage coefficient respectively, and I is the unit tensor.

[0062] Step 504: By combining the time-varying viscoelastic constitutive model with the Biot model, a wave propagation equation that includes both state-dependent time-varying viscoelasticity and Biot fluid-structure coupling mechanisms can be obtained:

[0063]

[0064] Where R1 and R2 are relaxation functions, U is the fluid displacement tensor, and ρ 11 ,ρ 12 ,ρ 22are several mass density coefficients of saturated porous media material system.

[0065] Step 505: Quantitatively analyze the wave propagation equation using the Helmholtz method in the plane wave method:

[0066]

[0067] Among them, ψ s and ψ f is the scalar potential function, ψ s and ψ f is the vector potential function, all potential functions satisfy the complex exponential form, and κ is the permeability.

[0068] Step 506: Substitute the result of step 505 into the wave propagation equation to obtain the longitudinal wave P wave equivalent equation:

[0069]

[0070] The equivalent equation of shear wave S wave is:

[0071]

[0072] In order to verify the rationality of this embodiment, the wave velocity propagation model of Longmaxi shale is verified and analyzed, as shown in the following example: Figure 3 The parameters of the time-varying constitutive relations and wave propagation model are shown in Table 3.

[0073] Table 3

[0074]

[0075]

[0076] In order to further demonstrate the advanced nature of the technology of this embodiment, a comparative analysis is conducted between the standard linear elastic wave propagation model when the state variable is always 1 and the classic Biot model when the state variable is always 1 and the relaxation time parameter is 0, and the wave velocity propagation curves of different models are obtained, as shown in FIG. Figure 3 As shown in (a)-(b).

[0077] from Figure 3It can be clearly seen that within the low-frequency range, the wave velocities of the proposed model and the linear elastic model disperse with increasing frequency, while the Biot model does not exhibit this phenomenon. Below 0.5 Hz, the experimental results are consistent with the calculated results of the linear elastic and Biot models. However, as frequency increases, the required dispersion in the linear elastic model occurs at a higher frequency than in the proposed model, while the frequency required to terminate the dispersion is lower, and the degree of dispersion in the linear elastic model is lower than that in the proposed model. Furthermore, the Biot model exhibits no velocity dispersion within this frequency range. The fundamental reason for this phenomenon is that, while the linear elastic model considers the viscoelastic constitutive relations of the porous saturated system, it assumes the constitutive properties of the saturated rock mass to be linear viscoelastic, ignoring time-varying dependencies. This results in a model that considers state variables that is superior in computational accuracy to the linear elastic model that relies solely on linear viscoelasticity. More specifically, when the dispersion phenomenon in the linear elastic model ends, the system's dispersion actually continues, with the P-wave frequency reaching 8 Hz and the S-wave frequency reaching 6 Hz. Therefore, we can regard 0.5 Hz as the characteristic frequency of viscoelasticity, and 8 Hz and 6 Hz as the time-varying characteristic frequencies of P-wave and S-wave. Another important reason is that the fluid-solid coupling constitutive relationship in the Biot model is assumed to be completely elastic, and the dissipation mechanism of the system only considers the friction dissipation caused by the relative motion between the solid phase and the liquid phase, while failing to consider other potential dissipation mechanisms. This assumption shows that the only friction dissipation mechanism in the Biot model is not sufficient to cause the dispersion of wave velocity. Therefore, the research results of this example emphasize the importance of considering time-varying effects and multiple dissipation mechanisms in porous media mechanics to improve the prediction accuracy and applicability of the model.

[0078] The above are merely preferred embodiments of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A dynamic propagation model analysis method for porous media materials at different frequencies for complex geological exploration, characterized by: include: Obtaining the material wave of the porous medium to be analyzed; Inputting the porous medium material wave to be analyzed into a dynamic propagation model to obtain analysis results, wherein the dynamic propagation model is constructed by combining a time-varying dependent viscoelastic constitutive model with a Biot model; Constructing the dynamic propagation model includes: The time-dependent state variables are introduced to modify the viscoelastic model of porous media and obtain the time-dependent viscoelastic constitutive equation. The ideal elastic constitutive equation is replaced by the time-varying viscoelastic constitutive equation, and the stress-strain equation of the rock solid is re-characterized; Combining the stress-strain equation with the poroelastic Biot model to obtain the wave propagation equation; Obtaining the time-varying dependent viscoelastic constitutive equation includes: Where σ is stress, ε is strain, η is fluid viscosity, s is the time-varying relaxation state variable, and E1 and E2 are the elastic moduli of the two spring elements in the viscoelastic model. The stress-strain equations for re-characterizing rock solids include: Where R1 and R2 are relaxation functions, u is the solid displacement tensor, T is the transpose sign, t is the relaxation time, e and γ are the volume strains of the solid skeleton and fluid, respectively, and β and are the Biot-Willis coefficient and the fluid storage coefficient, respectively, and I is a unit tensor; the wave propagation equation is analyzed using the Helmholtz quantitative analysis wave propagation equation to obtain the P-wave equivalent equation and the S-wave equivalent equation, and the formation parameters are analyzed based on the P-wave equivalent equation and the S-wave equivalent equation.

2. The method for analyzing the dynamic propagation model of porous medium material waves at different frequencies for complex geological exploration according to claim 1, characterized in that: The P-wave equivalent equation is: Among them, ψ s and ψ f is the scalar potential function, ψ s and ψ f is the vector potential function.

3. The method for analyzing dynamic propagation models of porous media waves at different frequencies for complex geological exploration according to claim 1, characterized in that: The S-wave equivalent equation is: Among them, ψ s and ψ f is the scalar potential function, ψ s and ψ f is the vector potential function, ρ 11 ,ρ 12 ,ρ 22 is the mass density coefficient of the saturated porous medium material system, and κ is the permeability.

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