Numerical simulation method of seismic frequency dispersion attenuation wave field in fluid-containing viscoelastic rock

Abstract

The present application belongs to the field of oil and gas resource seismic exploration, and provides a numerical simulation method of seismic frequency dispersion attenuation wave field of fluid-containing viscoelastic rock. The present application establishes a reflection coefficient calculation method which accurately describes the energy conversion relationship of seismic wave at the interface of viscoelastic rock, can reflect the reflection time difference caused by the seismic wave velocity dispersion, completely describes the frequency dispersion attenuation characteristics of the seismic wave propagation in the viscoelastic stratum rock, can be used for numerical simulation of the seismic wave field propagation characteristics of various different complex rocks, and provides an intuitive and efficient implementation approach for studying the seismic wave propagation law of complex viscoelastic medium.

Description

Technical Field

[0001] This invention belongs to the fields of conventional and unconventional oil and gas resource seismic exploration, carbon sequestration rock physics and seismic wave propagation simulation, and realizes a numerical simulation method for seismic dispersion attenuation wave field of fluid viscoelastic rocks. Background Technology

[0002] Studying the propagation characteristics of seismic wave fields in viscoelastic reservoirs is fundamental for utilizing the property information in seismic waves to detect subsurface stratigraphic structures, characterize reservoir parameters, and detect oil and gas. Numerical simulation of seismic wave fields based on wave equations can be used to describe the propagation characteristics of seismic waves in viscoelastic media; however, this method often faces huge computational costs in complex rock physics models, limiting its application.

[0003] Numerical simulation methods for seismic waves based on convolutional models are fast and easy to implement, and have been widely applied in practical seismic exploration, such as well-seismic calibration of synthetic seismic records and seismic inversion. Currently, convolutional models have been extended to viscoelastic frameworks to partially describe the dispersion attenuation characteristics of seismic waves. The dispersion attenuation of seismic waves manifests as a decrease in seismic reflection amplitude with increasing propagation distance, and variations in the reflection coefficient and reflection time at the same reflection interface with different frequencies. However, existing convolutional model algorithms within viscoelastic frameworks often neglect the frequency variation of seismic reflection time at specific stratigraphic interfaces, failing to fully and completely describe the dispersion attenuation characteristics of seismic wave fields in viscoelastic media. The method in this patented invention aims to solve this problem. Summary of the Invention

[0004] The purpose of this invention is to provide a numerical simulation method for the dispersion and attenuation wave field of seismic waves in viscoelastic rocks containing fluid. Its key feature is the establishment of a method for calculating the reflection coefficient that accurately describes the energy conversion relationship of seismic waves at the interface of viscoelastic rocks. This method reflects the reflection time difference caused by the velocity dispersion of seismic waves and comprehensively describes the dispersion and attenuation characteristics of seismic waves propagating in viscoelastic rock formations. The method mainly includes the following steps:

[0005] By using well logging and core data, the rock physical parameters required for modeling fluid-filled fractured pore rocks are obtained, including: rock particle bulk modulus and density, dry rock bulk modulus and shear modulus, porosity, and the bulk modulus, density, viscosity, occurrence radius and saturation of pore fluids.

[0006] Given a set of Frequency vector of each frequency Set the index number ;

[0007] From the frequency vector Extracting the index number Corresponding frequency value ;

[0008] According to the steps The rock physical parameters are used to calculate the rock density using a dynamic rock physics model. ,frequency Corresponding longitudinal wave phase velocity Longitudinal wave attenuation coefficient transverse wave phase velocity Shear wave attenuation coefficient , This refers to the two-way travel time of seismic waves;

[0009] Using the theory of seismic wave reflection in viscoelastic rocks, a frequency was established. Reflectance coefficient The calculation method is as follows:

[0010]

[0011] in, The angle of incidence of the seismic wave. This represents the seismic reference reflection coefficient calculated in this invention. This indicates taking the difference in parameters between the upper and lower strata;

[0012] The frequency is calculated using the following formula. Correspondingly, the non-steady-state reflection coefficient that fully describes the dispersion attenuation effect of seismic waves :

[0013]

[0014] The frequency is calculated using the following formula. Corresponding seismic wavelet components :

[0015]

[0016] in, This is the dominant frequency of the seismic wavelet;

[0017] Calculate the frequency using the following formula. Corresponding seismic wave field :

[0018]

[0019] in, This represents the convolution operation;

[0020] make Repeat steps to until Then, the final seismic dispersion attenuation wavefield data is calculated using the following formula. :

[0021] . Attached Figure Description

[0022] Figure 1 The four-layer geological model designed for this invention consists of three layers: the first, second, and fourth layers are fully elastic mudstone layers with thicknesses of 86m, 152m, and 200m, respectively; and the third layer is a viscoelastic gas-bearing sandstone layer with a thickness of 162m. Figure 2 The non-steady-state reflection coefficients, representing different frequencies in this invention embodiment, fully describe the seismic wave dispersion attenuation effect. The horizontal axis represents frequency in Hertz (Hz), and the vertical axis represents time in milliseconds (ms). Figure 3 The data represents seismic dispersion attenuation wavefield records at different incident angles. The horizontal axis represents time in milliseconds (ms), and the vertical axis represents amplitude, which is dimensionless. Detailed Implementation

[0023] To make the technical solution of the present invention clearer and its advantages more apparent, the specific embodiments of the technical solution of the present invention will be clearly and completely described below with reference to figures and tables. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the present invention.

[0024] Build as Figure 1 The geological model shown, based on well logging and core data, yields the P-wave and S-wave velocities and densities of each mudstone layer in the surrounding rock (Table 1); the bulk modulus and density of rock particles in the gas-bearing sandstone layer, as well as the bulk modulus, shear modulus, and porosity of dry rock (Table 2); and the bulk modulus, density, viscosity, radius of occurrence, and saturation of pore fluids (Table 3).

[0025] Table 1 Elastic parameters of mudstone

[0026] physical parameters Mudstone 1 Mudstone 2 Mudstone 3 Longitudinal wave velocity (m / s) 1710 2035 2035 Shear wave velocity (m / s) 1038 1237 1237 <![CDATA[Density (g / cm 3 ).]]> 2.08 2.109 2.109

[0027] Table 2 Physical parameters of the gas-bearing sandstone rock framework

[0028] physical parameters numerical values Rock particle bulk modulus (MPa) 37 <![CDATA[Rock particle density (g / cm 3 )]]> 2.65 Dry rock bulk modulus (MPa) 4.8 Dry rock shear modulus (MPa) 5.7 Porosity (%) 30

[0029] Table 3 Pore fluid physical parameters of gas-bearing sandstone

[0030] physical parameters water gas Bulk modulus (GPa) 2.25 0.012 <![CDATA[Density (g / cm 3 ).]]> 1.04 0.078 Viscosity (Pa • s) 0.03 0.0015 Radius (m) 0.4 0.29 Saturation (%) 60 40

[0031] Given a set of frequency vectors containing N=125 frequencies Set the index number ;

[0032] From the frequency vector Extracting the index number Corresponding frequency value ;

[0033] According to the steps The rock physical parameters are used to calculate the rock density using a dynamic rock physics model. ,frequency Corresponding longitudinal wave phase velocity Longitudinal wave attenuation coefficient transverse wave phase velocity Shear wave attenuation coefficient , This refers to the two-way travel time of seismic waves;

[0034] Using the theory of seismic wave reflection in viscoelastic rocks, a frequency was established. Reflectance coefficient The calculation method is as follows:

[0035]

[0036] in, The angle of incidence of the seismic wave. This represents the seismic reference reflection coefficient calculated in this invention. This indicates taking the difference in parameters between the upper and lower strata;

[0037] The frequency is calculated using the following formula. Correspondingly, the non-steady-state reflection coefficient that fully describes the dispersion attenuation effect of seismic waves ,like Figure 2 As shown:

[0038]

[0039] The frequency is calculated using the following formula. Corresponding seismic wavelet components :

[0040]

[0041] in, This is the dominant frequency of the seismic wavelet;

[0042] Calculate the frequency using the following formula. Corresponding seismic wave field :

[0043]

[0044] in, This represents the convolution operation;

[0045] make Repeat steps to until Then, the final seismic dispersion attenuation wavefield data is calculated using the following formula. ,like Figure 3 As shown:

[0046] .

[0047] Figure 2 As shown in the figure, when the incident angle of the seismic wave is θ=0º, the reflection coefficients at different frequencies are as follows: at the same frequency, the reflection coefficient of the bottom interface of the gas-bearing sandstone layer (located between 350ms and 400ms) has a significant amplitude attenuation compared to the reflection coefficient of the top interface of the gas-bearing sandstone layer (located at 250ms); at the bottom interface of the gas-bearing sandstone layer, the time position of the reflection coefficients at different frequencies gradually decreases with the increase of frequency.

[0048] Figure 3 The following is a record of the seismic dispersion attenuation wave field at different incident angles (θ=0º, 15º, 30º) according to an embodiment of the present invention. As can be seen from the figure, the seismic waves at the bottom of the gas-bearing sandstone layer (located between 350ms and 400ms) have obvious amplitude attenuation and phase change. The attenuation degree and phase change characteristics are different at different incident angles. The amplitude attenuation is due to the attenuation of seismic waves of different frequencies, and the phase change is due to the velocity dispersion of different frequencies.

[0049] The above embodiments demonstrate that the numerical simulation method proposed in this invention can fully describe the dispersion attenuation characteristics of the seismic wave field of viscoelastic rocks.

[0050] The advantages and novelty of this invention are as follows: A method for calculating the reflection coefficient that can accurately describe the energy conversion relationship of seismic waves at the interface of viscoelastic rocks was established; It fully demonstrates the difference in seismic reflection time caused by the velocity dispersion of seismic waves, and can completely describe the dispersion and attenuation characteristics of the seismic wave field of viscoelastic rocks; The method of this invention can be used for numerical simulation of the propagation characteristics of seismic wave fields in various complex rocks without solving complex wave equations, providing an intuitive and efficient approach to studying the propagation laws of seismic waves in complex viscoelastic media.

[0051] The above embodiments are only used to illustrate the present invention. The implementation steps of the method can be varied. Any equivalent transformations and improvements made on the basis of the technical solution of the present invention should not be excluded from the protection scope of the present invention.

Claims

1. A numerical simulation method for the seismic dispersion attenuation wave field of fluid-viscoelastic rocks, comprising the following steps: By using well logging and core data, the rock physical parameters required for modeling fluid-filled fractured pore rocks are obtained, including: rock particle bulk modulus and density, dry rock bulk modulus and shear modulus, porosity, and the bulk modulus, density, viscosity, occurrence radius and saturation of pore fluids. Given a set of Frequency vector of each frequency Set the index number ; From the frequency vector Extracting the index number Corresponding frequency value ; According to the steps The rock physical parameters are used to calculate the rock density using a dynamic rock physics model. ,frequency Corresponding longitudinal wave phase velocity Longitudinal wave attenuation coefficient Transverse wave phase velocity Shear wave attenuation coefficient , This refers to the two-way travel time of seismic waves; Using the theory of seismic wave reflection in viscoelastic rocks, a frequency was established. Reflectance coefficient The calculation method is as follows: ； in, The angle of incidence of the seismic wave. This represents the calculated seismic reference reflection coefficient. This indicates taking the difference in parameters between the upper and lower strata; The frequency is calculated using the following formula. Correspondingly, the non-steady-state reflection coefficient that fully describes the dispersion attenuation effect of seismic waves : ； The frequency is calculated using the following formula. Corresponding seismic wavelet components : ； in, This is the dominant frequency of the seismic wavelet; Calculate the frequency using the following formula. Corresponding seismic wave field : ； in, This represents the convolution operation; make Repeat steps to until Then, the final seismic dispersion attenuation wavefield data is calculated using the following formula. : 。

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