Sandstone reservoir pore structure parameter inversion method based on elastic modulus

Abstract

The present application provides a kind of sandstone reservoir pore structure parameter inversion method based on elastic modulus, which includes the following steps: step 1, the equivalent rock matrix bulk modulus of reservoir is calculated using the different rock component content in logging data;Step 2, for the fluid mixture in rock pore or fracture, the equivalent fluid volume modulus of reservoir is calculated;Step 3, the effective pore ratio parameter is calculated using the equivalent rock matrix modulus, the equivalent fluid volume modulus of reservoir, the longitudinal wave velocity, the transverse wave velocity and the density;Step 4, the equivalent pore structure parameter of reservoir is calculated.The sandstone reservoir pore structure parameter inversion method based on elastic modulus fully utilizes the elastic characteristics such as longitudinal wave velocity, transverse wave velocity, density and bulk modulus to obtain the equivalent pore structure parameter, which realizes the pore structure parameter used for reservoir prediction obtained by inversion from prestack seismic data.

Description

Technical Field

[0001] This invention relates to the field of seismic data interpretation technology for petroleum geophysical exploration, and in particular to a method for inverting sandstone reservoir pore structure parameters based on elastic modulus. Background Technology

[0002] Complex sedimentary environments and intense diagenesis and compaction result in highly heterogeneous reservoir pore spaces and complex pore structures. The size of these pores significantly impacts elastic parameters such as P-wave and S-wave velocities and density. Therefore, accurate acquisition of pore structure information is crucial for reservoir prediction. Domestic and international scholars have conducted research on pore structure in two main ways: the first involves laboratory rock physics testing of rock samples; the second involves using rock physics models to invert pore structure parameters. Different rock physics models have different pore structure parameters, each with its own symbolic physical meaning. Regarding rock physics testing, Nur (1991), Avseth (2005), and Lev Vernik (2010) et al., through extensive research, pointed out that rocks with the same porosity but different pore structures exhibit significant differences in acoustic velocity. Anselmetti (1999) and Eberli (2003) demonstrated through rock physics experiments that different rock pore structure types affect rock velocity. Liu Kaiyuan (2013), based on the Eshelby-Walsh model and the Gassmann equation, proposed a seismic porosity inversion method considering rock pore structure. Guo Jiliang et al. (2016) proposed a pore structure estimation method based on a DEM model, which uses well logging data and P-wave and S-wave transit times to calculate the porosity aspect ratio and uses the porosity aspect ratio to characterize the pore structure. Da Peng et al. (2016) proposed a pore structure estimation method based on the KT model and Biot coefficients, which uses well logging data to calculate the porosity aspect ratio and uses the porosity aspect ratio to characterize the pore structure. In rock physics, parameters such as pore aspect ratio, geometric factor, and pore size are mostly used to characterize pore structure. However, these parameters are too microscopic to be described at the seismic scale. In actual reservoir prediction, simpler and more effective parameters are often needed to characterize pore structure. Obtaining pore structure parameters through elastic moduli such as P-wave and S-wave velocities, density, and bulk modulus is helpful for achieving equivalent pore type classification at the seismic scale, which is of great significance for accurately characterizing reservoir features.

[0003] Chinese patent application CN201610191787.3 discloses a novel method for simultaneously inverting reservoir porosity, water saturation, and clay content parameters. This method includes: Step 1, collecting elastic parameters, well logging data, and core data; Step 2, combining rock elastic parameters with reservoir physical property parameters to establish a rock physics model; Step 3, establishing and solving an objective function for the three-parameter inversion of reservoir porosity, water saturation, and clay content; and Step 4, outputting the inversion results of reservoir porosity, water saturation, and clay content parameters by solving the objective function. This method combines rock physics and geostatistical analysis to develop a new method for reservoir property identification, obtaining reservoir porosity, saturation, and other physical property parameters, improving the objectivity and accuracy of reservoir property estimation results, and has significant economic and social implications.

[0004] Chinese patent application CN202010946137.1 discloses a reservoir parameter inversion method considering the second-order gradient of elastic impedance. The method includes predicting elastic impedance based on pre-stack seismic data and using this elastic impedance to predict reservoir parameters. Specifically, the method involves: first, deriving a simplified approximation of the saturated fluid-rock bulk modulus characterized by modified porosity and fluid bulk modulus; second, using this simplified approximation of the rock bulk modulus, deriving an approximation of the reflection coefficient characterized by density, modified porosity, and fluid bulk modulus for internal fractured reservoirs, and establishing an expression for elastic impedance; finally, predicting the elastic impedance volume using pre-stack seismic gathers at different angles, and using the second-order gradient of the elastic impedance to invert and predict the reservoir density, modified porosity, and fluid bulk modulus. Compared with existing technologies, the reservoir parameter inversion results of this invention exhibit higher stability and reliability.

[0005] Chinese patent application CN202110180269.2 discloses a pre-stack seismic probabilistic multichannel inversion method for multiporosity reservoirs. The method includes: Step 1, deriving the expression for the elastic modulus of rocks containing multiporosity; Step 2, deriving the seismic reflection coefficient equation characterizing the physical properties of multiporosity reservoirs; Step 3, verifying the accuracy and inversion feasibility of the reflection coefficients of multiporosity reservoirs; Step 4, constructing the posterior probability density distribution and objective functional of the parameters of the model to be inverted; Step 5, developing a pre-stack seismic multichannel step-by-step inversion algorithm using random sampling of a multi-Markov chain; and Step 6, developing a rock physical parameter inversion method based on a step-by-step simulation strategy. This invention considers the influence of reservoir pore structure on seismic reflection coefficients, develops a parameterization method for seismic reflection coefficients of multiporosity reservoirs and a pre-stack seismic probabilistic multichannel inversion technique, and achieves stable inversion of parameters such as multiporosity volume fraction, fluid bulk modulus, and porosity.

[0006] The existing technologies described above are significantly different from the present invention and have failed to solve the technical problem we want to address. Therefore, we have invented a new method for inverting sandstone reservoir pore structure parameters based on elastic modulus. Summary of the Invention

[0007] The purpose of this invention is to provide a sandstone reservoir pore structure parameter inversion method based on elastic modulus that fully utilizes elastic characteristics such as P-wave velocity, density, and bulk modulus to obtain equivalent pore structure parameters.

[0008] The objective of this invention can be achieved through the following technical measures: a method for inverting pore structure parameters of sandstone reservoirs based on elastic modulus, which includes:

[0009] Step 1: Calculate the equivalent bulk modulus of the reservoir matrix using the different rock component contents in the well logging data;

[0010] Step 2: For fluid mixtures in rock pores or fractures, calculate the reservoir equivalent fluid bulk modulus;

[0011] Step 3: Calculate the effective porosity parameters using parameters such as equivalent rock matrix modulus, reservoir equivalent fluid bulk modulus, P-wave velocity, S-wave velocity, and density.

[0012] Step 4: Calculate the equivalent pore structure parameters of the reservoir.

[0013] The objective of this invention can also be achieved through the following technical measures:

[0014] In step 1, the equivalent rock matrix bulk modulus of the reservoir is related to the mineral composition of the rock and is the basis for calculating the pore structure parameters. Based on rock physics models such as KT, VRH, and DEM, and guided by the generalized Gassmann theory, the equivalent rock matrix bulk modulus of the reservoir is calculated using the different rock component contents in the well logging data.

[0015] In step 1, the formula for calculating the equivalent bulk modulus of the reservoir matrix is:

[0016]

[0017] In the formula, K m The bulk modulus of the reservoir equivalent rock matrix is ​​represented by K1, K2, and K3, which represent the bulk modulus of clay, quartz, and calcite, respectively, and f1, f2, and f3 represent the clay content, quartz content, and calcite content, respectively.

[0018] In step 2, for the fluid mixture in the rock pores or fractures, the reservoir equivalent fluid bulk modulus is calculated according to the Reuss average theory.

[0019] In step 2, the formula for calculating the equivalent fluid bulk modulus of the reservoir is:

[0020]

[0021] In the formula, K f K represents the equivalent fluid bulk modulus of the reservoir. o K w f represents the bulk modulus of oil and the bulk modulus of water, respectively. o f w These represent oil saturation and water saturation, respectively.

[0022] In step 3, the reservoir equivalent rock matrix bulk modulus K obtained in steps 1 and 2 is used as the basis for calculation. m Equivalent fluid bulk modulus K of the reservoir f In order to further obtain the equivalent pore structure parameters of the reservoir, the effective pore ratio parameter was introduced.

[0023] In step 3, the formula for calculating the effective porosity parameter is:

[0024]

[0025] In the formula, F φ The effective porosity parameter is represented by φ, which represents the rock porosity, and K. sat It represents the equivalent bulk modulus of the reservoir under saturated fluid conditions.

[0026] In step 3, K sat The calculation is performed using observed P-wave and S-wave velocities and density parameters. The specific calculation formula is as follows:

[0027]

[0028] In the formula, V P V s ρ and ρ represent the longitudinal wave velocity, transverse wave velocity, and density of the rock, respectively.

[0029] In step 4, the pore structure parameter α is derived from the rock elastic parameters and porosity. The rock elastic parameters include P-wave and S-wave velocities, density, matrix bulk modulus, and fluid bulk modulus.

[0030] In step 4, the specific calculation formula for the pore structure parameter α is as follows:

[0031]

[0032] After obtaining the equivalent matrix bulk modulus K of the reservoir m reservoir equivalent fluid bulk modulus K fEffective porosity parameter F φ Given the rock porosity φ, the equivalent pore structure parameter α of the reservoir can be calculated using formula (5).

[0033] The sandstone reservoir pore structure parameter inversion method based on elastic modulus in this invention, under the guidance of generalized Gassmann theory and based on rock physics models such as KT, VRH, and DEM, uses elastic parameters such as P-wave and S-wave velocities, density, and bulk modulus, as well as physical property parameters such as clay content, quartz content, calcite content, and porosity, to calculate reservoir pore structure parameters. Analysis shows that there is a good correlation between the product of pore structure parameters and porosity and P-wave impedance. By inverting porosity and P-wave impedance from pre-stack seismic data, pore structure parameters can be further obtained. This invention realizes the inversion of pore structure parameters from pre-stack seismic data that can be used for reservoir prediction. Attached Figure Description

[0034] Figure 1 This is a graph showing actual logging parameters in a specific embodiment of the present invention;

[0035] Figure 2 This is a schematic diagram of the equivalent rock matrix bulk modulus of a reservoir in a specific embodiment of the present invention;

[0036] Figure 3 This is a schematic diagram of the reservoir equivalent fluid bulk modulus in a specific embodiment of the present invention;

[0037] Figure 4 This is a schematic diagram of the bulk modulus of saturated rock in a specific embodiment of the present invention;

[0038] Figure 5 This is a schematic diagram of the effective porosity parameters in a specific embodiment of the present invention;

[0039] Figure 6 This is a schematic diagram of the equivalent pore structure parameters of the reservoir in a specific embodiment of the present invention;

[0040] Figure 7 This is a flowchart of a specific embodiment of the sandstone reservoir pore structure parameter inversion method based on elastic modulus of the present invention;

[0041] Figure 8 This is a graph showing the fitting relationship between the product of porosity and pore structure parameters and longitudinal wave impedance in a specific embodiment of the present invention.

[0042] Figure 9 This is a comparison diagram of the calculated porosity and pore structure parameters on the well surface and the inversion results in a specific embodiment of the present invention;

[0043] Figure 10This is a cross-sectional view of pore structure parameters obtained by seismic data inversion in a specific embodiment of the present invention. Detailed Implementation

[0044] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0045] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments of the present invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, and / or combinations thereof.

[0046] The present invention discloses a method for inverting pore structure parameters of sandstone reservoirs based on elastic modulus. This method inverts pore structure parameters based on the reservoir's elastic modulus. The bulk modulus of the rock matrix and pore fluids is calculated using a rock physics model. The bulk modulus of saturated rock is calculated using known elastic parameters such as P-wave and S-wave velocities and densities. Based on these bulk moduli, the pore structure parameters of the reservoir are further inverted.

[0047] The following are several specific embodiments of the application of the present invention.

[0048] Example 1

[0049] In a specific embodiment 1 of the present invention, such as Figure 7 The diagram shows a flowchart of the wellbore sandstone reservoir pore structure parameter inversion method based on elastic modulus according to the present invention. The method specifically includes the following steps:

[0050] Step 101: Calculation of the equivalent rock matrix bulk modulus of the reservoir.

[0051] The equivalent bulk modulus of the reservoir matrix is ​​related to the mineral composition of the rock and is the basis for calculating pore structure parameters. Based on rock physics models such as KT, VRH, and DEM, and guided by generalized Gassmann theory, this invention calculates the equivalent bulk modulus of the reservoir matrix using the following expression based on the different rock component contents in well logging data:

[0052]

[0053] In the formula, K mThe bulk modulus represents the equivalent rock matrix bulk modulus of the reservoir. K1, K2, and K3 represent the bulk modulus of clay, quartz, and calcite, respectively, while f1, f2, and f3 represent the clay content, quartz content, and calcite content, respectively. The bulk moduli of the clay, quartz, and calcite minerals used in this invention are 21 GPa, 37 GPa, and 70.2 GPa, respectively, and can be accurately calibrated based on rock physics experimental test results in actual work areas.

[0054] Step 102, Calculation of reservoir equivalent fluid bulk modulus

[0055] For fluid mixtures in rock pores or fractures, this invention calculates the reservoir equivalent fluid bulk modulus using the following formula based on Reuss's average theory:

[0056]

[0057] In the formula, K f K represents the equivalent fluid bulk modulus of the reservoir. o K w f represents the bulk modulus of oil and the bulk modulus of water, respectively. o f w These represent oil saturation and water saturation, respectively. The bulk modulus of oil used in this invention is 1.02 GPa, and the bulk modulus of water is 2 GPa. These can be accurately calibrated in actual work areas based on rock physics experimental test results.

[0058] Step 103, Calculation of effective porosity parameters

[0059] The equivalent bulk modulus K of the reservoir matrix is ​​obtained using the above formula. m Equivalent fluid bulk modulus K of the reservoir f Subsequently, in order to further obtain the equivalent pore structure parameters of the reservoir, an effective pore ratio parameter was introduced, the calculation formula of which is as follows:

[0060]

[0061] In the formula, F φ The effective porosity parameter is represented by φ, which represents the rock porosity, and K. sat It represents the equivalent bulk modulus of the reservoir under saturated fluid conditions.

[0062] K sat The calculation can be performed using the observed P-wave and S-wave velocities and density parameters. The specific calculation formula is as follows:

[0063]

[0064] In the formula, V P V sρ and ρ represent the longitudinal wave velocity, transverse wave velocity, and density of the rock, respectively.

[0065] Step 104, Calculation of equivalent pore structure parameters of the reservoir

[0066] The pore structure parameter α is derived from rock elastic parameters (P-wave and S-wave velocities, density, matrix bulk modulus, fluid bulk modulus, etc.) and porosity. The specific calculation formula is as follows:

[0067]

[0068] After obtaining the equivalent matrix bulk modulus K of the reservoir m reservoir equivalent fluid bulk modulus K f Effective porosity parameter F φ Given the rock porosity φ, the equivalent pore structure parameter α of the reservoir can be calculated using formula (5).

[0069] Example 2

[0070] In a specific embodiment 2 of the present invention, actual data from a certain region is used to test the effectiveness of the invention. The longitudinal wave velocity V is known. P Shear wave velocity V s Density ρ, porosity φ, clay content V SH Calcite content V calcite Quartz content V quartz Water saturation S w 8 parameters (e.g.) Figure 1 The pore fluids consist of only two types: water and oil. Based on the calculation relationships of this invention, the equivalent rock matrix bulk modulus K of the reservoir is calculated from the content and bulk modulus of mineral components such as clay, calcite, and quartz. m ( Figure 2 The equivalent fluid bulk modulus K of the reservoir was calculated using the water saturation and the bulk modulus of oil and water. f ( Figure 3 The equivalent bulk modulus K of the reservoir under saturated fluid conditions was calculated based on the measured P-wave velocity, S-wave velocity, and density. sat ( Figure 4 ). K based on calculation m K f K sat The effective porosity parameter F can be calculated by combining the known porosity φ. φ ( Figure 5 Based on this, the pore structure parameter α can be calculated. Figure 6 ).

[0071] Example 3

[0072] In a specific embodiment 3 of the present invention, actual data from a certain region is used to test the effectiveness of the invention. After obtaining the porosity and P-wave impedance data of the work area through pre-stack seismic data inversion, the cross-section of surface porosity and P-wave impedance (e.g., ...) is used to analyze the data. Figure 8 The fitting relationship between them is obtained (the fitting relationship varies depending on the actual data, and is obtained based on the actual data). The specific fitting formula is as follows:

[0073] por*α=0.0124*Ip 2 -0.253*Ip+1.4185 (6)

[0074] Where por represents the porosity obtained from the inversion, α represents the inverted pore structure parameters, and Ip represents the P-wave impedance. Using the inverted porosity and P-wave impedance, the pore structure parameters are further inverted to obtain the pore structure parameters. The porosity and pore structure parameters obtained from the wellbore inversion are compared as follows: Figure 9 As shown in the figure, the inversion results are in good agreement with the actual calculation results, indicating the feasibility of the method of the present invention.

[0075] The above relationships are applied to seismic inversion data. Using the porosity and P-wave impedance data obtained from pre-stack inversion, pore structure parameter data can be further obtained through inversion. Figure 10 The image shows a profile of pore structure parameters obtained from pre-stack seismic data.

[0076] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0077] Except for the technical features described in the specification, all other technologies are known to those skilled in the art.

Claims

1. A method for inverting pore structure parameters of sandstone reservoirs based on elastic modulus, characterized in that, The method for inverting sandstone reservoir pore structure parameters based on elastic modulus includes: Step 1: Calculate the equivalent bulk modulus of the reservoir matrix using the different rock component contents in the well logging data; Step 2: For fluid mixtures in rock pores or fractures, calculate the reservoir equivalent fluid bulk modulus; Step 3: Calculate the effective porosity parameters using parameters such as equivalent rock matrix modulus, reservoir equivalent fluid bulk modulus, P-wave velocity, S-wave velocity, and density. Step 4: Calculate the equivalent pore structure parameters of the reservoir; In step 3, the reservoir equivalent rock matrix bulk modulus K obtained in steps 1 and 2 is used as the basis for calculation. m Equivalent fluid bulk modulus K of the reservoir f In order to further obtain the equivalent pore structure parameters of the reservoir, an effective pore ratio parameter was introduced; In step 3, the formula for calculating the effective porosity parameter is: In the formula, F φ The effective porosity parameter is represented by φ, which represents the rock porosity, and K. sat Represents the reservoir's equivalent bulk modulus under saturated fluid conditions; In step 3, K sat The calculation is performed using observed P-wave and S-wave velocities and density parameters. The specific calculation formula is as follows: In the formula, V P V s ρ and ρ represent the longitudinal wave velocity, transverse wave velocity, and density, respectively; In step 4, the pore structure parameter α is derived from the rock elastic parameters and porosity. The rock elastic parameters include P-wave and S-wave velocities, density, matrix bulk modulus, and fluid bulk modulus. In step 4, the specific calculation formula for the pore structure parameter α is as follows: After obtaining the equivalent matrix bulk modulus K of the reservoir m reservoir equivalent fluid bulk modulus K f Effective porosity parameter F φ Given the rock porosity φ, the equivalent pore structure parameter α of the reservoir can be calculated using formula (5).

2. The method for inverting sandstone reservoir pore structure parameters based on elastic modulus according to claim 1, characterized in that, In step 1, the equivalent bulk modulus of the reservoir rock matrix is ​​related to the mineral composition of the rock and is the basis for calculating the pore structure parameters. Based on rock physics models such as KT, VRH, and DEM, and guided by the generalized Gassmann theory, the equivalent bulk modulus of the reservoir rock matrix is ​​calculated using the content of different rock components in the well logging data.

3. The method for inverting sandstone reservoir pore structure parameters based on elastic modulus according to claim 2, characterized in that, In step 1, the formula for calculating the equivalent bulk modulus of the reservoir matrix is: In the formula, K m The bulk modulus of the reservoir equivalent rock matrix is ​​represented by K1, K2, and K3, which represent the bulk modulus of clay, quartz, and calcite, respectively, and f1, f2, and f3 represent the clay content, quartz content, and calcite content, respectively.

4. The method for inverting sandstone reservoir pore structure parameters based on elastic modulus according to claim 1, characterized in that, In step 2, for the fluid mixture in the rock pores or fractures, the reservoir equivalent fluid bulk modulus is calculated according to the Reuss average theory.

5. The method for inverting sandstone reservoir pore structure parameters based on elastic modulus according to claim 4, characterized in that, In step 2, the formula for calculating the equivalent fluid bulk modulus of the reservoir is: In the formula, K f K represents the equivalent fluid bulk modulus of the reservoir. o K w f represents the bulk modulus of oil and the bulk modulus of water, respectively. o f w These represent oil saturation and water saturation, respectively.

Images