Generalized sandstone petrophysical modeling method

Abstract

The application provides a universal sandstone rock physical modeling method, which comprises the following steps: step 1, collecting and clarifying reservoir data of a target layer in a work area, and determining the geological background of the work area; step 2, calculating the elastic modulus of a non-diagenetic sandstone reservoir based on a granular medium theory model according to logging physical parameters; step 3, calculating the elastic modulus of a strong diagenetic sandstone reservoir based on an equivalent medium theory model according to logging physical parameters; and step 4, constructing a universal rock elastic modulus calculation final equivalent elastic modulus for sandstone. The universal sandstone rock physical modeling method has wide applicability to sandstone and can be used to describe sandstone reservoirs with different porosities and different diagenetic degrees. The universal sandstone rock physical modeling method has wide application value in geophysical exploration and development.

Description

Technical Field

[0001] This invention relates to the field of geophysical exploration seismic interpretation and comprehensive research technology, and in particular to a general-purpose sandstone rock physical modeling method. Background Technology

[0002] Establishing the relationship between the physical and elastic parameters of sandstone and applying quantitative interpretation of actual seismic data is a crucial step in guiding oil and gas exploration and development.

[0003] In sandstone reservoirs, the theoretical basis for rock physics modeling varies significantly depending on the geological characteristics. Currently, there are two main theoretical systems of rock physics models: one is the granular medium theory system based on grain packing systems; the other is the equivalent medium theory system that ignores wave multiple scattering. The specific choice of rock physics model is an unavoidable issue in actual sandstone reservoir oil and gas exploration, as an incorrect model can introduce significant uncertainty into quantitative seismic interpretation.

[0004] Generally, the granular medium theory is a particle packing model derived from Hertz contact theory. It assumes that the particles are ideal spheres or ellipsoids. By defining the average number of contacts between particles (coordination number), it calculates the normal and tangential contact stiffness by defining contact stiffness, and finally calculates the equivalent elastic modulus of the particle packing. Therefore, the granular medium theory is used to describe undiagenetic, loose sandstone with a distinct framework of grains, significant particle contacts, and a defined coordination number. It is typically applicable to sandstone reservoirs with high porosity (above 25%).

[0005] The equivalent medium theory is derived from the first-order scattering theory of long waves. Since the pores and fissures inside rocks are much smaller than the wavelength, they can be considered as equivalent volumes when elastic waves pass through them. In the equivalent medium theory, the contained materials (usually pores and fissures) can be represented as geometric shapes with different aspect ratios, thereby calculating the equivalent elastic modulus of the rock. Generally speaking, it is applicable to situations where the content of contained materials is sparse, and is suitable for dense sandstones, such as those with low porosity (below 10%).

[0006] As mentioned above, these two major categories of rock physics theories yield completely different predictions for the elastic properties of sandstone. Therefore, combining the equivalent medium theory and the granular medium theory to establish a universal rock physics modeling method applicable to low porosity (less than 10%), medium porosity (10% to 25%), and high porosity (greater than 25%) is of great guiding significance for reservoir characterization and quantitative characterization of physical parameters.

[0007] Chinese patent application CN201610116051.X discloses a method for constructing a rock physical model for tight sandstone, comprising the following steps: constructing a matrix model of the core; constructing a framework model of the rock; constructing a fluid-bearing model of the rock; and predicting the elastic properties of the rock. This invention proposes a novel rock physical model for tight sandstone incorporating different pore characteristics, establishing a quantitative relationship between mineral composition, porosity, pore type, fluid-bearing properties, and rock elastic parameters. The model has been calibrated based on core and well logging data, fully demonstrating its promising application prospects.

[0008] Chinese patent application N202010900922.3 discloses a rock physics modeling and P-wave velocity estimation method considering compaction, comprising: step 1, obtaining the elastic modulus of rock minerals; step 2, obtaining well logging interpretation results; step 3, improving the VRH model to calculate the rock skeleton modulus; step 4, calculating the elastic modulus of dry rock; step 5, calculating the bulk modulus of oil and water respectively; step 6, calculating the mixed fluid modulus of oil and water; step 7, calculating the elastic modulus of saturated rock; and step 8, calculating the P-wave velocity of weakly consolidated sandstone. This rock physics modeling and P-wave velocity estimation method considering compaction improves existing rock skeleton calculation models, proposes the concept of rock consolidation factor, enhances the applicability of rock physics models, and has good application effects in calculating the P-wave velocity of shallow, weakly consolidated rocks.

[0009] Chinese patent application CN201910358736.9 relates to a fracture-pore type rock physical elastic template, belonging to the field of exploration rock geophysics. To study tight sandstone reservoirs with high gas saturation, well-developed microfractures, and strong heterogeneity, this model calculates the elastic modulus of mixed minerals using the Voigt-Reuss-Hill model; it uses a differential equivalent medium (DEM) model to describe the skeletal elastic modulus of fractured and porous rocks; it describes the local fluid characteristics within the pores using Biot-Rayleigh theory; and it reveals the relationship between elastic parameters and physical properties of tight sandstone reservoirs.

[0010] 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 general-purpose sandstone rock physical modeling method. Summary of the Invention

[0011] The purpose of this invention is to provide a general sandstone rock physics modeling method that can accurately predict P-wave velocity and S-wave velocity.

[0012] The objective of this invention can be achieved through the following technical measures: a general-purpose sandstone rock physical modeling method, which includes:

[0013] Step 1: Collect and clarify the target reservoir data in the work area to determine the geological background of the work area;

[0014] Step 2: Calculate the elastic modulus of the unformed sandstone reservoir based on the granular medium theoretical model, according to the well logging physical property parameters.

[0015] Step 3: Calculate the elastic modulus of the strongly formed sandstone reservoir based on the equivalent medium theoretical model, according to the well logging physical property parameters;

[0016] Step 4: Construct a general rock elastic modulus for sandstone and calculate the final equivalent elastic modulus.

[0017] The objective of this invention can also be achieved through the following technical measures:

[0018] In step 1, the well data of the work area are classified and statistically analyzed to clarify that the main reservoir lithology of the work area is sandstone.

[0019] In step 1, for sandstone and mudstone formations, sandstone is a typical reservoir while mudstone is a typical non-reservoir; geological and physical characteristics are obtained through geological statistics, well logging data, and well logging interpretation.

[0020] In step 2, the granular medium model refers to a series of petrological models derived from the theory of granulation to describe undiagenetic loose sandstone, including the Hertz-Mindlin model, the Digby model, the Walton model, the CCT model, and the CCM model.

[0021] In step 2, for the Hertz-Mindlin model, the Hertz-Mindlin calculation formula is as follows:

[0022]

[0023]

[0024]

[0025]

[0026] In the above formula, K HM and G HM Represents the bulk modulus and shear modulus calculated using the Hertz-Mindlin model, respectively; C represents the coordination number; φ0 represents porosity; G and v represent the shear modulus and Poisson's ratio of the framework mineral, respectively; P represents pressure; ρ represents density; V P_HM and V S_HM The values ​​represent the P-wave velocity and S-wave velocity calculated by the Hertz-Mindlin model.

[0027] In step 3, the equivalent medium theory refers to a series of rock physics models derived from long-wave scattering theory to describe equivalent medium volumes, including the Kuster-Tokosoz equation, the self-consistent approximation theory, and the differential equivalent medium model.

[0028] In step 3, the calculation formula for the differential equivalent medium model is as follows:

[0029]

[0030]

[0031]

[0032]

[0033] The above expression is a coupled expression that requires iterative solution, where the initial condition K... * (0) = K1, G * (0) = G1, y represents the content of phase 2; for fluid inclusions and cavity inclusions, y equals porosity. P and Q represent the shape factors of the pores, and the values ​​of P and Q can describe the pore shapes of spheres, ellipsoids, disks, and needles, respectively. The subscripts 1 and 2 in the lower right corner represent the first phase and the second phase, respectively. The bulk modulus and shear modulus obtained by iteratively solving (5) and (6) are K DEM and G DEM , that is, the input parameters in formulas (7) and (8). ρ represents density. V P_DEM and V S_DEM These represent the final equivalent P-wave velocity and S-wave velocity calculated using the DEM model, respectively.

[0034] In step 4, the following function is constructed to calculate the final equivalent elastic modulus E. eff E eff =αE EM +(1-α)E GM ,

[0035] Where E represents elastic wave velocity; the subscript EM represents the equivalent medium, and the subscript GM represents the particulate medium; the parameter α represents the weighting factor, which needs to be adjusted based on actual data.

[0036] In step 4, the weighting factor α represents the diagenesis of the reservoir. The larger the value of α, the stronger the diagenesis and the more the reservoir tends to be an equivalent medium; the smaller the value of α, the weaker the diagenesis and the more the reservoir tends to be a granular medium.

[0037] This invention presents a general-purpose sandstone petrophysical modeling method, belonging to the field of seismic interpretation and comprehensive research in geophysical exploration. The method first clarifies the geological background of the work area, determining that the target reservoir's lithology is sandstone. Secondly, it establishes a granular medium model capable of describing undiagenetic, loose sandstone and an equivalent medium model capable of describing strongly diagenetic, dense sandstone. Thirdly, the prediction results of the granular medium model and the equivalent medium model are used as the lower and upper boundaries, respectively. Finally, a weighting function is constructed, and the weighting coefficients are adjusted inversely by introducing actual data, completing the petrophysical modeling through boundary weighting. The proposed method is effective in modeling and can accurately predict P-wave and S-wave velocities. Due to the use of boundary weighting methods such as the HM model and the differential equivalent medium model, this invention has broad applicability to sandstone and can be used to describe sandstone reservoirs with different porosities and diagenetic degrees. It has wide application value in geophysical exploration and development. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the calculation results of the work area HM model in a specific embodiment of the present invention;

[0039] Figure 2 This is a schematic diagram of the calculation results of the differential equivalent medium model of the work area in a specific embodiment of the present invention;

[0040] Figure 3 This is a schematic diagram of the calculation results of a general rock physics model in a specific embodiment of the present invention;

[0041] Figure 4 This is a flowchart of a specific embodiment of the general sandstone rock physics modeling method of the present invention. Detailed Implementation

[0042] 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.

[0043] 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.

[0044] For sandstone reservoirs, the basic geological background of the work area is defined. Grainy medium models and equivalent medium models are established to predict the elastic modulus of sandstone. Using the concept of a boundary-weighted model, the elastic modulus is constructed. Weighting factors are adjusted to select the weighting coefficients for the grainy medium model and the equivalent medium model, thus establishing a general-purpose rock physical model for sandstone reservoirs.

[0045] The specific implementation method is as follows:

[0046] Step 1: Collect and clarify the target reservoir data in the work area to determine the geological background of the work area.

[0047] Step 2: Calculate the elastic modulus of the unformed sandstone reservoir based on the well logging physical property parameters and the particle medium theoretical model.

[0048] Step 3: Calculate the elastic modulus of the strongly formed sandstone reservoir based on the equivalent medium theoretical model, according to the well logging physical property parameters.

[0049] Step 4: Construct a general rock elastic modulus calculation function for sandstone: E eff =αE EM +(1-α)E GM And the weighting factor α is adjusted in reverse by calibrating with actual data.

[0050] This invention combines a granular medium model and an equivalent medium model to calculate the equivalent elastic wave velocity of rocks using a boundary-weighted approach. Theoretically, this universal model can describe both undiagenetic, loose sandstone and strongly diagenetic, dense sandstone. Furthermore, the weighting factor α indicates the diagenesis and density of the rock; a larger α value indicates a denser rock and stronger diagenesis, while a smaller α value indicates a looser rock and weaker diagenesis.

[0051] The following are several specific embodiments of the application of the present invention.

[0052] Example 1

[0053] In a specific embodiment 1 of the present invention, such as Figure 4 As shown, Figure 4 This is a flowchart of the general sandstone rock physical modeling method of the present invention. The general sandstone rock physical modeling method includes the following steps:

[0054] Step 101: Classify and statistically analyze the well data in the work area to determine that the main reservoir lithology in the work area is sandstone.

[0055] The geological background of the work area is clearly defined, with sandstone as the main reservoir lithology. For sandstone-mudstone formations, sandstone is a typical reservoir while mudstone is a typical non-reservoir. Geological and physical properties can be obtained through geological statistics, well logging data, and well logging interpretation.

[0056] Step 102: Construct a model based on the granular medium to describe the elastic properties of loose, undiagenetic sandstone, and calculate the equivalent elastic modulus of the rock based on the granular medium model.

[0057] Furthermore, the granular media model refers to a series of petrological models derived from the theory of granulation to describe undiagenetic loose sandstone, including but not limited to the Hertz-Mindlin model, the Digby model, the Walton model, the CCT model, and the CCM model.

[0058] Step 103: Construct an equivalent medium model to describe the elastic properties of sandstone with dense and strong diagenesis, and calculate the equivalent elastic modulus of the rock based on the equivalent medium model.

[0059] Furthermore, the equivalent medium theory refers to a series of rock physics models derived from long-wavelength scattering theory to describe equivalent mediums, including but not limited to the Kuster-Tokosoz equation (KT equation), the self-consistent approximation theory (SCA model), and the differential equivalent medium model (DEM model).

[0060] Step 104: Construct the following function to calculate the final equivalent elastic modulus: E eff =αE EM +(1-α)E GM Where E represents elastic wave velocity; the subscript EM represents equivalent medium, and the subscript GM represents granular medium; the parameter α represents the weighting factor, which needs to be adjusted based on actual data.

[0061] Furthermore, the weighting factor α represents the diagenesis of the reservoir to some extent. The larger the α value, the stronger the diagenesis, and the more the reservoir tends to be an equivalent medium; the smaller the α value, the weaker the diagenesis, and the more the reservoir tends to be a granular medium.

[0062] Example 2

[0063] In a specific embodiment 2 of the present invention, based on our proposed statistical rock physics modeling method for unformed sandstone, the following example is given: In this example, the work area is the CB block of Shengli Oilfield, and the target layer is the Guantao Formation. The geological background of the work area is a sandstone-mudstone profile.

[0064] Step 1: Collect and clarify the target reservoir data in the work area to determine the geological background of the work area;

[0065] The target work area is the CB region, and the target layer is the Guantao Formation, with a burial depth ranging from 1100m to 1800m. Well logging data indicates that the target layer is a typical sandstone-mudstone profile, and its lithology meets the prerequisites of this invention.

[0066] Step 2: Calculate the elastic modulus of the unformed sandstone reservoir based on the granular medium theoretical model according to the well logging physical property parameters.

[0067] In this embodiment, we use the Hertz-Mindlin model to calculate the elastic modulus and elastic wave velocity of sandstone in the target granular medium theoretical model. The Hertz-Mindlin calculation formula is as follows:

[0068]

[0069]

[0070]

[0071]

[0072] In the above formula, K HM and G HM The values ​​represent the bulk modulus and shear modulus calculated using the Hertz-Mindlin model (HM model), respectively; C represents the coordination number; φ represents porosity; G and v represent the shear modulus and Poisson's ratio of the framework mineral, respectively; P represents pressure; ρ represents density; and V represents... P_HM and V S_HM The values ​​represent the P-wave velocity and S-wave velocity calculated by the Hertz-Mindlin model.

[0073] In this embodiment, the input parameters are selected based on the rock physics analysis and well logging data analysis of the actual work area. The HM model calculation results are low, indicating that the target reservoir is not a pure unformed loose sandstone. The results calculated using the HM model can be used as the lower boundary.

[0074] Table 1 Modeling Parameters

[0075]

[0076]

[0077] Step 3: Calculate the elastic modulus of the strongly formed sandstone reservoir based on the equivalent medium theoretical model, according to the well logging physical property parameters.

[0078] In this embodiment, we use a differential equivalent medium model to calculate the elastic modulus and elastic wave velocity of strongly aggregate sandstone. The calculation formula for the differential equivalent medium model is as follows:

[0079]

[0080]

[0081]

[0082]

[0083] The above expression is a coupled expression that requires iterative solution, where the initial condition K... * (0) = K1, G * (0) = G1, where y represents the content of phase 2. For fluid inclusions and cavity inclusions, y equals porosity. The shape expressions for P and Q are detailed in Berryman's (1980) paper, which is not the subject of this invention and will not be repeated here.

[0084] In this embodiment, the input parameters of the model are shown in Table 1. The input parameters are selected based on the rock physics analysis and well logging data analysis of the actual work area. It can be seen that the calculation results of the differential equivalent model are significantly lower, indicating that the target reservoir is not a strongly formed tight sandstone. The results calculated using the differential equivalent medium model can be used as the upper boundary.

[0085] Step 4: Construct a general rock elastic wave velocity calculation function for sandstone: E eff =αE EM +(1-α)E GM The reverse adjustment weighting factor α was determined using actual data. Results show that the proposed method is effective in modeling and can accurately predict P-wave and S-wave velocities. Due to the boundary weighting method used for the HM model and the differential equivalent medium model, this scheme theoretically has broad applicability to sandstone and can be used to describe sandstone reservoirs with different porosities and diagenetic degrees. It has wide application value in geophysical exploration and development.

[0086] Example 3

[0087] In a specific embodiment 3 of the present invention, the invention is applied. Figure 1 The above shows the calculation results of the HM model for the example work area. The first column is porosity, the second is clay content, the third is P-wave velocity, and the fourth is S-wave velocity. In the third and fourth columns, solid lines represent actual well logging data, and dashed lines represent the results predicted by the HM model.

[0088] Figure 2 The above shows the calculation results of the differential equivalent medium model for the example work area. The first column represents porosity, the second column represents clay content, the third column represents P-wave velocity, and the fourth column represents S-wave velocity. In the third and fourth columns, solid lines represent actual well logging data, and dashed lines represent the results predicted by the differential equivalent medium model.

[0089] Figure 3The results of calculations using a general-purpose rock physics model for the example work area are shown. The first column represents porosity, the second column represents clay content, the third column represents P-wave velocity, and the fourth column represents S-wave velocity. In the third and fourth columns, solid lines represent actual well logging data, and dashed lines represent the general-purpose rock physics modeling results proposed in this invention.

[0090] 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.

[0091] Except for the technical features described in the specification, all other technologies are known to those skilled in the art.

Claims

1. A general-purpose physical modeling method for sandstone, characterized in that, This general-purpose sandstone rock physics modeling method includes: Step 1: Collect and clarify the target reservoir data in the work area to determine the geological background of the work area; Step 2: Calculate the elastic modulus of the unformed sandstone reservoir based on the granular medium theoretical model, according to the well logging physical property parameters. Step 3: Calculate the elastic modulus of the strongly formed sandstone reservoir based on the equivalent medium theoretical model, according to the well logging physical property parameters; Step 4: Construct a general rock elastic modulus model for sandstone and calculate the final equivalent elastic modulus; In step 4, the following function is constructed to calculate the final equivalent elastic modulus E. eff : in, Represents elastic wave velocity; subscript Represents the equivalent medium, subscript Represents particulate media; parameters These represent weighting factors and need to be adjusted using actual data. In step 4, weighting factors This represents the diagenesis of the reservoir. The higher the value, the stronger the diagenesis, and the more the reservoir tends to be an equivalent medium; The smaller the value, the weaker the diagenesis, and the more the reservoir tends to be a granular medium.

2. The general sandstone rock physical modeling method according to claim 1, characterized in that, In step 1, the well data of the work area are classified and statistically analyzed to clarify that the main reservoir lithology of the work area is sandstone.

3. The general sandstone rock physical modeling method according to claim 2, characterized in that, In step 1, for sandstone and mudstone formations, sandstone is a typical reservoir while mudstone is a typical non-reservoir; geological and physical characteristics are obtained through geological statistics, well logging data, and well logging interpretation.

4. The general sandstone rock physical modeling method according to claim 1, characterized in that, In step 2, the granular medium model refers to a series of petrological models derived from the theory of granulation to describe undiagenetic loose sandstone, including the Hertz-Mindlin model, the Digby model, the Walton model, the CCT model, and the CCM model.

5. The general sandstone rock physical modeling method according to claim 4, characterized in that, In step 2, for the Hertz-Mindlin model, the Hertz-Mindlin calculation formula is as follows:

6. The general sandstone rock physical modeling method according to claim 1, characterized in that, In step 3, the equivalent medium theory refers to a series of rock physics models derived from long-wave scattering theory to describe equivalent medium volumes, including the Kuster-Tokosoz equation, the self-consistent approximation theory, and the differential equivalent medium model.

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