Method, apparatus and device for establishing a maximum relaxation saturation rock physics model

Abstract

The present specification relates to the technical field of oil and gas exploration, and particularly relates to a method, device and equipment for establishing a maximum relaxation saturation rock physics model. The method for establishing the maximum relaxation saturation rock physics model comprises: determining a fluid-solid composite medium model of rock, the fluid-solid composite medium model being a heterogeneous model; determining physical property parameters of the rock in a seismic wave propagation process according to the fluid-solid composite medium model; determining a propagation velocity of a seismic wave in the rock according to the physical property parameters; and establishing a maximum relaxation saturation model of the rock according to the propagation velocity and the physical property parameters, the maximum relaxation saturation model being used to predict fluid saturation of a target reservoir. The maximum relaxation saturation model of the present specification embodiment can accurately describe the relationship between seismic data and reservoir physical properties and reservoir fluid content. Through the maximum relaxation saturation model, the accuracy of reservoir fluid content prediction can be improved.

Description

Technical Field

[0001] This specification relates to the field of oil and gas exploration technology, and in particular to a method, apparatus and equipment for establishing a rock physics model with maximum relaxation saturation. Background Technology

[0002] Rock physics modeling is a fundamental technique in reservoir prediction. The accuracy and rationality of rock physics modeling directly affect the reliability of subsequent reservoir predictions. Existing rock physics theoretical models, such as those based on the Gassmann equation and Biot theory, often idealize actual rocks through certain assumptions, thereby establishing the variation law between physical parameters and fluidity through physical principles to predict the fluidity of reservoirs.

[0003] However, underground rocks, especially sedimentary rocks, are extremely complex. They exhibit indescribable heterogeneity and disorder at various scales. This contradicts the idealized assumptions of many theoretical models. Therefore, existing rock physics models cannot accurately predict the fluidity of reservoirs, which is detrimental to guiding seismic exploration. Summary of the Invention

[0004] This specification provides a method, apparatus, and computer equipment for establishing a rock physics model with maximum relaxation saturation, in order to improve the accuracy of reservoir fluidity prediction.

[0005] This specification provides an embodiment of a method for establishing a rock physics model with maximum relaxation saturation, including:

[0006] A fluid-solid composite medium model for the rock is determined, wherein the fluid-solid composite medium model is a heterogeneous model;

[0007] Based on the fluid-solid composite medium model, the physical properties of the rock during seismic wave propagation were determined;

[0008] Determine the propagation velocity of seismic waves in rocks based on physical property parameters;

[0009] Based on propagation velocity and physical property parameters, a maximum relaxation saturation model for rocks is established. This maximum relaxation saturation model is used to predict the fluid saturation of the target reservoir.

[0010] This specification also provides an embodiment of a rock physics model establishment device with maximum relaxation saturation, comprising:

[0011] The first determining unit is used to determine the fluid-solid composite medium model of the rock, wherein the fluid-solid composite medium model is a heterogeneous model;

[0012] The second determining unit is used to determine the physical property parameters of the rock during the propagation of seismic waves based on the fluid-solid composite medium model.

[0013] The third determining unit is used to determine the propagation velocity of seismic waves in rocks based on physical property parameters;

[0014] A unit is established to build a maximum relaxation saturation model for rocks based on propagation velocity and physical property parameters. The maximum relaxation saturation model is used to represent the predicted fluid saturation of the target reservoir.

[0015] This specification also provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the above-described method for establishing a rock physics model with maximum relaxation saturation.

[0016] The method described in this specification can determine the fluid-solid composite medium model of rock, which is a heterogeneous model; it can determine the physical properties of rock during seismic wave propagation based on the fluid-solid composite medium model; it can determine the propagation velocity of seismic waves in rock based on the physical properties; and it can establish a maximum relaxation saturation model of rock based on the propagation velocity and physical properties. The maximum relaxation saturation model in this specification is based on seismic waves. The wavelength of seismic waves is much larger than the length of pores in a heterogeneous porous medium. Seismic waves are insensitive to heterogeneity and disorder at various complex microscales. What is observed in seismic waves is the average elastic effect of the porous medium within the seismic wave wavelength. Therefore, the maximum relaxation saturation model can macroscopically reflect the difficult-to-describe heterogeneity and disorder exhibited by reservoir rocks at various scales, avoiding various idealized assumptions in existing theoretical models. The maximum relaxation saturation model can accurately describe the relationship between seismic data and reservoir physical properties and reservoir fluidity. The maximum relaxation saturation model can improve the accuracy of reservoir fluidity prediction and provide effective guidance for seismic exploration. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments or prior art of this specification, the drawings used in the description of the embodiments or prior art will be briefly introduced below. The drawings described below are only some embodiments recorded in this specification. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a flowchart illustrating the method for establishing a rock physics model with maximum relaxation saturation in the embodiments of this specification.

[0019] Figure 2This is a schematic diagram of the fluid-solid composite medium model in the embodiments of this specification;

[0020] Figure 3 This is a graph showing the relationship between the longitudinal wave velocity and water saturation in tight sandstone gas reservoirs in the embodiments of this specification.

[0021] Figures 4a-4e This is a graph showing the relationship between longitudinal wave velocity and water saturation in the embodiments of this specification;

[0022] Figure 5 This is a graph showing the relationship between longitudinal wave velocity and water saturation in the embodiments of this specification;

[0023] Figure 6 This is a graph showing the relationship between porosity and water saturation in the embodiments of this specification;

[0024] Figure 7 This is a graph showing the relationship between porosity and water saturation in the embodiments of this specification;

[0025] Figure 8 This is an example of a P-wave velocity inversion profile for a clastic oil and gas reservoir in the embodiments of this specification;

[0026] Figure 9 This is a schematic diagram of the structure of the device for establishing a rock physics model with maximum relaxation saturation in the embodiments of this specification. Detailed Implementation

[0027] The technical solutions in the embodiments of this specification will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this specification, and not all embodiments. The specific embodiments described herein are only used to explain this disclosure, and not to limit this disclosure. All other embodiments obtained by those skilled in the art based on the described embodiments of this disclosure are within the scope of protection of this disclosure. In addition, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations.

[0028] Furthermore, most existing theoretical models are based on the variation of seismic wave propagation velocity with frequency under water saturation conditions, rarely addressing the variation of seismic wave propagation velocity with gas saturation and / or water saturation. Saturated rocks in actual formations are a combination of a dry rock skeleton (including various mineral components and rock particles) and pore fluids. Different mineral components and particles possess different mechanical properties and elastic characteristics. To obtain the equivalent elastic modulus of the entire assembly, it is necessary to know the elastic properties of the pore fluids, the elastic properties of the dry rock skeleton, and the fluid flow induced by wave propagation. The bridge to this is establishing a physical theoretical model of the rock. The maximum relaxation saturation rock physical model establishment method described in this specification can establish a maximum relaxation saturation model of the rock. This maximum relaxation saturation model can accurately describe the relationship between the physical properties of the rock and its seismic elastic properties, providing a foundation and tool for predicting reservoir parameters using seismic elastic parameters. The maximum relaxation saturation rock physical model establishment method can be applied to computer equipment such as servers.

[0029] Please see Figure 1 The method for establishing the maximum relaxation saturation rock physics model may include the following steps.

[0030] Step 11: Determine the fluid-solid composite medium model to represent the rock.

[0031] In some embodiments, the rock can be a complex porous medium with multiple scales. The rock can include saturated rock. The saturated rock can include a dry rock framework and fluids within the pores. The dry rock framework can include solid particles formed from various mineral components and rock grains, as well as the pores. The fluid can include gaseous fluids and liquid fluids; the gaseous fluid can include air, natural gas, etc., and the liquid fluid can include water, etc.

[0032] In some embodiments, by constructing a fluid-solid composite medium model, saturated rocks in actual reservoirs can be equivalently represented, facilitating the acquisition of rock physical properties. The fluid-solid composite medium model can be a heterogeneous model. See also... Figure 2 The fluid-solid composite medium model can be a sphere. Specifically, the fluid-solid composite medium model can be a double-layered patchy sphere. The fluid-solid composite medium model can include an inner solid spherical region and an outer hollow spherical region. The inner solid spherical region is used to represent the medium formed by the coupling of solid particles and gas fluid. The outer hollow spherical region is used to represent the medium formed by the coupling of solid particles and liquid fluid. The center of the inner solid spherical region is the same as the center of the fluid-solid composite medium model. The inner solid spherical region can be specifically understood as a sub-sphere in the fluid-solid composite medium model, and the outer hollow spherical region can be specifically understood as the region outside the sub-spheres in the fluid-solid composite medium model.

[0033] The fluid-solid composite medium model is heterogeneous, with the media formed by the coupling of solid particles with different fluids located in different regions. Furthermore, the media formed by the coupling of solid particles with gaseous fluids is located inside, while the media formed by the coupling of solid particles with liquid fluids is located on the outside. Therefore, the fluid-solid composite medium model can accurately simulate the physical properties of rocks in the real world.

[0034] In some embodiments, the radius of the internal solid spherical region and the radius of the fluid-solid composite medium model can be obtained; the fluid-solid composite medium model can be constructed based on the radius of the internal solid spherical region and the radius of the fluid-solid composite medium model. The radius of the internal solid spherical region and the radius of the fluid-solid composite medium model can be input by users such as researchers on the computer device, or they can be obtained in other ways. This specification does not specifically limit these methods.

[0035] Step 12: Determine the physical properties of the rock during the propagation of seismic waves based on the fluid-solid composite medium model.

[0036] In some embodiments, formulas for physical property parameters corresponding to a fluid-solid composite medium model can be determined. These formulas are used to determine physical property parameters. Specifically, the formulas may include Poisson's ratio formula, Young's modulus formula, and density formula. The Poisson's ratio formula may include... The Young's modulus formula may include E n =2μ n (1+σ n The density formula may include...

[0037] In the Poisson's ratio formula, Young's modulus formula, and density formula above, n is taken from 1 and 2. When n = 1, it represents the inner solid spherical region; when n = 2, it represents the outer hollow spherical region. σ n Let σ1 represent the Poisson's ratio, and σ2 represent the Poisson's ratio of the inner solid spherical region. E represents the Poisson's ratio of the outer hollow spherical region. n E1 represents the Young's modulus of the inner solid spherical region, and E2 represents the Young's modulus of the outer hollow spherical region. n The symbols represent fluids: f1 represents the gaseous fluid within the solid inner sphere region, and f2 represents the liquid fluid within the hollow outer sphere region. n μ1 represents the shear modulus of the inner solid spherical region, and μ2 represents the shear modulus of the outer hollow spherical region. This represents the bulk modulus of a porous medium containing fluid. This represents the bulk modulus of the internal solid spherical region. This represents the bulk modulus of the outer hollow spherical region. K represents the bulk modulus of the dry rock skeleton. s It represents the bulk modulus of solid particles in a rock. ρ represents the porosity of a rock. s This represents the density of solid particles in a rock. This indicates the density of the fluid within the solid sphere's interior. S1 represents the density of the fluid within the outer hollow sphere region, S2 represents the saturation degree of the inner sphere region (e.g., gas saturation), and ρ represents the saturation degree of the outer hollow sphere region (e.g., water saturation). * This represents the equivalent density of the rock.

[0038] In some embodiments, the rock is a non-uniform porous medium. When seismic waves propagate in a non-uniform porous medium, the seismic wave stress field induces fluid flow within the pores. The interaction between the dry rock skeleton and the fluid also significantly affects the velocity of the seismic waves, causing attenuation and dispersion. Therefore, when seismic waves propagate in a fluid-solid composite medium model, a partial volume change occurs on the outer surface of the model, and the resulting pressure can be calculated from this volume change. Specifically, in the absence of seismic waves, no fluid flow occurs, and the average bulk modulus of the fluid-solid composite medium model can be represented as K0. In the presence of seismic waves, the seismic wave stress field induces fluid flow within the pores, causing the fluid-solid composite medium model to expand, with the expansion amplitude represented as D0. During seismic wave propagation, the bulk modulus of the fluid-solid composite medium model can be represented by the pressure P0 applied by the seismic wave and the expansion amplitude D0. For example, the bulk modulus of the fluid-solid composite medium model can be the ratio between the pressure P0 and the expansion amplitude D0. Considering axisymmetric stress and displacement, the functional relationship between pressure P0 and expansion amplitude D0 can be expressed using Young's modulus and Poisson's ratio. The following formula is obtained.

[0039]

[0040]

[0041] In formulas (1) and (2) above, a and b represent the radius of the inner solid spherical region and the radius of the fluid-solid composite medium model, respectively; P0 represents the pressure exerted on the outer sphere, P i This represents the pressure exerted on the internal solid spherical region by P0.

[0042] Under the influence of an applied seismic wave field, the displacement on the outer surface of the fluid-solid composite medium model can be expressed as:

[0043] u r (b)=U0e iωt (3)

[0044] The pressure on the outer surface caused by this displacement can be expressed as P0e. iωt .

[0045] The volumetric strain (the ratio of volume change to total volume) caused by the displacement of the outer surface in a fluid-solid composite medium model can be expressed as:

[0046]

[0047] From this, we can obtain

[0048] The bulk modulus of a fluid-solid composite medium model can be expressed as the ratio between pressure P0 and expansion amplitude D0:

[0049]

[0050] The following describes the specific process of determining the expression for P0 / U0 to obtain K0, starting from formulas (1) and (2).

[0051] Introducing x = P0 / U0, y = P i / U0, thus obtaining P0=xU0, P i =yU0.

[0052] Let P0 = xU0 and P i Substituting =yU0 into formulas (1) and (2), we can obtain the following formula:

[0053]

[0054]

[0055] By rearranging formulas (6) and (7), we can obtain:

[0056]

[0057]

[0058] Formulas (8) and (9) are a system of algebraic equations about x and y. Calculations yield the following results. The expression for the bulk modulus is given by formula (5). The bulk modulus expression for the fluid-solid composite medium model can be obtained as follows:

[0059]

[0060] In the above formula (10), S1 represents the saturation of the internal solid sphere region, and

[0061] The bulk modulus K0 can be expressed as a function of Young's modulus E and Poisson's ratio σ. Therefore, according to formula (10), we can obtain:

[0062]

[0063] E n =2μ n (1+σ n (12)

[0064] It should be noted that existing technologies often assume that the gas in the rock pores is very light and compressible, thus neglecting gas-related parameters (such as bulk modulus). and density Only skeleton-related parameters (e.g., bulk modulus) are used. and bulk modulus K s The Poisson's ratio is calculated using the following method. For example, the Poisson's ratio σ1 of the internal solid spherical region is calculated using only the parameters related to the skeleton. The embodiments in this specification consider the influence of gases; the Poisson's ratio formula includes factors arising from gas-related parameters, i.e.:

[0065]

[0066] In the above formula (13):

[0067] Therefore, from the above formula (13), we can obtain:

[0068]

[0069] In the above formula (14), α represents the consolidation parameter, which indicates the degree of consolidation between the framework particles. For example, for sandstone, 2 < α < 20. When the bulk moduli of the gaseous fluid and the framework particles are known, dK depends on α and

[0070] It should also be noted that existing technologies often assume that the gas in the rock pores is very light and compressible, thus neglecting gas-related parameters (such as bulk modulus). and density The calculation of equivalent density also suffers from the problem of neglecting gas-related parameters. The embodiments in this specification consider the influence of gases, and the equivalent density formula includes gas-related parameters (such as density). ).

[0071] In some embodiments, the physical properties of the rock may include porosity, Poisson's ratio, Young's modulus, and density. In practical applications, multiple porosities and multiple fluid saturations may be selected. Each porosity may correspond to one or more of the multiple fluid saturations. The fluid saturations may include water saturation and / or gas saturation. Multiple Poisson's ratios of the rock can be calculated using the Poisson's ratio formula based on the selected multiple porosities and multiple fluid saturations; multiple Young's moduli of the rock can be calculated using the Young's modulus formula based on the multiple Poisson's ratios; and multiple densities of the rock can be calculated using the density formula based on the multiple porosities.

[0072] Specifically, for each of the multiple porosities, the porosity and the corresponding fluid saturations can be substituted into the Poisson's ratio formula to obtain multiple Poisson's ratios; the multiple Poisson's ratios can be substituted into the Young's modulus formula to obtain multiple Young's moduli; and the porosity can be substituted into the density formula to obtain an equivalent density. Specifically, substituting the porosity and the corresponding fluid saturations into the Poisson's ratio formula to obtain multiple Poisson's ratios can include: for each of the multiple fluid saturations, substituting the porosity and the fluid saturation into the Poisson's ratio formula to obtain one Poisson's ratio. Calculating multiple Young's moduli of the rock based on the multiple Poisson's ratios using the Young's modulus formula can include: for each of the multiple Poisson's ratios, substituting the Poisson's ratio into the Young's modulus formula to obtain one Young's modulus. Thus, each porosity can correspond to multiple fluid saturations, multiple Poisson's ratios, multiple Young's moduli, and one equivalent density. There can also be a correspondence between fluid saturation, Poisson's ratio, Young's modulus, and equivalent density. For example, a fluid saturation can correspond to a Poisson's ratio, a Young's modulus, and an equivalent density.

[0073] It should be noted that fluid saturation includes water saturation and / or gas saturation; Poisson's ratio includes the Poisson's ratio σ1 of the inner solid spherical region and / or the Poisson's ratio σ2 of the outer hollow spherical region; and Young's modulus includes the Young's modulus E1 of the inner solid spherical region and the Young's modulus E2 of the outer hollow spherical region. For example, if fluid saturation can be water saturation, then Poisson's ratio can be the Poisson's ratio σ2 of the outer hollow spherical region, and Young's modulus can be the Young's modulus E2 of the outer hollow spherical region.

[0074] In some scenario examples, the fluids in saturated rock include gaseous fluids such as air and natural gas, and the liquid fluids include water. The sum of the water saturation and the gas saturation can equal 1.

[0075] Step 13: Determine the propagation velocity of seismic waves in the rock based on the physical property parameters.

[0076] In some embodiments, the propagation velocity of seismic waves can be calculated based on the physical property formulas such as Poisson's ratio, Young's modulus, and density determined by the fluid-solid composite medium model, thereby amplifying the sensitivity of seismic waves to fluids.

[0077] The propagation velocity may include the P-wave velocity of the seismic wave. The formula for the P-wave velocity may include... Among them, V p σ represents the longitudinal wave velocity, where n is chosen from 1 and 2; when n = 1, it represents the inner solid spherical region, and when n = 2, it represents the outer hollow spherical region; n σ1 represents the Poisson's ratio of the inner solid spherical region, and σ2 represents the Poisson's ratio of the outer hollow spherical region; E n ρ represents Young's modulus, where E1 represents the Young's modulus of the inner solid spherical region and E2 represents the Young's modulus of the outer hollow spherical region; * This represents the equivalent density of the rock. Of course, the propagation velocity can also include the transverse wave velocity. The formula for transverse wave velocity can include...

[0078] In some embodiments, multiple propagation velocities can be calculated using a seismic wave velocity formula based on the multiple Poisson ratios, the multiple Young's moduli, and the multiple densities, wherein the propagation velocities correspond to the porosity and the fluid saturation.

[0079] For example, multiple longitudinal wave velocities can be calculated using a formula based on the multiple Poisson ratios, the multiple Young's moduli, and the multiple densities, where the longitudinal wave velocities correspond to the porosity and the fluid saturation.

[0080] After step 12, multiple porosities, multiple fluid saturations, multiple Poisson's ratios, multiple Young's moduli, and multiple equivalent densities can be obtained. Each porosity can correspond to multiple fluid saturations, multiple Poisson's ratios, multiple Young's moduli, and one equivalent density. Therefore, for each porosity, the multiple Poisson's ratios, multiple Young's moduli, and one equivalent density corresponding to that porosity can be substituted into the seismic wave propagation velocity formula to calculate the multiple propagation velocities corresponding to that porosity. For example, for each porosity, the multiple Poisson's ratios, multiple Young's moduli, and one equivalent density corresponding to that porosity can be substituted into the P-wave velocity formula to calculate the multiple P-wave velocities corresponding to that porosity. Specifically, for example, for each porosity, the Poisson's ratio σ² of multiple external hollow spherical regions, the Young's modulus E² of multiple external hollow spherical regions, and one equivalent density ρ can be used. * Substituting into the P-wave velocity formula, multiple P-wave velocities V corresponding to this porosity are calculated.p .

[0081] Step 14: Based on the propagation speed and physical property parameters, establish a model for the maximum relaxation saturation of the rock.

[0082] In some embodiments, a dataset can be constructed, which corresponds to porosity and includes multiple pairs of fluid saturation and propagation velocity; the maximum relaxation saturation corresponding to porosity can be determined based on the fluid saturation and propagation velocity in the dataset; and a maximum relaxation saturation model can be established based on porosity and the maximum relaxation saturation corresponding to porosity.

[0083] Through steps 12 and 13, multiple seismic wave propagation velocities can be obtained for selected porosity and fluid saturation levels. Each porosity can correspond to multiple fluid saturations and multiple propagation velocities. Therefore, multiple datasets can be constructed. Each dataset can correspond to one porosity and can include multiple pairs of fluid saturations and propagation velocities. Each pair of fluid saturations and propagation velocities can include one fluid saturation and one corresponding propagation velocity. In practical applications, for each selected porosity, multiple fluid saturations and multiple propagation velocities corresponding to that porosity can be obtained as the fluid saturation and propagation velocities in the dataset corresponding to that porosity. The multiple fluid saturations and multiple propagation velocities in each dataset can have a corresponding relationship, thereby determining multiple pairs of fluid saturations and propagation velocities.

[0084] For each of the multiple datasets, a maximum relaxation saturation can be determined based on multiple pairs of fluid saturation and propagation velocities within that dataset, serving as the maximum relaxation saturation corresponding to the porosity of that dataset. For example, a pair of fluid saturation and propagation velocities with the minimum propagation velocity can be selected from the multiple pairs, and the fluid saturation in that pair can be used as the maximum relaxation saturation. The maximum relaxation saturation can be the fluid saturation corresponding to the minimum propagation velocity. For example, the maximum relaxation saturation can be the water saturation corresponding to the minimum P-wave velocity. Thus, multiple maximum relaxation saturations can be obtained for the selected multiple porosities. Each porosity can correspond to one maximum relaxation saturation. Therefore, a maximum relaxation saturation model can be established based on multiple porosities and their corresponding maximum relaxation saturations. For example, a relationship curve can be plotted based on multiple porosities and their corresponding maximum relaxation saturations; the plotted relationship curve can be fitted to obtain the maximum relaxation saturation model. The maximum relaxation saturation model can accurately describe the relationship between seismic data and reservoir properties and fluidity. For example, the maximum relaxation saturation model can be used to represent the relationship between fluid saturation and propagation velocity, which may include: as fluid saturation increases, propagation velocity first decreases and then increases. For example, as water saturation increases, P-wave velocity first decreases and then increases. The maximum relaxation saturation model may include:

[0085]

[0086] In equation (15) above, Sw MR Sw represents the maximum relaxation saturation (%), Sw0 represents the initial water saturation (%), and Sw H Indicates the maximum water saturation (%). Indicates porosity (%) denoted by , where represents the critical porosity (%) and k represents the permeability (mD).

[0087] In some embodiments, the maximum relaxation saturation model can be used to predict the fluid saturation of a target reservoir. Specifically, the maximum relaxation saturation corresponding to the porosity of the target reservoir can be determined based on the maximum relaxation saturation model; a first linear relationship and a second linear relationship of the target reservoir can be determined based on the maximum relaxation saturation, wherein the first linear relationship and the second linear relationship represent the linear relationship between P-wave velocity and water saturation; the P-wave velocity volume of seismic waves in the target reservoir can be obtained; and the water saturation volume corresponding to the P-wave velocity volume can be determined based on the first linear relationship and the second linear relationship.

[0088] The maximum relaxation saturation model can be used to represent the following relationship between fluid saturation and propagation velocity: as fluid saturation increases, propagation velocity first decreases and then increases. On both sides of the maximum relaxation saturation, the relationship between P-wave velocity and water saturation can be equivalent to a linear relationship. Therefore, a first water saturation interval and a second water saturation interval can be divided with the maximum relaxation saturation as the boundary; within the first water saturation interval, the first linear relationship can be determined; within the second water saturation interval, the second linear relationship can be determined. The water saturation in the first water saturation interval is less than the maximum relaxation saturation. The water saturation in the second water saturation interval is greater than or equal to the maximum relaxation saturation. The first linear relationship can be an inverse linear relationship, that is, the P-wave velocity is inversely correlated with the magnitude of water saturation. The second linear relationship can be a positive linear relationship, that is, the P-wave velocity is positively correlated with the magnitude of water saturation.

[0089] Seismic wave data from the target reservoir can be inverted to obtain a P-wave velocity volume. This P-wave velocity volume comprises multiple P-wave velocities. For each P-wave velocity in the volume, a first linear relationship and a second linear relationship can be applied to obtain two water saturations. These two water saturations are located on either side of the maximum relaxation saturation. That is, one of the two water saturations is greater than or equal to the maximum relaxation saturation, and the other is less than the maximum relaxation saturation. This yields the water saturation volume corresponding to the P-wave velocity volume. The water saturation volume comprises multiple water saturations.

[0090] Please see Figure 3 Triangular points, large rhombus points, small rhombus points, and circular points correspond to datasets S1, S2, S3, and S4, respectively. Dataset S1 has a porosity of 8.62% and a permeability of 0.2 mD. Dataset S2 has a porosity of 4.5% and a permeability of 0.278 mD. Dataset S3 has a porosity of 11.06% and a permeability of 0.228 mD. Dataset S4 has a porosity of 8.96% and a permeability of 0.092 mD. Figure 3 It can be seen that under different porosity and permeability conditions, as the water saturation increases, the longitudinal wave velocity first decreases and then increases. The low point of the longitudinal wave velocity moves towards the end of decreasing gas saturation as the porosity increases (that is, the low point of the longitudinal wave velocity moves towards the end of increasing water saturation as the porosity increases).

[0091] The multiple datasets may include datasets S5, S6, S7, S8, and S9. Please refer to [link / reference]. Figure 4a Dataset S5 corresponds to a porosity of 5%, a permeability of 0.001 mD, and a maximum relaxation saturation of 0.13. Please refer to [link / reference]. Figure 4b Dataset S6 corresponds to a porosity of 10%, a permeability of 0.017 mD, and a maximum relaxation saturation of 0.29. Please refer to [link / reference]. Figure 4c Dataset S7 corresponds to a porosity of 15%, a permeability of 0.281 mD, and a maximum relaxation saturation of 0.84. Please refer to [link / reference]. Figure 4d Dataset S8 corresponds to a porosity of 20%, a permeability of 4.63 mD, and a maximum relaxation saturation of 0.94. Please refer to [link / reference]. Figure 4e Dataset S9 corresponds to a porosity of 25%, a permeability of 76.14 mD, and a maximum relaxation saturation of 0.96. It should be noted that... Figures 4a-4e In the diagram, the box represents the point corresponding to the maximum relaxation saturation. k represents the permeability. Indicates porosity.

[0092] Please see Figure 5 By synthesizing data on the variation of P-wave velocity with water saturation under different porosity and permeability conditions, and verifying this data with low-frequency measurement data, a systematic description of the variation law of P-wave velocity with water saturation in the seismic band can be achieved. Furthermore, the minimum point of P-wave velocity exhibits a clear variation law with changes in physical properties (such as porosity and permeability). It should be noted that... Figure 5 In the diagram, circular dots represent points corresponding to the maximum relaxation saturation. 2%, 6%, ..., 34%, etc., represent porosity. Diamonds represent points obtained after testing the rock sample. The porosity of the rock sample is 12.6%.

[0093] Please see Figure 6 It illustrates the relationship between porosity and water saturation. Figure 6 In the graph, the horizontal axis represents porosity, with different porosities corresponding to different permeabilities. The vertical axis represents water saturation. The dashed line represents the water saturation corresponding to the lowest velocity point under different porosity and permeability conditions, i.e., the maximum relaxation saturation.

[0094] Please see Figure 7 It illustrates the relationship between P-wave velocity, maximum relaxation saturation, and porosity as reflected in the maximum relaxation saturation model. Solid dots represent the maximum relaxation saturation and its corresponding P-wave velocity, with each dot corresponding to a different porosity and permeability condition (porosity and permeability). The color of the dots changing from dark to light represents a decrease in porosity.

[0095] Please see Figure 8To verify the reliability of the laws reflected by the maximum relaxation saturation model, the embodiments in this specification also extract the P-wave velocity inversion profile near the coring well. A water well is located at the lower part of the structure. Oil and gas co-exist in the middle and lower parts of the structure. A pure gas reservoir is located at the top of the structure. The velocity variations on both flanks of the structure are symmetrical. According to the general law of natural gas enrichment, the higher the structure, the higher the gas saturation. Although the exact gas saturation at the top is unknown, the relationship between gas saturation and P-wave velocity can be semi-quantitatively analyzed by examining the characteristics of velocity variations along the formation and their relative relationship with the top of the structure. It can be seen that as water saturation increases, the P-wave velocity decreases significantly; after reaching a certain water saturation level, the P-wave velocity reaches its lowest point; then, with further increases in water saturation, the P-wave velocity begins to increase again. This is consistent with the relationship between seismic data and reservoir physical properties and fluidity revealed by the maximum relaxation saturation model.

[0096] It should be noted that, compared with existing rock physics models, such as those based on the Gassmann equation and Biot theory, the phenomenon described by existing rock physics models—that the P-wave velocity decreases with increasing gas saturation—does not entirely hold true in actual exploration. Under high porosity and permeability conditions (e.g., porosity of 30% or higher), the fluid is basically uniformly distributed, and the Gassmann equation can describe the relationship between velocity and gas saturation within the seismic band quite well. However, under medium- and low-porosity and permeability conditions, existing rock physics models exhibit significant limitations in application. Therefore, existing rock physics models cannot effectively guide seismic exploration, especially for medium- and low-porosity and permeability natural gas reservoirs. Directly using existing rock physics models to interpret seismic band exploration problems carries considerable risk.

[0097] The methods described in this specification can determine the fluid-solid composite medium model of rocks, wherein the fluid-solid composite medium model is a heterogeneous model; based on the fluid-solid composite medium model, the physical properties of rocks during seismic wave propagation can be determined; based on the physical properties, the propagation velocity of seismic waves in rocks can be determined; and based on the propagation velocity and physical properties, a maximum relaxation saturation model of rocks can be established. The maximum relaxation saturation model in this specification is based on seismic waves. The wavelength of seismic waves is much larger than the length of pores in a heterogeneous porous medium. Seismic waves are insensitive to heterogeneity and disorder at various complex microscales; what is observed in seismic waves is the average elastic effect of a porous medium within the wavelength of the seismic wave. Therefore, the maximum relaxation saturation model can macroscopically reflect the indescribable heterogeneity and disorder exhibited by reservoir rocks at various scales, avoiding various idealized assumptions in existing theoretical models. The maximum relaxation saturation model can accurately describe the relationship between seismic data and reservoir physical properties and reservoir fluidity. The maximum relaxation saturation model can improve the accuracy of reservoir fluidity prediction and provide effective guidance for seismic exploration.

[0098] The method described in this specification can determine the Young's modulus, Poisson's ratio, and density of complex porous media based on a fluid-solid composite medium model. Therefore, compared to traditional rock physics models, the difference in the gas-water P-wave and S-wave velocities calculated using the new model is increased from 4% to over 15%. When the difference reaches over 10%, gas content can be predicted entirely using seismic data. Therefore, the new model provides an important foundation for predicting gas saturation.

[0099] The method described in the embodiments of this specification establishes a maximum relaxation saturation model. This maximum relaxation saturation rock physics theoretical model is the first to systematically reveal the variation law of P-wave velocity in seismic bands with physical properties (porosity and permeability conditions) and gas content. It reveals new laws and explains the underlying mechanism. After velocity dispersion correction using the maximum relaxation saturation model, the sensitivity of seismic elastic parameters to lithology and gas content is increased by 8 times in carbonate gas layer identification.

[0100] Please see Figure 9 This specification provides an apparatus for establishing a rock physics model with maximum relaxation saturation, comprising the following units.

[0101] The first determining unit 21 is used to determine the fluid-solid composite medium model of the rock, wherein the fluid-solid composite medium model is a heterogeneous model;

[0102] The second determining unit 22 is used to determine the physical property parameters of the rock during the propagation of seismic waves based on the fluid-solid composite medium model.

[0103] The third determining unit 23 is used to determine the propagation velocity of seismic waves in rocks based on physical property parameters;

[0104] Establishment unit 24 is used to establish a maximum relaxation saturation model of the rock based on the propagation speed and physical property parameters. The maximum relaxation saturation model is used to predict the fluid saturation of the target reservoir.

[0105] This specification also provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the above-described method for establishing a rock physics model with maximum relaxation saturation.

[0106] This specification also provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the above-described method for establishing a rock physics model with maximum relaxation saturation.

[0107] This specification also provides a computer program product, which includes a computer program that, when executed by a processor, implements the above-described method for establishing a rock physics model with maximum relaxation saturation.

[0108] Those skilled in the art will understand that this specification can be provided as a method, system, or computer program product. Therefore, this specification may take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware. Furthermore, this specification may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0109] This specification is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments thereof. It should be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. The computer may be a personal computer, laptop computer, cellular phone, camera phone, smartphone, personal digital assistant, media player, navigation device, email device, game console, tablet computer, wearable device, or any combination of these devices.

[0110] The functional units in the embodiments of this specification can be integrated into one processing unit, or each functional unit can exist physically separately, or two or more functional units can be integrated into one processing unit.

[0111] Those skilled in the art will understand that the descriptions of the various embodiments in this specification have different focuses, and parts not described in detail in a certain embodiment can be referred to in the relevant descriptions of other embodiments. Furthermore, it is understood that those skilled in the art, after reading this specification, can conceive of any combination of some or all of the embodiments listed in this specification without creative effort, and such combinations are also within the scope of disclosure and protection of this specification.

[0112] Although this specification has been described through embodiments, those skilled in the art will understand that the above embodiments are merely illustrative of the core ideas of this specification. Those skilled in the art will appreciate that many variations and modifications are possible with this specification. It is intended that the appended claims encompass these variations and modifications without departing from the spirit of this specification.

Claims

1. A method for establishing a rock physics model with maximum relaxation saturation, characterized in that, include: A fluid-solid composite medium model for rock is determined, wherein the fluid-solid composite medium model is a heterogeneous model; the fluid-solid composite medium model includes an inner solid spherical region and an outer hollow spherical region, wherein the inner solid spherical region is used to represent the medium formed by the coupling of solid particles and gas fluid, and the outer hollow spherical region is used to represent the medium formed by the coupling of solid particles and liquid fluid; Based on the fluid-solid composite medium model, the physical properties of the rock during seismic wave propagation are determined; these physical properties include porosity, Poisson's ratio, Young's modulus, and density. The steps for determining physical property parameters include: determining the Poisson's ratio formula, Young's modulus formula, and density formula corresponding to the fluid-solid composite medium model; calculating multiple Poisson's ratios of the rock using the Poisson's ratio formula based on selected multiple porosities and multiple fluid saturations; calculating multiple Young's moduli of the rock using the Young's modulus formula based on the multiple Poisson's ratios; and calculating multiple densities of the rock using the density formula based on the multiple porosities. The process for determining propagation velocity includes: calculating multiple propagation velocities using the seismic wave velocity formula based on the multiple Poisson's ratios, the multiple Young's moduli, and the multiple densities, wherein the propagation velocities correspond to the porosity and the fluid saturation. Determine the propagation velocity of seismic waves in rocks based on physical property parameters; A maximum relaxation saturation model for rocks is established based on propagation velocity and physical property parameters. This maximum relaxation saturation model is used to predict the fluid saturation of a target reservoir. The steps of establishing the maximum relaxation saturation model include: constructing a dataset corresponding to porosity and including multiple pairs of fluid saturation and propagation velocity; determining the maximum relaxation saturation corresponding to porosity based on the fluid saturation and propagation velocity in the dataset; and establishing the maximum relaxation saturation model based on the porosity and its corresponding maximum relaxation saturation. The maximum relaxation saturation model includes... Among them, Sw MR Sw represents the maximum relaxation saturation, Sw0 represents the initial water saturation, and Sw H Indicates the maximum water saturation. Indicates porosity. denoted by , where represents the critical porosity and k represents the permeability.

2. The method according to claim 1, characterized in that, The Poisson's ratio formula includes The Young's modulus formula includes E n =2μ n (1+σ n ); The density formula includes Where n is chosen from 1 and 2; when n = 1, it represents the inner solid spherical region, and when n = 2, it represents the outer hollow spherical region; σ n σ1 represents the Poisson's ratio of the inner solid spherical region, and σ2 represents the Poisson's ratio of the outer hollow spherical region; E n E1 represents the Young's modulus of the inner solid spherical region, and E2 represents the Young's modulus of the outer hollow spherical region; f n The fluids are represented as follows: f1 represents the gaseous fluid within the solid inner sphere region, and f2 represents the liquid fluid within the hollow outer sphere region; μ n μ1 represents the shear modulus of the inner solid spherical region, and μ2 represents the shear modulus of the outer hollow spherical region. This represents the bulk modulus of a porous medium containing fluid. This represents the bulk modulus of the internal solid spherical region. This represents the bulk modulus of the outer hollow spherical region; K represents the bulk modulus of the dry rock skeleton. s This represents the bulk modulus of solid particles in a rock. ρ represents the porosity of a rock. s This represents the density of solid particles in a rock. This indicates the density of the fluid within the solid sphere's interior. S1 represents the density of the fluid within the outer hollow sphere region, S2 represents the saturation level of the inner sphere region, and ρ represents the saturation level of the outer hollow sphere region. * This represents the equivalent density of the rock.

3. The method according to claim 1, characterized in that, The steps involved in calculating the propagation velocity of seismic waves include: Based on the multiple Poisson's ratios, multiple Young's moduli, and multiple densities, multiple longitudinal wave velocities are calculated using a longitudinal wave velocity formula, and the longitudinal wave velocities correspond to the porosity and the fluid saturation. The formula for longitudinal wave velocity includes Among them, V p σ represents the longitudinal wave velocity, where n is chosen from 1 and 2; when n = 1, it represents the inner solid spherical region, and when n = 2, it represents the outer hollow spherical region; n σ1 represents the Poisson's ratio of the inner solid spherical region, and σ2 represents the Poisson's ratio of the outer hollow spherical region; E n ρ represents Young's modulus, where E1 represents the Young's modulus of the inner solid spherical region and E2 represents the Young's modulus of the outer hollow spherical region; * This represents the equivalent density of the rock.

4. The method according to claim 1, characterized in that, The method further includes: Based on the maximum relaxation saturation model, determine the maximum relaxation saturation corresponding to the porosity of the target reservoir; Based on the maximum relaxation saturation, a first linear relationship and a second linear relationship for the target reservoir are determined. The first linear relationship and the second linear relationship are used to represent the linear relationship between P-wave velocity and water saturation. Obtain the P-wave velocity volume of seismic waves in the target reservoir; Based on the first and second linear relationships, the water saturation volume corresponding to the longitudinal wave velocity volume is determined.

5. A device for establishing a rock physics model with maximum relaxation saturation, characterized in that, include: The first determining unit is used to determine the fluid-solid composite medium model of the rock, wherein the fluid-solid composite medium model is a heterogeneous model; the fluid-solid composite medium model includes an inner solid spherical region and an outer hollow spherical region, wherein the inner solid spherical region is used to represent the medium formed by the coupling of solid particles and gas fluid, and the outer hollow spherical region is used to represent the medium formed by the coupling of solid particles and liquid fluid; The second determining unit is used to determine the physical property parameters of the rock during the propagation of seismic waves based on the fluid-solid composite medium model; the physical property parameters include porosity, Poisson's ratio, Young's modulus, and density. The steps for determining physical property parameters include: determining the Poisson's ratio formula, Young's modulus formula, and density formula corresponding to the fluid-solid composite medium model; calculating multiple Poisson's ratios of the rock using the Poisson's ratio formula based on selected multiple porosities and multiple fluid saturations; calculating multiple Young's moduli of the rock using the Young's modulus formula based on the multiple Poisson's ratios; and calculating multiple densities of the rock using the density formula based on the multiple porosities. The process for determining propagation velocity includes: calculating multiple propagation velocities using the seismic wave velocity formula based on the multiple Poisson's ratios, the multiple Young's moduli, and the multiple densities, wherein the propagation velocities correspond to the porosity and the fluid saturation. The third determining unit is used to determine the propagation velocity of seismic waves in rocks based on physical property parameters; A unit is established to build a maximum relaxation saturation model for rocks based on propagation velocity and physical property parameters. This maximum relaxation saturation model is used to predict the fluid saturation of a target reservoir. The steps of building the maximum relaxation saturation model include: constructing a dataset corresponding to porosity and including multiple pairs of fluid saturation and propagation velocity; determining the maximum relaxation saturation corresponding to the porosity based on the fluid saturation and propagation velocity in the dataset; and building the maximum relaxation saturation model based on the porosity and its corresponding maximum relaxation saturation. The maximum relaxation saturation model includes... Among them, Sw MR Sw represents the maximum relaxation saturation, Sw0 represents the initial water saturation, and Sw H Indicates the maximum water saturation. Indicates porosity. denoted by , where represents the critical porosity and k represents the permeability.

6. A computer device, characterized in that, include: processor; Memory used to store processor-executable instructions; The processor executes the instructions to implement the method as described in any one of claims 1-4.

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