Method, device and equipment for establishing maximum relaxation saturation rock physical model

Abstract

The invention relates to the technical field of oil-gas exploration, in particular to a maximum relaxation saturation rock physical model establishing method, device and equipment. The maximum relaxation saturation rock physical model establishing method comprises the steps that a fluid-solid composite medium model of rock is determined, and the fluid-solid composite medium model is a heterogeneous model; according to the fluid-solid composite medium model, physical property parameters of rocks in the seismic wave propagation process are determined; according to the physical property parameters, the propagation speed of seismic waves in the rock is determined; according to the propagation velocity and the physical property parameters, a maximum relaxation saturation model of the rock is established, and the maximum relaxation saturation model is used for predicting the fluid saturation of the target reservoir. According to the embodiment of the invention, the maximum relaxation saturation model can accurately describe the relationship between the seismic data and the reservoir physical property and the reservoir fluid-containing property. Through the maximum relaxation saturation model, the accuracy degree of reservoir fluid-containing property prediction can be improved.

Description

Technical Field

[0001] The present invention relates to the field of oil and gas exploration technology, and in particular to a method, device and equipment for establishing a maximum relaxation saturation rock physics model. Background Art

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

[0003] However, underground rocks, especially sedimentary rocks, are very complex. They show indescribable heterogeneity and disorder at all scales. This is contrary to the idealized assumptions of many theoretical models. Therefore, the existing rock physics theoretical models cannot accurately predict the fluid content of the reservoir, which is not conducive to guiding seismic exploration. Summary of the invention

[0004] The embodiments of this specification provide a method, apparatus and computer equipment for establishing a maximum relaxation saturation rock physics model to improve the accuracy of reservoir fluid content prediction.

[0005] The embodiment of this specification provides a method for establishing a maximum relaxation saturation rock physics model, comprising:

[0006] Determining a fluid-solid composite medium model of rock, wherein the fluid-solid composite medium model is a heterogeneous model;

[0007] According to the fluid-solid composite medium model, the physical parameters of rocks during the propagation of seismic waves are determined;

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

[0009] According to the propagation velocity and physical property parameters, a maximum relaxation saturation model of rock is established, and the maximum relaxation saturation model is used to predict the fluid saturation of the target reservoir.

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

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

[0012] The second determination unit is used to determine the physical property parameters of the rock during the propagation of the seismic wave according to the fluid-solid composite medium model;

[0013] A third determination unit is used to determine the propagation speed of seismic waves in the rock according to the physical property parameters;

[0014] The establishment unit is used to establish a maximum relaxation saturation model of rock according to the propagation velocity and physical property parameters, and the maximum relaxation saturation model is used to represent the fluid saturation of the predicted target reservoir.

[0015] The embodiments of the present specification also provide a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the above-mentioned method for establishing a maximum relaxation saturation rock physics model when executing the computer program.

[0016] The method in the embodiment of this specification can determine the fluid-solid composite medium model of the rock, and the fluid-solid composite medium model is a heterogeneous model; the physical parameters of the rock during the propagation of seismic waves can be determined according to the fluid-solid composite medium model; the propagation speed of seismic waves in the rock can be determined according to the physical parameters; the maximum relaxation saturation model of the rock can be established according to the propagation speed and the physical parameters. The maximum relaxation saturation model of the embodiment of this specification is established based on seismic waves. The wavelength of the seismic wave is much larger than the length of the pores in the heterogeneous porous medium. Seismic waves are insensitive to the heterogeneity and disorder at various complex microscopic scales. Seismic waves observe the average elastic effect of the porous medium within the wavelength of the seismic wave. Therefore, the maximum relaxation saturation model can reflect the indescribable heterogeneity and disorder of the reservoir rock at all scales on a macroscopic level, avoiding various idealized assumptions of existing theoretical models. The maximum relaxation saturation model can accurately describe the relationship between seismic data and reservoir physical properties and reservoir fluid content. The maximum relaxation saturation model can improve the accuracy of reservoir fluid content prediction and provide effective guidance for seismic exploration. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of this specification or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. The drawings described below are only some embodiments recorded in this specification. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0018] Figure 1 A schematic diagram of a process for establishing a maximum relaxation saturation rock physics model in an embodiment of this specification;

[0019] Figure 2Schematic diagram of a fluid-solid composite medium model in an embodiment of this specification;

[0020] Figure 3 This is a graph showing the relationship between the P-wave velocity and water saturation of a tight sandstone gas reservoir in the embodiments of this specification;

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

[0022] Figure 5 This is a graph showing the relationship between the longitudinal wave velocity and the 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 the P-wave velocity inversion profile of a clastic oil and gas reservoir in the embodiments of this specification;

[0026] Fig. 9 This is a schematic diagram of the structure of the device for establishing the maximum relaxation saturation rock physics model in the embodiments of this specification. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of this specification will be clearly and completely described below in conjunction with the drawings in the embodiments of this specification. Obviously, the described embodiments are only part of the embodiments of this specification, rather than all of the embodiments. The specific embodiments described herein are only used to explain the present disclosure, rather than to limit the present disclosure. Based on the described embodiments of the present disclosure, all other embodiments obtained by those of ordinary skill in the art are within the scope of protection of the present 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] In addition, in the prior art, most theoretical models are based on the change of the propagation velocity of seismic waves with frequency under water-saturated conditions, and rarely involve the change of the propagation velocity of seismic waves with gas saturation and / or water saturation. The saturated rock in the actual stratum is a combination of a dry rock skeleton (including various mineral components and rock particles) and pore fluid. Different mineral components and particles have 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 fluid, the elastic properties of the dry rock skeleton, and the fluid flow induced by the wave propagation process. The bridge is to establish a physical theoretical model of rock. The maximum relaxation saturation rock physics model establishment method of the embodiment of this specification can establish a maximum relaxation saturation model of rock. The maximum relaxation saturation model can accurately describe the relationship between the physical properties of rock and the seismic elastic properties, and provide a basis and tool for predicting reservoir parameters using seismic elastic parameters. The maximum relaxation saturation rock physics model establishment method can be applied to computer equipment such as servers.

[0029] See also 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 used to represent the rock.

[0031] In some embodiments, the rock may be a multi-scale complex porous medium. The rock may include a saturated rock. The saturated rock may include a dry rock skeleton and fluid in the pores. The dry rock skeleton may include solid particles formed by various mineral components and rock particles and the pores. The fluid may include a gas fluid and a liquid fluid, the gas fluid may include air, natural gas, etc., and the liquid fluid may include water, etc.

[0032] In some embodiments, by constructing a fluid-solid composite medium model, the saturated rock in the actual reservoir can be equivalent to obtain the physical property parameters of the rock. The fluid-solid composite medium model can be a heterogeneous model. Figure 2 . The fluid-solid composite medium model can be a sphere. The fluid-solid composite medium model can specifically be a double-layer plaque sphere. The fluid-solid composite medium model can include an inner solid sphere region and an outer hollow sphere region. The inner solid sphere region is used to represent the medium formed by the coupling of solid particles and gas fluid. The outer hollow sphere region is used to represent the medium formed by the coupling of solid particles and liquid fluid. The center of the inner solid sphere region is the same as the center of the fluid-solid composite medium model. The inner solid sphere region can specifically be understood as a sub-sphere in the fluid-solid composite medium model, and the outer hollow sphere region can specifically be understood as the region outside the sub-sphere in the fluid-solid composite medium model.

[0033] The fluid-solid composite medium model is heterogeneous, and the medium formed by the coupling of solid particles and different fluids is located in different areas. In addition, the medium formed by the coupling of solid particles and gas fluid is located inside, and the medium formed by the coupling of solid particles and liquid fluid is located 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 inner solid sphere region and the radius of the fluid-solid composite medium model can be obtained; the fluid-solid composite medium model can be constructed according to the radius of the inner solid sphere region and the radius of the fluid-solid composite medium model. The radius of the inner solid sphere region and the radius of the fluid-solid composite medium model can be input by a user such as a research and development personnel on the computer device, and of course can also be obtained in other ways, which is not specifically limited in the embodiments of this specification.

[0035] Step 12: Based on the fluid-solid composite medium model, determine the physical parameters of the rock during the propagation of seismic waves.

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

[0037] In the above Poisson's ratio formula, Young's modulus formula and density formula: n is taken from 1 and 2. When n = 1, it represents the inner solid sphere area, and when n = 2, it represents the outer hollow sphere area. σ n represents the Poisson’s ratio, σ1 represents the Poisson’s ratio of the inner solid sphere area, and σ2 represents the Poisson’s ratio of the outer hollow sphere area. n represents Young's modulus, E1 represents the Young's modulus of the inner solid sphere area, and E2 represents the Young's modulus of the outer hollow sphere area. n represents the fluid, f1 represents the gas fluid in the inner solid sphere area, and f2 represents the liquid fluid in the outer hollow sphere area. n represents the shear modulus, μ1 represents the shear modulus of the inner solid sphere region, and μ2 represents the shear modulus of the outer hollow sphere region. represents the bulk modulus of the porous medium containing the fluid, represents the bulk modulus of the inner solid sphere region, represents the bulk modulus of the outer hollow sphere region. represents the bulk modulus of the dry rock skeleton, K s Represents the bulk modulus of solid particles in rocks. Represents the porosity of the rock. s represents the density of solid particles in rock, represents the density of the fluid in the inner solid sphere region, represents the density of the fluid in the outer hollow sphere region, S1 represents the saturation of the inner sphere region (e.g., gas saturation), S2 represents the saturation of the outer hollow sphere region (e.g., water saturation), ρ * Represents the equivalent density of rock.

[0038] In some embodiments, the rock is a non-uniform porous medium. When seismic waves propagate in a non-uniform porous medium, the flow of fluid in the pores is triggered under the seismic wave stress field. The interaction between the dry rock skeleton and the fluid also has a great influence on the velocity of the seismic waves, causing the attenuation and dispersion of the seismic waves. For this reason, when seismic waves propagate in a fluid-solid composite medium model, a partial volume change occurs on the external surface of the fluid-solid composite medium model, and the pressure generated thereby can be calculated based on the volume change. Specifically, in the absence of seismic waves, the fluid does not flow, and the average bulk modulus of the fluid-solid composite medium model can be expressed as K0. In the presence of seismic waves, the seismic wave stress field triggers the flow of fluid in the pores, causing the fluid-solid composite medium model to expand, and the expansion amplitude can be expressed as D0. During the propagation of seismic waves, the bulk modulus of the fluid-solid composite medium model can be expressed by the pressure P0 and the expansion amplitude D0 applied by the seismic wave. 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 the axisymmetric stress and displacement, the functional relationship between the pressure P0 and the expansion amplitude D0 can be expressed by Young's modulus and Poisson's ratio. The following formula is obtained.

[0039]

[0040]

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

[0042] Under the influence of the external 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 the displacement can be expressed as P0e iωt .

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

[0046]

[0047] From this we can get

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

[0049]

[0050] The following describes the specific process of determining the expression of P0 / U0 to obtain K0 based on formula (1) and formula (2).

[0051] Introduce x=P0 / U0,y=P i / U0, we get P0=xU0, P i =yU0.

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

[0053]

[0054]

[0055] Arranging formula (6) and formula (7), we can get:

[0056]

[0057]

[0058] Formula (8) and Formula (9) are algebraic equations about x and y. Calculations can yield According to the bulk modulus shown in formula (5), The bulk modulus expression of the fluid-solid composite medium model can be obtained:

[0059]

[0060] In the above formula (10), S1 represents the saturation of the inner solid sphere area, 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 in the prior art, it is often assumed that the gas in the rock pores is very light and compressible, so the gas-related parameters (such as bulk modulus and density ). Only dry skeleton related parameters (such as bulk modulus) are used. and bulk modulus K s ) to calculate the Poisson's ratio. For example, only the dry skeleton related parameters are used to calculate the Poisson's ratio σ1 of the inner solid sphere area. The embodiment of this specification takes into account the influence of gas, and the Poisson's ratio formula includes the factors generated by the gas related parameters, namely:

[0065]

[0066] In the above formula (13):

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

[0068]

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

[0070] It should also be noted that in the prior art, it is often assumed that the gas in the rock pores is very light and compressible, so the gas-related parameters (such as bulk modulus and density The calculation of equivalent density also has the problem of ignoring gas-related parameters. The embodiments of this specification take the influence of gas into consideration, 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 the multiple fluid saturations. Alternatively, each porosity may correspond to one or more fluid saturations among the multiple fluid saturations. The fluid saturation may include water saturation and / or gas saturation. Based on the selected multiple porosities and multiple fluid saturations, multiple Poisson's ratios of the rock may be calculated using the Poisson's ratio formula; based on the multiple Poisson's ratios, multiple Young's moduli of the rock may be calculated using the Young's modulus formula; based on the multiple porosities, multiple densities of the rock may be calculated using the density formula.

[0072] Specifically, for each of the multiple porosities, the porosity and the multiple fluid saturations corresponding to the porosity 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; the porosity can be substituted into the density formula to obtain an equivalent density. Wherein, the substituting the porosity and the multiple fluid saturations corresponding to the porosity into the Poisson's ratio formula to obtain multiple Poisson's ratios can specifically include: for each of the multiple fluid saturations, the porosity and the fluid saturation can be substituted into the Poisson's ratio formula to obtain a Poisson's ratio. The calculating multiple Young's moduli of the rock according to the multiple Poisson's ratios through the Young's modulus formula can specifically include: for each of the multiple Poisson's ratios, the Poisson's ratio can be substituted into the Young's modulus formula to obtain a Young's modulus. In this way, each porosity can correspond to multiple fluid saturations, multiple Poisson's ratios, multiple Young's moduli, and an equivalent density. There may also be a corresponding relationship between fluid saturation, Poisson's ratio, Young's modulus, and equivalent density. For example, a fluid saturation may correspond to a Poisson's ratio, a Young's modulus, and an equivalent density.

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

[0074] In some scenario examples, the fluid in the saturated rock includes gas fluid and liquid fluid, the gas fluid includes air, natural gas, etc., and the liquid fluid includes water. The sum of the water saturation and the gas saturation may be equal to 1.

[0075] Step 13: Determine the propagation speed of seismic waves in rocks based on the physical parameters.

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

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

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

[0079] For example, a plurality of longitudinal wave velocities may be calculated according to the plurality of Poisson's ratios, the plurality of Young's moduli, and the plurality of densities by a longitudinal wave velocity formula, wherein the longitudinal wave velocity corresponds 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. Among them, each porosity can correspond to multiple fluid saturations, multiple Poisson's ratios, multiple Young's moduli, and an equivalent density. To this end, for each porosity, the multiple Poisson's ratios, multiple Young's moduli, and an equivalent density corresponding to the porosity can be substituted into the seismic wave propagation velocity formula to calculate the multiple propagation velocities corresponding to the porosity. For example, for each porosity, the multiple Poisson's ratios, multiple Young's moduli, and an equivalent density corresponding to the porosity can be substituted into the longitudinal wave velocity formula to calculate the multiple longitudinal wave velocities corresponding to the porosity. Specifically, for example, for each porosity, the Poisson's ratios σ2 of multiple external hollow sphere regions, the Young's modulus E2 of multiple external hollow sphere regions, and an equivalent density ρ * Substituting into the P-wave velocity formula, we can calculate the multiple P-wave velocities V corresponding to the porosity.p .

[0081] Step 14: Establish the maximum relaxation saturation model of rock based on the propagation velocity and physical property parameters.

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

[0083] After step 12-step 13, multiple seismic wave propagation velocities can be obtained for multiple selected porosities and multiple selected fluid saturations. Each porosity can correspond to multiple fluid saturations and multiple propagation velocities. To this end, multiple data sets can be constructed. Each data set can correspond to a porosity and can include multiple pairs of fluid saturations and propagation velocities. Each pair of fluid saturation and propagation velocity can include a fluid saturation and a corresponding propagation velocity. In practical applications, for each selected porosity, multiple fluid saturations and multiple propagation velocities corresponding to the porosity can be obtained as the fluid saturation and propagation velocity in the data set corresponding to the porosity. The multiple fluid saturations and multiple propagation velocities in each data set can have a corresponding relationship, so that multiple pairs of fluid saturations and propagation velocities can be determined.

[0084] For each of the multiple data sets, the maximum relaxation saturation can be determined based on the multiple pairs of fluid saturation and propagation velocity in the data set as the maximum relaxation saturation corresponding to the porosity of the data set. For example, a pair of fluid saturation and propagation velocity with the minimum propagation velocity can be selected from the multiple pairs of fluid saturation and propagation velocity, and the fluid saturation in the pair of fluid saturation and propagation velocity 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 longitudinal wave velocity. In this way, for the selected multiple porosities, corresponding multiple maximum relaxation saturations can be obtained. Each porosity can correspond to a maximum relaxation saturation. Therefore, a maximum relaxation saturation model can be established based on multiple porosities and the maximum relaxation saturations corresponding to the multiple porosities. For example, a relationship curve can be drawn based on multiple porosities and the maximum relaxation saturations corresponding to the multiple porosities; the drawn relationship curve can be fitted to obtain a maximum relaxation saturation model. The maximum relaxation saturation model can accurately describe the relationship between seismic data and reservoir physical properties and reservoir fluid content. For example, the maximum relaxation saturation model can be used to represent the relationship between fluid saturation and propagation velocity, which may include: as the fluid saturation increases, the propagation velocity first decreases and then increases. For example, as the water saturation increases, the longitudinal wave velocity first decreases and then increases. The maximum relaxation saturation model may include:

[0085]

[0086] In the above formula (15), Sw MR represents the maximum relaxation saturation (%), Sw0 represents the initial water saturation (%), Sw H Indicates the maximum water saturation (%), represents the porosity (%), 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 the target reservoir. Specifically, the maximum relaxation saturation corresponding to the porosity of the target reservoir can be determined according to the maximum relaxation saturation model; the first linear relationship and the second linear relationship of the target reservoir can be determined according to the maximum relaxation saturation, and the first linear relationship and the second linear relationship are used to represent the linear relationship between the P-wave velocity and the water saturation; the P-wave velocity body of the seismic wave in the target reservoir can be obtained; and the water saturation body corresponding to the P-wave velocity body can be determined according to 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 the fluid saturation increases, the propagation velocity first decreases and then increases. On both sides of the maximum relaxation saturation, the relationship between the P-wave velocity and the water saturation can be equivalent to a linear relationship. Therefore, the first water saturation interval and the second water saturation interval can be divided based on the maximum relaxation saturation; 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 a reverse linear relationship, that is, the P-wave velocity is negatively correlated with the water saturation. The second linear relationship can be a positive linear relationship, that is, the P-wave velocity is positively correlated with the water saturation.

[0089] The seismic wave data of the target reservoir can be inverted to obtain a P-wave velocity body. The P-wave velocity body includes multiple P-wave velocities. For each P-wave velocity in the P-wave velocity body, the first linear relationship and the second linear relationship can be substituted respectively to obtain two water saturations. The two water saturations are located on both sides 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 water saturation is less than the maximum relaxation saturation. In this way, a water saturation body corresponding to the P-wave velocity body can be obtained. The water saturation body includes multiple water saturations.

[0090] See also Figure 3 The triangular points, large diamond points, small diamond points and circular points correspond to data sets including S1, S2, S3 and S4 respectively. The porosity corresponding to data set S1 is 8.62%, and the corresponding permeability is 0.2mD. The porosity corresponding to data set S2 is 4.5%, and the corresponding permeability is 0.278mD. The porosity corresponding to data set S3 is 11.06%, and the corresponding permeability is 0.228mD. The porosity corresponding to data set S4 is 8.96%, and the corresponding permeability is 0.092mD. According to Figure 3 It can be seen that under different porosity and permeability conditions, as the water saturation increases, the P-wave velocity first decreases and then increases, and the low point of the P-wave velocity moves toward the end where the gas saturation decreases as the porosity increases (that is, the low point of the P-wave velocity moves toward the end where the water saturation increases as the porosity increases).

[0091] The plurality of data sets may include data sets S5, S6, S7, S8, and S9. Figure 4a The corresponding porosity of data set S5 is 5%, the corresponding permeability is 0.001mD, and the corresponding maximum relaxation saturation is 0.13. Figure 4b The corresponding porosity of data set S6 is 10%, the corresponding permeability is 0.017mD, and the corresponding maximum relaxation saturation is 0.29. Figure 4c The corresponding porosity of data set S7 is 15%, the corresponding permeability is 0.281mD, and the corresponding maximum relaxation saturation is 0.84. Figure 4d The corresponding porosity of data set S8 is 20%, the corresponding permeability is 4.63mD, and the corresponding maximum relaxation saturation is 0.94. Figure 4e The porosity of data set S9 is 25%, the permeability is 76.14 mD, and the maximum relaxation saturation is 0.96. It should be noted that Figure 4a-4e In the figure, the box indicates the point corresponding to the maximum relaxation saturation. k represents the permeability, Indicates porosity.

[0092] See also Figure 5 By combining the data of the change of P-wave velocity with water saturation under different porosity and permeability conditions and verifying it with low-frequency measurement data, we can systematically describe the change law of P-wave velocity in the seismic band with water saturation. And with the change of physical properties (such as porosity and permeability), the lowest point of P-wave velocity shows obvious change law. It should be noted that Figure 5 In the graph, the circular points represent the points corresponding to the maximum relaxation saturation. 2%, 6%, ..., 34%, etc. represent the porosity. The diamonds represent the points obtained after testing the rock sample. The porosity of the rock sample is 12.6%.

[0093] See also Figure 6 . It shows the relationship between porosity and water saturation. Figure 6 In the figure, the horizontal axis is porosity, different porosities correspond to different permeabilities, the vertical axis is water saturation, and the dotted line represents the water saturation corresponding to the low velocity point under different porosity and permeability conditions (porosity and permeability), that is, the maximum relaxation saturation.

[0094] See also Figure 7 . It shows the relationship between P-wave velocity, maximum relaxation saturation, and porosity reflected by the maximum relaxation saturation model. The solid dots represent the maximum relaxation saturation and its corresponding P-wave velocity, and each dot corresponds to a different porosity and permeability condition (porosity and permeability). The color of the dots changes from dark to light, which means that the porosity changes from large to small.

[0095] See also Figure 8. In order to verify the reliability of the law reflected by the maximum relaxation saturation model, the embodiment of this specification also extracts the P-wave velocity inversion profile near the coring well. There is a water well in the low part of the structure. Oil and gas are produced simultaneously in the middle and low parts of the structure. There is a pure gas reservoir at the top of the structure. The change in velocity on both wings of the structure is 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 the characteristics of velocity changes along the layer and its relative relationship with the top of the structure. It can be seen that as the water saturation increases, the P-wave velocity decreases significantly; after reaching a certain water saturation, the P-wave velocity reaches the lowest point; then as the water saturation increases, the P-wave velocity begins to increase again. This is consistent with the relationship between seismic data and reservoir physical properties and reservoir fluid properties revealed by the maximum relaxation saturation model.

[0096] It should be noted that compared with existing rock physics theoretical models, such as those based on the Gassmann equation, Biot theory, etc., the phenomenon described by the existing rock physics theoretical models that the longitudinal wave velocity decreases with increasing gas saturation is not completely true in actual exploration. Under high porosity and permeability conditions (such as porosity of 30% or higher), the fluid is basically evenly distributed. At this time, the Gassmann equation can better describe the relationship between velocity and gas saturation in the seismic band. However, under medium and low porosity and permeability conditions, the existing rock physics theoretical models show great application limitations. Therefore, the existing rock physics theoretical models cannot effectively guide seismic exploration, especially seismic exploration of medium and low porosity and permeability natural gas reservoirs. There is a great risk in directly using existing rock physics theoretical models to explain seismic band exploration problems.

[0097] The method in the embodiment of this specification can determine the fluid-solid composite medium model of the rock, and the fluid-solid composite medium model is a heterogeneous model; the physical parameters of the rock during the propagation of seismic waves can be determined according to the fluid-solid composite medium model; the propagation speed of seismic waves in the rock can be determined according to the physical parameters; the maximum relaxation saturation model of the rock can be established according to the propagation speed and the physical parameters. The maximum relaxation saturation model of the embodiment of this specification is established based on seismic waves. The wavelength of the seismic wave is much larger than the length of the pores in the heterogeneous porous medium. Seismic waves are insensitive to various complex microscopic heterogeneities and disorder. What seismic waves observe is the average elastic effect of a porous medium within the wavelength of the seismic wave. Therefore, the maximum relaxation saturation model can reflect the indescribable heterogeneity and disorder of the reservoir rock at all scales on a macroscopic level, avoiding various idealized assumptions of existing theoretical models. The maximum relaxation saturation model can accurately describe the relationship between seismic data and reservoir physical properties and reservoir fluid content. The maximum relaxation saturation model can improve the accuracy of reservoir fluid content prediction and provide effective guidance for seismic exploration.

[0098] The method in the embodiments of this specification can determine the Young's modulus, Poisson's ratio and density of the complex porous medium based on the fluid-solid composite medium model. Therefore, compared with the traditional rock physics theoretical model, the difference in the gas-water longitudinal and transverse wave velocity ratio calculated based on the new model is increased from 4% to more than 15%. When the difference reaches more than 10%, the gas content can be predicted by seismic data. Therefore, the new model provides an important basis for the prediction of gas saturation.

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

[0100] See also Fig. 9 The embodiment of this specification provides a device for establishing a maximum relaxation saturation rock physics model, including the following units.

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

[0102] A second determination unit 22 is used to determine the physical property parameters of the rock during the propagation of the seismic wave according to the fluid-solid composite medium model;

[0103] A third determination unit 23 is used to determine the propagation velocity of seismic waves in the rock according to the physical property parameters;

[0104] The establishing unit 24 is used to establish a maximum relaxation saturation model of rock according to the propagation velocity and the physical property parameters, and the maximum relaxation saturation model is used to predict the fluid saturation of the target reservoir.

[0105] The embodiments of the present specification also provide a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the above-mentioned method for establishing a maximum relaxation saturation rock physics model when executing the computer program.

[0106] The embodiments of the present specification also provide a computer-readable storage medium, wherein the computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the above-mentioned method for establishing a maximum relaxation saturation rock physics model is implemented.

[0107] The embodiments of this specification also provide a computer program product, which includes a computer program. When the computer program is executed by a processor, the above-mentioned maximum relaxation saturation rock physics model establishment method is implemented.

[0108] Those skilled in the art will appreciate that this specification may be provided as a method, system, or computer program product. Therefore, this specification may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, this specification may take the form of a computer program product implemented 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 the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products of the embodiments of this specification. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. The computer can be a personal computer, a laptop computer, a cellular phone, a camera phone, a smart phone, a personal digital assistant, a media player, a navigation device, an email device, a game console, a tablet computer, a wearable device, or a combination of any of these devices.

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

[0111] Those skilled in the art will understand that the description of each embodiment in this specification has its own emphasis. For parts not described in detail in a certain embodiment, reference can be made to the relevant description of other embodiments. In addition, it is understood that after reading this specification, those skilled in the art can think of any combination of some or all of the embodiments listed in this specification without creative work, and these combinations are also within the scope of disclosure and protection of this specification.

[0112] Although the present specification is described by way of examples, it is known to those skilled in the art that the above examples are only used to help understand the core idea of ​​the present specification. It is understood by those skilled in the art that there are many variations and changes in the present specification. It is hoped that the appended claims include these variations and changes without departing from the spirit of the present specification.

Claims

1. A method for establishing a maximum relaxation saturation rock physics model, characterized in that: include: Determining a fluid-solid composite medium model of rock, wherein the fluid-solid composite medium model is a heterogeneous model; According to the fluid-solid composite medium model, the physical parameters of rocks during the propagation of seismic waves are determined; Determine the propagation speed of seismic waves in rocks based on physical parameters; According to the propagation velocity and physical property parameters, a maximum relaxation saturation model of rock is established, and the maximum relaxation saturation model is used to predict the fluid saturation of the target reservoir.

2. The method according to claim 1, characterized in that The fluid-solid composite medium model includes an inner solid sphere region and an outer hollow sphere region, wherein the inner solid sphere region is used to represent a medium formed by coupling of solid particles and gas fluid, and the outer hollow sphere region is used to represent a medium formed by coupling of solid particles and liquid fluid.

3. The method according to claim 2, characterized in that The physical property parameters include porosity, Poisson's ratio, Young's modulus and density; The steps for determining the physical property parameters include: Determine the Poisson's ratio formula, Young's modulus formula and density formula corresponding to the fluid-solid composite medium model; According to the selected multiple porosities and multiple fluid saturations, multiple Poisson's ratios of the rock are calculated by using the Poisson's ratio formula; Calculating multiple Young's moduli of the rock using a Young's modulus formula according to the multiple Poisson's ratios; Calculating multiple densities of the rock using a density formula according to the multiple porosities; The process of determining the propagation velocity includes: A plurality of propagation velocities are calculated according to the plurality of Poisson's ratios, the plurality of Young's moduli, and the plurality of densities by using a seismic wave velocity formula, wherein the propagation velocities correspond to the porosity and the fluid saturation.

4. The method according to claim 3, 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 selected from 1 and 2; when n = 1, it represents the inner solid sphere area, and when n = 2, it represents the outer hollow sphere area; σ n represents Poisson’s ratio, σ1 represents the Poisson’s ratio of the inner solid sphere area, and σ2 represents the Poisson’s ratio of the outer hollow sphere area; E n represents Young's modulus, E1 represents Young's modulus of the inner solid sphere region, and E2 represents Young's modulus of the outer hollow sphere region; f n represents the fluid, f1 represents the gas fluid in the inner solid sphere area, and f2 represents the liquid fluid in the outer hollow sphere area; μ n represents the shear modulus, μ1 represents the shear modulus of the inner solid sphere region, and μ2 represents the shear modulus of the outer hollow sphere region; represents the bulk modulus of the porous medium containing the fluid, represents the bulk modulus of the inner solid sphere region, represents the bulk modulus of the outer hollow sphere region; represents the bulk modulus of the dry rock skeleton, K s Represents the bulk modulus of solid particles in rock; Represents the porosity of rock; ρ s represents the density of solid particles in rock, represents the density of the fluid in the inner solid sphere region, represents the density of the fluid in the outer hollow sphere region, S1 represents the saturation of the inner sphere region, S2 represents the saturation of the outer hollow sphere region, ρ * Represents the equivalent density of rock.

5. The method according to claim 3, characterized in that: The steps in calculating the seismic wave propagation velocity include: Calculating a plurality of longitudinal wave velocities according to the plurality of Poisson's ratios, the plurality of Young's moduli, and the plurality of densities by a longitudinal wave velocity formula, wherein the longitudinal wave velocities correspond to the porosity and the fluid saturation; The longitudinal wave velocity formula includes Among them, V p represents the longitudinal wave velocity, n is taken from 1 and 2; when n = 1, it represents the inner solid sphere area, when n = 2, it represents the outer hollow sphere area; σ n represents Poisson’s ratio, σ1 represents the Poisson’s ratio of the inner solid sphere area, and σ2 represents the Poisson’s ratio of the outer hollow sphere area; E n represents Young's modulus, E1 represents Young's modulus of the inner solid sphere region, and E2 represents Young's modulus of the outer hollow sphere region; ρ * Represents the equivalent density of rock.

6. The method according to claim 1, characterized in that The steps in establishing the maximum relaxation saturation model include: constructing a data set corresponding to porosity and including multiple pairs of fluid saturation and propagation velocity; Based on the fluid saturation and propagation velocity in the data set, the maximum relaxation saturation corresponding to the porosity is determined; According to the porosity and the maximum relaxation saturation corresponding to the porosity, a maximum relaxation saturation model is established.

7. The method according to claim 1 or 6, characterized in that: The maximum relaxation saturation model includes Among them, Sw MR represents the maximum relaxation saturation, Sw0 represents the initial water saturation, Sw H represents the maximum water saturation, represents the porosity, represents the critical porosity and k represents the permeability.

8. The method according to claim 1, characterized in that The method further comprises: According to the maximum relaxation saturation model, the maximum relaxation saturation corresponding to the porosity of the target reservoir is determined; Determining a first linear relationship and a second linear relationship of the target reservoir according to the maximum relaxation saturation, wherein the first linear relationship and the second linear relationship are used to represent a linear relationship between the P-wave velocity and the water saturation; Acquire the longitudinal wave velocity body of seismic waves in the target reservoir; The water saturation body corresponding to the P-wave velocity body is determined according to the first linear relationship and the second linear relationship.

9. A device for establishing a maximum relaxation saturation rock physics model, characterized in that: include: A first determining unit is used to determine a fluid-solid composite medium model of the rock, wherein the fluid-solid composite medium model is a heterogeneous model; The second determination unit is used to determine the physical property parameters of the rock during the propagation of the seismic wave according to the fluid-solid composite medium model; A third determination unit is used to determine the propagation speed of seismic waves in the rock according to the physical property parameters; The establishment unit is used to establish a maximum relaxation saturation model of rock according to the propagation velocity and physical property parameters, and the maximum relaxation saturation model is used to predict the fluid saturation of the target reservoir.

10. A computer device, characterized in that: include: processor; a memory for storing processor-executable instructions; The processor implements the method according to any one of claims 1 to 8 by executing the instructions.

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