Sensitivity elastic parameter, parametric model, method and system for determining water saturation

Abstract

The embodiment of the present application provides a sensitive elastic parameter, a parameter model, a determination method and system of water saturation, and belongs to the field of seismic exploration. The determination method comprises the following steps: scanning a rock sample to obtain a three-dimensional digital core model, which comprises a rock matrix model and a pore model of the three-dimensional digital core; constructing an elastic parameter model of the three-dimensional digital core under a plurality of water saturations according to the rock matrix model and the pore model of the three-dimensional digital core; simulating the elastic parameter model of the three-dimensional digital core under the plurality of water saturations to obtain elastic simulation parameters; and determining an elastic parameter sensitive to water saturation according to the elastic simulation parameters and a sensitivity threshold. The present application solves the problem of low sensitivity of conventional elastic parameters to water saturation, and improves the accuracy of calculating water saturation. In addition, the water saturation of the target wellbore can be effectively predicted by using the water saturation prediction model.

Description

Technical Field

[0001] This invention relates to the field of seismic exploration technology, specifically to a method and system for determining sensitive elastic parameters, parameter models, and water saturation. Background Technology

[0002] Tight reservoirs are unconventional reservoirs with low porosity and low permeability. Studying the relationship between their elastic parameters and fluid saturation is of great significance for oil and gas reservoir exploration and development.

[0003] In existing technologies, the relationship between the elastic properties of rocks and water saturation is mainly studied through rock physics experiments. However, there have been difficulties in using rock physics experiments to study the relationship between the elastic parameters and water saturation of tight reservoirs containing a certain amount of non-connected isolated pores. These difficulties are mainly manifested in two aspects: First, it is difficult to determine the original fluid type in the non-connected isolated pores, making it difficult to calculate the water saturation; second, due to the low porosity and low permeability characteristics of tight reservoirs, there are problems of insufficient saturation and high bound water saturation during the saturation and dehydration processes, resulting in certain errors in the measured relationship between water saturation and elastic parameters.

[0004] Three-dimensional digital core elastic parameter numerical simulation can quantitatively study the influence of rock matrix, pore structure, and pore fluid on rock elastic parameters. Existing numerical simulation methods mainly use the finite element method to solve the stress-strain field under the minimum potential energy condition to deduce conventional elastic parameters.

[0005] Currently, there are two main problems with the methods for calculating elastic parameters in three-dimensional digital cores: First, the stress-strain method is difficult to calculate the elastic modulus of dry (vacuum-filled pores, i.e., zero P-wave and S-wave velocities) rocks with stable and high-precision calculations, which affects the accuracy of water saturation calculations. Second, the stress-strain method cannot simulate the propagation of elastic wave fields in three-dimensional digital cores. Summary of the Invention

[0006] The purpose of this invention is to provide a method and system for determining sensitive elastic parameters, parameter models, and water saturation. This method utilizes sensitivity to determine elastic parameters sensitive to water saturation, while existing technologies directly use conventional elastic parameters, which have very low sensitivity to water saturation. Therefore, this method solves the problem of low sensitivity of conventional elastic parameters for water saturation in tight reservoirs in existing technologies, thereby improving the accuracy of water saturation calculation. Furthermore, by using the elastic parameters sensitive to water saturation to further construct an elastic parameter model, it can be effectively applied to the prediction of water saturation in target wellbores.

[0007] To achieve the above objectives, embodiments of the present invention provide a method for determining elastic parameters sensitive to water saturation. The method includes: scanning a rock sample to obtain a three-dimensional digital core model, wherein the three-dimensional digital core model includes a rock matrix model and a pore model of the three-dimensional digital core; constructing elastic parameter models of the three-dimensional digital core at multiple water saturation levels based on the rock matrix model and pore model of the three-dimensional digital core; simulating the elastic parameter models of the three-dimensional digital core at multiple water saturation levels to obtain elastic simulation parameters; and determining the elastic parameters sensitive to water saturation based on the elastic simulation parameters and a sensitivity threshold.

[0008] Optionally, the elastic parameter model of the three-dimensional digital core under multiple water saturation levels includes the elastic parameter model of the pores of the three-dimensional digital core. Constructing the elastic parameter model of the pores under multiple water saturation levels of the three-dimensional digital core includes: based on the pore model of the three-dimensional digital core, obtaining multiple water saturations corresponding to the fluid types in the pores according to multiple preset water saturations, and obtaining the elastic parameters of the multiple water saturations corresponding to the fluid types in the pores according to the fluid types in the pores, so as to construct the elastic parameter model of the pores under multiple water saturation levels of the three-dimensional digital core.

[0009] Optionally, the step of obtaining multiple water saturations corresponding to the fluid type in the pores based on the pore model of the three-dimensional digital core, according to multiple preset water saturations, includes: determining the minimum value n of the number of water layers k to be filled, based on the preset water saturation S and the following formula. in, Let N represent the porosity of the i-th layer, and N represent the number of pore layers. This represents the porosity of water, and k represents the number of water layers that need to be filled; based on the minimum value n and the porosity of water... Obtain multiple water saturation levels corresponding to the fluid type in the pores.

[0010] Optionally, the elastic simulation parameters include P-wave velocity, S-wave velocity, and elastic parameters, wherein the elastic parameters include the P-wave / S-wave velocity ratio, bulk modulus, Poisson's ratio, Lamé constant, and shear modulus; determining the elastic parameters sensitive to water saturation based on the elastic simulation parameters and a sensitivity threshold includes: determining a sensitivity function of the elastic parameters and a sensitivity function of a new elastic parameter based on the elastic simulation parameters; determining the sensitivity of the elastic parameters and / or the new elastic parameters within a specific water saturation range based on the sensitivity function of the elastic parameters and / or the sensitivity function of the new elastic parameters; and determining the elastic parameters and / or the new elastic parameters whose sensitivity is greater than the sensitivity threshold as elastic parameters sensitive to water saturation.

[0011] Optionally, determining the sensitivity function of the new elastic parameter based on the elastic simulation parameters includes: determining the new elastic parameter according to the following formula, wherein the new elastic parameter includes the pore space modulus M and the pore fluid bulk modulus K. f M = (K sat -K dry ) / β 2 , And based on the new elastic parameter, determine the sensitivity function of the new elastic parameter, where K s K represents the bulk modulus of the rock matrix. dry K represents the bulk modulus of dry rock. s With K dry Determined based on the longitudinal wave velocity, transverse wave velocity, and elastic parameters; K sat K represents the bulk modulus of saturated fluid rock. sat Determined based on the longitudinal wave velocity, transverse wave velocity, and elastic parameters; This indicates the porosity of the rock sample.

[0012] Optionally, determining the sensitivity function of the elastic parameter or the sensitivity function of the new elastic parameter includes: based on y(S) w And the following formula, determine y(S) w The sensitivity function A) w : Among them, S w Indicates water saturation, y(S) w )) represents the elastic parameter or a new elastic parameter at different water saturation levels.

[0013] On the other hand, the present invention also provides a method for predicting a saturation model for water saturation, the method comprising: determining an elastic parameter K sensitive to water saturation according to the method for determining the elastic parameter sensitive to water saturation. f Based on the elastic parameter K, which is sensitive to water saturation. f And the following formula is used to construct the water saturation prediction model: S w =a*K f b , among which, S w K represents the degree of water saturation. f denoted by , where a and b represent the bulk modulus of the saturated fluid, and a and b represent the undetermined coefficients of the water saturation prediction model.

[0014] Furthermore, the present invention also provides a method for determining the water saturation of a target wellbore, the method comprising: determining the bulk modulus K of the rock matrix in the target wellbore based on multiple parameter curves of the target wellbore. sBulk modulus K of dry rock dry and the bulk modulus K of saturated fluid rock sat Based on the bulk modulus K of the rock matrix in the target wellbore. s Bulk modulus K of dry rock dry , Saturated fluid rock bulk modulus K sat And the method for determining the elastic parameter sensitive to water saturation, and determining the pore fluid bulk modulus K. f ; and based on the water saturation prediction model and the pore fluid bulk modulus K f Determine the water saturation of the target wellbore.

[0015] Optionally, the plurality of parameter curves include a longitudinal wave velocity curve, a transverse wave velocity curve, a density curve, and a saturation curve.

[0016] Accordingly, the present invention also provides a system for determining elastic parameters sensitive to water saturation. The system includes: a scanning device for scanning a rock sample to obtain a three-dimensional digital core model, wherein the three-dimensional digital core model includes a rock matrix model and a pore model of the three-dimensional digital core; a construction device for constructing elastic parameter models of the three-dimensional digital core at multiple water saturation levels based on the rock matrix model and pore model of the three-dimensional digital core; an acquisition device for simulating the elastic parameter models of the three-dimensional digital core at multiple water saturation levels to obtain elastic simulation parameters; and a determination device for determining the elastic parameters sensitive to water saturation based on the elastic simulation parameters and a sensitivity threshold.

[0017] Accordingly, the present invention also provides a water saturation prediction model system, the system comprising: a construction device for determining the elastic parameter K, which is sensitive to water saturation, as determined by the determination method. f Based on the elastic parameter K, which is sensitive to water saturation. f And the following formula is used to construct the water saturation prediction model: S w =a*K f b , among which, S w K represents the degree of water saturation. f denoted by , where a and b represent the bulk modulus of the saturated fluid, and a and b represent the undetermined coefficients of the water saturation prediction model.

[0018] Accordingly, the present invention also provides a system for determining the water saturation of a target wellbore, the system comprising: a first determining device, configured to determine the bulk modulus K of the rock matrix in the target wellbore based on multiple parameter curves of the target wellbore. s Bulk modulus K of dry rock dry and the bulk modulus K of saturated fluid rocksat The second determining device is used to determine the bulk modulus K of the rock matrix in the target wellbore. s Bulk modulus K of dry rock dry , Saturated fluid rock bulk modulus K sat And the method for determining the elastic parameter sensitive to water saturation, and determining the pore fluid bulk modulus K. f ; and a third determining device, used to determine the water saturation prediction model and the pore fluid bulk modulus K. f Determine the water saturation of the target wellbore.

[0019] Using the above technical solution, rock samples are scanned to obtain a three-dimensional digital core model, which includes a rock matrix model and a pore model. Based on the rock matrix model and pore model, elastic parameter models at multiple water saturation levels are constructed. These elastic parameter models at multiple water saturation levels are simulated to obtain elastic simulation parameters, which include both conventional and new elastic parameters. The elastic parameters with a sensitivity greater than a sensitivity threshold and / or the new elastic parameters are then identified as water saturation-sensitive elastic parameters. Once the water saturation-sensitive elastic parameters are determined, a water saturation prediction model is constructed using these parameters, and this model is used to predict the water saturation in the target wellbore or during earthquakes.

[0020] Other features and advantages of the embodiments of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0021] The accompanying drawings are provided to further illustrate embodiments of the present invention and form part of the specification. They are used together with the following detailed description to explain the embodiments of the present invention, but do not constitute a limitation thereof. In the drawings:

[0022] Figure 1 This is a flowchart of a method for determining elastic parameters sensitive to water saturation provided in an embodiment of the present invention;

[0023] Figure 2 This is a flowchart of constructing an elastic parameter model provided in an embodiment of the present invention;

[0024] Figure 3a This is a rock matrix model of a three-dimensional digital core provided in the embodiments of the present invention;

[0025] Figure 3b This is a rock pore model of a three-dimensional digital core provided in the embodiments of the present invention;

[0026] Figure 4 This is the saturated gas velocity model of a three-dimensional digital core provided in this embodiment of the invention;

[0027] Figure 5a This is a longitudinal wave field diagram of dry rock from a three-dimensional digital core provided in an embodiment of the present invention;

[0028] Figure 5b This is a shear wave field diagram of dry rock from a three-dimensional digital core provided in this embodiment of the invention;

[0029] Figure 6 This is a flowchart of the determined sensitive elastic parameters provided in the embodiments of the present invention;

[0030] Figure 7a It is a sensitivity parameter of the elastic parameters of water and air provided in the embodiments of the present invention;

[0031] Figure 7b It is a sensitivity parameter of the elasticity parameters of water and oil provided in the embodiments of the present invention;

[0032] Figure 8a It is a sensitivity parameter of the elastic simulation parameters of water and gas provided in the embodiments of the present invention;

[0033] Figure 8b It is a sensitivity parameter of the elastic simulation parameters of water and oil provided in the embodiments of the present invention;

[0034] Figure 9a This is the water and air saturation prediction model provided in the embodiments of the present invention;

[0035] Figure 9b This is the water saturation prediction model for water and oil provided in the embodiments of the present invention;

[0036] Figure 10 This is a system for determining elastic parameters that are sensitive to water saturation, provided in an embodiment of the present invention. Detailed Implementation

[0037] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the scope of the present invention.

[0038] Figure 1 This is a flowchart of a method for determining an elastic parameter sensitive to water saturation, provided in an embodiment of the present invention. The determination method includes the following steps S101-S104.

[0039] S 101. Scan the rock sample to obtain a three-dimensional digital core model.

[0040] The three-dimensional digital core model includes a rock matrix model and a pore model of the three-dimensional digital core.

[0041] Specifically, the rock samples are cores taken from tight reservoir sections, and a three-dimensional digital core model is obtained by scanning the rock samples. Existing technologies such as X-ray CT scanning can be used to perform image filtering, optimal threshold segmentation, and porosity quantification analysis on the CT scan images to obtain the three-dimensional digital core model. The three-dimensional digital core model includes a rock matrix model and a pore model. To distinguish the rock matrix from the pores in the three-dimensional digital core model, the pores can be assigned a number, such as 0. Depending on the mineral type of the rock matrix, numbers such as 2, 3, 4, ..., N can be assigned (the rock matrix is ​​composed of N mineral components, commonly including quartz, calcite, argillaceous material, clay, etc.). Assigning different numbers to the pores and rock matrix is ​​only for easy identification of their specific locations on the three-dimensional digital core model and has no actual physical meaning.

[0042] refer to Figure 3a This is a model of the rock matrix from a constructed 3D digital core. The rock matrix has two mineral components: black quartz (86.691%), white clay (2.434%), and the remainder is porosity (10.875%). The model size is 300*300*300 pixels, with a pixel size of 3μm. (Reference) Figure 3b The pore model of the constructed 3D digital core has a porosity of 10.875%. Both models are 300*300*300 pixels in size, the same pixel size as the CT image scanning resolution (3μm). In the 3D digital core model, pores can be represented by the number 0, quartz by 2, and clay by 3. Quantitative analysis of the 3D porosity of the dense sandstone rock sample revealed that the 3D digital core model contains 28,054 pores; the minimum equivalent diameter is 3.7221μm, the maximum equivalent diameter is 508.373μm, and the average equivalent diameter is 5.76969μm.

[0043] S102. Based on the rock matrix model and pore model of the three-dimensional digital core, construct elastic parameter models of the three-dimensional digital core under multiple water saturation conditions.

[0044] Based on the rock matrix model of the 3D digital core obtained in the above steps, refer to the *Handbook of Rock Physics* according to the mineral composition of the rock matrix and assign corresponding elastic parameters to each mineral composition. For example, if the mineral types of the rock matrix include quartz, calcite, clay, and argillaceous material (refer to the corresponding elastic parameters according to the actual mineral types), consult the corresponding elastic parameters for quartz, calcite, clay, and argillaceous material respectively to establish an elastic parameter model of the rock matrix of the 3D digital core (i.e., the mapping relationship between the rock matrix and the values ​​of the elastic parameters). The method for establishing the elastic parameter model of the rock matrix of the 3D digital core is the same regardless of whether its composition is quartz, calcite, or a mixture thereof; specifically, refer to the values ​​of the elastic parameters corresponding to the mineral compositions of the rock matrix according to the actual situation.

[0045] Based on the pore model of the three-dimensional digital core obtained in the above steps, different fluid types are assigned to the pores (different fluid types can be assigned according to actual needs). The fluid types in this invention mainly include water and gas, and water and oil. Specifically, the pore model of the three-dimensional digital core can be assigned two fluid types. For the pore model of the three-dimensional digital core with water and gas as the fluid type, the initial state of the pores is set to all natural gas, which can be represented by the number 1. For the pore model of the three-dimensional digital core with water and oil as the fluid type, the initial state of the pores is set to all oil, which can also be represented by the number 1. Depending on the different fluid types and water saturation levels, elastic parameters are assigned to the fluid types in the pores at multiple water saturation levels by consulting the *Rock Physics Handbook*, thereby constructing elastic parameter models of the pores at multiple water saturation levels for multiple three-dimensional digital cores (i.e., the mapping relationship between water saturation and elastic parameter values). This invention will be illustrated using an example where the fluid type in the pores is water and gas. For example, if the fluid type in the pores is water and gas, when the water saturation is 10%, the corresponding value of the elastic parameter is determined by consulting the *Rock Physics Handbook*; when the water saturation is 20%, another value of the elastic parameter is determined by consulting the *Rock Physics Handbook*; and so on, thus obtaining the elastic parameter models of the pores at multiple water saturation levels in a three-dimensional digital core. The method for obtaining the elastic parameter models of the pores at multiple water saturation levels when the fluid type in the pores is water and oil is the same as when the fluid type is water and gas, and will not be repeated here.

[0046] Among them, the elastic parameter model of the rock matrix and the elastic parameter model of the pores of the three-dimensional digital core constructed in the above manner constitute the elastic parameter model of the three-dimensional digital core under multiple water saturation levels. That is, the elastic parameter model of the three-dimensional digital core under multiple water saturation levels includes the elastic parameter model of the rock matrix and the elastic parameter model of the pores of the three-dimensional digital core.

[0047] Furthermore, the construction of the elastic parameter model of the pores under multiple water saturation levels of the three-dimensional digital core specifically includes the following steps S1021-S1022.

[0048] S1021. Based on the pore model of three-dimensional digital rock core, multiple water saturations corresponding to the fluid types in the pores are obtained according to multiple preset water saturations.

[0049] To change the water saturation of the pores in a three-dimensional digital core, multiple preset water saturations can be set to obtain multiple water saturations corresponding to the fluid types in the pores.

[0050] S1022. Based on the fluid type in the pores, obtain the elastic parameters of multiple water saturation levels corresponding to the fluid type in the pores, so as to construct the elastic parameter model of the pores under multiple water saturation levels of the three-dimensional digital core.

[0051] Specifically, to construct elastic parameter models of the three-dimensional digital core at multiple water saturation levels, the piston displacement principle can be used to change the water saturation of the pores under different fluid types by water-driven oil or water-driven gas. For example, when the fluid type is water and gas or water and oil, the water saturation of the three-dimensional digital core is changed by the piston displacement principle (e.g., preset water saturation of 10%, 20%, ..., 100%), and the elastic parameters at multiple water saturation levels are obtained by consulting the "Rock Physics Handbook". Simultaneously, combined with the rock matrix elastic parameter model of the three-dimensional digital core established in step S102, the elastic parameter models of the pores at multiple water saturation levels of the three-dimensional digital core are constructed.

[0052] Furthermore, obtaining multiple water saturations corresponding to the fluid type in the pores based on multiple preset water saturations includes: determining the minimum value n of the number of water layers k to be filled based on the preset water saturation S and the following formula. in, Let M represent the porosity of the i-th layer, and M represent the number of pore layers. This represents the porosity of water, and k represents the number of water layers that need to be filled; based on the minimum value n and the porosity of water... Obtain multiple water saturation levels corresponding to the fluid type in the pores.

[0053] Specifically, taking the fluid type in the pores as water and gas as an example, assuming the three-dimensional digital core model is divided into several layers N along the Z-axis, and assuming the initial filling state of the pores in each layer is natural gas, in order to change the water saturation of the pores, the piston displacement principle is used to change the water saturation of the pores by water-driven gas filling. As the proportion of water in the water-driven gas filling pores increases, the water saturation of the pores increases. Considering that the pore proportion is not uniformly distributed along the Z-axis, the value of k for determining the number of water layers to be filled is not necessarily an integer value or a fixed value (for example, it may be 2-3 layers). Preferably, in this embodiment of the invention, the minimum value n of k is taken as the actual number of water layers to be filled.

[0054] The following formula can be used for calculation: in, Let N represent the porosity of the i-th layer, and N represent the number of pore layers. The pore size represents the proportion of water, and k represents the number of water layers that need to be filled. Therefore, given a known water saturation level S, the proportion of water in the pores can be determined. Then, the value of k can be calculated (which can be understood as the estimated number of water layers that need to be filled in the pores). By changing the minimum value n of the number of water layers k, the porosity of water when the number of water layers is n can be calculated. Right now (When the exact minimum value n is calculated, the corresponding porosity of the water can be calculated.) (i.e., the actual water saturation) to obtain multiple water saturations corresponding to the fluid type in the pores.

[0055] S103. Simulate the elastic parameter models of the three-dimensional digital core under multiple water saturation levels to obtain elastic simulation parameters.

[0056] After constructing elastic parameter models of the three-dimensional digital core at multiple water saturation levels using the steps described above, simulations are performed. The specific simulation method is as follows: Using existing techniques, such as the Voigt-Reuss-Hill formula (i.e., the brittleness index formula), the equivalent elastic modulus of the rock matrix of the three-dimensional digital core is calculated. For example... Figure 4 This is a simulated 3D digital core model of saturated gas (100% gas content). In the figure, white represents gas-bearing pores, and black represents the rock matrix. The bulk modulus of the gas is set at 0.02 GPa, the shear modulus at 0, and the density at 0.1 g / cm³. The equivalent elastic modulus of the rock matrix is ​​38.04 GPa, the shear modulus at 42.27 GPa, and the density at 2.647 g / cm³.

[0057] The present invention uses the Voigt-Reuss-Hill formula to calculate the equivalent elastic modulus of the rock matrix in a three-dimensional digital core. Compared with the existing technology that uses the finite element method to solve the stress-strain field under the minimum potential energy condition to back-derive the equivalent elastic modulus, the method is more accurate and the results are more precise.

[0058] To ensure the integrity of the experimental data, the elastic parameter models of the three-dimensional digital core at multiple water saturation levels were placed in the center of a large, uniform background model to establish a three-dimensional digital core test model. The elastic parameters of the background model are the same as the equivalent elastic modulus of the rock matrix in the elastic parameter models of the three-dimensional digital core at multiple water saturation levels.

[0059] Both P-wave and S-wave plane sources were used, with the source positioned at the top of the test model. Two sets of receivers were located at the top (on the same centerline as the source) and bottom of the elastic parametric models of multiple water saturation levels in the three-dimensional digital core, respectively. The elastic wave field of multiple water saturation cores under different fluid types was simulated using the three-dimensional elastic wave equation staggered grid finite difference numerical simulation method.

[0060] A three-dimensional elastic wave equation-based staggered-grid finite-difference numerical simulation method was adopted, solving the problem that existing stress-strain methods cannot simulate the propagation of elastic wave fields in three-dimensional digital rock cores. (Reference) Figure 5a This is a snapshot of the P-wave field from a three-dimensional digital dry rock (vacuum) numerical simulation of a dense sandstone sample. Accordingly, Figure 5b This is a snapshot of the transverse wave field. It can be seen that the method of this invention can stably and accurately simulate the propagation of elastic wave fields in dry rock, as well as in water and air, and water and oil.

[0061] Preferably, the three-dimensional elastic wave equation is a three-dimensional first-order stress-degree elastic wave equation in an isotropic elastic medium, and the specific formula is as follows: Wherein, the seismic wave field vector Q=(ν x ,ν y ,ν z , σ xx , σ yy , σ zz , σ yz , σ xz , σ xy ) T A1, A2, and A3 are respectively

[0062]

[0063]

[0064]

[0065] In the formula, ρ represents the density of the medium, which is a known value; λ and μ are Lamé constants, which are known values; v represents the velocity, which is a known value; and σ represents the stress, which is a known value.

[0066] The pore distribution of dense sandstone rock samples is highly non-uniform. The following analysis uses the three-dimensional digital core elastic wave field simulation results of these non-uniformly porous dense sandstone rock samples at multiple water saturation levels to analyze the influence of pore fluid on rock elasticity, as well as the relationship between different fluid saturation levels and P-wave velocity and S-wave velocity of dense sandstone samples in three-dimensional digital cores.

[0067] S104. Based on the elastic simulation parameters and the sensitivity threshold, determine the elastic parameters that are sensitive to water saturation.

[0068] The elastic simulation parameters include longitudinal wave velocity, transverse wave velocity, and elastic parameters, including the ratio of longitudinal to transverse wave velocities, bulk modulus, Poisson's ratio, Lamé constant, and shear modulus.

[0069] refer to Figure 6 The flowchart, S104, specifically includes the following steps S1041-S1043.

[0070] S1041. Determine the sensitivity function of the elastic parameters and the sensitivity function of the new elastic parameters based on the elastic simulation parameters.

[0071] The above simulation method can be used to obtain elastic simulation parameters. Using these parameters and existing techniques such as equivalent medium theory and the Gassmann equation, the bulk modulus K of dry rock can be calculated. dry Bulk modulus K of saturated fluid rock sat Wherein, the bulk modulus K of the rock matrix s This refers to the equivalent elastic modulus of the rock matrix of the three-dimensional digital core, calculated using existing technology and the Voigt-Reuss-Hill formula in step S103 above.

[0072] The new elastic parameters are determined according to the following formula, wherein the new elastic parameters include the pore space modulus M and the pore fluid bulk modulus K. f M = (K sat -K dry ) / β 2 , And based on the new elastic parameter, determine the sensitivity function of the new elastic parameter. Wherein, K s K represents the bulk modulus of the rock matrix. dry K represents the bulk modulus of dry rock. s With Kdry Determined based on the longitudinal wave velocity, transverse wave velocity, and elastic parameters; K sat K represents the bulk modulus of saturated fluid rock. sat Determined based on the longitudinal wave velocity, transverse wave velocity, and elastic parameters; This represents the porosity of the rock sample, a known value obtained from the experiment.

[0073] Specifically, the bulk modulus K of the rock matrix is ​​determined based on elastic simulation parameters. s Bulk modulus K of dry rock dry and the bulk modulus K of saturated fluid rocks sat Furthermore, based on Biot's theory of saturated fluid porous media and its low-frequency approximation conditions, two elastic parameters sensitive to the saturation of different fluids (gas / water, oil / water) can be constructed: the pore space modulus M and the pore fluid bulk modulus K. f .

[0074] After determining two new elastic parameters (i.e., new elastic parameters in addition to the five conventional elastic parameters), the elastic parameters (in this paper, the conventional elastic parameters are referred to as the P-wave / S-wave velocity ratio, bulk modulus, Poisson's ratio, Lamé constant, and shear modulus) and the new elastic parameters M and K are used. f The sensitivity functions of the elastic parameters and the new elastic parameters are determined respectively.

[0075] S1042. Determine the sensitivity of the elastic parameter and / or the new elastic parameter within a specific water saturation range based on the sensitivity function of the elastic parameter and / or the sensitivity function of the new elastic parameter.

[0076] Further, determining the sensitivity function of the elastic parameter or the sensitivity function of the new elastic parameter includes: based on y(S w And the following formula, determine y(S) w The sensitivity function A) w : Among them, S w Indicates water saturation, y(S) w ) represents the elastic parameter or a new elastic parameter at different water saturation levels.

[0077] Specifically, y(S w () represents different water saturation levels S w The elastic parameter is either a new elastic parameter or a variable, where y represents any elastic parameter. Using the formula... Determine the sensitivity function, refer to Figure 7a The figure shows the sensitivity of conventional elastic parameters for rock samples with fluid types of water and gas. Figure 7bThe figure shows the sensitivity of conventional elastic parameters for rock samples with fluid types of water and oil. From... Figure 7a and Figure 7b As can be seen from this, conventional elastic parameters (the ratio of longitudinal to transverse wave velocities V) p / V s Poisson's ratio (P'sratio) and bulk modulus (K) sat Lamé constant and shear modulus Mu are not sensitive to pore fluid saturation, especially when the fluid type is water and oil, the sensitivity to water saturation is very low (less than 5%).

[0078] S1043. The elastic parameter with sensitivity greater than the sensitivity threshold and / or the new elastic parameter are determined as elastic parameters sensitive to water saturation.

[0079] Based on the sensitivity function calculation formula in step S1042, refer to Figure 8a The sensitivity of conventional and novel elastic parameters to different water saturation levels for fluid types of water and gas shows that the new elastic parameters, pore space modulus M and pore fluid bulk modulus K, exhibit sensitivity at various water saturation levels. f At a specific water saturation level ( Figure 8a When the specific water saturation is between 0% and 80%, the sensitivity to water saturation is between 17% and 40%, while the sensitivity of conventional elastic parameters to water saturation between 0% and 80% is below 10% (reference). Figure 8a In addition to K f And the other broken lines besides M, that is Figure 7a (The broken line corresponding to the conventional elastic parameters in the graph).

[0080] refer to Figure 8b The sensitivity of conventional and novel elastic parameters to different water saturation levels for fluid types of water and oil shows that the new elastic parameters, pore space modulus M and pore fluid bulk modulus K, exhibit sensitivity to these parameters. f At a specific water saturation level ( Figure 8b When the specific water saturation is between 0% and 60%, the sensitivity to water saturation is between 10% and 30%, while the sensitivity of conventional elastic parameters to water saturation between 0% and 60% is less than 5% (reference). Figure 8b Except for K f And the broken line other than M, that is Figure 7b (The broken line corresponding to the conventional elastic parameters in the graph).

[0081] This shows that regardless of whether the fluid type is water and gas or water and oil, both new elastic parameters are sensitive to water saturation within a certain range, but this does not affect their sensitivity to water saturation. Therefore, a specific water saturation level represents water saturation within a certain range.

[0082] For fluid types of water and gas and water and oil, the new elastic parameters M and K are given. f The sensitivity within a specific water saturation range is significantly higher than that of conventional elastic parameters to water. In this embodiment of the invention, the sensitivity threshold is preferably set to 10%, but it can be set to other values ​​as needed; this invention does not impose specific limitations. Elastic parameters with a sensitivity greater than the sensitivity threshold of 10% and / or the new elastic parameters are determined as elastic parameters sensitive to water saturation, thus determining the new elastic parameters M and K. f This is an elastic parameter sensitive to water saturation. Among them, the pore fluid bulk modulus K... f The pore space modulus M is more sensitive to water saturation. Furthermore, these two elastic parameters have clear physical meanings, and they will inevitably become new and important parameters for predicting reservoir rock saturation.

[0083] This method identifies a new elastic parameter that is sensitive to water saturation, solving the problem that conventional elastic parameters of tight reservoirs in the prior art are not sensitive to water saturation, thereby improving the accuracy of water saturation calculation.

[0084] Using the above technical solution, rock samples are scanned to obtain a three-dimensional digital core model, wherein the three-dimensional digital core model includes a rock matrix model and a pore model of the three-dimensional digital core; based on the rock matrix model and pore model of the three-dimensional digital core, elastic parameter models of the three-dimensional digital core under multiple water saturation levels are constructed; the elastic parameter models of the three-dimensional digital core under multiple water saturation levels are simulated to obtain elastic simulation parameters, wherein the elastic model parameters include both conventional elastic parameters and new elastic parameters; then the elastic parameters with sensitivity greater than the sensitivity threshold and / or the new elastic parameters are determined as elastic parameters sensitive to water saturation.

[0085] The embodiments of the present invention determine an elastic parameter that is sensitive to water saturation, which solves the problem that conventional elastic parameters in the prior art are not sensitive to water saturation. Thus, the elastic parameter that is sensitive to water saturation can be further used as a prediction of actual well logging or seismic water saturation.

[0086] On the other hand, the present invention also provides a method for predicting water saturation, the method comprising: determining the elastic parameter K sensitive to water saturation according to the method for determining the elastic parameter sensitive to water saturation. f Based on the elastic parameter K, which is sensitive to water saturation. f And the following formula is used to construct the water saturation prediction model: S w =a*K fb , among which, S w K represents the degree of water saturation. f denoted by , where a and b represent the bulk modulus of the saturated fluid, and a and b represent the undetermined coefficients of the water saturation prediction model.

[0087] Specifically, after determining the elastic parameters sensitive to water saturation, in order to further utilize these water-sensitive elastic parameters to characterize the prediction of actual well logging or seismic water saturation, this invention also needs to construct a water saturation prediction model. (Reference) Figure 8a and Figure 8b It can be seen that the new sensitive elasticity parameter K f The sensitivity to water saturation is greater than that of the new sensitive elastic parameter M. Therefore, the new elastic parameter K is preferred in the embodiments of the present invention. f Construct a water saturation prediction model, with the following formula: S w =a*K f b Where a and b represent the undetermined coefficients of the water saturation prediction model. (Reference) Figure 9a This is an elastic parameter model for rock samples where the fluid type in the pores is water and gas. Figure 9a The discrete points in the equation are the elastic parameters K for different water saturations determined through step S1042 above. f The value of is, that is Figure 8a Zhong K f The points on the corresponding broken line. Similarly, refer to... Figure 9b This is an elastic parameter model for rock samples where the fluid type in the pores is water and oil. Figure 9b The discrete points in the equation are the elastic parameters K for different water saturations determined through step S1042 above. f The value of is, that is Figure 8b Zhong K f The points on the corresponding broken line. As can be seen from the figure, the constructed model can well characterize the pore fluid bulk modulus K of dense rocks. f The variation patterns of water saturation at multiple levels are observed. Based on existing techniques, a water saturation prediction model S is fitted to discrete points. w =a*K f b The undetermined coefficients a are 59.7 and b is 0.76.

[0088] When the pore fluid bulk modulus K of the rock is determined f When there is a certain deviation from the theoretical value, the present invention uses the following method to correct the bulk modulus of the fluid: taking the minimum value as a reference, it is corrected to the bulk modulus of saturated gas, and the corresponding difference is used to correct all bulk moduli. The same correction method is also applied to the case where the fluid type is water and oil saturated.

[0089] After determining the elastic parameters that are sensitive to water saturation, a water saturation prediction model is constructed using the elastic parameters that are sensitive to water saturation. This water saturation prediction model is then used to predict the water saturation in the target wellbore or to predict the water saturation during an earthquake.

[0090] Furthermore, the present invention also provides a method for determining the water saturation of a target wellbore, the method comprising: determining the bulk modulus K of the rock matrix in the target wellbore based on multiple parameter curves of the target wellbore. s Bulk modulus K of dry rock dry and the bulk modulus K of saturated fluid rock sat Based on the bulk modulus K of the rock matrix in the target wellbore. s Bulk modulus K of dry rock dry , Saturated fluid rock bulk modulus K sat And the method for determining the elastic parameter sensitive to water saturation, and determining the pore fluid bulk modulus K. f ; and based on the aforementioned water saturation prediction model and pore fluid bulk modulus K f Determine the water saturation of the target wellbore.

[0091] Furthermore, the multiple parameter curves include the longitudinal wave velocity curve, the transverse wave velocity curve, the density curve, and the saturation curve.

[0092] Specifically, after establishing a water saturation prediction model, this elastic parameter model can be used to predict the actual water saturation of the wellbore. First, existing technologies such as well logging curves can be used to obtain multiple parameter curves of the target wellbore to be explored. These curves include P-wave velocity, S-wave velocity, density, and saturation curves. Based on these multiple parameter curves, the bulk modulus K of the rock matrix in the target wellbore can be determined. s Bulk modulus K of dry rock dry and the bulk modulus K of saturated fluid rock sat And using the formula in step S1041 above, the elastic parameter K, which is sensitive to water saturation, can be determined. f After determining the elastic parameter K, which is sensitive to water saturation... f Then, the water saturation prediction model S constructed based on the above steps is used. w =a*K f b This allows for the prediction of water saturation in the target wellbore. The method for predicting water saturation during earthquakes is the same as the method for predicting water saturation in the target wellbore, and will not be repeated here.

[0093] The method for determining the water saturation of a target wellbore using the above technical solution can be applied to the fields of well logging water saturation measurement or seismic water saturation measurement. This allows for the quantitative evaluation of the oil and gas content of tight reservoirs, as well as the quantitative analysis of the water and oil saturation, and the water and gas saturation of tight reservoirs. It overcomes the shortcomings of conventional methods in identifying oil-water reservoirs and predicting oil-water saturation with low reliability, providing a new approach for the exploration and development of tight reservoirs. It also has high application value in the fields of three-dimensional digital core analysis and computational rock physics.

[0094] Accordingly, such as Figure 10 The present invention also provides a system for determining elastic parameters sensitive to water saturation. The system includes: a scanning device 10 for scanning a rock sample to obtain a three-dimensional digital core model, wherein the three-dimensional digital core model includes a rock matrix model and a pore model of the three-dimensional digital core; a construction device 11 for constructing elastic parameter models of the three-dimensional digital core at multiple water saturation levels based on the rock matrix model and pore model of the three-dimensional digital core; an acquisition device 12 for simulating the elastic parameter models of the three-dimensional digital core at multiple water saturation levels to obtain elastic simulation parameters; and a determination device 13 for determining the elastic parameters sensitive to water saturation based on the elastic simulation parameters and a sensitivity threshold.

[0095] For details regarding the determination of the aforementioned elastic parameters sensitive to water saturation and their effects, please refer to the relevant explanations of the determination method for the aforementioned elastic parameters sensitive to water saturation, which will not be repeated here.

[0096] Accordingly, the present invention also provides a water saturation prediction model system, the system comprising: a construction device for determining the elastic parameter K, which is sensitive to water saturation, as determined by the determination method. f Based on the elastic parameter K, which is sensitive to water saturation. f And the following formula is used to construct the water saturation prediction model: S w =a*K f b Among them, S w K represents the degree of water saturation. f denoted by , where a and b represent the bulk modulus of the saturated fluid, and a and b represent the undetermined coefficients of the water saturation prediction model.

[0097] For details regarding the prediction of water saturation and its effects, please refer to the relevant explanation of the prediction of water saturation mentioned above, which will not be repeated here.

[0098] Accordingly, the present invention also provides a system for determining the water saturation of a target wellbore, the system comprising: a first determining device, configured to determine the bulk modulus K of the rock matrix in the target wellbore based on multiple parameter curves of the target wellbore. s Bulk modulus K of dry rock dry and the bulk modulus K of saturated fluid rock sat The second determining device is used to determine the bulk modulus K of the rock matrix in the target wellbore. s Bulk modulus K of dry rock dry , Saturated fluid rock bulk modulus K sat And the method for determining the elastic parameter sensitive to water saturation, and determining the pore fluid bulk modulus K. f ; and a third determining device, used for the water saturation prediction model and the pore fluid bulk modulus K. f Determine the water saturation of the target wellbore.

[0099] The first determining device, the second determining device, and the third determining device can be the same or different devices; this invention does not impose specific limitations. For details regarding the determination of the target wellbore's water saturation and its effects, please refer to the relevant description of the method for determining the target wellbore's water saturation, which will not be repeated here.

[0100] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can 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.

[0101] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will 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. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0102] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0103] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0104] In a typical configuration, a computing device includes one or more processors (CPU), input / output interfaces, network interfaces, and memory.

[0105] Memory may include non-persistent memory in computer-readable media, such as random access memory (RAM) and / or non-volatile memory, such as read-only memory (ROM) or flash RAM. Memory is an example of computer-readable media.

[0106] Computer-readable media includes both permanent and non-permanent, removable and non-removable media that can store information using any method or technology. Information can be computer-readable instructions, data structures, modules of programs, or other data. Examples of computer storage media include, but are not limited to, phase-change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technologies, CD-ROM, digital versatile optical disc (DVD) or other optical storage, magnetic tape, magnetic magnetic disk storage or other magnetic storage devices, or any other non-transferable medium that can be used to store information accessible by a computing device. As defined herein, computer-readable media does not include transient computer-readable media, such as modulated data signals and carrier waves.

[0107] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0108] The above are merely embodiments of the present invention and are not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A method for determining an elastic parameter sensitive to water saturation, characterized in that, The determination method includes: The rock sample is scanned to obtain a three-dimensional digital core model, wherein the three-dimensional digital core model includes a rock matrix model and a pore model of the three-dimensional digital core. Based on the rock matrix model and pore model of the three-dimensional digital core, elastic parameter models of the three-dimensional digital core under multiple water saturation conditions are constructed. The elastic parameter models of the three-dimensional digital core under multiple water saturation levels were simulated to obtain elastic simulation parameters; and Based on the elastic simulation parameters and the sensitivity threshold, the elastic parameters sensitive to water saturation are determined.

2. The method for determining the elastic parameter sensitive to water saturation according to claim 1, characterized in that, The elastic parameter models of the three-dimensional digital core at multiple water saturation levels include the elastic parameter models of the pores in the three-dimensional digital core. The construction of the elastic parameter model for the three-dimensional digital core at multiple water saturation levels includes: Based on the pore model of the three-dimensional digital core, multiple water saturations corresponding to the fluid types in the pores are obtained according to multiple preset water saturations, and Based on the fluid type in the pores, elastic parameters of multiple water saturation levels corresponding to the fluid type in the pores are obtained to construct elastic parameter models of the pores under multiple water saturation levels in the three-dimensional digital core.

3. The method for determining the elastic parameter sensitive to water saturation according to claim 2, characterized in that, The pore model based on the three-dimensional digital core, which obtains multiple water saturations corresponding to the fluid type in the pores according to multiple preset water saturations, includes: Based on the preset water saturation S and the following formula, determine the minimum value n of the number of water layers k that need to be filled. in, Let N represent the porosity of the i-th layer, and N represent the number of pore layers. This indicates the porosity of the water, and k represents the number of water layers that need to be filled. Based on the minimum value n and the porosity of water This allows us to obtain multiple water saturation levels corresponding to the fluid type in the pores.

4. The method for determining the elastic parameter sensitive to water saturation according to claim 1, characterized in that, The elastic simulation parameters include P-wave velocity, S-wave velocity, and elastic parameters, including the P-wave / S-wave velocity ratio, bulk modulus, Poisson's ratio, Lamé constant, and shear modulus. The determination of elastic parameters sensitive to water saturation based on elastic simulation parameters and sensitivity thresholds includes: The sensitivity function of the elastic parameter and the sensitivity function of the new elastic parameter are determined based on the elastic simulation parameters. Based on the sensitivity function of the elastic parameter and / or the sensitivity function of the new elastic parameter, determine the sensitivity of the elastic parameter and / or the new elastic parameter within a specific water saturation range; and The elastic parameter with a sensitivity greater than the sensitivity threshold and / or the new elastic parameter are determined as elastic parameters sensitive to water saturation.

5. The method for determining the elastic parameter sensitive to water saturation according to claim 4, characterized in that, The step of determining the sensitivity function of the new elastic parameter based on the elastic simulation parameters includes: The new elastic parameters are determined according to the following formula, wherein the new elastic parameters include the pore space modulus M and the pore fluid bulk modulus. : ， ， ,as well as Based on the new elasticity parameter, determine the sensitivity function of the new elasticity parameter. in, The bulk modulus of the rock matrix is ​​represented by... The bulk modulus of dry rock. and Determined based on the longitudinal wave velocity, transverse wave velocity, and elastic parameters; The bulk modulus of a rock saturated with fluid is represented by its bulk modulus. Determined based on the longitudinal wave velocity, transverse wave velocity, and elastic parameters; This indicates the porosity of the rock sample.

6. The method for determining the elastic parameter sensitive to water saturation according to claim 5, characterized in that, The determination of the sensitivity function for the elastic parameter or the sensitivity function for the new elastic parameter includes: according to And the following formula, determine Sensitivity function : ， in, Indicates water saturation. This represents the elastic parameter or a new elastic parameter at different water saturation levels.

7. A method for constructing a water saturation prediction model, characterized in that, The method includes: The method for determining the elastic parameter sensitive to water saturation as described in claim 5 determines the pore fluid bulk modulus. ; Based on the pore fluid bulk modulus The water saturation prediction model is constructed using the following formula: in, Indicates water saturation. a、b This represents the undetermined coefficients in the water saturation prediction model.

8. A method for determining the water saturation of a target wellbore, characterized in that, The method includes: Based on multiple parameter curves of the target wellbore, the bulk modulus of the rock matrix in the target wellbore is determined. Bulk modulus of dry rock and saturated fluid rock bulk modulus ; Based on the bulk modulus of the rock matrix in the target wellbore Bulk modulus of dry rock saturated fluid rock bulk modulus And the method for determining the elastic parameter sensitive to water saturation as described in claim 5, for determining the pore fluid bulk modulus. as well as The water saturation prediction model and pore fluid bulk modulus as described in claim 7 Determine the water saturation of the target wellbore.

9. The method for determining the water saturation of a target wellbore according to claim 8, characterized in that, The multiple parameter curves include the longitudinal wave velocity curve, the transverse wave velocity curve, the density curve, and the saturation curve.

10. A system for determining elastic parameters sensitive to water saturation, characterized in that, The determining system includes: A scanning device is used to scan rock samples to obtain a three-dimensional digital core model, wherein the three-dimensional digital core model includes a rock matrix model and a pore model of the three-dimensional digital core. A construction device is used to construct elastic parameter models of the three-dimensional digital core at multiple water saturation levels based on the rock matrix model and pore model of the three-dimensional digital core. Acquisition device, used to simulate elastic parameter models of the three-dimensional digital core at multiple water saturation levels to obtain elastic simulation parameters; and A determining device is used to determine elastic parameters that are sensitive to water saturation based on the elastic simulation parameters and the sensitivity threshold.

11. A system for constructing a water saturation prediction model, characterized in that, The system includes: A construction apparatus is used to determine the pore fluid bulk modulus using the method for determining water saturation-sensitive elastic parameters according to claim 5. ; Based on the pore fluid bulk modulus The water saturation prediction model is constructed using the following formula: in, Indicates water saturation. , b This represents the undetermined coefficients in the water saturation prediction model.

12. A system for determining the water saturation of a target wellbore, characterized in that, The system includes: A first determining device is used to determine the bulk modulus of the rock matrix in the target wellbore based on multiple parameter curves of the target wellbore. Bulk modulus of dry rock and saturated fluid rock bulk modulus ; The second determining device is used to determine the bulk modulus of the rock matrix in the target wellbore. Bulk modulus of dry rock saturated fluid rock bulk modulus And the method for determining the elastic parameter sensitive to water saturation as described in claim 5, for determining the pore fluid bulk modulus. as well as The third determining device is used for the water saturation prediction model and pore fluid bulk modulus as described in claim 7. Determine the water saturation of the target wellbore.

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