A shale hydration damage continuous evaluation method based on acoustic wave and mori-tanaka method
By combining acoustic wave and Mori-Tanaka methods, fracture density is calculated, which solves the problems of poor core continuity and large error in existing technologies, and realizes continuous and accurate evaluation of shale hydration damage.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SOUTHWEST PETROLEUM UNIV
- Filing Date
- 2026-02-09
- Publication Date
- 2026-06-23
Smart Images
Figure CN122266569A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of drilling operation technology, and in particular to a method for continuous evaluation of shale hydration damage based on acoustic waves and the Mori-Tanaka method. Background Technology
[0002] When drilling in shale formations, the significant bedding structure, micro- and nano-pores, and strong heterogeneity of shale result in its extremely high water absorption and hydration capacity. Intrusive aqueous fluids can cause hydration damage to the shale structure, leading to the development of microfractures, deterioration of the rock mass structure, and reduction in mechanical strength. This exacerbates the risk of wellbore collapse and instability, severely hindering safe and efficient drilling. Therefore, accurately evaluating the structural and strength changes of shale during the hydration process is crucial for optimizing drilling techniques and ensuring wellbore stability.
[0003] Currently, methods for evaluating shale hydration damage in laboratory settings are typically based on the assumption that core samples from the same area have consistent properties and exhibit similar variation patterns under different experimental conditions. A common evaluation method involves subjecting multiple core samples to hydration treatment at different times and under different conditions, then measuring their acoustic parameters in a dried state to indirectly reflect the degree of hydration damage. However, this method has the following significant shortcomings: ① It does not fully consider the strong heterogeneity of shale itself; differences in properties between different core samples introduce significant experimental errors; ② It requires multiple core samples for discrete testing, increasing core consumption and leading to discrete and inconsistent experimental results; ③ Acoustic testing is usually conducted after core drying, and the interference of water saturation on the acoustic signal cannot be eliminated during continuous non-destructive testing, making it difficult to accurately characterize the structural changes caused by hydration; ④ Existing methods cannot achieve continuous, non-destructive tracking and evaluation of hydration damage for the same core sample. Obtaining an intermediate state through repeated drying or destructive mechanical experiments would damage the sample and interrupt continuous observation. Summary of the Invention
[0004] This invention addresses the problems of the inability to continuously evaluate hydration damage in the same core sample, the influence of water saturation on acoustic testing, and the inability to avoid errors introduced by core heterogeneity. It provides a method for continuous evaluation of shale hydration damage based on acoustic testing and the Mori-Tanaka method.
[0005] This invention is achieved through the following technical solution:
[0006] This application provides a method for continuous evaluation of shale hydration damage based on acoustic waves and the Mori-Tanaka method, comprising the following steps:
[0007] S1. Measure the basic parameters of shale core, such as porosity, mass, density, and longitudinal and transverse wave velocities, and calculate the elastic modulus, bulk modulus, and shear modulus of the shale core.
[0008] At time S2 and hydration t, the measured core mass was: The calculations only consider the shale pores saturated with water to obtain the first Mori-Tanaka method shale elastic parameters;
[0009] S3, Assuming the fracture density of the shale at hydration time t. Calculate the shale elastic parameters using the second Mori-Tanaka method after introducing fracture density;
[0010] S4. Measure the mass, density, and P- and S-wave velocities of the shale at hydration time t, calculate the shale elastic parameters based on acoustic waves, and determine whether the relative error between the acoustic-based shale elastic parameters and the elastic parameters calculated using Mori-Tanaka theory is less than a preset value; if the relative error is less than the preset value, output the fracture density. If the relative error is not less than the preset value, increase the crack density until the relative error is less than the preset value.
[0011] S5. Based on the output fracture density, using the initial elastic parameters of the shale as input parameters, and combining Mori-Tanaka theory, the elastic parameters of the dry rock at hydration time t are calculated, and the hydration damage coefficient is calculated based on the hydration damage coefficient calculation formula.
[0012] Compared with the prior art, this application has at least the following beneficial effects:
[0013] This application enables non-destructive acoustic testing of the same core sample at different hydration stages, and combines theoretical models to eliminate the influence of water saturation, thereby achieving continuous and accurate evaluation of structural damage during shale hydration. Attached Figure Description
[0014] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.
[0015] Figure 1 This is a flowchart of a continuous evaluation method for shale hydration damage based on acoustic waves and the Mori-Tanaka method, as shown in the embodiment.
[0016] Figure 2 The values shown are the calculated values of the crack density in the examples and the values in the literature.
[0017] Figure 3 The values shown are the calculated damage coefficient values from the examples and the values from the literature. Detailed Implementation
[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.
[0019] It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined with each other. It should also be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments; similar or identical parts between embodiments can be referred to interchangeably.
[0020] This embodiment discloses a continuous evaluation method for shale hydration damage based on acoustic waves and the Mori-Tanaka method. The theoretical basis of this method is as follows:
[0021] For an object containing inclusions, the relationship between its macroscopic stress and strain tensor is as follows:
[0022] (1)
[0023]
[0024] In the above formula, The bulk modulus after homogenization. Let J be the homogenized shear modulus, J be the spherical tensor, and K be the eccentric tensor. Let G be the elastic tensor and G be the strain tensor.
[0025] The elastic tensors of the substrate and inclusions are respectively:
[0026] (2)
[0027] In the above formula, k m μ m These are the base elastic tensor, volume tensor, and shear tensor of an object containing inclusions, respectively. k inc μ inc These are the inclusion elasticity tensor, volume tensor, and shear tensor of an object containing inclusions, respectively.
[0028] The macroscopic elasticity tensor can be written in the following form:
[0029] (3)
[0030] In the above formula, For elastic tensors, Generally refers to the vectors of a point r in all directions. For local tensors, It is a microscopic elastic tensor.
[0031] Therefore, by solving This local tensor can be used to solve the above equations. According to the Mori-Tanaka method, the local tensors of the substrate and inclusions can be written as:
[0032] (4)
[0033] In the above formula, Let be the local tensor of the base of an object containing inclusions. Let be the local tensor of inclusions in an object containing inclusions. The volume fraction of the base. Let Hill be the inclusion Hill tensor for an object containing inclusions. S E For Eshelby tensors; , Let be the basis elasticity tensor of an object containing inclusions. Let be the inclusion elasticity tensor of an object containing inclusions.
[0034] By solving the above equations, we can obtain the Mori-Tanaka macroscopic elastic tensor, as well as the equivalent bulk modulus and shear modulus of the inclusion model:
[0035] (5)
[0036] In the above formula, C MT k MT μ MT These are the equivalent elastic modulus, equivalent bulk modulus, and equivalent shear modulus of an object containing inclusions, respectively; k m μ m The bulk modulus and shear modulus of the substrate of an object containing inclusions, k inc μ inc These are the bulk modulus and shear modulus of the inclusions in an object containing inclusions, respectively; φ inc This represents the volume fraction of inclusions in an object containing inclusions.
[0037] The definitions of all variables need to be supplemented.
[0038] in, , .
[0039] In formula (5), given the bulk modulus and shear modulus of the substrate and inclusions, the equivalent volume and shear modulus of the object containing inclusions can be obtained. For partially saturated fluid in pores, formula (5) can be derived as follows:
[0040] (6)
[0041] (7)
[0042] In the above formula, The bulk modulus of the core when the pore shape is coin-shaped and partially saturated with fluid. The core shear modulus when the pore shape is coin-shaped and partially saturated with fluid. The pore equivalent bulk modulus of a partially saturated fluid. , , φ represents porosity. This represents the initial bulk modulus of the shale core. The initial shear modulus of the shale core. The bulk modulus of a liquid. S is the bulk modulus of the gas, S is the fluid saturation, and e is a coefficient; in some embodiments, e is 3.
[0043] The intrusive water phase during shale hydration can be divided into two parts: one part enters the original shale pores, and the other part saturates the resulting hydration fractures. The volume of the intrusive water phase in the shale is obtained from the difference between the core mass at hydration time t and the initial core mass.
[0044] (8)
[0045] In the above formula, Let t be the volume of water phase that enters the shale core at hydration time. The density of water, The core mass at time t represents the hydration time of the shale core. This refers to the quality of the shale core before it is hydrated.
[0046] Substituting equation (8) into equations (6) and (7) yields the elastic parameters obtained using the first Mori-Tanaka method when only the pore portion of the shale is saturated, based on the unhydrated core. These parameters serve as the basic input parameters for the second Mori-Tanaka method.
[0047] In some embodiments, a second homogenization method is used to obtain the equivalent elastic modulus of hydration damage cracks in shale. Since hydration damage cracks in shale are caused by water entering the micropores and are a major cause of shale strength reduction, and the resulting hydration cracks are filled with fluid, the Mori-Tanaka method can be written as follows for inclusions with an aspect ratio of α and a crack density of ε saturated fracture:
[0048] (9)
[0049] In the above formula, T is an intermediate parameter. Shale fracture density, , , , , The equivalent Poisson's ratio, equivalent bulk modulus, equivalent elastic modulus, and equivalent shear modulus of the shale core obtained using the second Mori-Tanaka method are shown below. , , , These represent the equivalent Poisson's ratio, equivalent bulk modulus, equivalent elastic modulus, and equivalent shear modulus of the shale core obtained using the first Mori-Tanaka method; ω is the influence factor of saturated water. , This refers to the porosity of the fracture.
[0050] like Figure 1 As shown in this embodiment, a method for continuous evaluation of shale hydration damage based on acoustic waves and the Mori-Tanaka method is disclosed, including the following steps:
[0051] S1. Measure the basic parameters of shale core, such as porosity, mass, density, and longitudinal and transverse wave velocities, and calculate the elastic modulus, bulk modulus, and shear modulus of the shale core.
[0052] At time S2 and hydration time t, the core mass was measured as follows: The elastic parameters of the first Mori-Tanaka method, which only considers the saturated water in the shale pores, are calculated by combining formulas (6), (7), and (8).
[0053] S3, assuming shale fracture density at hydration time t. Combined with formula (9), the elastic parameters of shale under the second Mori-Tanaka method after introducing the fracture density are calculated;
[0054] S4. Simultaneously measure the mass, density, and P- and S-wave velocities of the shale at hydration time t. Further calculate the shale elastic parameters based on acoustic parameters, and determine whether the relative error between the acoustic-based elastic parameters and the elastic parameters calculated using Mori-Tanaka theory is less than 5%. Calculate the increased fracture density. Output the fracture density until the judgment condition is met. ;
[0055] S5. Based on crack density And based on the initial elastic parameters of shale The elastic parameters of the dried rock at hydration time t were calculated using Mori-Tanaka theory as input. Define the hydration damage coefficient D = 1 - / .
[0056] Therefore, the structural damage of the same rock during the hydration process can be obtained using the above method, thus achieving continuous non-destructive evaluation of the hydration damage process.
[0057] The following formula is used to calculate the shale elastic parameters based on acoustic waves:
[0058]
[0059] In the above formula, E, k, and μ are the elastic modulus, bulk modulus, and shear modulus, respectively. The density of shale; and These represent the longitudinal wave velocity and transverse wave velocity of shale, respectively.
[0060] In some embodiments, the shale continuous non-destructive evaluation method based on acoustic waves and the Mori-Tanaka method includes the following steps:
[0061] S1. Prepare standard shale cores with a diameter of 2.5 cm and a length of 5 cm, and dry them in an oven at 60℃ to constant weight. Measure the core mass. Porosity φ, density And the longitudinal and transverse wave velocities, to calculate the initial elastic parameters (elastic modulus) of the shale. bulk modulus shear modulus ).
[0062] S2. 300 mL of deionized water was added to a high-temperature, high-pressure reactor, and the shale core was placed inside. Hydration was carried out under the set temperature and pressure conditions. The core mass was measured at regular intervals. The longitudinal and transverse wave velocities were tested, and the elastic parameters (elastic modulus) of the shale at hydration time t were further calculated based on the acoustic parameters. bulk modulus shear modulus ).
[0063] S3, First Mori-Tanaka Theory Treatment: Based on the quality of the core after hydration By combining the above formulas (6), (7), and (8), the elastic parameters of shale at hydration time t, considering only the saturated water in the pores, are obtained.
[0064] Specifically, the elastic parameters of the dried rock at hydration time t are calculated using the following formula:
[0065]
[0066] In the above formula, v is the Poisson's ratio of the initial shale, and ε is the fracture density. For elastic modulus, Bulk modulus Shear modulus Let t be the elastic modulus of the dry rock at hydration time t. Let be the bulk modulus of the dried rock at time t after hydration. Let t be the shear modulus of the dry rock at time t after hydration.
[0067] S4. Second Mori-Tanaka theoretical treatment: Introducing fracture density ε and combining it with formula (9) to calculate the elastic parameters (elastic modulus) in the shale rock physical model after the first Mori-Tanaka treatment, after introducing fracture density. bulk modulus shear modulus The relative error between the elastic parameters calculated using acoustic parameters and the elastic parameters calculated using Mori-Tanaka theory was less than 5% when the fracture density was gradually increased until the hydration time t.
[0068] S5. Based on the fracture density obtained in S4, the Mori-Tanaka theory is applied in conjunction with the initial elastic parameters of the shale (elastic modulus). bulk modulus shear modulus The elastic parameters (elastic modulus) of the shale under dry conditions at hydration time t were calculated. bulk modulus shear modulus Then, the hydration damage coefficient D is calculated.
[0069]
[0070] In the above formula, D is the hydration damage coefficient. This represents the initial elastic modulus of shale. Let be the elastic modulus of the shale in its dry state at time t after hydration.
[0071] In some embodiments, the fracture density and damage coefficient are calculated based on the parameters in Reference 1 (Xiong Jian, Zhu Mengyuan, Li Wenmiao, et al. Evolution of physical properties of different lithologies under high temperature. Natural Gas Industry, 2023, 43(12):14-24.) and the methods described above, as shown in Table 1. Figure 2 and Figure 3 As shown, the results indicate that the parameters calculated using the method of this invention have a small relative error compared to the parameters in the literature, demonstrating the feasibility of using the method of this invention to continuously evaluate shale hydration damage.
[0072] Table 1: Crack Density and Damage Coefficient
[0073]
[0074] The above are merely preferred embodiments of the present invention and are not intended to limit the present 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 principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A method for continuous evaluation of shale hydration damage based on acoustic waves and the Mori-Tanaka method, characterized in that, Includes the following steps: S1. Measure the porosity, mass, density, and longitudinal and transverse wave velocities of shale cores, and calculate the initial elastic parameters of the shale; At time S2 and hydration t, the measured core mass was: The elastic parameters of shale were calculated using the first Mori-Tanaka method when only the shale pores were saturated with water. S3, Assuming the fracture density of the shale at hydration time t. The second Mori-Tanaka method was used to calculate the elastic parameters of shale after introducing fracture density; S4. Measure the mass, density, and P- and S-wave velocities of the shale at hydration time t, calculate the shale elastic parameters based on acoustic waves, and determine whether the relative error between the acoustic-based shale elastic parameters and the elastic parameters calculated using the second Mori-Tanaka method is less than a preset value; if the relative error is less than the preset value, output the fracture density. If the relative error is not less than the preset value, increase the crack density until the relative error is less than the preset value. S5. Based on the output fracture density, using the initial elastic parameters of the shale as input parameters, and combining the specified formula under the unsaturated fracture condition of the Mori-Tanaka theory, calculate the elastic parameters of the dry rock at hydration time t, and calculate the hydration damage coefficient.
2. The method for continuous evaluation of shale hydration damage based on acoustic waves and the Mori-Tanaka method according to claim 1, characterized in that, The preset value for the relative error is 5%.
3. The method for continuous evaluation of shale hydration damage based on acoustic waves and the Mori-Tanaka method according to claim 1, characterized in that, In step S5, the formula for calculating the hydration damage coefficient is: ， In the above formula, The hydration damage coefficient is... This represents the initial elastic modulus of shale. Let t be the elastic modulus of the dry rock at time t after hydration.
4. The method for continuous evaluation of shale hydration damage based on acoustic waves and the Mori-Tanaka method according to claim 1, characterized in that, Elastic parameters include elastic modulus bulk modulus shear modulus .
5. A method for continuous evaluation of shale hydration damage based on acoustic waves and the Mori-Tanaka method according to claim 1 or 4, characterized in that, The elastic parameters for the first Mori-Tanaka method, considering only the saturated water in the shale pores, are calculated based on the following formula. （6） （7） In the above formula, The bulk modulus of the core when the pore shape is coin-shaped and partially saturated with fluid. The core shear modulus when the pore shape is coin-shaped and partially saturated with fluid. The pore equivalent bulk modulus of a partially saturated fluid. , , φ represents porosity. This represents the initial bulk modulus of the shale core. The initial shear modulus of the shale core. The bulk modulus of a liquid. Where is the bulk modulus of the gas, S is the fluid saturation, and e is a coefficient; The volume of water phase in the intrusive shale is obtained from the difference between the core mass at hydration time t and the initial core mass: （8） In the above formula, Let t be the volume of water phase that enters the shale core at hydration time. The density of water, The core mass at time t represents the hydration time of the shale core. The quality of shale core before hydration. Substituting equation (8) into equations (6) and (7) yields the elastic parameters of shale obtained using the first Mori-Tanaka method, considering only the pore portion as saturated based on the unhydrated core. These parameters serve as the basic input parameters for the second Mori-Tanaka method.
6. A method for continuous evaluation of shale hydration damage based on acoustic waves and the Mori-Tanaka method according to claim 1 or 5, characterized in that, The formula for the second Mori-Tanaka method is: (9) In the above formula, T is an intermediate parameter. Shale fracture density, , , , , The equivalent Poisson's ratio, equivalent bulk modulus, equivalent elastic modulus, and equivalent shear modulus of the shale core obtained using the second Mori-Tanaka method are shown below. , , , These represent the equivalent Poisson's ratio, equivalent bulk modulus, equivalent elastic modulus, and equivalent shear modulus of the shale core obtained using the first Mori-Tanaka method; ω is the influence factor of saturated water. , This refers to the porosity of the fracture.
7. A method for continuous evaluation of shale hydration damage based on acoustic waves and the Mori-Tanaka method according to claim 1 or 4, characterized in that, The elastic parameters of shale based on acoustic waves are calculated using the following formula: ， In the above formula, E, k, and μ are the elastic modulus, bulk modulus, and shear modulus, respectively. The density of shale; and These represent the longitudinal wave velocity and transverse wave velocity of shale, respectively.
8. A method for continuous evaluation of shale hydration damage based on acoustic waves and the Mori-Tanaka method according to claim 1, characterized in that, The elastic parameters of the dried rock at hydration time t are calculated using the following formula: ， In the above formula, v is the Poisson's ratio of the initial shale, and ε is the fracture density. For elastic modulus, Bulk modulus Shear modulus Let t be the elastic modulus of the dry rock at hydration time t. Let be the bulk modulus of the dried rock at time t after hydration. Let t be the shear modulus of the dry rock at time t after hydration.