Method and system for measuring cross-scale rock elastic mechanical parameters

Abstract

The invention discloses a cross-scale rock elastic mechanical parameter measurement method and system, and relates to the technical field of rock measurement, and the method comprises the following steps: obtaining nano-scale rock elastic mechanical parameters and micro elastic-plastic deformation of rock through a nanoindentation experiment, so as to construct a molecular dynamics model of the rock; according to the molecular dynamics model of the rock, using an inclusion homogenization theory to upgrade the rock elastic mechanics parameters of the nanoscale to the rock elastic mechanics parameters of the centimeter scale, so as to construct a rock elastic mechanics parameter conversion model, and using environmental data in an in-situ environment for correction; and inputting the nano-scale rock elastic mechanical parameters into the corrected rock elastic mechanical parameter conversion model to obtain centimeter-scale rock elastic mechanical parameters. According to the invention, centimeter-scale rock elastic mechanical parameters in a deep stratum in-situ environment can be accurately measured.

Description

Technical Field

[0001] The present invention relates to the field of rock measurement technology, and in particular to a method and system for measuring cross-scale rock elastic mechanical parameters. Background Art

[0002] Elastic mechanical parameters of rocks, such as the elastic modulus and Poisson's ratio, can not only reflect the deformation characteristics and mechanical behavior of rocks, but their measurement accuracy also directly affects the precise detection of resource endowment characteristics.

[0003] Existing rock mechanics testing methods employ a variety of methods. Indoor core analysis, due to the destruction of in-situ conditions, results in highly discrete test results and distorted inversion results. Fidelity coring methods are too expensive to be widely adopted. While indentation tests can obtain linear elastic moduli, existing methods struggle to accurately measure the rheological and plastic transformations that occur in rocks under high-temperature and high-pressure conditions in deep formations. Nano- to millimeter-scale indentation tests struggle to achieve precise control in deep reservoirs, and the lack of theoretical models that scale from nanometer to centimeter makes it difficult to accurately obtain macroscopic rock mechanics parameters.

[0004] In summary, the above technologies cannot accurately measure the rock elastic mechanical parameters at the centimeter scale in the in-situ environment of deep formations. Summary of the Invention

[0005] The embodiments of the present invention provide a method and system for measuring cross-scale rock elastic mechanical parameters, which can solve the problem in the prior art that it is impossible to accurately measure centimeter-scale rock elastic mechanical parameters in an in-situ environment of deep formations.

[0006] An embodiment of the present invention provides a method for measuring cross-scale rock elastic parameters, comprising the following steps: Collect core samples from deep reservoirs and the environmental data of the core samples; Through nanoindentation experiments, the microscopic elastic mechanical parameters and microscopic elastic-plastic deformation of the core samples at the nanoscale are obtained to construct a molecular dynamics model of the core samples; Based on the molecular dynamics model of the core sample, the inclusion homogenization theory is used to predict the macroscopic equivalent mechanical parameters of the core sample's microscopic elastic mechanical parameters at the nanoscale, and the rock elastic mechanical parameters of the core sample at the centimeter scale are obtained to construct a rock elastic mechanical parameter conversion model; Test the rock elasticity parameters of the molecular dynamics model of the core sample under the influence of different environmental data; based on the rock elasticity parameters, use the environmental data of the core sample to modify the rock elasticity parameter conversion model; The nanometer-scale rock elastic mechanical parameters are input into the modified rock elastic mechanical parameter conversion model to obtain the centimeter-scale rock elastic mechanical parameters.

[0007] Furthermore, the microscopic elastic mechanical parameters of the core sample at the nanoscale are predicted using the inclusion homogenization theory to obtain the rock elastic mechanical parameters of the core sample at the centimeter scale. The specific steps include: X-ray diffraction, scanning electron microscopy, energy spectrum analysis, and atomic force microscopy were performed on the core samples used in the nanoindentation experiments to obtain the mineral conformation and microstructure of the core samples at the nanoscale. MATLAB was used to perform a three-dimensional numerical reconstruction of the core samples to obtain a multiphase medium mechanical model composed of different minerals and pores. According to the multiphase medium mechanics model, the core sample is microscopically considered to be a complex composed of multiple media such as quartz, feldspar, carbonate rock, clay, and porous media. Each medium is divided into high-strength phase, medium-strength phase, and low-strength phase according to the strength or hardness of each medium. The Mori-Tanaka model in the inclusion homogenization theory is used to calculate the equivalent mechanical parameters of the high-strength phase, medium-strength phase, and low-strength phase based on the data obtained from the nanoindentation experiment. The low-strength phase is used as the matrix, and the high-strength phase and the medium-strength phase are embedded in the low-strength phase as inclusion phases; The three-phase medium mechanics model consists of high-strength phase, medium-strength phase and low-strength phase; The three-phase medium mechanical model as a physical model is converted into an equivalent mechanical parameter model, wherein the conversion includes: According to the variational principle and constitutive equation, the stress field is asymptotically expanded to obtain the material constants of the equivalent core sample, and the stress and strain distributions at the nanometer and centimeter scales are obtained, completing the upgrading of the microscopic elastic mechanical parameters of the rock at the nanometer scale to the rock elastic mechanical parameters at the centimeter scale.

[0008] Furthermore, the rock elasticity parameter conversion model is corrected according to the environmental data, and the specific steps include: Based on environmental data and the results of nanoindentation experiments, a molecular dynamics model of rocks under different temperatures and confining pressures was established; The velocity of the atoms in the isothermal layer is recalibrated at each fixed time step, and the displacement of mineral atoms at different indentation stages is recorded; The shear deformation of the core sample during the nanoindentation experiment was obtained through Von Mises stress analysis. The dislocation extraction algorithm was used to identify the dislocations of the atomic shear deformation, obtain the dislocation line length, and obtain the results of the effects of high temperature and high pressure on plastic deformation, phase transformation mechanism, and defect evolution. According to the nanoindentation experiment, the loading process, load holding process and unloading process are recorded to obtain the load-displacement-time curve; Based on the impact results and load-displacement-time curves, the microelastic modulus, creep compliance, and Poisson's ratio of the core samples in the nanoindentation test under high temperature and high pressure are obtained, and the changing trends of the microelastic modulus, creep compliance, and Poisson's ratio with increasing temperature and pressure are plotted; The process of pressing a centimeter-level indenter into rock is regarded as a closed thermodynamic system. Based on the surface contact properties and heat conduction theory, the density function and cumulative temperature rise distribution function of the rock are established. Apply the actual temperature and ground stress distribution in the environmental data to the homogenized rock model to obtain a finite element-discrete element numerical simulation model under multi-physics field coupling conditions; By considering the rock damage failure criterion DP to simulate the mechanical state of the indenter during rock crushing, the average stress-strain field of the centimeter-scale indentation process considering the influence of temperature and pressure is obtained. The rock elastic parameter conversion model is modified based on the average stress-strain field during the centimeter-level indentation process.

[0009] An embodiment of the present invention provides a system for measuring cross-scale rock elastic parameters, including: The sample acquisition module is used to collect core samples from deep reservoirs and the environmental data of the core samples; The parameter upgrade module is used to obtain the microscopic elastic parameters and microscopic elastic-plastic deformation of core samples at the nanoscale through nanoindentation experiments, thereby constructing a molecular dynamics model of the core samples. Based on the molecular dynamics model of the core samples, the inclusion homogenization theory is used to predict the macroscopic equivalent mechanical parameters of the microscopic elastic parameters of the core samples at the nanoscale, thereby obtaining the rock elastic parameters of the core samples at the centimeter scale and constructing a rock elastic parameter conversion model. The model correction module is used to test the rock elasticity parameters of the molecular dynamics model of the core sample under the influence of different environmental data; based on the rock elasticity parameters, the rock elasticity parameter conversion model is corrected using the environmental data of the core sample; The parameter measurement module is used to input the nanometer-scale rock elastic mechanical parameters into the modified rock elastic mechanical parameter conversion model to obtain the centimeter-scale rock elastic mechanical parameters.

[0010] The embodiments of the present invention provide a method and system for measuring cross-scale rock elastic parameters. Compared with the prior art, the advantageous effects thereof are as follows: The rock elastic mechanical parameters obtained by nanoindentation experiment accurately reflect the rock elastic mechanical parameters. The inclusion homogenization theory can upgrade the microscopic elastic mechanical parameters of rock at nanoscale to the rock elastic mechanical parameters at centimeter scale to construct a rock elastic mechanical parameter conversion model. The rock elastic mechanical parameter conversion model is corrected by the environmental data of the core sample, and the nanoscale rock elastic mechanical parameters are input into the corrected rock elastic mechanical parameter conversion model, which can eventually accurately obtain the centimeter scale rock elastic mechanical parameters in the original position environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 A flow chart of a method for measuring cross-scale rock elastic parameters provided by an embodiment of the present invention; Figure 2 A schematic diagram of a load-displacement variation curve for a method for measuring cross-scale rock elastic parameters provided by an embodiment of the present invention; Figure 3 A schematic diagram of the nanoindentation process of a method for measuring cross-scale rock elastic parameters provided by an embodiment of the present invention; Figure 4 Schematic diagram of different stages of nanoindentation molecular dynamics simulation of a method for measuring cross-scale rock elastic parameters provided by an embodiment of the present invention; Figure 5 A simplified geometric model of an equivalent conical indenter for a method for measuring cross-scale rock elastic parameters provided by an embodiment of the present invention; Figure 6 A three-dimensional numerical reconstruction process of rock microscopic surface morphology and deformation characteristics in a cross-scale rock elastic mechanical parameter measurement method provided in an embodiment of the present invention; Figure 7 Schematic diagram of converting a rock physics model into an equivalent mechanical parameter model for a method for measuring cross-scale rock elastic parameters provided by an embodiment of the present invention, wherein (a) is the rock physics model, and (b) is the equivalent mechanical parameter model; Figure 8 A heterogeneous (mineral + pore) digital core construction process for a cross-scale rock elasticity parameter measurement method provided in an embodiment of the present invention; Figure 9 A schematic diagram of a global inversion prediction method based on limited measuring points for a cross-scale rock elasticity parameter measurement method provided by an embodiment of the present invention; Figure 10A diagram of the nanoindentation molecular dynamics simulation process of a method for measuring cross-scale rock elastic parameters provided in an embodiment of the present invention, wherein (a) is the initial state (no contact); (b) is an indentation of 1 nanometer; (c) is an indentation of 2.5 nanometers; (d) is the maximum indentation depth; (e) is unloading of 2.5 nanometers; and (f) is complete unloading. DETAILED DESCRIPTION

[0012] To make the above-mentioned objects, features, and advantages of the present invention more readily apparent, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings. The following description sets forth numerous specific details to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art may make similar modifications without departing from the scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0013] See also Figure 1 The embodiment of the present invention provides a method for measuring cross-scale rock elastic parameters, comprising the following steps: Step 1: Collect core samples from deep reservoirs and the environmental data of the core samples.

[0014] Step 2: Through nanoindentation experiments, the microscopic elastic parameters and microscopic elastic-plastic deformation of the core sample at the nanoscale are obtained to construct a molecular dynamics model of the core sample. Based on the molecular dynamics model of the core sample, the macroscopic equivalent mechanical parameters of the microscopic elastic parameters of the core sample at the nanoscale are predicted using the inclusion homogenization theory. The rock elastic parameters of the core sample at the centimeter scale are obtained to construct a rock elastic parameter conversion model. The rock elastic parameters of the molecular dynamics model of the core sample are tested under the influence of different environmental data. Based on the rock elastic parameters, the rock elastic parameter conversion model is modified using the environmental data of the core sample.

[0015] Step 3: Input the nanometer-scale rock elastic mechanical parameters into the modified rock elastic mechanical parameter conversion model to obtain the centimeter-scale rock elastic mechanical parameters.

[0016] 1. Nanoindentation Experiment Preparation: (1) Select the deep reservoir rock sample to be tested and process it into a size and shape suitable for nanoindentation experiment.

[0017] (2) Treat the sample surface to ensure that it is flat and clean to reduce the impact of surface roughness on the measurement results.

[0018] 2. Nanoindentation experiment process: (1) Use a nanoindenter to conduct indentation experiments on the treated rock samples and record the load-displacement-time curves during loading, holding, and unloading.

[0019] (2) Calculate the rock's microscopic elastic modulus, hardness and other mechanical parameters through experimental data.

[0020] 3. Molecular dynamics simulation: (1) Based on the results of nanoindentation experiments, a molecular dynamics model of rock is established to simulate the microscopic deformation process of rock under indentation.

[0021] (2) Analyze the changes in atomic dislocations and slip bands to reveal the microscopic elastic-plastic deformation mechanism of rocks.

[0022] The specific plans for the above parts are as follows: Molecular dynamics mechanism and microscopic constitutive model establishment of rock nanoindentation process: This part is mainly based on indoor nanoindentation experiments combined with molecular dynamics simulations to study the motion state of rock matrix atoms during nanoprobe loading, holding and unloading, explore the mathematical relationship between indentation depth and pressure, and establish rock microelastic modulus, nonlinear Poisson's ratio and constitutive relationship models.

[0023] ① Cores are sampled from different types of deep reservoirs (sandstone, shale, coal, etc.), processed into thin sections, and then nanoindentation experiments are performed on the rock samples to determine the load-displacement curves and indentation depth-time curves of different minerals. After the nanoindentation experiments, SEM scans are performed on the indentation locations to understand the surface deformation and microcrack development characteristics of the indentations.

[0024] The nanoindentation test process is divided into loading-holding-unloading stages. First, a continuous load is applied to the rock sample. When the load reaches the set value, the load is maintained for a certain period of time. This stage can reflect the creep characteristics of the sample. After that, the load is unloaded at a certain rate. The typical loading and unloading curve is as follows: Figure 2 As shown. It can reflect the trend of pressure changing with the indentation depth. During the unloading process, since plastic deformation is irreversible, the reduction of the indentation depth can be attributed to the elastic recovery of the material, that is, the unloading process is a process of pure elastic deformation. Therefore, the elastic modulus of the rock material can be calculated based on the load-displacement curve and the relevant parameters of the indenter: first, the unloading part of the load-displacement curve is fitted into an exponential equation, and the contact stiffness is obtained by calculating the maximum slope of the fitting curve; then the indentation depth is regarded as consisting of the depth where the indenter is not in contact with the test sample and the depth of contact between the indenter and the sample, as shown in Figure 3As shown in the figure, the contact area during the test can be determined, and elastic mechanical parameters such as the elastic modulus and microhardness of the rock during the loading phase can be calculated. The indentation depth-time curve is obtained during the loading process of the experiment. The creep behavior of the sample is described based on the three basic elements and combination patterns of rock rheology. The creep parameters of the rock sample are identified using the nonlinear optimization least squares method, and a creep model that conforms to the sample curve is determined. This allows the establishment of a linear viscoelastic mathematical model for the deformation process of rock during the entire nanoindentation process.

[0025] Second, a molecular dynamics method was used to simulate the deformation process of rock nanoindentation experiments, studying the changes in atomic dislocations and slip bands during loading, holding, and unloading. A molecular dynamics model of the rock was established based on the nanoindenter tip shape and the mineral composition distribution of the experimental rock. The indenter was assumed to be rigid, and the rock matrix was divided into a Newtonian layer of atoms, a thermostatic layer of atoms, and a fixed layer of atoms. The top surface of the rock remained free, while the outermost two layers of atoms on the remaining surfaces were fixed. Because the indenter was much smaller than the matrix and fixed boundary conditions were applied within the matrix, scale effects were negligible. The initial temperature of the matrix was 0 K, and the velocity of the thermostatic layer atoms was adjusted at regular intervals to maintain a constant temperature. During the simulation, the interactions between the atoms in the rock matrix were simulated using an embedded atom potential (EAM), and the interactions between the matrix and indenter atoms were simulated using a Morse potential. The interaction forces between the atoms were obtained by differentiating the potential function. The z-direction component of the sum of the interaction forces of all atoms below the indenter is the applied load. The load at different displacements was then calculated to obtain the load-displacement curve during nanoindentation. The continuous stiffness measurement method is used in the load-holding process. The creep and stress relaxation data of the rock sample are obtained by applying a certain frequency load for a long time. The load-displacement-time curve obtained by simulation is compared with the experimental results, and the boundary conditions of the model are adjusted to ensure the accuracy of the simulation results. The entire nanoindentation process is divided into four stages: the indenter approaches the rock, the indenter presses into the rock, the indenter is lifted, and the indenter returns to the starting position. Figure 4 As shown in the figure, the relationship between the atomic configuration and dislocation configuration and the intrusion depth in each stage is simulated respectively, and the critical pressure depth and change law of the appearance of slip bands and dislocation loops are analyzed, thereby revealing the microscopic elastic-plastic deformation mechanism of rock under intrusion.

[0026] ③The complete nanoindentation process is a typical nonlinear mechanical behavior, and the relaxation or creep of deep stratum rocks under constant external load is unavoidable. Its lateral strain response and longitudinal deformation are often asynchronous. Therefore, it is necessary to consider the influence of rock plastic deformation and creep. According to the experimental and molecular dynamics simulation results, the linear viscoelastic mathematical model established above is modified. First, the Poisson's ratio of the rock is determined, and then the constitutive relationship of the rock in the plastic deformation stage is established. The process of the indenter pressing into the rock is regarded as a problem of a rigid body pressing into an isotropic linear viscoelastic half-plane. The method of equal height corresponding to the cross-sectional area of ​​the indenter is used to equate the pyramidal indenter to a geometrically simplified model of a conical indenter, such as Figure 5 As shown in the figure, theoretical expressions for the variation of rock shear creep compliance and tensile creep compliance with penetration depth during the indentation of a Berkovich indenter into a linear viscoelastic body are derived using continuum mechanics methods. Then, an equation for the evolution of the rock Poisson's ratio with penetration creep compliance is derived, combining the load-displacement curves obtained by nanoindentation. Because the boundary conditions in the region near the indenter and the rock deformation vary with penetration depth, the plastic parameters of the rock are difficult to obtain using analytical methods. A dimensional analysis method is used to combine nonlinear finite element methods with dimensional functions. A forward analysis is first performed using a finite element model to simulate the stress conditions of the rock during nanoindentation. This results in a series of nonlinear fitting equations. These equations are then inverted and calculated using nanoindentation tests to obtain the material's plastic properties, ultimately deriving a complete elastic-plastic-creep constitutive relationship for the rock material.

[0027] 4. Scale upgrade and parameter conversion: (1) Combining the mineral composition and microstructure of rocks, and using the inclusion homogenization theory, the mechanical parameters at the nanoscale are upgraded to the centimeter scale.

[0028] (2) Through numerical simulation and theoretical analysis, a rock elastic parameter conversion model from nanometer to centimeter scale is established to achieve accurate conversion of parameters from microscopic to macroscopic scale.

[0029] The specific plans for the above parts are as follows: Study on the coordination of rock elastic parameters scaling from nanometer to centimeter: The mechanical parameters of individual rock mineral components obtained through nanoindentation testing do not represent the mechanical properties at the macroscale; micromechanical parameters must be upscaled to the macroscale. This section, building on the microelastic mechanical parameters obtained by nanoindentation and drawing on the homogenization concept of inclusion theory, conducts upscaling research to obtain macroscopic elastic modulus and Poisson's ratio performance parameters, ensuring the coordination of rock deformation and damage mechanisms at different scales during the upscaling process.

[0030] ① X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and atomic force microscopy (AFM) tests were carried out on the cores used in the nanoindentation experiment to obtain the mineral conformation and microstructure of the cores used in the indentation experiment at the nanoscale. First, the mineral composition of the rock was obtained by testing the rock cuttings particles with XRD; then the SEM scanning electron microscope was used to calibrate the positions of different minerals and the mineral microstructure; combined with the element positioning results of EDS, the elemental composition of each mineral and the existing understanding of the microstructure of common minerals, the mineral fabric characteristics of the core observation area were analyzed. Finally, the probe force-mineral deformation curve of each pixel point of the rock sample was tested by AFM to obtain the surface morphology, mineral deformation and mechanical parameter distribution. The AFM height image can intuitively reflect the roughness and pore distribution of the mineral surface, and the image chromaticity value is positively correlated with the sample surface height value. MATLAB was used to perform three-dimensional numerical reconstruction of the rock microscopic surface morphology and deformation characteristics, extract the chromaticity image data, and establish a matrix expression for the core microscopic surface morphology and mineral distribution, such as Figure 6 Based on the elastic parameters at different locations obtained by nanoindentation experiment, combined with the surface mineral distribution matrix, the minerals at different locations are located, and a multiphase medium mechanical model composed of different minerals and pores is established.

[0031] ② Upscaling is performed using the Mori-Tanaka model, assuming that multiphase materials are treated as inhomogeneous media with no interaction between the phases. By considering the mutual perturbations between the included phases and utilizing Eshelby's equivalent inclusion theory and the mean stress method, equivalent mechanical parameters of the mineral phases are derived. The interaction between rock phases is assumed to be multiple inclusion phases embedded in a matrix phase, thus approximating the physical model of the rock. Based on the multiphase mechanical model, the rock is microscopically approximated as a complex composed of quartz, feldspar, carbonate, clay, and a porous medium. Based on the microscale strength or hardness of the minerals, they are divided into three categories: high-strength, medium-strength, and low-strength phases. The low-strength phase is treated as the matrix material, while the other two are included phases embedded in the low-strength phase. Mechanical parameters of high-strength and medium-strength minerals can be directly obtained from nanoindentation data combined with EDS calibration. Considering the influence of microporosity in low-strength minerals on nanoindentation results, equivalent mechanical parameters of low-strength minerals are calculated by converting the porosity of the low-strength minerals and indentation test data. These three categories constitute a three-phase medium mechanical model, which can be regarded as isotropic at the nanoscale. The conversion between the rock physics model and the equivalent mechanical parameter model is as follows: Figure 7 (a) and Figure 7(b) The microscopic displacement and stress fields are asymptotically expanded. Based on the variational principle and the rock microscopic constitutive equation, the asymptotic expansion of the stress field is derived. Substituting this into the equilibrium equation yields a series of governing equations, which in turn determine the equivalent rock material constants and the stress and strain distributions at both the nanometer and centimeter scales.

[0032] ③ By testing the elastic properties of each nanoindentation point, a frequency distribution curve of the rock's elastic parameters was obtained. The entire experimental data was deconvolved using Gaussian fitting, allowing the average mechanical properties corresponding to different minerals to be differentiated and calculated, resulting in the mechanical properties and volume fractions of each phase. The frequency distribution curve obtained from the nanoindentation experiments was deconvolved using cumulative distribution functions and probability density functions. Deconvolution analysis revealed the area fraction of each phase over the entire indentation surface. The elastic parameters of the included phases were weighted averaged to calculate the equivalent elastic modulus and Poisson's ratio after upscaling and homogenization. Based on the Mori-Tanaka modulus mean field equivalent transformation principle, a homogenized rock model was constructed using discrete element methods. Finite element methods were then used to calculate the forces acting on the indenter during penetration, simulating the macroscopic stress distribution and deformation characteristics of the rock. The global response of the average stress-strain field of the macrostructure during centimeter-scale penetration was determined. The numerical simulation model was calibrated using descriptions of the local stress-strain field and comparisons with multi-point nanoindentation test results.

[0033] 5. In-situ measurement and data correction: (1) Collect environmental data such as temperature and pressure in the deep formation in situ environment.

[0034] (2) Based on in-situ environmental data, the rock elastic parameter model is modified to improve measurement accuracy and reliability.

[0035] The specific plans for the above parts are as follows: In-situ occurrence environment correction of multi-scale rock elastic parameters: Based on the scale upgrade of rock elastic mechanical parameters, this part further considers the high temperature and high pressure conditions of deep formations, reveals the influence of temperature and pressure on the microscopic elastic mechanical parameters of rocks, and proposes a calculation model for the macroscopic elastic modulus and Poisson's ratio of rocks in the in-situ bottom hole environment.

[0036] ① Through field measurements in coring wells and relevant literature, while-drilling, well logging, and well history data were collected to obtain temperature and pressure data for reservoirs at different depths for subsequent in situ geological environment correction. A molecular dynamics model of rock was established under different temperatures and confining pressures. The atomic velocities in the isothermal layer were recalibrated every 100 time steps to ensure that nanoindentation tests were conducted at each specified temperature. The displacements of mineral atoms were recorded at different indentation stages. Von Mises stress calculations were used to analyze the shear deformation behavior of the rock during nanoindentation. Dislocation analysis was used to identify atomic dislocations and calculate dislocation line lengths. This allowed the analysis of the effects of high temperature and high pressure on plastic deformation, phase transformation mechanisms, and defect evolution. Load-displacement-time curves were used to calculate the microelastic modulus, creep compliance, and Poisson's ratio of the rock specimens during nanoindentation under high temperature and high pressure. Trends in these parameters with increasing temperature and pressure were plotted.

[0037] ② The process of centimeter-scale indenter penetration into rock is considered a closed thermodynamic system. Based on surface contact properties and heat conduction theory, the actual downhole temperature and ground stress distribution are introduced into the homogenized rock model, and a finite element-discrete element numerical simulation model is constructed under multi-physics field coupling conditions. To more accurately describe the damage or failure process of rock during indentation testing, the DP failure criterion that considers rock damage is used to simulate the mechanical state of the indenter during rock crushing. This results in the average stress-strain field of the centimeter-scale penetration process, which takes into account the influence of temperature and pressure. This allows the in-situ calculation model of macroscopic elastic mechanical parameters to be derived.

[0038] ③ Triaxial rock mechanics experiments are currently the primary method for obtaining the elastic modulus and Poisson's ratio of rock cores. To verify the accuracy of the in-situ calculation model for macroelastic parameters, triaxial compressive strength tests were conducted on the same rock cores used in the indentation experiments, based on the actual downhole temperature field and in-situ stress distribution. Based on the stress-strain relationship obtained from the experiments, the finite element-discrete element numerical simulation model was further modified. By varying the model's initial conditions, the sensitivity of the macroelastic modulus and Poisson's ratio to different temperature and pressure combinations was analyzed, and the trend of the macroelastic parameters as temperature and pressure increased was plotted.

[0039] Finally, the global elastic parameters are inverted and evaluated based on the in-situ array indentation data: This part is based on the nonlinear calculation model and numerical solution method of single indentation of reservoir elastic mechanical parameters in the in-situ environment. It continues to carry out centimeter-level lattice indentation experiments, establishes a large-scale heterogeneous digital core model, and constructs a global elastic mechanical parameter inversion evaluation method under finite lattice test data conditions through spatial interpolation method.

[0040] ① Select large-sized rock cores for centimeter-scale indentation experiments. Due to the large penetration depth in centimeter-scale indentation tests, the influence of rock surface roughness on the experimental results can be ignored, and the macroscopic constitutive relationship of the rock can be directly reflected. Using a sequential indentation method, the elastic modulus measured in some areas is too large due to the heterogeneity of the rock. Therefore, this project intends to adopt a random lattice indentation method, and reduce the discreteness through mathematical statistical analysis of the test results. After the experiment is loaded to the maximum load, it is maintained for a period of time to eliminate the influence of creep on the test results. In order to consider the influence of the spatial position of each measuring point, the stress-strain curve obtained based on the single-point indentation model is compared with the stress-strain curve of each measuring point of the lattice indentation, and a correction coefficient is proposed. The previously established single-point macroscopic elastic mechanical parameter in-situ calculation model is calibrated to calculate the elastic modulus and Poisson's ratio of each measuring point under the lattice mode.

[0041] ② Using a large field of view scanning electron microscope, mineral quantitative analyzer and other equipment to conduct digital core image acquisition experiments on full-scale cores. Based on the acquired core digital images, a heterogeneous digital core model considering the rock mineral strength and pore structure is established through rock multi-component digital core modeling, pore network model extraction and multi-scale pore network model construction. By constructing the heterogeneous pore structure characteristics and the mineral distribution and inherent mechanical properties at their spatial positions, the heterogeneous mechanical characteristics inside the three-dimensional digital core are reproduced. The construction process is as follows: Figure 8 As shown in the figure, a full-scale core heterogeneity model was established based on the digital core and the discrete element method. The finite element method was used to simulate the mechanical response of a centimeter-scale indenter penetrating a random lattice into the rock. The simulation results were corrected through centimeter-scale lattice indentation experiments. Combined with the previously established finite element-discrete element numerical simulation model under multi-physics field coupling conditions, the surface stress distribution characteristics of the rock under in-situ high temperature and high pressure conditions were simulated.

[0042] ③ Based on the surface stress distribution of the above finite element-discrete element simulation, combined with the calculation formula of macro elastic parameters in the lattice mode, the elastic modulus and Poisson's ratio of each measuring point are obtained in the model. By performing spatial interpolation of each sample point by the natural adjacent point spatial interpolation method, the elastic mechanical parameter field of different rock surfaces can be obtained. The global inversion numerical imaging of deep learning under the constraint of limited node information is carried out to achieve global inversion under the results of limited measurement points, and finally form a global distribution image of rock elastic mechanical parameters. The basic process of inversion is as follows: Figure 9 shown.

[0043] The present invention can achieve the following effects: 1. Use nanoindentation technology to obtain the micromechanical parameters of rocks and reveal the microscopic deformation mechanism through molecular dynamics simulation.

[0044] 2. Drawing on the inclusion homogenization theory, we can achieve the upgrade of rock elastic parameters from nanometer to centimeter scales, ensuring the coordination of mechanical parameter conversion at different scales.

[0045] 3. Combined with the in-situ environmental data of deep formations, the rock elastic parameter model is modified to improve measurement accuracy and reliability.

[0046] An embodiment of the present invention provides a system for measuring cross-scale rock elastic parameters, including: The sample acquisition module is used to collect core samples from deep reservoirs and the environmental data of the core samples.

[0047] The parameter upgrade module is used to obtain the microscopic elastic mechanical parameters and microscopic elastic-plastic deformation of core samples at the nanoscale through nanoindentation experiments, so as to construct a molecular dynamics model of the core samples. Based on the molecular dynamics model of the core samples, the inclusion homogenization theory is used to predict the macroscopic equivalent mechanical parameters of the microscopic elastic mechanical parameters of the core samples at the nanoscale, and the rock elastic mechanical parameters of the core samples at the centimeter scale are obtained to construct a rock elastic mechanical parameter conversion model.

[0048] The model correction module is used to test the rock elastic mechanics parameters of the molecular dynamics model of the core sample under the influence of different environmental data; based on the rock elastic mechanics parameters, the rock elastic mechanics parameter conversion model is corrected using the environmental data of the core sample.

[0049] The parameter measurement module is used to input the nanometer-scale rock elastic mechanical parameters into the modified rock elastic mechanical parameter conversion model to obtain the centimeter-scale rock elastic mechanical parameters.

[0050] A specific embodiment is as follows: This embodiment discloses a method for measuring cross-scale rock elastic parameters, the specific steps of which are as follows: S1. Experimental materials and equipment.

[0051] Experimental materials: Fine sandstone samples from an oil field were selected, whose main mineral components include quartz, feldspar, carbonate rock and clay.

[0052] Experimental equipment: Nano Indenter G200 nanoindenter, maximum load 500 mN, minimum resolution 50 nN, minimum displacement resolution 0.01 nm. X-ray diffractometer (XRD), scanning electron microscope (SEM), atomic force microscope (AFM). Molecular dynamics simulation software LAMMPS.

[0053] S2. Implementation steps.

[0054] (1) Nanoindentation test + scanning electron microscope + atomic force microscope combined test Sample preparation: The fine sandstone sample was processed into a cube with a side length of 1 cm and the surface was polished to ensure flatness.

[0055] ①Atomic force microscope test.

[0056] AFM probe force-deformation curves were used to measure the surface morphology, mineral deformation, and mechanical parameter distribution. A 5×5 array of points was used for the AFM, with 50 μm spacing between each point. A total of 100 points were collected across four cores.

[0057] ②Nanoindentation test.

[0058] Selection of maximum load: Set the maximum load value of the nanoindentation test to 20mN.

[0059] Selection of holding time: Select holding time as 10s.

[0060] Selection of loading rate: Set the loading rate of the nanoindentation test to 100 mN / min.

[0061] Selection of unloading rate: The unloading rate is also 100mN / min.

[0062] The nanoindentation test used a 5×5 matrix with 50 μm spacing between indentations. A total of 100 load-displacement curves were collected (the points used were the same as for atomic force microscopy).

[0063] Data processing: After the test, 25 load-displacement curves were obtained for each core. The hardness, elastic modulus, and fracture toughness were calculated respectively, and their average values ​​were obtained as the final results of the mechanical parameters obtained by the nanoindentation test.

[0064] ③Scanning electron microscope.

[0065] The indentation morphology was depicted using SEM, and EDS was used to analyze the sample surface and locate specific minerals (the selection of points is the same as for nanoindentation).

[0066] ④Result analysis.

[0067] Record the load-displacement curves during loading, holding, and unloading processes, and calculate the micro-elastic modulus and hardness of the rock.

[0068] The contact stiffness is calculated by fitting the exponential equation to the unloading curve: .

[0069] in, is the contact stiffness, which is the initial slope of the unloading part of the macro indentation load-displacement curve, is the load, is the displacement, is the maximum penetration depth of the indenter.

[0070] Calculate the contact area: .

[0071] in, is the contact area, is the maximum load, is a constant, and is taken as 0.75 for the Bosch indenter.

[0072] Calculate the elastic modulus: .

[0073] in, is the elastic modulus, is the indenter correction coefficient, which is 1.034 for the Bosch indenter.

[0074] (2) Molecular dynamics simulation.

[0075] Model Construction: Based on the XRD and SEM analysis results, a multiphase model of the rock was constructed, including minerals such as quartz, feldspar, carbonates, and clay. LAMMPS software was used, and the EAM potential field model was selected.

[0076] Simulation parameter settings: Initial temperature: 300K; time step: 1fs; simulation time: 300ps.

[0077] Simulation process: Initialize atomic positions and velocities, and use the Verlet algorithm for time integration.

[0078] Calculate the interatomic interaction forces: .

[0079] in, is the interatomic force, is the atomic motion speed, is the distance between the two particles.

[0080] Record the displacement and stress distribution of atoms during the indentation process, such as Figure 10 (a) to Figure 10 (f) shown.

[0081] Result analysis: The microscopic elastic-plastic deformation mechanism of rock is analyzed through the load-displacement curve obtained by simulation.

[0082] The micro elastic modulus and Poisson's ratio are obtained according to the load-displacement curve: .

[0083] .

[0084] Where, is the micro elastic modulus, is the axial stress, is the axial strain, is the microscopic Poisson's ratio, is the transverse strain, is the axial strain.

[0085] (3) Scale upgrade and parameter conversion.

[0086] Multiphase medium mechanics model: Rock is considered as a complex consisting of high-strength phase (quartz, feldspar), medium-strength phase (carbonate rock) and low-strength phase (clay).

[0087] The equivalent mechanical parameters are calculated using the Mori-Tanaka model: .

[0088] in, is the equivalent elastic modulus, is the bulk modulus, is the shear modulus, which is obtained by the following formula: .

[0089] in, 、 and are the bulk modulus, shear modulus and volume fraction of a certain phase of mineral respectively; and They represent the Poisson's ratio and elastic modulus of a certain phase of mineral respectively; r=0, 1, 2 represent high-strength phase, medium-strength phase and low-strength phase respectively.

[0090] Equivalent bulk modulus of the low-strength phase and equivalent shear modulus They are: .

[0091] in, and are the bulk modulus and shear modulus of the low-strength phase, respectively: is the porosity of the sample being tested.

[0092] Equivalent Poisson's ratio for: Where, is the rock hardness and is the highest point in the load-displacement curve. is the brittleness coefficient, is the material type related scaling factor.

[0093] (4) In-situ environmental correction.

[0094] Environmental data acquisition: Collect in-situ downhole environmental data, including temperature and pressure.

[0095] Model modification: Adjust the rock elastic mechanics parameter model based on in-situ environmental data: .

[0096] .

[0097] in, and is a correction function of temperature and pressure.

[0098] S3. Experimental results and analysis.

[0099] Nanoindentation test results: micro elastic modulus: 30GPa; hardness: 5GPa.

[0100] Molecular dynamics simulation results: The simulation shows that the rock matrix undergoes elastic and plastic deformation during the indenter penetration process, and the formation of atomic dislocations and slip bands is consistent with the experimental results.

[0101] Scale upgrade results: Equivalent elastic modulus at centimeter scale: 25GPa; Poisson's ratio: 0.3.

[0102] In-situ environmental correction results: elastic modulus after in-situ correction: 28 GPa; Poisson's ratio: 0.32.

[0103] This study, using nanoindentation experiments combined with molecular dynamics simulations, reveals the microscopic deformation mechanisms of rocks. The inclusion homogenization theory successfully achieves parameter upgrades from nanometer to centimeter scales, and in-situ environmental data correction further improves measurement accuracy. This method enables high-precision measurement of rock elastic parameters in-situ in deep reservoirs, providing strong technical support for deep resource development.

[0104] Through the above experiments, it is confirmed that the measurement method of the present invention can achieve the following effects: 4. High-precision in-situ measurement of the elastic mechanical parameters of deep reservoir rocks at the nanometer-centimeter scale has been achieved, filling the gap in existing technologies in this field.

[0105] 5. By combining molecular dynamics with macroscopic mechanical models, we have improved our understanding of the nature of rock microdeformation and provided new perspectives and methods for the development of rock mechanics theory.

[0106] 6. Provide strong technical support for the scientific understanding and safe and efficient development of deep geological resources, and promote the development of related industries.

[0107] 7. This method is highly innovative and practical, and can be widely used in the exploration and development of deep resources such as oil, natural gas, and coal, and has broad application prospects.

[0108] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A method for measuring cross-scale rock elastic parameters, characterized in that: The following steps are involved: Collect core samples from deep reservoirs and the environmental data of the core samples; Through nanoindentation experiments, the microscopic elastic mechanical parameters and microscopic elastic-plastic deformation of the core samples at the nanoscale are obtained to construct a molecular dynamics model of the core samples; Based on the molecular dynamics model of the core sample, the inclusion homogenization theory is used to predict the macroscopic equivalent mechanical parameters of the core sample's microscopic elastic mechanical parameters at the nanoscale, and the rock elastic mechanical parameters of the core sample at the centimeter scale are obtained to construct a rock elastic mechanical parameter conversion model; Test the rock elasticity parameters of the molecular dynamics model of the core sample under the influence of different environmental data; based on the rock elasticity parameters, use the environmental data of the core sample to modify the rock elasticity parameter conversion model; The nanometer-scale rock elastic mechanical parameters are input into the modified rock elastic mechanical parameter conversion model to obtain the centimeter-scale rock elastic mechanical parameters.

2. The method for measuring cross-scale rock elastic parameters according to claim 1, characterized in that: The method of using the inclusion homogenization theory to predict the macroscopic equivalent mechanical parameters of the core sample's microscopic elastic mechanical parameters at the nanoscale to obtain the core sample's rock elastic mechanical parameters at the centimeter scale specifically comprises the following steps: X-ray diffraction, scanning electron microscopy, energy spectrum analysis, and atomic force microscopy were performed on the core samples used in the nanoindentation experiments to obtain the mineral conformation and microstructure of the core samples at the nanoscale. MATLAB was used to perform a three-dimensional numerical reconstruction of the core samples to obtain a multiphase medium mechanical model composed of different minerals and pores. According to the multiphase medium mechanics model, the core sample is microscopically considered to be a complex composed of multiple media such as quartz, feldspar, carbonate rock, clay, and porous media. Each medium is divided into high-strength phase, medium-strength phase, and low-strength phase according to the strength or hardness of each medium. The Mori-Tanaka model in the inclusion homogenization theory is used to calculate the equivalent mechanical parameters of the high-strength phase, medium-strength phase, and low-strength phase based on the data obtained from the nanoindentation experiment. The low-strength phase is used as the matrix, and the high-strength phase and the medium-strength phase are embedded in the low-strength phase as inclusion phases; The three-phase medium mechanics model consists of high-strength phase, medium-strength phase and low-strength phase; The three-phase medium mechanical model as a physical model is converted into an equivalent mechanical parameter model, wherein the conversion includes: According to the variational principle and constitutive equation, the stress field is asymptotically expanded to obtain the material constants of the equivalent core sample, and the stress and strain distributions at the nanometer and centimeter scales are obtained, completing the upgrading of the microscopic elastic mechanical parameters of the rock at the nanometer scale to the rock elastic mechanical parameters at the centimeter scale.

3. The method for measuring cross-scale rock elastic parameters according to claim 1, characterized in that: The method of using the environmental data of the core sample to correct the rock elasticity parameter conversion model specifically includes the following steps: Based on environmental data and the results of nanoindentation experiments, a molecular dynamics model of rocks under different temperatures and confining pressures was established; The velocity of the atoms in the isothermal layer is recalibrated at each fixed time step, and the displacement of mineral atoms at different indentation stages is recorded; The shear deformation of the core sample during the nanoindentation experiment was obtained through Von Mises stress analysis. The dislocation extraction algorithm was used to identify the dislocations of the atomic shear deformation, obtain the dislocation line length, and obtain the results of the effects of high temperature and high pressure on plastic deformation, phase transformation mechanism, and defect evolution. According to the nanoindentation experiment, the loading process, load holding process and unloading process are recorded to obtain the load-displacement-time curve; Based on the impact results and load-displacement-time curves, the microelastic modulus, creep compliance, and Poisson's ratio of the core samples in the nanoindentation test under high temperature and high pressure are obtained, and the changing trends of the microelastic modulus, creep compliance, and Poisson's ratio with increasing temperature and pressure are plotted; The process of pressing a centimeter-level indenter into rock is regarded as a closed thermodynamic system. Based on the surface contact properties and heat conduction theory, the density function and cumulative temperature rise distribution function of the rock are established. Apply the actual temperature and ground stress distribution in the environmental data to the homogenized rock model to obtain a finite element-discrete element numerical simulation model under multi-physics field coupling conditions; By considering the rock damage failure criterion DP to simulate the mechanical state of the indenter during rock crushing, the average stress-strain field of the centimeter-scale indentation process considering the influence of temperature and pressure is obtained. The rock elastic parameter conversion model is modified based on the average stress-strain field during the centimeter-level indentation process.

4. A cross-scale rock elastic parameters measurement system, characterized by: include: The sample acquisition module is used to collect core samples from deep reservoirs and the environmental data of the core samples; The parameter upgrade module is used to obtain the microscopic elastic parameters and microscopic elastic-plastic deformation of core samples at the nanoscale through nanoindentation experiments, thereby constructing a molecular dynamics model of the core samples. Based on the molecular dynamics model of the core samples, the inclusion homogenization theory is used to predict the macroscopic equivalent mechanical parameters of the microscopic elastic parameters of the core samples at the nanoscale, thereby obtaining the rock elastic parameters of the core samples at the centimeter scale and constructing a rock elastic parameter conversion model. The model correction module is used to test the rock elasticity parameters of the molecular dynamics model of the core sample under the influence of different environmental data; based on the rock elasticity parameters, the rock elasticity parameter conversion model is corrected using the environmental data of the core sample; The parameter measurement module is used to input the nanometer-scale rock elastic mechanical parameters into the modified rock elastic mechanical parameter conversion model to obtain the centimeter-scale rock elastic mechanical parameters.

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