A 3D printing core preparation method coupling discrete element simulation and mechanical experiment

Abstract

The application discloses a 3D printing core preparation method coupled with discrete element simulation and mechanical experiment, and the method comprises six steps of printing a core, soaking the core, constructing a model, first-time calibration of the model, second-time calibration of the model and formula fitting. Compared with the prior art, the 3D printing core preparation method coupled with discrete element simulation and mechanical experiment has the advantages that the preparation of 3D printing cores with different strengths is realized, the rock shortage in underground energy storage engineering rock mechanics experiments is avoided, and the requirements of rock mechanics experiments in underground energy storage engineering are met.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of rock mechanics, and particularly to a 3D printed core preparation method coupling discrete element simulation and mechanical experiment. BACKGROUND

[0002] Natural rock, as an opaque, heterogeneous and porous medium material, has very complex rock mechanics response characteristics. It is still difficult to accurately characterize its rock mechanics parameters and determine the mechanical failure mechanism during rock damage evolution. In-depth understanding of the mechanical damage characteristics of rock under different stress conditions helps to ensure the safe operation of underground gas storage and the stable development of geological resources. 3D printing technology has developed rapidly in recent years. It is based on a digital model and uses layer-by-layer printing and accumulation to produce objects. It has been applied in the fields of rock mechanics and geological engineering by scholars. Compared with traditional rock sample preparation, 3D printing technology can finely control the size of the rock, greatly shorten the sample preparation period, accurately control the amount of material, and reduce the manufacturing cost. 3D printed cores can be regarded as relatively homogeneous materials, avoiding the differences caused by the heterogeneity of natural rock mass. From the existing research, it can be found that 3D printed cores made of silica sand are closer to natural rock in terms of macroscopic physical and mechanical properties and microscopic structural characteristics. At the same time, 3D printed cores can well replace natural rock materials for rock mechanics property research in some aspects.

[0003] Numerical simulation technology is one of the important means to study the rock mechanics properties of oil and gas reservoirs. In recent years, with the rise of the development boom of unconventional resources, significant progress has been made in the study of the micro-fracture mechanism of depleted oil and gas reservoir rocks through numerical simulation technology. Numerical methods can visualize the stress field and strain field inside the rock, and intuitively display the structural changes of the rock. Existing rock mechanics research results mainly focus on the study of macro-fracture forms and macro-mechanical parameters of rock, ignoring the influence of the heterogeneity of rock internal particle size at the micro-scale on rock mechanics properties. The micro-mechanical failure mechanism of rock has not been well studied. At the micro-scale, rock is composed of particles of different sizes. Whether it is tensile failure or shear failure, the damage to the rock and the micro-cracks formed can be considered as the destruction of the bonding between the internal particles of the rock.

[0004] Therefore, how to provide a 3D printed core preparation method coupling discrete element simulation and mechanical experiment, so that it can link the simulation results with the experimental data, evaluate the influence of the particle micro-parameters and the inherent heterogeneity of the particles on the macro-mechanical properties of the rock, and realize the preparation of 3D printed cores with different strengths, is a technical problem that needs to be solved by those skilled in the art. SUMMARY

[0005] In view of the problems in the prior art, the technical problem to be solved by the present application is to provide a 3D printed core preparation method coupled with discrete element simulation and mechanical experiment, so that the simulation results and experimental data can be linked, the influence of the particle micro parameter and the particle inherent heterogeneity of the 3D printed core on the macro mechanical property of the rock can be evaluated, and the 3D printed cores with different strengths can be prepared.

[0006] To achieve the above-mentioned object, the present application provides a 3D printed core preparation method coupled with discrete element simulation and mechanical experiment, which comprises the following steps: printing a core: selecting 3D printed core raw materials, and obtaining a plurality of 3D printed cores through 3D printing; selecting a part of the 3D printed cores for macro mechanical parameter testing, and obtaining the macro mechanical parameters of the 3D printed cores; soaking the cores: soaking another part of the 3D printed cores in the printed cores in a binder, and obtaining 3D printed cores with different cycle saturation treatment times through different cycle saturation treatments; performing uniaxial compression tests on the obtained 3D printed cores with different cycle saturation treatment times, and obtaining the uniaxial compressive strength of the 3D printed cores with different cycle saturation treatment times; constructing a model: establishing a discrete element numerical simulation initial model of the simulated 3D printed core; first calibrating the model: calibrating the discrete element numerical simulation initial model by using the macro mechanical parameters of the 3D printed cores obtained from the printed cores, and obtaining a discrete element numerical simulation model of the simulated 3D printed core; second calibrating the model: calibrating the discrete element numerical simulation model of the 3D printed core by using the uniaxial compressive strength of the 3D printed cores with different cycle saturation treatment times, and obtaining discrete element numerical simulation models with different cycle saturation treatment times; formula fitting: combining the discrete element numerical simulation models with different cycle saturation treatment times and the uniaxial compressive strength corresponding to the cycle saturation treatment times, and fitting and regressing to obtain a functional relationship between the cycle saturation treatment times, the micro cohesion and the compressive strength; and preparing 3D printed cores with different strengths according to the functional relationship obtained by fitting and regressing.

[0007] In the first aspect, the raw materials of the 3D printed core have a determined particle size distribution; and the raw materials of the 3D printed core are quartz sand.

[0008] In the first aspect, the binder in the soaking core is a silica sol solution.

[0009] In the first aspect, the establishment of the discrete element numerical simulation initial model of the simulated 3D printed core specifically comprises: establishing the discrete element numerical simulation initial model of the simulated 3D printed core based on the parallel bond model in the discrete element numerical simulation software and in combination with the particle size distribution of the 3D printed core raw materials.

[0010] In the first aspect, the macroscopic mechanical parameters of the 3D printed core obtained by the printing core are used to calibrate the initial discrete element numerical simulation model, and an accurate discrete element numerical simulation model simulating the 3D printed core is obtained, specifically comprising: adjusting a variable related to the macroscopic mechanical parameters of the 3D printed core obtained by the printing core in the initial discrete element numerical simulation model, so that the error between the numerical value of the obtained initial discrete element numerical simulation model and the macroscopic mechanical parameters of the 3D printed core obtained by the printing core is not more than 1%, and an accurate discrete element numerical simulation model simulating the 3D printed core is obtained.

[0011] In the first aspect, the macroscopic mechanical parameters of the 3D printed core include Poisson's ratio, Young's modulus, cohesion, internal friction angle, and tensile strength.

[0012] In the first aspect, the uniaxial compressive strength of the 3D printed core obtained by different cycle saturation treatment times is used to calibrate the discrete element numerical simulation model of the 3D printed core, and a discrete element numerical simulation model with different cycle saturation treatment times is obtained, specifically comprising: adjusting the numerical value of the micro-cohesion in the discrete element numerical simulation model obtained by the first calibration model, so that the uniaxial compressive strength model value obtained has an error of not more than 1% with the uniaxial compressive strength of the 3D printed core with different cycle saturation treatment times, and a discrete element numerical simulation model with different cycle saturation treatment times is obtained.

[0013] In the first aspect, the function relationship of the regression fitting is Wherein, the a1, b1, c1 are empirical parameters determined by the 3D printed core raw materials and the binder; the y is the compressive strength, and the x is the cycle saturation treatment times.

[0014] Advantages:

[0015] The application discloses a 3D printing core preparation method combining discrete element simulation and mechanical experiment, which comprises the following steps: selecting 3D printing raw materials and determining the particle size distribution of the 3D printing raw materials; establishing a discrete element numerical simulation initial model for simulating the 3D printing core based on a parallel bond model in a discrete element numerical simulation software, and the establishment of the discrete element numerical simulation initial model for simulating the 3D printing core needs to be combined with the particle size distribution of the 3D printing raw materials; printing a plurality of 3D printing cores layer by layer through a 3D printer; selecting a part of the 3D printing cores to test the macro mechanical parameters of the 3D printing cores, and taking the obtained macro mechanical parameters as the calibration basis of the subsequent discrete element numerical simulation initial model for simulating the 3D printing core; immersing another part of the 3D printing cores in a binder, and performing cyclic saturation treatment for different times to change the cohesion between the particles of the raw materials in the 3D printing core and to enhance the compressive strength of the 3D printing core; performing uniaxial compression test on the 3D printing cores subjected to the cyclic saturation treatment for different times to obtain the compressive strength of the 3D printing cores subjected to the cyclic saturation treatment for different times, and taking the compressive strength as the calibration value of the subsequent discrete element numerical simulation model; the formula in the parallel bond model is related to the macro mechanical parameters of the 3D printing core, and by changing a data in the formula, the difference between the model value of the macro mechanical parameter and the actual test value of the macro mechanical parameter of the 3D printing core is less than 1%, so that the calibration of the discrete element numerical simulation initial model is achieved, and an accurate discrete element numerical simulation model for simulating the 3D printing core is obtained; the relationship between the micro cohesion, the cyclic saturation treatment times of the 3D printing core and the compressive strength is obtained, the compressive strength of the 3D printing core subjected to different cyclic saturation treatment times is known, and the relationship between the cyclic saturation treatment times and the compressive strength is obtained; in the obtained discrete element numerical simulation model, the micro cohesion and the compressive strength have a certain formula relationship, the model value of the compressive strength is obtained by changing the value of the micro cohesion, the actual test value of the compressive strength is compared, and the difference between the model value of the compressive strength and the actual test value of the compressive strength is not more than 1%, so that the discrete element numerical simulation model corresponding to the cyclic saturation times is obtained; the discrete element numerical simulation models with different cyclic saturation treatment times are obtained due to the cyclic saturation treatment for different times; and the function relationship between the cyclic saturation treatment times, the micro cohesion and the compressive strength is obtained by fitting regression through the discrete element numerical simulation models with different cyclic saturation treatment times and the uniaxial compressive strength corresponding to the cyclic saturation treatment times, so that in the process of preparing the 3D printing core with different strengths, the cyclic saturation times in the binder can be selected according to the compressive strength of the 3D printing core or the micro cohesion in the 3D printing core.Meanwhile, the required function relationship of the number of cyclic saturation treatment, the micro cohesion and the compressive strength can be obtained by adjusting the type of the 3D printed core raw material or the particle size distribution of the 3D printed core raw material or the type of the binder, so that the 3D printed core with different compressive strengths of different requirements can be obtained; since the rock sample needs to be destroyed in the laboratory experiment, the two factors of heterogeneity and destructive experiment are superimposed, which increases the uncertainty of the results, the 3D printed core preparation method coupling the discrete element simulation and the mechanical experiment can realize the preparation of the 3D printed core with different strengths through the experimental-DEM simulation joint framework, which can exclude the material heterogeneity, accurately simulate the rock damage and micro crack propagation process, and quantify the regulation effect of the post-processing process on the cohesion of the 3D printed core, so that the rock shortage in the rock mechanics experiment of the underground energy storage engineering can be avoided, and the requirements of the rock mechanics experiment in the underground energy storage engineering are met; in summary, the 3D printed core preparation method coupling the discrete element simulation and the mechanical experiment can correspond the essence of the mechanical controllability of the 3D printed core and the requirements of the formation rock experiment in the engineering site according to the influence of the mineral micro scale characteristics and the particle distribution on the macro mechanical characteristics of the 3D printed core through the experimental-digital elevation model multi-scale analysis, overcome the influence of the heterogeneity of the particle size in the rock on the mechanical properties of the rock, provide theoretical and technical support for the accurate preparation and engineering application of the 3D printed core, and realize the preparation of the 3D printed core with different strengths, which has a positive guiding significance for the application of the rock mechanics field in the underground energy storage. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments or the prior art, the drawings needed in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0017] Figure 1 is a flow chart of the 3D printed core preparation method coupling the discrete element simulation and the mechanical experiment of the present application;

[0018] Figure 2 is the particle size distribution of the raw material quartz sand of the 3D printed core in example 1;

[0019] Figure 3 is the uniaxial compressive strength of the 3D printed core obtained by 0, 1, 2, 3 and 5 times of cyclic saturation treatment in example 1;

[0020] Figure 4 is the initial discrete element numerical simulation model of the simulated 3D printed core in example 1;

[0021] Figure 5 It is the functional relationship between the number of cyclic saturation treatments, micro-cohesion, and compressive strength obtained from the fitted regression in Example 1. Detailed Implementation

[0022] The technical solutions in the embodiments of this specification will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this specification, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments in this specification are within the scope of protection of this invention.

[0023] Example 1

[0024] like Figure 1 As shown in the figure, this embodiment provides a method for preparing 3D printed rock cores by coupling discrete element simulation and mechanical experiment. The method includes: printing rock cores: selecting 3D printed rock core raw materials and obtaining several 3D printed rock cores through 3D printing; selecting a portion of the 3D printed rock cores for macroscopic mechanical parameter testing to obtain the macroscopic mechanical parameters of the 3D printed rock cores; soaking the rock cores: soaking another portion of the 3D printed rock cores in a binder and performing different cycles of saturation treatment to obtain 3D printed rock cores with different cycles of saturation treatment; performing uniaxial compression tests on the 3D printed rock cores with different cycles of saturation treatment to obtain the uniaxial compressive strength of the 3D printed rock cores with different cycles of saturation treatment; and building a model: establishing a preliminary discrete element numerical simulation model for simulating 3D printed rock cores. First model calibration: The initial discrete element numerical simulation model is calibrated using the macroscopic mechanical parameters of the 3D printed rock core obtained from the printed rock core, thus obtaining an accurate discrete element numerical simulation model for simulating the 3D printed rock core. Second model calibration: The discrete element numerical simulation model of the 3D printed rock core is calibrated using the uniaxial compressive strength of the 3D printed rock core obtained after different cycles of saturation treatment, thus obtaining discrete element numerical simulation models with different cycles of saturation treatment. Formula fitting: Combining the discrete element numerical simulation models with different cycles of saturation treatment and the corresponding uniaxial compressive strength after different cycles of saturation treatment, a regression fitting is performed to obtain the functional relationship between the number of cycles of saturation treatment, microscopic cohesion, and compressive strength. Based on the fitted regression functional relationship, 3D printed rock cores with different strengths are prepared.

[0025] The application discloses a 3D printing core preparation method combining discrete element simulation and mechanical experiment, which comprises the following steps: selecting 3D printing raw materials and determining the particle size distribution of the 3D printing raw materials; establishing a discrete element numerical simulation initial model for simulating the 3D printing core based on a parallel bond model in a discrete element numerical simulation software, and the establishment of the discrete element numerical simulation initial model for simulating the 3D printing core needs to be combined with the particle size distribution of the 3D printing raw materials; printing a plurality of 3D printing cores layer by layer through a 3D printer; selecting a part of the 3D printing cores to test the macro mechanical parameters of the 3D printing cores, and taking the obtained macro mechanical parameters as the calibration basis of the subsequent discrete element numerical simulation initial model for simulating the 3D printing core; immersing another part of the 3D printing cores in a binder, and performing cyclic saturation treatment for different times to change the cohesion between the particles of the raw materials in the 3D printing core and to enhance the compressive strength of the 3D printing core; performing uniaxial compression test on the 3D printing cores subjected to the cyclic saturation treatment for different times to obtain the compressive strength of the 3D printing cores subjected to the cyclic saturation treatment for different times, and taking the compressive strength as the calibration value of the subsequent discrete element numerical simulation model; the formula in the parallel bond model is related to the macro mechanical parameters of the 3D printing core, and by changing a data in the formula, the difference between the model value of the macro mechanical parameter and the actual test value of the macro mechanical parameter of the 3D printing core is less than 1%, so that the calibration of the discrete element numerical simulation initial model is achieved, and an accurate discrete element numerical simulation model for simulating the 3D printing core is obtained; the relationship between the micro cohesion, the cyclic saturation treatment times of the 3D printing core and the compressive strength is obtained, the compressive strength of the 3D printing core subjected to different cyclic saturation treatment times is known, and the relationship between the cyclic saturation treatment times and the compressive strength is obtained; in the obtained discrete element numerical simulation model, the micro cohesion and the compressive strength have a certain formula relationship, the model value of the compressive strength is obtained by changing the value of the micro cohesion, the actual test value of the compressive strength is compared, and the difference between the model value of the compressive strength and the actual test value of the compressive strength is not more than 1%, so that the discrete element numerical simulation model corresponding to the cyclic saturation times is obtained; the discrete element numerical simulation models with different cyclic saturation treatment times are obtained due to the cyclic saturation treatment for different times; and the function relationship between the cyclic saturation treatment times, the micro cohesion and the compressive strength is obtained by fitting regression through the discrete element numerical simulation models with different cyclic saturation treatment times and the uniaxial compressive strength corresponding to the cyclic saturation treatment times, so that in the process of preparing the 3D printing core with different strengths, the cyclic saturation times in the binder can be selected according to the compressive strength of the 3D printing core or the micro cohesion in the 3D printing core.Meanwhile, the required cyclic saturation processing times, the function relationship of the micro-agglomerative force and the compressive strength can be obtained by adjusting the type of the 3D printed core raw material or the particle size distribution of the 3D printed core raw material or the type of the binder, so that the 3D printed core with different compressive strength can be obtained according to different requirements. Since the rock sample needs to be destroyed in the laboratory experiment, the two factors of heterogeneity and destructive experiment are superimposed, which increases the uncertainty of the results. The 3D printed core preparation method coupling the discrete element simulation and the mechanical experiment can realize the preparation of the 3D printed core with different strength through the experimental-DEM simulation joint framework, which can exclude the material heterogeneity, accurately simulate the rock damage and micro-crack propagation process, and quantify the regulation effect of the post-processing technology on the cohesion of the 3D printed core, so that the rock shortage in the rock mechanics experiment of the underground energy storage engineering can be avoided, and the requirements of the rock mechanics experiment in the underground energy storage engineering can be met. The 3D printed core preparation method coupling the discrete element simulation and the mechanical experiment can correspond the essence of the mechanical controllability of the 3D printed core to the requirements of the formation rock experiment on the engineering site according to the influence of the mineral micro-scale characteristics and the particle distribution on the macro-mechanical characteristics of the 3D printed core, and the 3D printed core preparation and engineering application can be provided with theoretical and technical support by the multi-scale analysis of the experimental-digital elevation model, which has a positive guiding significance for the application of the rock mechanics field in the underground energy storage.

[0026] In some possible implementations, the 3D printed core has a determined particle size distribution, and the raw material of the 3D printed core is quartz sand.

[0027] Specifically, the present application is mainly used for studying the influence of the non-homogeneity of the internal particle size of the rock at the micro-scale on the mechanical properties of the rock, and the 3D printed core raw material with different particle size distribution is required. The quartz sand has high temperature resistance and stable chemical properties, and belongs to a better 3D printed core raw material. The raw material of the 3D printed core can be selected and adjusted according to the performance of the actual rock in the underground energy storage engineering.

[0028] In some possible implementations, the binder in the soaked core is a silica sol solution.

[0029] Specifically, in the soaking process, the silica sol solution can penetrate into the interior of the 3D printed core, act on the micro-particles and strengthen the micro-agglomerative force between the micro-particles, so as to improve the compressive strength of the 3D printed core. The binder can be selected and adjusted according to the actual requirements.

[0030] In some possible implementation manners, the establishing the discrete element numerical simulation initial model of the simulated 3D printed core specifically comprises: establishing the discrete element numerical simulation initial model of the simulated 3D printed core based on a parallel bond model in discrete element numerical simulation software, and in combination with the particle size distribution of the 3D printed core raw material.

[0031] Specifically, the discrete element numerical simulation initial model of the simulated 3D printed core is constructed based on a known parallel bond model, and after the particle size distribution of the 3D printed core raw material is input, the discrete element numerical simulation initial model also needs to be calibrated according to the actual macroscopic mechanical parameters of the 3D printed core.

[0032] In some possible implementation manners, the calibrating the discrete element numerical simulation initial model by the macroscopic mechanical parameters of the 3D printed core obtained from the printed core to obtain the discrete element numerical simulation model accurately simulating the 3D printed core specifically comprises: adjusting a variable in the discrete element numerical simulation initial model related to the macroscopic mechanical parameters of the 3D printed core obtained from the printed core, so that the error between the model value of the discrete element numerical simulation initial model obtained and the macroscopic mechanical parameters of the 3D printed core obtained from the printed core is not more than 1%, and obtaining the discrete element numerical simulation model accurately simulating the 3D printed core; the macroscopic mechanical parameters of the 3D printed core include Poisson's ratio, Young's modulus, cohesion, internal friction angle, and tensile strength.

[0033] Specifically, the discrete element numerical simulation model obtained after calibration by the macroscopic mechanical parameters of the 3D printed core can more accurately simulate the macroscopic performance of the 3D printed core.

[0034] In some possible implementation manners, the calibrating the discrete element numerical simulation model of the 3D printed core by the uniaxial compressive strength of the 3D printed core obtained in different numbers of cyclic saturation treatments to obtain discrete element numerical simulation models with different numbers of cyclic saturation treatments specifically comprises: adjusting the value of the micro-cohesion in the discrete element numerical simulation model obtained in the first calibration model, so that the uniaxial compressive strength model value obtained has an error of not more than 1% with the uniaxial compressive strength of the 3D printed core in different numbers of cyclic saturation treatments, and obtaining the discrete element numerical simulation model with different numbers of cyclic saturation treatments.

[0035] Specifically, the micro-agglomerating force reflects the bonding between the particles of the 3D printed core with internal particle heterogeneity at the micro scale; in the first calibration of the discrete element numerical simulation model, the micro-agglomerating force has a certain formula relationship with the compressive strength, and the compressive strength of the 3D printed core with different cyclic saturation treatment times is known, the compressive strength value obtained by actual test under different cyclic saturation times is calibrated, and the discrete element numerical simulation model under different cyclic saturation times is obtained, and the agglomerating force value in the discrete element numerical simulation model under different cyclic saturation times corresponds to the compressive strength under different cyclic saturation times.

[0036] In some possible implementations, the function relationship of the fitted regression is y = a1x2+ b1x + c1, wherein the a1, b1, and c1 are empirical parameters determined by the 3D printed core raw material and the binder; the y is the compressive strength, and the x is the cyclic saturation treatment times.

[0037] Specifically, the function relationship of the cyclic saturation treatment times, the micro-agglomerating force, and the compressive strength is obtained by fitting and regression through the discrete element numerical simulation models with different cyclic saturation treatment times and the uniaxial compressive strength corresponding to the cyclic saturation treatment times, and the micro-agglomerating force has a certain function formula relationship with the compressive strength, so that in the process of preparing the 3D printed core with different strengths, the cyclic saturation times in the binder can be selected according to the compressive strength of the 3D printed core obtained as needed or the micro-agglomerating force inside the 3D printed core, so that the 3D printed core with different compressive strengths is obtained through 3D printing.

[0038] In order to further illustrate the technical solutions of the present application and support the technical problems to be solved by the present application, specific example explanations are given below, such as Example 1.

[0039] Example 1

[0040] A 3D printed core preparation method coupling discrete element simulation and mechanical experiment, the 3D printed core preparation method coupling discrete element simulation and mechanical experiment comprises:

[0041] Printed core: select quartz sand as the 3D printed core raw material, the particle size distribution of the quartz sand is as shown in Figure 2 ; set the 25mm x 50mm standard core size to be printed layer by layer by a 3D printer to obtain a plurality of 3D printed cores; select a part of the 3D printed cores for macro mechanical parameter test to obtain the macro mechanical parameters of the 3D printed cores, the macro mechanical parameters of the 3D printed cores including Poisson's ratio, Young's modulus, cohesion, internal friction angle, and tensile strength;

[0042] Soaking core: soaking another part of the 3D printed core in the silica sol solution, and after 0, 1, 2, 3, 5 cycles of saturation treatment, 3D printed cores with different cycle saturation treatment times are obtained, and the 3D printed cores with 0, 1, 2, 3, 5 cycles of saturation treatment are respectively subjected to uniaxial compression test, and the uniaxial compressive strength of the 3D printed cores with 0, 1, 2, 3, 5 cycles of saturation treatment is obtained, and the uniaxial compressive strength obtained is as shown in Figure 3 ;

[0043] Model building: based on the parallel bonding model in the discrete element numerical simulation software, and combined with the particle size distribution of the raw material of the 3D printed core, a discrete element numerical simulation initial model of the 3D printed core is established, as shown in Figure 4 ; Figure 4 It can be seen that the particle size of the particles in the model is heterogeneous;

[0044] First calibration model: by adjusting a variable in the discrete element numerical simulation initial model related to the macroscopic mechanical parameters of the 3D printed core obtained in the printed core, the error between the model value of the discrete element numerical simulation initial model obtained and the macroscopic mechanical parameters of the 3D printed core obtained in the printed core is not more than 1%, and an accurate discrete element numerical simulation model of the 3D printed core is obtained;

[0045] Second calibration model: by adjusting the value of the micro-agglomeration force in the discrete element numerical simulation model obtained in the first calibration model, the uniaxial compressive strength model value with an error of not more than 1% to the uniaxial compressive strength of the 3D printed core with 0, 1, 2, 3, 5 cycles of saturation treatment is obtained, and a discrete element numerical simulation model with different cycle saturation treatment times is obtained;

[0046] Formula fitting: combined with the discrete element numerical simulation model with different cycle saturation treatment times and the corresponding uniaxial compressive strength of the cycle saturation treatment, a function relationship formula of the cycle saturation treatment, the micro-agglomeration force and the compressive strength is obtained by regression fitting, , wherein the a1, b1, c1 are empirical parameters determined by the 3D printed core raw material and the binder; the y is the compressive strength, and the x is the cycle saturation treatment; the function relationship formula of the regression fitting is as shown in Figure 5 ; according to the function relationship formula of the regression fitting, 3D printed cores with different strengths are prepared.

[0047] The preferred embodiments of the present application have been described above in detail. It should be understood that modifications and variations to the preferred embodiments could be made by those skilled in the art in light of the teachings above. It is therefore contemplated that the application can encompass other variations and modifications that fall within the scope of the claims.

Claims

1. A method for preparing 3D-printed rock cores by coupling discrete element simulation and mechanical experiment, characterized in that, The method for preparing 3D-printed rock cores that couples discrete element simulation with mechanical experiments includes: Printed rock core: Select 3D printing rock core raw materials and obtain several 3D printed rock cores through 3D printing; select a portion of the 3D printed rock cores for macroscopic mechanical parameter testing to obtain the macroscopic mechanical parameters of the 3D printed rock cores; Immersing the core: Immerse another part of the 3D printed core in the binder and perform different cycles of saturation treatment to obtain 3D printed cores with different cycles of saturation treatment. Perform uniaxial compression tests on the 3D printed cores with different cycles of saturation treatment to obtain the uniaxial compressive strength of the 3D printed cores with different cycles of saturation treatment. Model building: Establishing an initial discrete element numerical simulation model for 3D printed rock cores; First model calibration: The initial discrete element numerical simulation model is calibrated using the macroscopic mechanical parameters of the 3D printed rock core obtained from the printed rock core, so as to obtain an accurate discrete element numerical simulation model for simulating the 3D printed rock core. Second calibration model: The discrete element numerical simulation model of the 3D printed rock core is calibrated by obtaining the uniaxial compressive strength of the 3D printed rock core with different cycles of saturation treatment, and discrete element numerical simulation models with different cycles of saturation treatment are obtained. Formula fitting: By combining discrete element numerical simulation models with different cycles of saturation treatment and the corresponding uniaxial compressive strength for the number of cycles of saturation treatment, the functional relationship between the number of cycles of saturation treatment, micro-cohesion and compressive strength is obtained through fitting regression. Based on the fitted regression functional relationship, 3D printed rock cores with different strengths are prepared. The process of calibrating the initial discrete element numerical simulation model using the macroscopic mechanical parameters of the 3D printed rock core obtained from the printed rock core, and obtaining an accurate discrete element numerical simulation model for simulating the 3D printed rock core, specifically includes: adjusting a variable in the initial discrete element numerical simulation model that is related to the macroscopic mechanical parameters of the 3D printed rock core obtained from the printed rock core, so that the error between the model value of the initial discrete element numerical simulation model and the macroscopic mechanical parameters of the 3D printed rock core obtained from the printed rock core does not exceed 1%, thereby obtaining an accurate discrete element numerical simulation model for simulating the 3D printed rock core; The discrete element numerical simulation model of the 3D printed rock core is calibrated by obtaining the uniaxial compressive strength of the 3D printed rock core with different cycles of saturation treatment. Specifically, the discrete element numerical simulation model with different cycles of saturation treatment is obtained by adjusting the value of micro-cohesion in the discrete element numerical simulation model obtained in the first calibration model, and obtaining a uniaxial compressive strength model value with an error of no more than 1% compared with the uniaxial compressive strength of the 3D printed rock core with different cycles of saturation treatment. The functional relationship for fitting the regression is as follows: Wherein, a1, b1, and c1 are empirical parameters determined by the 3D printed core material and the binder; y is the compressive strength, and x is the number of cyclic saturation treatments.

2. The method for preparing 3D-printed rock cores by coupling discrete element simulation and mechanical experiment as described in claim 1, characterized in that: The raw material of the 3D printed rock core has a defined particle size distribution; the raw material of the 3D printed rock core is quartz sand.

3. The method for preparing 3D-printed rock cores by coupling discrete element simulation and mechanical experiment as described in claim 2, characterized in that: The binder in the soaked rock core is a silica sol solution.

4. The method for preparing 3D-printed rock cores by coupling discrete element simulation and mechanical experiment as described in claim 3, characterized in that, The establishment of the initial discrete element numerical simulation model for simulating 3D printed rock cores specifically includes: establishing the initial discrete element numerical simulation model for simulating 3D printed rock cores based on the parallel bonding model in the discrete element numerical simulation software and in combination with the particle size distribution of the raw materials of the 3D printed rock cores.

5. The method for preparing 3D-printed rock cores by coupling discrete element simulation and mechanical experiment as described in claim 4, characterized in that: The macroscopic mechanical parameters of the 3D printed core include Poisson's ratio, Young's modulus, cohesion, internal friction angle, and tensile strength.

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