A layered artificial rock sample and preparation method thereof

Abstract

The present invention discloses a layered artificial rock sample and a preparation method thereof. The preparation method comprises the following steps: testing and analyzing the downhole core rock of the reservoir to be studied to obtain the mineral composition and mechanical properties of the core rock; based on this, determining the ratio of the matrix mineral and the binder of the layered artificial rock sample; casting rock plates with different surface roughness; preparing layered rock samples containing bedding planes with different bonding strengths, and testing the mechanical properties of each bedding plane, selecting the bedding plane roughness closest to the downhole core rock; preparing the layered artificial rock sample according to the determined ratio of the matrix mineral and the binder and the bedding plane roughness. The present invention can prepare a layered artificial rock sample that can quantitatively characterize the mechanical properties of the bedding plane and effectively restore the mechanical characteristics of natural reservoir rocks. Using it in a hydraulic fracturing indoor experiment can improve the scientific nature of the experimental results and is conducive to revealing the hydraulic fracturing crack expansion mechanism.

Description

Technical Field

[0001] The invention relates to the field of oil and gas field reservoir fracturing transformation experiments, and in particular to a layered artificial rock sample and a preparation method thereof. Background Art

[0002] Shale oil is a type of petroleum stored in shale formations rich in organic matter and nano-scale pores. It has great development potential and is an important oil and gas replacement resource. However, shale oil reservoirs are generally dense and well-stratified. At this stage, hydraulic fracturing technology is needed to artificially transform the reservoirs, that is, to use hydraulic energy to generate hydraulic fractures in the reservoir and activate natural fractures to form a complex fracture network, thereby greatly increasing the oil leakage area of ​​the reservoir and realizing efficient and economical exploitation of shale oil.

[0003] At present, the efficient and economic development of shale oil faces a series of challenges. For example, due to the influence of the bedding of reservoir development, the extension distance of hydraulic fractures in the height direction is short, which significantly affects the single-well controlled reserves of oil wells. Therefore, clarifying the fracture extension mechanism during shale oil hydraulic fracturing and then optimizing the fracturing construction process is expected to increase the single-well controlled reserves of oil wells.

[0004] Scholars generally use numerical simulation and indoor experiments to conduct research on hydraulic fracturing crack expansion. In shale oil hydraulic fracturing indoor experiments, both natural rock samples and artificial rock samples can be used as research objects. Natural rock samples can be taken from the core rock at the bottom of the well, but they are generally used for quasi-triaxial fracturing indoor experiments due to the size of the wellbore. Natural rock samples used for true triaxial fracturing indoor experiments are usually taken from surface outcrops, and their burial conditions are quite different from the burial geological conditions of underground reservoir rocks, resulting in inconsistent mechanical properties between the two. In addition, natural rock samples are affected by weak surfaces such as bedding. Even if the rock samples are taken from the same location, there are certain differences between the processed rock samples, which increases the uncertainty of the experimental results.

[0005] Artificial rock samples effectively reduce the differences between experimental rock samples and can improve the repeatability of experimental results. The difficulty in preparing artificial rock samples that simulate natural shale oil reservoir rocks lies in how to reproduce the influence of bedding on the mechanical properties of homogeneous rock samples. This kind of artificial rock sample that takes into account the influence of bedding is generally called a layered artificial rock sample. At present, there are two main methods for preparing such artificial rock samples, namely, bonding different types of rock slabs with adhesives, and adding interlayer rock slabs when casting homogeneous samples. However, the layered artificial rock samples prepared by these methods can only qualitatively characterize the bonding strength of the bedding, and cannot restore the mechanical properties of natural reservoir rocks.

[0006] Therefore, it is necessary to propose a new method for preparing layered artificial rock samples that can quantitatively characterize the mechanical properties of the bedding and effectively restore the mechanical characteristics of natural reservoirs. Summary of the invention

[0007] The purpose of the present invention is to provide a layered artificial rock sample and a preparation method thereof. The present invention prepares a layered artificial rock sample that can quantitatively characterize the mechanical properties of the bedding and effectively restore the mechanical characteristics of natural reservoir rocks. The layered artificial rock sample is used in indoor hydraulic fracturing experiments to improve the scientific nature of the experimental results and is conducive to revealing the hydraulic fracturing crack expansion mechanism.

[0008] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0009] In one aspect, the present invention provides a method for preparing a layered artificial rock sample, comprising the following steps:

[0010] Test and analyze the downhole core rock of the reservoir to be studied to obtain the mineral composition and mechanical properties of the core rock;

[0011] Determining the ratio of matrix minerals and binders of the layered artificial rock sample based on the mineral composition and mechanical properties of the cored rock;

[0012] Casting rock slabs with different surface roughness using matrix minerals and binders according to the determined proportions;

[0013] The obtained rock slabs are used to prepare layered rock samples containing bedding planes with different cementation strengths, and the mechanical properties of each bedding plane are tested;

[0014] Based on the test results of mechanical properties of each bedding plane, the bedding plane roughness closest to the downhole core rock is selected;

[0015] The layered artificial rock sample is prepared according to the determined ratio of matrix mineral to binder and the roughness of the bedding surface.

[0016] According to the preparation method of the present invention, preferably, the testing and analysis of the downhole cored rocks of the reservoir to be studied includes: conducting XRD mineral composition testing on the downhole cored rocks of the reservoir to be studied to clarify the mineral composition of the rocks; conducting macroscopic and microscopic rock mechanics experiments to measure the tensile strength, compressive strength, shear strength, elastic modulus, Poisson's ratio and fracture toughness and other mechanical properties of the cored rocks.

[0017] According to the preparation method of the present invention, preferably, the process of determining the ratio of matrix mineral and binder of the layered artificial rock sample based on the mineral composition and mechanical properties of the cored rock comprises:

[0018] According to the mineral composition of the cored rock, determine the matrix mineral composition and proportion of the layered artificial rock sample, and select the appropriate cementing material;

[0019] After using a mold to cast the matrix minerals and binders in a certain ratio into a homogeneous artificial rock sample, macro and micro rock mechanics tests are carried out to obtain the rock mechanics parameters of the artificial rock sample; the rock mechanics parameters of the cored rock and the artificial rock sample are compared, and the ratio of the matrix minerals and binders of the artificial rock sample is adjusted based on the mineral composition of the cored rock until the rock mechanics parameters of the artificial rock sample meet the requirements.

[0020] Since the preparation process of artificial rock samples is different from the deposition process of actual formation rock minerals, there are differences in mineral distribution, pore structure and other characteristics between artificial rock samples and core rocks. The mechanical properties of rock samples cast according to the mineral ratio of core rocks may be quite different from those of core rocks. Therefore, it is necessary to adjust the ratio of matrix minerals and cementing materials of artificial rock samples until the rock mechanics parameters of artificial rock samples meet the requirements.

[0021] According to the preparation method of the present invention, preferably, the rock mechanics parameters of the artificial rock sample meet the requirements, which means: its strength parameter is higher than the strength parameter of the cored rock, and the other rock mechanics parameters are the same as or basically consistent with the cored rock; the strength parameters include tensile strength, compressive strength and shear strength. More preferably, the strength parameter of the artificial rock sample is 20-30% higher than that of the cored rock, and the error of the other rock mechanics parameters with the cored rock is less than 20%.

[0022] During the adjustment process, the strength parameters of the artificial rock samples are higher than those of the cored rock. The reason is that when the bedding is subsequently formed in the artificial rock samples, the mechanical strength of the rock samples will decrease.

[0023] The properties of the rock samples of different layers of the layered artificial rock sample of the present invention may be consistent or may have great differences, which are reflected in the ratio of minerals and cements, and are all set based on actual formation conditions.

[0024] According to the preparation method of the present invention, preferably, the mineral composition and proportion of the matrix mineral of the layered artificial rock sample are set according to the mineral composition of the cored rock, and in order to reduce the difficulty of the experiment, the mineral composition with a mineral content of less than 10% in the cored rock is ignored; the matrix mineral includes quartz, feldspar, dolomite and kaolinite. In order to simplify the experiment, the matrix mineral uses cheap materials such as quartz sand of different mesh sizes to replace different minerals, and the binder is a cement slurry made by mixing cement and water.

[0025] According to the preparation method of the present invention, preferably, the process of casting rock slabs with different surface roughnesses using matrix minerals and binders according to the determined ratio includes:

[0026] Between two partitions with a certain surface roughness, a mixture of a determined matrix mineral and a binder according to a determined ratio is used to cast a rock slab with a certain surface roughness on both sides;

[0027] Similarly, rock slabs with different surface roughnesses are prepared using partitions with different surface roughnesses.

[0028] Processing partitions with different surface roughness, casting rock slabs with different surface roughness, realizing the strength of the bonding between the rock slab and the mixture, thereby simulating the bonding strength of different layers of the stratum. In order to simulate weak bonding, the partitions with smooth surfaces can also be processed to make the surface of the rock slab smooth.

[0029] Specifically, a first mold is used here, and the two opposite inner surfaces of the first mold are provided with grooves for inserting and installing the partitions. Furthermore, the grooves are evenly spaced at a certain distance, so that the installation positions of adjacent partitions can be adjusted to prepare rock slabs of different thicknesses, which can simulate the different layer heights of natural rock samples. As mentioned above, two partitions with a certain surface roughness are inserted into the grooves, and a rock slab is cast between the two partitions. It is understood by those skilled in the art that after the casting is completed, the rock slab is obtained by compacting it, and after curing for 24 hours, the mold is removed to obtain the rock slab. Unless otherwise specified, the casting described in the present invention includes the steps of compaction, curing and demolding.

[0030] According to the preparation method of the present invention, preferably, the process of using the obtained rock slabs to prepare layered rock samples containing bedding planes with different bonding strengths comprises:

[0031] The mixture is poured into a mold to a certain thickness, and after the surface is vibrated and compacted, a rock plate with a certain surface roughness is placed therein so that it is in full contact with the surface of the lower layer; a certain pressure is applied to the rock plate to simulate the compaction effect from above when pouring the experimental rock sample; the mold is disassembled to obtain a layered rock sample with a bedding plane having a certain bonding strength;

[0032] Similarly, rock plates with different surface roughness were used to prepare layered rock samples containing bedding planes with different cementation strengths;

[0033] Among them, the surface of the rock plate is the bedding plane in the layered artificial rock sample.

[0034] In the embodiment of the present invention, the mold used in this process is the second mold. In order to save costs and facilitate sampling, this process is completed when the pouring height is greater than 8 cm. The strength of the bonding between the rock slab and the mixture is achieved through the different surface roughness of the rock slab, thereby simulating the bonding strength of the bedding surface in the natural rock sample.

[0035] When preparing the rock samples for the bedding surface bonding strength test, considering the time and cost factors, the height of the rock samples did not reach the height of the rock samples cast in the indoor experiment. In order to simulate the compaction of the upper mixture and rock slab during the casting of the experimental rock samples, a certain weight of iron plate can be placed on the top of the rock samples during the setting to achieve the effect of applying a certain pressure. Similarly, the mold is removed after 24 hours of setting.

[0036] According to the preparation method of the present invention, preferably, the mechanical properties of each bedding plane tested include tensile strength, compressive strength, shear strength, elastic modulus, Poisson's ratio and fracture toughness.

[0037] According to the preparation method of the present invention, preferably, the process of preparing the layered artificial rock sample according to the determined ratio of matrix mineral to binder and the roughness of the bedding surface comprises:

[0038] Using the determined ratio of matrix mineral to binder and the partition corresponding to the determined bedding surface roughness, a plurality of rock plates having the determined surface roughness are prepared;

[0039] A mixture of matrix mineral and binder of a certain thickness is poured in the mold from bottom to top, and then the prepared rock slab is placed; finally, the mold is demoulded to obtain the layered artificial rock sample.

[0040] In the process of preparing the layered artificial rock sample of the present invention, the rock plate can not only be placed horizontally on the mixture, but also have an inclination angle of 0° to 45° with the horizontal direction according to the actual conditions of the stratum.

[0041] According to the preparation method of the present invention, preferably, the layered artificial rock sample includes a simulated wellbore; when casting the layered artificial rock sample, the simulated wellbore is preset in a mold, and if the simulated wellbore passes through a rock plate, a hole having a diameter consistent with that of the simulated wellbore is drilled in advance at a corresponding position of the rock plate.

[0042] According to the preparation method of the present invention, preferably, the well type of the simulated wellbore is a vertical well, a radial horizontal well or a horizontal well.

[0043] According to the preparation method of the present invention, preferably, when the well type of the simulated wellbore is a vertical well, the wellbore is placed vertically; when the well type of the simulated wellbore is a radial horizontal well, the main wellbore is first placed vertically, and when the mixture is close to the height of the radial horizontal well position, the radial horizontal wellbore is installed through the threads on the main wellbore to avoid the inability to place the interlayer rock plate; when the simulated wellbore is a horizontal well, the horizontal wellbore is placed horizontally.

[0044] The present invention can prepare layered artificial rock samples that can quantitatively characterize the mechanical properties of bedding planes and effectively restore the mechanical characteristics of natural reservoir rocks. Using them in indoor hydraulic fracturing experiments can improve the scientific nature of the experimental results and help reveal the hydraulic fracturing crack expansion mechanism.

[0045] Another aspect of the present invention provides a layered artificial rock sample obtained by the above preparation method.

[0046] The present invention is based on the mineral composition of the real downhole core of the stratum to be studied, and uses real mineral particles to cast rock samples; at the same time, by changing the surface roughness of the rock plate to quantitatively characterize the bonding strength of the interface, on the one hand, it can simulate the real stratum sedimentation conditions, and on the other hand, by simulating the layered rock samples with different bonding strengths between strata through the roughness of the rock plate surface, and using the standard rock samples obtained after the casting to compare with the real core, finally determine the bonding strength of the bedding surface that meets the real downhole core. The present invention provides a method for preparing a layered artificial rock sample that meets the actual conditions of the stratum, which is of great significance for the indoor experimental research of hydraulic fracturing of layered reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 Flow chart of a method for preparing a layered artificial rock sample in an embodiment.

[0048] Figure 2 It is a schematic vertical cross-sectional view of the first mold in the embodiment.

[0049] Figure 3 It is a top view of the first mold in the embodiment.

[0050] Figure 4 It is a schematic vertical cross-sectional view of the second mold in the embodiment.

[0051] Figure 5 It is a schematic vertical cross-sectional view of the third mold in the embodiment.

[0052] Figure 6 This is a schematic diagram of the vertical well layered rock sample after casting in the embodiment.

[0053] Figure 7 It is a schematic diagram after the radial horizontal well layered rock sample casting is completed in the embodiment.

[0054] Figure 8 This is a schematic diagram of the horizontal well layered rock sample after casting in the embodiment.

[0055] Description of reference numerals:

[0056] 1. Left wall of mold, 2. Right wall of mold, 3. Mold bottom plate, 4. Mold base, 5. Type I partition, 6. Type II partition, 7. Type III partition, 8. Hemispherical groove, 9. Front wall of mold, 10. Rear wall of mold, 11. Groove, 12-15. Type I partition, 16. Vertical wellbore, 17. Rock layer formed by later injection of mixture, 18. Rock slab cast in advance, 19. Bedding plane, 20. Radial horizontal wellbore, 21. Horizontal wellbore. DETAILED DESCRIPTION

[0057] In order to explain the present invention more clearly, the present invention is further described below in conjunction with preferred embodiments. It should be understood by those skilled in the art that the following specific description is illustrative rather than restrictive, and should not be used to limit the scope of protection of the present invention.

[0058] In order to prepare layered artificial rock samples that meet the actual conditions of the formation and apply them to indoor experiments of hydraulic fracturing of layered reservoirs, thereby further improving the accuracy of the test results, the present invention proposes a method for preparing layered artificial rock samples for indoor experiments of hydraulic fracturing, such as Figure 1 As shown, the preparation method comprises the following steps:

[0059] S101: Test and analyze the downhole core rock of the reservoir to be studied to obtain the mineral composition and mechanical properties of the core rock; specifically:

[0060] Select downhole core samples from the reservoir to be studied to carry out XRD mineral composition testing to clarify the mineral composition of the rock; carry out macro and micro rock mechanics experiments to measure the tensile strength, compressive strength, shear strength, elastic modulus, Poisson's ratio and fracture toughness and other mechanical properties of the core samples.

[0061] S102: Determine the ratio of matrix minerals and binders of the layered artificial rock sample based on the mineral composition and mechanical properties of the cored rock; specifically:

[0062] According to the mineral composition of the cored rock, the matrix mineral composition and proportion of the artificial rock sample are determined, and a suitable binder is selected. For the sake of brief description, the matrix mineral in this embodiment is selected from quartz sand of different mesh sizes, and the binder is selected from cement slurry made by mixing cement and water.

[0063] Using a mold, quartz sand of different mesh sizes, cement and water are cast in a certain ratio into a homogeneous artificial rock sample, and then macro and micro rock mechanics tests are carried out to obtain the rock mechanics parameters of the artificial rock sample; the rock mechanics parameters of the cored rock and the artificial rock sample are compared, and the contents of quartz sand of different mesh sizes, cement and water in the artificial rock sample are adjusted based on the mineral composition of the cored rock sample until the strength parameter of the artificial rock sample is 20-30% higher than that of the cored rock, and the errors of the remaining rock mechanics parameters are less than 20%; the strength parameters include tensile strength, compressive strength and shear strength.

[0064] It should be noted that the strength parameters of artificial rock samples need to be higher than those of cored rock samples because the mechanical strength of the rock samples will decrease when stratification is subsequently formed in the artificial rock samples.

[0065] Preferably, the properties of rock samples in different layers of the layered artificial rock sample can be consistent or have significant differences, which are reflected in the ratio of minerals and cements, all of which are set based on actual formation conditions.

[0066] Preferably, the mineral ratio for preparing the artificial rock sample is set according to the mineral composition of the downhole core, and the minerals include but are not limited to quartz, feldspar, dolomite, kaolinite and other minerals; to reduce the difficulty of the experiment, the mineral components with a mineral content of less than 10% in the downhole core can be ignored; to simplify the experiment, cheap materials such as quartz sand of different mesh sizes can also be used instead of different minerals.

[0067] S103: Casting rock slabs with different surface roughness using matrix minerals and binders according to the determined proportions; specifically:

[0068] The partitions 5 (type I partition), 6 (type II partition), and 7 (type III partition) with a plurality of tiny hemispherical grooves 8 distributed on the machined surface are inserted and installed in the first mold (such as Figure 2 quartz sand of different mesh sizes, cement and water are mixed evenly according to the ratio determined in S102 to form cement mortar, which is poured between the partitions. After compaction, the upper surface is polished and smoothed. After 24 hours, the mold is disassembled and the rock slabs with different surface roughness are taken out. The surface of the rock slab can simulate the bedding surface 19 of the natural rock sample.

[0069] like Figure 3 As shown, the front wall 9 and the rear wall 10 of the first mold have multiple grooves 11 with an interval of 5 cm and a depth of 1 cm for installing partitions. Rock slabs of different thicknesses can be cast by changing the installation positions of adjacent partitions, and different layer heights of natural rock samples can be simulated. For example, a 5 cm thick rock slab can be cast between Type I partitions 12 and Type I partitions 13, and a 10 cm thick rock slab can be cast between Type I partitions 14 and Type I partitions 15.

[0070] Since a plurality of tiny hemispherical grooves 8 are distributed on the surface of the partition, after curing for 24 hours, the first mold can be disassembled to obtain a rock plate 18 with a thickness of 5 cm and different surface roughnesses, and the surface of the rock plate simulates the bedding plane 19 in the layered artificial rock sample.

[0071] Rock slabs with different surface roughness are prepared using partitions with different surface roughness.

[0072] The first mold used in this step is as follows Figure 2 and Figure 3 As shown, the mold includes a left wall 1, a right wall 2, a bottom plate 3, a base 4, a front wall 9, and a rear wall 10. Grooves 11 for inserting and installing partitions are provided on the front wall 9 and the rear wall 10. Different types of partitions have different surface roughness.

[0073] S104: using the obtained rock slabs to prepare layered rock samples containing bedding planes with different bonding strengths, and testing the mechanical properties of each bedding plane; specifically:

[0074] Pour cement mortar into the second mold (such as Figure 4 As shown in the figure, after reaching a height of 5 cm, the cement mortar surface was vibrated and compacted with a hammer, and then the prepared rock slab was placed, and the rock slab was lightly pressed with a hammer in multiple places to make it fully contact with the cement mortar surface below; an iron block was placed on the rock slab to simulate the compaction effect of the upper part when pouring the experimental rock sample. After 24 hours, the mold was disassembled to obtain a layered rock sample with a bedding plane with a certain bonding strength.

[0075] The rock plates with different surface roughness prepared by S103 were used to prepare layered rock samples with bedding planes of different bonding strengths. Macroscopic and microscopic rock mechanics tests were carried out to measure the mechanical properties of each rock sample, such as tensile strength, compressive strength, shear strength, elastic modulus, Poisson's ratio and fracture toughness. As a preferred method, the rock plate can not only be placed horizontally on the mixture, but also have an inclination of 0° to 45° with the horizontal direction according to the actual conditions of the stratum.

[0076] S105: Based on the test results of the mechanical properties of each bedding surface, the bedding surface roughness closest to the downhole core rock is selected; specifically:

[0077] The mechanical property test results of each bedding surface obtained in S103 are compared with the downhole core rock, and finally the bedding surface bonding strength that meets the downhole core rock is determined, that is, the surface roughness of the experimentally simulated layered artificial rock slab.

[0078] S106: preparing the layered artificial rock sample according to the determined ratio of matrix mineral to binder and the roughness of the bedding surface. Specifically:

[0079] Select a separator that meets the requirements, and use the method in S103 to prepare a 5 cm thick rock plate 18 with a specific surface roughness; pre-place a vertical wellbore 16 with a diameter of 3 cm in the third mold (such as Figure 5 As shown in S104, cement mortar is poured in; using the method in S104, cement mortar is poured in and rock slabs 18 are placed in sequence to prepare layered rock samples; the height of each cement mortar pouring is 2.5cm, 5cm, 5cm, 5cm, and 2.5cm respectively; it should be noted that if the vertical wellbore passes through the rock slab, a hole consistent with the diameter of the simulated wellbore needs to be drilled in the center of the rock slab with a drill bit in advance (a cylindrical hole with a diameter of 3cm in this embodiment). After 24 hours, demoulding is performed, and the layered artificial rock sample with a layer height of 2.5cm, 5cm, 5cm, 5cm, 5cm, 5cm, 5cm, and 2.5cm from top to bottom is completed, as shown in FIG. Figure 6 As shown, 18 is the rock plate poured in advance, 17 is the rock layer formed by pouring the mixture later, and 19 is the bedding plane. It should be noted that if the simulated wellbore passes through the rock plate, it is necessary to drill out in advance at the corresponding position of the rock plate.

[0080] The well type of the simulated wellbore can be a vertical well, a radial horizontal well and a horizontal well; when the well type of the simulated wellbore is a vertical well, the vertical wellbore 16 is placed vertically; when the well type of the simulated wellbore is a radial horizontal well, the main wellbore (vertical wellbore 16) is first placed vertically, and when the mixture is close to the height of the radial horizontal well position, the radial horizontal wellbore 20 is installed through the threads on the main wellbore to avoid the inability to place the interlayer rock plate. The obtained artificial rock sample is as follows Figure 7 When the simulated wellbore is a horizontal well, the horizontal wellbore 21 is placed horizontally, and the artificial rock sample is as shown in Figure 8 shown.

[0081] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the protection scope of the present invention.

Claims

1. A method for preparing a layered artificial rock sample, characterized in that: The preparation method comprises the following steps: Test and analyze the downhole core rock of the reservoir to be studied to obtain the mineral composition and mechanical properties of the core rock; Determining the ratio of matrix minerals and binders of the layered artificial rock sample based on the mineral composition and mechanical properties of the cored rock; Casting rock slabs with different surface roughness using matrix minerals and binders according to the determined proportions; The obtained rock slabs are used to prepare layered rock samples containing bedding planes with different cementation strengths, and the mechanical properties of each bedding plane are tested; Based on the test results of mechanical properties of each bedding plane, the bedding plane roughness closest to the downhole core rock is selected; The layered artificial rock sample is prepared according to the determined ratio of matrix mineral to binder and the roughness of bedding surface; The process of using the obtained rock slabs to prepare layered rock samples containing bedding planes with different bonding strengths comprises: The mixture is poured into a mold to a certain thickness, and after the surface is vibrated and compacted, a rock plate with a certain surface roughness is placed to make it fully contact with the lower surface; a certain pressure is applied to the rock plate to simulate the compaction effect from above when pouring the experimental rock sample; the mold is disassembled to obtain a layered rock sample with a bedding plane with a certain bonding strength; Similarly, rock plates with different surface roughness were used to prepare layered rock samples containing bedding planes with different cementation strengths; Among them, the surface of the rock slab is the bedding plane in the layered artificial rock sample; through the different surface roughness of the rock slab, the strength of the bonding between the rock slab and the mixture is achieved, thereby simulating the bonding strength of the bedding plane in the natural rock sample.

2. The preparation method according to claim 1, characterized in that: The testing and analysis of the downhole cored rocks of the reservoir to be studied includes: conducting XRD mineral composition testing on the downhole cored rocks of the reservoir to be studied to clarify the mineral composition of the rocks; conducting macroscopic and microscopic rock mechanics experiments to measure the tensile strength, compressive strength, shear strength, elastic modulus, Poisson's ratio and fracture toughness of the cored rocks.

3. The preparation method according to claim 1, characterized in that: The process of determining the ratio of matrix minerals and binders of the layered artificial rock sample based on the mineral composition and mechanical properties of the cored rock comprises: According to the mineral composition of the cored rock, determine the matrix mineral composition and proportion of the layered artificial rock sample, and select the appropriate cementing material; After using a mold to cast the matrix minerals and binders in a certain ratio into a homogeneous artificial rock sample, macro and micro rock mechanics tests are carried out to obtain the rock mechanics parameters of the artificial rock sample; the rock mechanics parameters of the cored rock and the artificial rock sample are compared, and the ratio of the matrix minerals and binders of the artificial rock sample is adjusted based on the mineral composition of the cored rock until the rock mechanics parameters of the artificial rock sample meet the requirements.

4. The preparation method according to claim 3, characterized in that: The rock mechanics parameters of the artificial rock sample meet the requirements if: its strength parameter is higher than the strength parameter of the cored rock, and the other rock mechanics parameters are the same as or basically consistent with those of the cored rock; the strength parameters include tensile strength, compressive strength and shear strength.

5. The preparation method according to claim 4, characterized in that: The strength parameter of the artificial rock sample is 20-30% higher than that of the cored rock, and the error between the remaining rock mechanical parameters and the cored rock is less than 20%.

6. The preparation method according to claim 1, characterized in that: The mineral composition and proportion of the matrix minerals of the layered artificial rock sample are set according to the mineral composition of the cored rock, and the mineral components with a mineral content of less than 10% in the cored rock are ignored; the matrix minerals include quartz, feldspar, dolomite and kaolinite.

7. The preparation method according to claim 1, characterized in that: The matrix mineral is selected from quartz sand of different mesh sizes, and the binder is selected from cement slurry prepared by mixing cement and water.

8. The preparation method according to claim 1, characterized in that: The process of casting rock slabs with different surface roughnesses using matrix minerals and binders according to a determined ratio includes: Between two partitions with a certain surface roughness, a mixture of matrix mineral and binder according to a determined ratio is used to cast a rock slab with a certain surface roughness on both sides; Similarly, rock slabs with different surface roughnesses are prepared using partitions with different surface roughnesses.

9. The preparation method according to claim 8, characterized in that: The mechanical properties of each bedding plane tested include tensile strength, compressive strength, shear strength, elastic modulus, Poisson's ratio and fracture toughness.

10. The preparation method according to claim 1, characterized in that: The process of preparing the layered artificial rock sample according to the determined ratio of matrix mineral to binder and the roughness of bedding surface comprises: Using the determined ratio of matrix mineral to binder and the partition corresponding to the determined bedding surface roughness, a plurality of rock plates having the determined surface roughness are prepared; A mixture of matrix mineral and binder of a certain thickness is poured in the mold from bottom to top, and then the prepared rock slab is placed; finally, the mold is demoulded to obtain the layered artificial rock sample.

11. The preparation method according to claim 1 or 10, characterized in that: The layered artificial rock sample includes a simulated wellbore; when casting and preparing the layered artificial rock sample, the simulated wellbore is preset in a mold, and if the simulated wellbore passes through a rock plate, a hole having the same diameter as the simulated wellbore is drilled in advance at a corresponding position of the rock plate.

12. The preparation method according to claim 11, characterized in that: The well type of the simulated wellbore is a vertical well, a radial horizontal well or a horizontal well.

13. The preparation method according to claim 12, characterized in that: When the well type of the simulated wellbore is a vertical well, the wellbore is placed vertically; when the well type of the simulated wellbore is a radial horizontal well, the main wellbore is placed vertically first, and when the mixture is close to the height of the radial horizontal well position, the radial horizontal wellbore is installed through the threads on the main wellbore to avoid the inability to place the interlayer rock plate; when the simulated wellbore is a horizontal well, the horizontal wellbore is placed horizontally.

14. A layered artificial rock sample obtained by the preparation method according to any one of claims 1 to 13.

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