Experimental interbedded core and method of making

Abstract

The application provides an experimental interbedded core and a preparation method, and relates to the technical field of oil and gas exploration and development. The application comprises the following steps: obtaining a plurality of natural cores of interbedded rocks in a research block and logging data of a formation to be analyzed; numbering the plurality of natural cores and respectively testing second physical properties of the numbered natural cores; calculating second thicknesses of each layer in the experimental interbedded core; determining a target core with the highest similarity to the physical properties of each layer in the interbedded rock formation from the plurality of natural cores; cutting the target core according to the second thicknesses to obtain a core block with a corresponding thickness; and sequentially bonding the core block into an integrated body in the vertical order of the rock layers to obtain the experimental interbedded core. The experimental interbedded core prepared by the method of the application can truly reflect the interlayer mechanical differences of the formation to be analyzed, reduces the usage amount of natural cores, can carry out mechanical property experiments on any formation, improves the convenience of use, and reduces the experimental cost.

Description

Technical Field

[0001] This application relates to the field of oil and gas exploration and development technology, and in particular to an experimental interbedded rock core and its preparation method. Background Technology

[0002] As oil and gas exploration continues to expand into deeper and unconventional reservoirs, interbedded sandstone and shale have become important targets for oil and gas exploration. Their significant heterogeneity and complex mechanical response make fracturing and stimulation difficult, and there is an urgent need for high-fidelity experimental interbedded cores to accurately characterize their mechanical properties.

[0003] In existing technologies, artificial rock cores are typically prepared by mixing rock powder with a binder, layering and molding the mixture, pressing it into shape, and then drying it. While such methods can simulate single lithologies or simple combinations, they are difficult to accurately reproduce the precise lithological sequence, layer thickness ratio, and differences in physical properties found in naturally interbedded layers.

[0004] Therefore, existing methods cannot effectively construct experimental interbedded cores that are highly consistent with the target formation structure, which limits the reliability and applicability of fracturing simulation. Summary of the Invention

[0005] This application provides an experimental interbedded core and its preparation method. By extracting the vertical sequence, thickness and physical properties of the strata to be analyzed based on well logging data, a target core with matching physical properties is selected from a small number of monolithic natural cores. The cores are then cut according to a scaling ratio and bonded together in sequence to prepare a high-fidelity experimental interbedded core.

[0006] In a first aspect, this application provides a method for preparing interbedded core samples for experiments, the method comprising:

[0007] The study obtained multiple natural cores of interbedded rocks in the research block and well logging data of the strata to be analyzed. The natural cores were sandstone or shale cores of a single lithology. The well logging data included the vertical sequence of the strata to be analyzed, the first thickness of each layer in the downhole interbedded rocks, and the first physical properties of each layer.

[0008] Multiple natural rock cores were numbered, and the second physical properties of each numbered natural rock core were tested.

[0009] Based on the first thickness and the preset scaling ratio, calculate the second thickness of each corresponding layer in the interbedded core used in the experiment;

[0010] By comparing the similarity between the first physical property and the second physical property, the target core with the highest similarity to each layer of rock in the interbedded layer below the well is determined from multiple natural cores.

[0011] The target core is cut according to the second thickness to obtain core blocks of the corresponding thickness;

[0012] Following the vertical order of the rock strata, the core blocks were sequentially bonded together to obtain the interbedded core for the experiment.

[0013] In one possible design, both the first and second physical properties include at least one of density, porosity, and longitudinal wave time difference.

[0014] The similarity between the first and second physical properties was compared to identify the target cores from multiple natural cores that showed the highest similarity to each layer of rock in the interbedded formations below the well, including:

[0015] For any layer in the interbedded layers, traverse all numbered natural cores and calculate the difference index value between the corresponding first physical property and the second physical property of each numbered natural core.

[0016] The natural core with the smallest difference index value was selected as the target core.

[0017] In one possible design, the formula for calculating the difference index between the corresponding first physical property and the second physical property of each numbered natural core is as follows:

[0018]

[0019] Where S is the difference index value, Let be the density of the i-th layer in the underground interlayer, where i is an integer greater than or equal to 1. Let be the density of the j-th natural core sample, where j is an integer from 1 to X, and X is the total number of core samples. Let i be the porosity of the i-th layer in the downhole interlayer. Let J be the porosity of the j-th natural core sample. Let be the P-wave time difference of the i-th layer in the downhole interlayer. Let be the P-wave time difference of the j-th natural core sample.

[0020] In one possible design, the process of obtaining the density of the i-th layer in the downhole interlayer includes:

[0021] Obtain a density data sequence that varies with depth obtained from density logging. The density data sequence contains multiple first sampling points, each of which includes a first depth value and a corresponding density value.

[0022] Based on the first thickness of the i-th layer in the downhole interlayer, the first sampling points in the density data sequence located within the depth range of the i-th layer are divided into a first initial dataset;

[0023] The first sampling points in the first initial dataset are sorted in ascending order according to the first depth value, and the first sampling points within the preset length range of the top and bottom ends are removed;

[0024] Calculate the absolute value of the difference between the density values ​​of two adjacent first sampling points as the first difference. If the first difference is greater than the preset first threshold, then the first initial dataset is segmented at the corresponding depth position to obtain multiple consecutive first subsets.

[0025] Calculate the density mean for each first subset of data to obtain a set of first subset mean values; sort the set of first subset mean values ​​by numerical size and calculate their first overall mean.

[0026] Divide the first subset average into two sets of averages: the first set contains all first subset averages that are greater than the first total average, and the second set contains all first subset averages that are less than or equal to the first total average.

[0027] The density of the i-th layer is calculated based on the average value of the first subset of the first group and the average value of the first subset of the second group.

[0028] In one possible design, the formula for calculating the density of the i-th layer, based on the average value of the first subset of the first group and the average value of the first subset of the second group, is as follows:

[0029]

[0030] Where R is the number of average values ​​of the first subset in the first group. Let be the average of the r-th first subset in the first group, and T be the number of averages of the first subsets in the second group. Let be the average value of the t-th first subset in the second group.

[0031] In one possible design, the formula for calculating the porosity of the i-th layer in the downhole interlayer is:

[0032]

[0033] in, The preset rock skeleton density is the lithology corresponding to the i-th layer of rock. This is the preset pore fluid density of the formation fluid corresponding to the i-th layer.

[0034] In one possible design, the process of obtaining the P-wave time difference of the i-th layer in the downhole interlayer includes:

[0035] Acquire a depth-varying P-wave time difference data sequence obtained from acoustic logging. The P-wave time difference data sequence contains multiple second sampling points, each of which includes a second depth value and the corresponding P-wave time difference value.

[0036] Based on the first thickness of the i-th layer in the downhole interlayer, the second sampling points in the P-wave time difference data sequence located within the depth range of the i-th layer are divided into a second initial dataset;

[0037] The second sampling points in the second initial dataset are sorted in ascending order of their second depth values, and the second sampling points within the preset length range of their top and bottom ends are removed.

[0038] Calculate the absolute value of the difference between the P-wave time difference values ​​of two adjacent second sampling points as the second difference value. If the second difference value is greater than the preset second threshold, then the second initial dataset is segmented at the corresponding depth position to obtain multiple consecutive second subset datasets.

[0039] For each second subset of data, calculate the average P-wave time difference to obtain a set of second subset averages; sort the set of second subset averages by numerical value and calculate their second overall average;

[0040] Divide a set of second subset averages into two sets of averages: the first set contains all second subset averages that are greater than the second total average, and the second set contains all second subset averages that are less than or equal to the second total average.

[0041] The longitudinal wave time difference of the i-th layer is calculated based on the average value of the second subset of the first group and the average value of the second subset of the second group.

[0042] In one possible design, the formula for calculating the P-wave time difference of the i-th layer, based on the average value of the second subset of the first group and the average value of the second subset of the second group, is as follows:

[0043]

[0044] Where L is the number of values ​​representing the average of the second subset in the first group. Let K be the average of the l-th first subset in the first group, and K be the number of averages of the second subset in the second group. It is the average value of the kth second subset in the second group.

[0045] In one possible design, core blocks are sequentially bonded together according to the vertical order of the rock strata to obtain an interbedded core for experimentation, including:

[0046] Before bonding, the end faces of each core block that are used to contact each other are subjected to coarse grinding and fine grinding respectively to obtain a flat end face with a preset roughness.

[0047] Apply the adhesive evenly to the bonding surfaces of adjacent core blocks;

[0048] Following the vertical sequence of rock strata, core blocks coated with adhesive are stacked vertically to form a core column, and pressure is applied vertically, with the vertical direction simulating the sedimentary strata.

[0049] The core column is placed in a constant temperature environment at a preset temperature for a preset time to cure the adhesive completely, resulting in an experimental interlayered core with a complete structure.

[0050] Secondly, this application provides an experimental interbedded core, which is prepared using an experimental interbedded core preparation method according to the first aspect of the invention. It includes multiple core blocks that are sequentially bonded together according to the vertical order of the rock strata to be analyzed. Each core block is cut from natural sandstone or natural shale of a single lithology, and the lithology, vertical order, thickness and physical properties of each core block are respectively matched to the corresponding rock strata to be analyzed in the downhole.

[0051] Based on the implementation methods provided in the above aspects, this application can be further combined to provide more implementation methods.

[0052] This application provides an experimental interbedded core and its preparation method, comprising: First, acquiring multiple natural cores of interbedded rocks within a study block and well logging data of the formation to be analyzed. The natural cores are sandstone or shale cores of a single lithology. The well logging data includes the vertical sequence of the formation to be analyzed, the first thickness of each layer in the downhole interbedded core, and the first physical properties of each layer. Next, the multiple natural cores are numbered, and the second physical properties of each numbered natural core are tested. Then, based on the first thickness and a preset scaling ratio, the second thickness of each corresponding layer in the experimental interbedded core is calculated. Subsequently, the first physical properties and the second physical properties are compared for similarity, and the target core with the highest similarity to the physical properties of each layer in the downhole interbedded core is determined from the multiple natural cores. Then, the target core is cut according to the second thickness to obtain core blocks of the corresponding thickness. Finally, the core blocks are sequentially bonded together according to the vertical sequence of the strata to obtain the experimental interbedded core. The following technical effects were achieved: By strictly matching the vertical sequence, single-layer thickness, and primary physical properties of the interbedded rock formations in the well, the prepared interbedded cores for experiments closely approximate the real formation in terms of structural sequence and physical property distribution, significantly outperforming the homogenization or simplified simulation of traditional artificial cores (such as rock powder pressing), providing a more reliable physical model for fracturing mechanics experiments. Only a small amount of natural sandstone or shale cores of a single lithology are needed to assemble any complex interbedded sequence. This effectively avoids the limitations of scarce, high-cost, and uncontrollable layer thickness of natural interbedded cores, making it particularly suitable for scenarios where it is difficult to obtain complete cores, such as thin interbedded layers and deep reservoirs. It not only reduces the amount of natural cores used but also enables mechanical property experiments on any formation, improving ease of use and reducing experimental costs. Using well logging data as input, experimental interbedded cores can be flexibly constructed for different blocks, well sections, and strata without the need to re-proportion raw materials or adjust process parameters, greatly improving the universality and engineering applicability of the experiments. The core blocks used are derived from natural rocks, preserving the microstructure, pore network, mineral composition, and mechanical response characteristics of authentic sandstone / shale. This avoids the property distortions introduced by cementing agents and particle mixing in artificial cores, making the mechanical test results more geologically representative. The resulting interbedded cores can accurately reflect interlayer mechanical differences, stress shielding effects, and fracture cross-layer behavior. They can be directly used in key experiments such as hydraulic fracturing physical simulation, fracture pressure prediction, and fracture propagation path analysis, significantly improving the scientific rigor and success rate of fracturing design. Attached Figure Description

[0053] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0054] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0055] Figure 1 This is a schematic flowchart of a method for preparing interbedded core samples for experimental use, provided as an embodiment of this application. Detailed Implementation

[0056] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims.

[0057] In the embodiments of this application, the terms "first" and "second" are used to distinguish identical or similar items with substantially the same function and effect. Those skilled in the art will understand that the terms "first" and "second" do not limit the quantity or execution order, and that "first" and "second" do not necessarily imply difference. It should be noted that in the embodiments of this application, the words "exemplary" or "for example" are used to indicate that something is being used as an example, illustration, or description. Any embodiment or design scheme described as "exemplary" or "for example" in this application should not be construed as being better or more advantageous than other embodiments or design schemes. Specifically, the use of "exemplary" or "for example" is intended to present the relevant concepts in a concrete manner. In the embodiments of this application, "at least one" refers to one or more, and "more than one" refers to two or more.

[0058] It should be noted that the phrase "at...time" in the embodiments of this application can refer to the instant at which a certain situation occurs, or to a period of time after the occurrence of a certain situation; the embodiments of this application do not specifically limit this. Furthermore, the experimental interbedded core preparation method provided in the embodiments of this application is merely an example; an experimental interbedded core preparation method may include more or fewer elements.

[0059] As oil and gas exploration continues to expand into deeper and unconventional reservoirs, interbedded sandstone and shale formations have become important target formations for increasing oil and gas reserves and production due to their widespread distribution, favorable source-reservoir-seal combinations, and abundant shale gas / tight oil resources. However, these reservoirs are typically formed by alternating vertical deposition of sandstone and shale, exhibiting strong lithological heterogeneity, anisotropic mechanical properties, and complex stress transfer mechanisms. This leads to significant challenges during hydraulic fracturing, including unpredictable fracture propagation paths, difficulties in penetrating the layers, and limited stimulation volume. Therefore, there is an urgent need for experimental interbedded core samples that can accurately reflect the structural characteristics of subsurface interbedded formations to precisely characterize the mechanical response behavior of each individual layer and interlayer interfaces, providing a reliable basis for fracturing design and optimization.

[0060] In existing technologies, artificial cores are mostly prepared by mixing rock powders of different particle sizes (such as quartz sand, clay, shale powder, etc.) with a binder in a certain proportion, then layering them into a mold, applying pressure, and drying and solidifying them. Although this method has some effect in simulating homogeneous or weakly heterogeneous reservoirs, it is essentially a reconstructed artificial core, which is difficult to precisely control the clarity of lithological interfaces, the continuity of single-layer thickness, and the authenticity of the original pore structure and physical properties of the rock. More importantly, this method cannot dynamically adapt to the formation characteristics of different blocks and well sections. If a new interbedded sequence needs to be simulated, the raw material ratio often needs to be readjusted and new samples prepared, which is time-consuming and costly. Moreover, the physical properties of the obtained core (such as density, porosity, P-wave transit time, etc.) deviate significantly from the actual formation, making it difficult to meet the requirements of high-precision mechanical experiments.

[0061] Therefore, existing technologies have significant shortcomings in constructing structurally accurate, property-matched, and customizable interbedded core samples for experiments, which severely restricts the depth of research on fracturing mechanisms in complex interbedded reservoirs and the reliability of engineering applications.

[0062] Based on this, this application proposes an experimental interbedded core and its preparation method, which can be used in the field of oil and gas exploration and development technology, aiming to solve the above-mentioned technical problems of the prior art. By acquiring well logging data from the study block, the vertical sequence of the strata to be analyzed, the actual thickness of each layer, and the corresponding physical properties (including density, porosity, P-wave transit time, etc.) are extracted. Simultaneously, multiple single-lithology natural sandstone or natural shale cores from the interbedded rocks within the study block are collected, and their physical properties are tested. Target cores that are closest to the physical properties of each downhole layer are selected from the natural cores, and then, according to a preset scaling ratio, the target cores are cut into core blocks of corresponding thickness. Finally, the core blocks are sequentially bonded together according to the vertical sequence of the strata to be analyzed, forming a high-fidelity experimental interbedded core with complete structure, matching physical properties, and accurate stratigraphic sequence. This fully utilizes limited natural core resources, achieves high-precision physical simulation of any interbedded strata, and significantly improves the efficiency of experimental interbedded core preparation and the geological representativeness of the experimental results.

[0063] The technical solution of this application and how the technical solution of this application solves the above-mentioned technical problems are described in detail below with specific embodiments. These specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments. The embodiments of this application will now be described with reference to the accompanying drawings.

[0064] Figure 1 This is a schematic flowchart illustrating a method for preparing interbedded core samples for experimental use, provided as an embodiment of this application. Figure 1 As shown, the method includes:

[0065] S101. Obtain multiple natural core samples of interbedded rocks within the study block, as well as well logging data of the strata to be analyzed.

[0066] In this embodiment of the application, the natural core is a sandstone core or shale core of a single lithology, and the logging data includes the vertical sequence of the strata to be analyzed, the first thickness of each layer in the downhole interlayer, and the first physical properties of each layer.

[0067] Specifically, well logging data can be used as the geological basis and natural single-lithological cores as the physical property carriers. Through a combination of data-driven and physical reconstruction methods, high-fidelity, customizable interbedded cores for verification can be efficiently constructed.

[0068] Specifically, firstly, multiple natural core samples of interbedded rocks within the study block, as well as well logging data of the formation to be analyzed, can be obtained. The natural core samples are all of a single lithology, meaning each core contains only one type of rock—sandstone or shale—to ensure uniform and characterizable physical properties. The well logging data are derived from conventional or imaging logging curves of the target well section of the formation to be analyzed, and include at least the vertical sequence of the formation (i.e., the lithological sedimentary sequence from top to bottom), the first thickness of each layer in the interbedded formation (i.e., the actual formation thickness), and the first physical properties of each layer (such as density, porosity, and P-wave transit time).

[0069] S102. Number the multiple natural rock cores and test the second physical properties of each numbered natural rock core.

[0070] Specifically, multiple natural core samples can be uniquely numbered, and the secondary physical properties of each numbered core sample can be tested separately. The testing process can employ existing non-destructive or minimally invasive methods (such as gamma density meters, sonic logging simulations, helium porosimeters, etc.) to ensure that the natural core samples can be subsequently used for cutting, while obtaining accurate key parameters such as density, porosity, and P-wave transit time.

[0071] Table 1. Schematic diagram of the secondary physical properties of natural rock cores

[0072]

[0073] Table 1 shows the number, lithology, and corresponding secondary physical properties of each natural core sample.

[0074] S103. Calculate the second thickness of each layer in the interbedded core used in the experiment based on the first thickness and the preset scaling ratio.

[0075] Specifically, the second thickness required for each layer in the experimental interbedded core can be calculated based on the first thickness of each layer in the well logging data and the preset scaling ratio (e.g., 1:169 or determined according to the size of the experimental equipment) to adapt to the size requirements of the laboratory core holder or mechanical testing device.

[0076] S104. Compare the similarity between the first physical property and the second physical property, and determine the target core with the highest similarity to each layer of rock in the interbedded layers below the well from multiple natural cores.

[0077] Specifically, the first physical properties of each layer in the downhole interbedded formation can be compared with the second physical properties of all numbered natural cores. By establishing a multi-parameter fusion matching model (such as a normalized difference index), the cores that are closest to the physical properties of the single layer of the formation to be analyzed are selected from multiple natural cores as target cores. This process ensures that each artificial layer originates from real rock, rather than artificial composite materials, thus preserving the microstructure and mechanical response characteristics of natural rock.

[0078] S105. Cut the target core according to the second thickness to obtain a core block of the corresponding thickness.

[0079] Specifically, based on the second thickness calculated above, the target core can be precisely cut (e.g., using a diamond wire cutter) to obtain core blocks with precise thickness. Each core block can then be further marked to record its corresponding stratum location and original number.

[0080] Table 2. Numbering and parameter values ​​of core blocks corresponding to natural cores.

[0081]

[0082] Table 2 shows the second thickness of each core block, the corresponding natural core number, lithology, second physical properties, and the first thickness corresponding to each second thickness.

[0083] S106. Following the vertical order of the rock strata, the core blocks are bonded together to obtain the interbedded core for the experiment.

[0084] Specifically, the core blocks can be stacked sequentially along the vertical direction of the simulated formation deposition, strictly following the vertical sequence of the rock strata revealed by well logging data, and then bonded together with adhesive to form a structurally complete, authentically sequenced, and physically matched interbedded core for experimental use. This interbedded core can be directly used to conduct rock mechanics tests (such as triaxial compression and hydraulic fracturing simulations), providing a reliable experimental basis for unconventional reservoir fracturing design.

[0085] Through the above methods, the embodiments of this application have achieved a technological breakthrough in efficiently reproducing any complex interbedded structure with a small amount of natural core resources, significantly reducing the dependence on natural interbedded cores and improving the geological representativeness and engineering applicability of experimental interbedded cores.

[0086] This embodiment provides a method for preparing interbedded cores for experiments. First, multiple natural cores of interbedded rocks within the study block and well logging data of the formation to be analyzed are obtained. The natural cores are sandstone or shale cores of a single lithology. The well logging data includes the vertical sequence of the formation to be analyzed, the first thickness of each layer in the downhole interbedded rocks, and the first physical properties of each layer. Then, the multiple natural cores are numbered, and the second physical properties of each numbered natural core are tested. Next, based on the first thickness and a preset scaling ratio, the second thickness of each corresponding layer in the interbedded core for experiments is calculated. Subsequently, the first physical properties and the second physical properties are compared for similarity, and the target core with the highest similarity to the physical properties of each layer in the downhole interbedded rocks is determined from the multiple natural cores. Then, the target core is cut according to the second thickness to obtain core blocks of the corresponding thickness. Finally, the core blocks are sequentially bonded together according to the vertical sequence of the rock layers to obtain the interbedded core for experiments.

[0087] The following technical effects were achieved: By strictly matching the vertical sequence, single-layer thickness, and primary physical properties of the interbedded rock formations in the well, the prepared interbedded cores for experiments closely approximate the real formation in terms of structural sequence and physical property distribution, significantly outperforming the homogenization or simplified simulation of traditional artificial cores (such as rock powder pressing), providing a more reliable physical model for fracturing mechanics experiments. Only a small amount of natural sandstone or shale cores of a single lithology are needed to assemble any complex interbedded sequence. This effectively avoids the limitations of scarce, high-cost, and uncontrollable layer thickness of natural interbedded cores, making it particularly suitable for scenarios where it is difficult to obtain complete cores, such as thin interbedded layers and deep reservoirs. It not only reduces the amount of natural cores used but also enables mechanical property experiments on any formation, improving ease of use and reducing experimental costs. Using well logging data as input, experimental interbedded cores can be flexibly constructed for different blocks, well sections, and strata without the need to re-proportion raw materials or adjust process parameters, greatly improving the universality and engineering applicability of the experiments. The core blocks used are derived from natural rocks, preserving the microstructure, pore network, mineral composition, and mechanical response characteristics of authentic sandstone / shale. This avoids the property distortions introduced by cementing agents and particle mixing in artificial cores, making the mechanical test results more geologically representative. The resulting interbedded cores can accurately reflect interlayer mechanical differences, stress shielding effects, and fracture cross-layer behavior. They can be directly used in key experiments such as hydraulic fracturing physical simulation, fracture pressure prediction, and fracture propagation path analysis, significantly improving the scientific rigor and success rate of fracturing design.

[0088] In one possible design, both the first and second physical properties include at least one of density, porosity, and P-wave transit time. The first and second physical properties are compared for similarity. From multiple natural cores, the target core with the highest similarity to the physical properties of each layer in the downhole interbedded formations is determined. This includes: for any layer in the downhole interbedded formations, traversing all numbered natural cores, calculating the difference index value between the corresponding first physical property and the second physical property of each numbered natural core; and selecting the natural core with the smallest difference index value as the target core.

[0089] Specifically, the primary physical properties of each rock layer in the downhole interbedded formations and the secondary physical properties of the natural core both include at least one of density, porosity, and P-wave transit time. These three types of parameters can respectively reflect the quality characteristics, reservoir capacity, and acoustic / mechanical response characteristics of the rock, and are key indicators for characterizing the lithological differences and mechanical behavior between sandstone and shale, possessing high geological representativeness and measurability.

[0090] To achieve accurate matching, a quantitative similarity comparison mechanism can be employed. For any layer in the downhole interbedded layers, all numbered natural cores can be traversed, and the difference index value between the first physical property of that layer and the second physical property of any other natural core can be calculated one by one. This difference index value comprehensively considers the relative deviations of multiple physical property parameters and can be constructed in a normalized form to eliminate the influence of dimensions and highlight the physical significance of the property matching.

[0091] In one possible design, the formula for calculating the difference index between the corresponding first physical property and the second physical property of each numbered natural core is as follows:

[0092]

[0093] Where S is the difference index value, Let be the density of the i-th layer in the underground interlayer, where i is an integer greater than or equal to 1. Let be the density of the j-th natural core sample, where j is an integer from 1 to X, and X is the total number of core samples. Let i be the porosity of the i-th layer in the downhole interlayer. Let J be the porosity of the j-th natural core sample. Let be the P-wave time difference of the i-th layer in the downhole interlayer. Let be the P-wave time difference of the j-th natural core sample.

[0094] After completing the traversal calculations of all natural cores, the natural core with the smallest difference index value can be selected as the target core for that formation. Since a smaller difference index indicates closer physical properties, this ensures that the selected target core has the highest similarity to the downhole interlayers in key dimensions such as density, porosity, and / or P-wave transit time. This process is performed independently for each layer in the interlayers, ultimately establishing a one-to-one natural core mapping relationship for the entire vertical sequence of the formations to be analyzed, laying the data foundation for the subsequent preparation of high-fidelity core blocks.

[0095] This matching method not only avoids the uncertainty of subjective experience judgment, but also supports multi-parameter fusion decision-making, which significantly improves the scientificity and repeatability of target core selection, thereby ensuring that the experimental interbedded cores finally bonded together truly reflect the heterogeneous characteristics of the strata to be analyzed in terms of physical properties.

[0096] In one possible design, the process of obtaining the density of the i-th layer in the downhole interlayer includes: acquiring a density data sequence varying with depth obtained from density logging, the density data sequence containing multiple first sampling points, each first sampling point including a first depth value and a corresponding density value. Based on the first thickness of the i-th layer in the downhole interlayer, the first sampling points within the depth range of the i-th layer in the density data sequence are divided into a first initial dataset. The first sampling points in the first initial dataset are sorted in ascending order by their first depth values, and the first sampling points within a predetermined length range at their top and bottom are removed. The absolute value of the difference between the density values ​​of two adjacent first sampling points is calculated as the first difference. If the first difference is greater than a predetermined first threshold, the first initial dataset is segmented at the corresponding depth position to obtain multiple consecutive first subsets. The density average value is calculated for each first subset, resulting in a set of first subset average values. The set of first subset average values ​​are sorted by numerical value, and their first overall average value is calculated. Divide the first subset average into two sets of averages: the first set contains all first subset averages greater than the first overall average, and the second set contains all first subset averages less than or equal to the first overall average. Calculate the density of the i-th layer based on the first subset averages of the first set and the second set.

[0097] Specifically, the density of the i-th layer in the downhole interbedded layers can be extracted from the original density logging data through a set of interference-resistant and adaptive data processing procedures to more realistically reflect the main physical properties of the rock layer.

[0098] Specifically, firstly, a density data sequence that varies continuously with depth can be acquired by a density logging instrument (such as a gamma-gamma density logging instrument). This density data sequence consists of multiple first sampling points, each containing a pair of values: a first depth value and the corresponding density value, representing the volume density of the formation at that depth.

[0099] Subsequently, based on the first thickness of the i-th layer and its upper and lower boundary depths determined by well logging interpretation or stratigraphic division results, all first sampling points located within the depth range of that layer can be selected from the aforementioned density data sequence and combined into a first initial dataset as the basis for subsequent processing.

[0100] In addition, to eliminate the influence of outliers near the layer interface caused by lithological transition, mud invasion or logging response lag, the first sampling points in the first initial dataset can be arranged in ascending order of the first depth value (to ensure depth continuity), and the first sampling points within a preset end length range at the top and bottom can be removed, for example, the first sampling points within a range of 30 millimeters (mm) can be removed, thereby retaining the relatively stable main data within the layer.

[0101] Next, the absolute value of the density difference between two adjacent first sampling points can be calculated and defined as the first difference. If any first difference exceeds a preset first threshold (e.g., 0.2 grams per cubic centimeter, which can be adjusted according to lithology and regional geological characteristics, and is not specifically limited here), it is considered that there is a significant abrupt change in physical properties (which may correspond to micro-cracks, interlayers, or lithological changes). The first initial dataset can then be segmented at this adjacent depth location, ultimately resulting in several consecutive first subsets. The density change within each first subset is gradual, representing a relatively homogeneous lithological segment.

[0102] Furthermore, the density mean can be calculated for each first subset separately to obtain a set of first subset mean values. To reduce the interference of extremely high or low value subsets on the overall analysis, the set of first subset mean values ​​can be sorted in ascending order of numerical value, and their first overall mean (i.e., the arithmetic mean of all first subset mean values) can be calculated.

[0103] Then, using this first overall average as a boundary, all first subset averages are divided into two groups. The first group contains all first subset averages greater than the first overall average, reflecting high-density feature segments. The second group contains all first subset averages less than or equal to the first overall average, reflecting low-density feature segments.

[0104] Finally, the density of the i-th layer It can be calculated by averaging the average values ​​of the two first subsets separately and then merging them with equal weights.

[0105] In one possible design, the formula for calculating the density of the i-th layer, based on the average value of the first subset of the first group and the average value of the first subset of the second group, is as follows:

[0106]

[0107] Where R is the number of average values ​​of the first subset in the first group. Let be the average of the r-th first subset in the first group, and T be the number of averages of the first subsets in the second group. Let be the average value of the t-th first subset in the second group.

[0108] This embodiment effectively takes into account the characteristics of both high and low ends of the heterogeneity within the rock strata through segmented identification and group weighting strategies, avoiding the problem of simple averaging masking local differences in physical properties. This results in obtaining more representative and robust layer density parameters, providing a reliable basis for subsequent accurate matching with natural rock cores.

[0109] In one possible design, the formula for calculating the porosity of the i-th layer in the downhole interlayer is:

[0110]

[0111] in, The preset rock skeleton density is the lithology corresponding to the i-th layer of rock. This is the preset pore fluid density of the formation fluid corresponding to the i-th layer.

[0112] Specifically, the porosity of the i-th layer in the downhole interlayer It can be obtained through rock physics model inversion method. This is the density of the rock matrix (mineral grains), excluding pore space. A standard value can be selected based on the lithology; for example, the rock skeleton density for sandstone is approximately 2.65 grams per cubic centimeter (g / cm³). 3 The rock skeleton density of shale is approximately 2.60 g / cm³. 3 The specific value of the preset rock skeleton density can be calibrated based on regional geological data or laboratory measured data.

[0113] The preset pore fluid density for the pore fluid in the i-th formation layer can be determined based on the type of formation fluid. For example, the preset pore fluid density for water is 1.0 g / cm³. 3 The preset pore fluid density corresponding to the oil is 0.80 g / cm³. 3 Up to 0.90 g / cm 3 The preset pore fluid density corresponding to the gas is 0.001 g / cm³. 3 Up to 0.01 g / cm 3 .

[0114] The above formula for calculating porosity is based on the principle of mass conservation and a mixture density model, assuming that the rock consists of a solid skeleton and pore fluid phases, and its total bulk density is a weighted average of the skeleton and fluid phases by volume. Therefore, using known... , and Porosity can then be calculated. .

[0115] This embodiment avoids the complex experimental procedures required for direct porosity measurement (such as helium porosimeter testing) and can quickly calculate the porosity distribution of multi-layered interbedded reservoirs using conventional well logging data. It is particularly suitable for deep or unconventional reservoirs lacking natural core samples. Furthermore, since porosity is a crucial parameter affecting rock mechanical behavior (such as elastic modulus and compressive strength), its accurate acquisition plays a key supporting role in subsequent natural core matching and mechanical testing.

[0116] Furthermore, to improve calculation accuracy, well logging interpretation results can be combined with practical applications. and Regional corrections or the introduction of auxiliary parameters such as acoustic time difference for joint inversion can further enhance the reliability of porosity calculation.

[0117] In one possible design, the process of obtaining the P-wave transit time (POT) of the i-th layer in the downhole interlayer includes: acquiring a POT data sequence varying with depth obtained from sonic logging, the POT data sequence containing multiple second sampling points, each second sampling point including a second depth value and a corresponding POT value. Based on the first thickness of the i-th layer in the downhole interlayer, the second sampling points within the depth range of the i-th layer in the POT data sequence are divided into a second initial dataset. The second sampling points in the second initial dataset are sorted in ascending order by their second depth values, and second sampling points within a predetermined length range at their top and bottom are removed. The absolute value of the difference between the POT values ​​of two adjacent second sampling points is calculated as the second difference. If the second difference is greater than a predetermined second threshold, the second initial dataset is segmented at the corresponding depth position to obtain multiple consecutive second subsets. The average POT value is calculated for each second subset, resulting in a set of second subset average values. The set of second subset average values ​​are sorted by numerical value, and their second overall average value is calculated. The average value of a second subset is divided into two sets of average values. The first set contains all second subset average values ​​that are greater than the second overall average value, and the second set contains all second subset average values ​​that are less than or equal to the second overall average value. The P-wave time difference of the i-th layer is calculated based on the average values ​​of the second subsets of the first and second sets.

[0118] Specifically, the P-wave time difference of the i-th layer in the downhole interlayer can be robustly calculated using a structured data extraction process that is consistent with the density parameter processing logic, so as to more realistically reflect the overall characteristics of the rock layer in acoustic response.

[0119] Specifically, firstly, a sequence of P-wave transit time data that varies continuously with depth can be acquired by an acoustic logging instrument. This P-wave transit time data sequence consists of multiple second sampling points, each containing a pair of values: a second depth value and the corresponding P-wave transit time value, representing the time required for the P-wave to travel a unit distance in the formation at that depth.

[0120] Subsequently, based on the first thickness of the i-th layer and its upper and lower boundary depths determined by the well logging interpretation, all second sampling points located within the depth range of that layer can be selected from the aforementioned P-wave time difference data sequence and integrated into a second initial dataset as the basic unit for subsequent processing.

[0121] In addition, to eliminate abnormal responses near the layer interface caused by factors such as lithological abrupt changes, wellbore disturbance, or mud invasion, the second sampling points in the second initial dataset can be arranged in ascending order of the second depth value (to ensure depth continuity), and sampling points within a preset end length range at the top and bottom can be removed, for example, second sampling points within a range of 30 millimeters (mm) can be removed, thereby retaining the relatively stable main acoustic response data within the layer.

[0122] Next, the absolute value of the difference between the P-wave transit times between two adjacent second sampling points can be calculated and defined as the second difference. If any second difference exceeds a preset second threshold (e.g., 5 microseconds per foot, which can be adjusted according to regional lithological characteristics or noise levels, and is not specifically limited here), it is considered that there is a significant abrupt change in acoustic properties (possibly corresponding to cracks, interlayers, or lithological interfaces). The second initial dataset can then be segmented at this adjacent depth location, ultimately resulting in several consecutive second subsets. Within each second subset, the P-wave transit time changes gradually, representing an acoustically homogeneous segment.

[0123] Furthermore, the average P-wave time difference is calculated for each second subset of data, thus obtaining a set of second subset averages. To avoid a single average masking the non-homogeneity, the set of second subset averages can be sorted in ascending order of numerical value, and a second overall average (i.e., the arithmetic mean of all second subset averages) can be calculated.

[0124] Then, using this second overall average as a boundary, all second subset averages are divided into two groups. The first group contains all second subset averages greater than the second overall average, reflecting characteristics of slower sound wave propagation (such as shale and fractured sections). The second group contains all second subset averages less than or equal to the second overall average, reflecting characteristics of faster sound wave propagation (such as tight sandstone).

[0125] Finally, the P-wave time difference of the i-th layer It can be calculated by averaging the average values ​​of the two sets of second subsets separately and then merging them with equal weights.

[0126] In one possible design, the formula for calculating the P-wave time difference of the i-th layer, based on the average value of the second subset of the first group and the average value of the second subset of the second group, is as follows:

[0127]

[0128] Where L is the number of values ​​representing the average of the second subset in the first group. Let K be the average of the l-th first subset in the first group, and K be the number of averages of the second subset in the second group. It is the average value of the kth second subset in the second group.

[0129] This embodiment effectively preserves the dual-mode characteristics of acoustic heterogeneity within rock strata through segmented identification and group weighting strategies. The obtained longitudinal wave transit time can not only be used for lithological discrimination, but also for calculating elastic parameters (such as Young's modulus and Poisson's ratio), and serves as one of the key physical property indicators for matching with natural rock cores, significantly improving the physical fidelity of the interbedded rock cores prepared for experiments.

[0130] In one possible design, core blocks are sequentially bonded together according to the vertical order of the rock strata to obtain an interbedded core for experimentation. This includes: before bonding, coarsely grinding and finely grinding the contact surfaces of each core block to obtain smooth surfaces with a predetermined roughness. Adhesive is uniformly applied to the contact surfaces of adjacent core blocks. The adhesive-coated core blocks are then stacked vertically in sequence to form a core column, and pressure is applied vertically, simulating the vertical direction of sedimentary formations. The core column is then placed in a constant-temperature environment at a predetermined temperature for a predetermined time to allow the adhesive to fully cure, resulting in a structurally complete interbedded core for experimentation.

[0131] Specifically, to ensure that the prepared interbedded rock cores for experiments can truly simulate the vertical sedimentary characteristics of underground strata in terms of mechanical properties and structural integrity, the bonding process of the core blocks must strictly follow the geological direction and interface control requirements.

[0132] Specifically, firstly, before bonding, the end faces (i.e., upper and lower surfaces) of each core block that will contact each other can be finely surface-treated. For example, rough grinding can be performed first using a grinding wheel or coarse-grained sandpaper to remove burrs, debris, and uneven areas generated during the cutting process. Subsequently, fine grinding can be performed using fine-grained sandpaper or polishing paste to achieve a smooth surface, free of obvious scratches, and with a preset roughness, such as 1.6 micrometers to 3.2 micrometers. This preset roughness ensures effective wetting and mechanical bonding of the adhesive while preventing excessive gaps from affecting interlayer stress transfer.

[0133] Next, a high-strength structural adhesive suitable for rock materials can be selected and evenly applied to the bonding surfaces of adjacent core blocks. The coating thickness can be controlled within the range of 0.1 mm to 0.3 mm to ensure a continuous adhesive layer free of bubbles and dry spots, while avoiding excessive overflow and contamination of the core side. The viscosity of the adhesive can be from 50 mPa·s to 200 mPa·s, such as epoxy resin or modified acrylic structural adhesives suitable for rock bonding, to ensure good interfacial wettability and mechanical strength after curing.

[0134] Subsequently, core blocks coated with adhesive can be stacked vertically in strict accordance with the vertical sequence of the target strata (i.e., from bottom to top or from top to bottom) to form a complete cylindrical core column. Here, "vertical" specifically refers to the vertical direction simulating actual geological deposition, i.e., the axial loading direction in the laboratory coordinate system, to ensure that the stress path in subsequent mechanical tests is consistent with the actual underground conditions. After stacking, a constant pressure, such as 0.5 MPa to 2 MPa, can be applied vertically to the entire core column to expel excess adhesive, eliminate interfacial voids, and promote the adhesive to fully fill micropores, thereby forming a high-strength, low-defect interlayer bonding surface.

[0135] Finally, the pressurized core column can be transferred to a pre-set constant temperature environment (e.g., 40°C to 60°C, the specific temperature can be determined based on the adhesive's curing characteristics) and kept at this temperature for a pre-set curing time (e.g., 12 to 48 hours) to allow the adhesive to complete its full cross-linking reaction and reach its final strength. After curing, the pressure is released and the core column is removed, yielding a structurally complete, accurately sequenced, and firmly interfaced interbedded core for experimental use.

[0136] This bonding process effectively solves common problems in traditional bonding, such as interlayer slip, interface debonding, or stress concentration, through a three-pronged control strategy of end-face treatment, directional stacking, and pressure curing. It significantly improves the reliability and repeatability of artificial experimental interbedded cores in mechanical tests such as triaxial compression or hydraulic fracturing simulation, and provides high-quality physical model support for the study of unconventional reservoir fracturing mechanisms.

[0137] Furthermore, this application embodiment also provides an experimental interbedded core, which is prepared using an experimental interbedded core preparation method described in the above embodiment. It includes multiple core blocks that are sequentially bonded together according to the vertical order of the rock strata to be analyzed. Each core block is cut from natural sandstone or natural shale of a single lithology, and the lithology, vertical order, thickness and physical properties of each core block are respectively matched to the corresponding rock strata to be analyzed in the downhole.

[0138] Specifically, the interbedded rock core used in this experiment is a physical product prepared according to the preparation method of interbedded rock cores in any of the aforementioned embodiments. Its structure is not formed by traditional artificial methods such as rock powder pressing or cement mixing, but is reconstructed from real natural rock materials, and has significant geological representativeness and mechanical authenticity.

[0139] Specifically, the interbedded core samples used in this experiment consisted of multiple core blocks bonded together vertically. Each core block was stacked strictly according to the vertical sequence of the strata to be analyzed, ensuring that its sequence structure was completely consistent with the strata being analyzed. Each core block was prepared by cutting a natural core of a single lithology, meaning that each block contained only one type of natural sandstone or natural shale, preserving the original rock's mineral composition, pore structure, microfracture network, and inherent mechanical properties, thus avoiding the distortion of physical properties introduced by artificial materials.

[0140] More importantly, each core block is consistent with the corresponding rock layer in the downhole analysis in four aspects: lithology, vertical position, geometric thickness, and physical properties (such as density, porosity, and P-wave transit time). The thickness is scaled according to a preset ratio to fit the experimental equipment, while the physical properties are matched by well logging inversion and comparison with a natural core database. This allows for the simultaneous reconstruction of the true characteristics of the interbedded underground reservoir at both the macroscopic structure and microscopic response levels.

[0141] Therefore, the interbedded rock core used in this experiment is not only a physical model, but also a data-driven, geologically constrained, and materially realistic digital twin rock core. It can be directly used in rock mechanics experiments such as triaxial compression and hydraulic fracturing simulation, providing a highly reliable experimental basis for fracturing design of unconventional oil and gas reservoirs, research on fracture propagation mechanisms, and optimization of engineering parameters.

[0142] The technical solutions of this application have been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it is readily understood by those skilled in the art that the scope of protection of this application is obviously not limited to these specific embodiments. The above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for preparing interbedded rock cores for experimental use, characterized in that, include: Obtain multiple natural cores of interbedded rocks within the study block and well logging data of the strata to be analyzed. The natural cores are sandstone or shale cores of a single lithology. The well logging data includes the vertical sequence of the strata to be analyzed, the first thickness of each layer in the downhole interbedded rocks, and the first physical properties of each layer. The plurality of natural rock cores were numbered, and the second physical property of each numbered natural rock core was tested; both the first physical property and the second physical property include at least one of density, porosity and P-wave transit time; Based on the first thickness and the preset scaling ratio, the second thickness of each corresponding layer in the interbedded core used in the experiment is calculated; the interbedded core used in the experiment is used to simulate the structure and properties of real strata. For any layer in the downhole interbedded layers, traverse all numbered natural cores and calculate the difference index value between the corresponding first physical property and the second physical property of each numbered natural core; The natural core with the smallest difference index value was selected as the target core. The target core is cut according to the second thickness to obtain core blocks of the corresponding thickness; According to the vertical order of the rock strata, the core blocks are bonded together in sequence to obtain the interbedded rock core for the experiment; The formula for calculating the difference index between the corresponding first physical property and the second physical property of each numbered natural core is as follows: Wherein, S is the value of the difference index. Let be the density of the i-th layer in the underground interlayer, where i is an integer greater than or equal to 1. Let be the density of the j-th natural core sample, where j is an integer from 1 to X, and X is the total number of core samples. Let i be the porosity of the i-th layer in the downhole interlayer. Let J be the porosity of the j-th natural core sample. Let be the P-wave time difference of the i-th layer in the downhole interlayer. Let be the P-wave time difference of the j-th natural core sample.

2. The method according to claim 1, characterized in that, The process of obtaining the density of the i-th layer in the downhole interlayer includes: Obtain a density data sequence that varies with depth obtained from density logging. The density data sequence contains multiple first sampling points, each of which includes a first depth value and a corresponding density value. Based on the first thickness of the i-th layer in the downhole interlayer, the first sampling points in the density data sequence located within the depth range of the i-th layer are divided into a first initial dataset; The first sampling points in the first initial dataset are sorted in ascending order according to the first depth value, and the first sampling points within the preset length range of the top and bottom ends are removed; Calculate the absolute value of the difference between the density values ​​of two adjacent first sampling points as the first difference. If the first difference is greater than a preset first threshold, then the first initial dataset is segmented at the corresponding depth position to obtain multiple consecutive first subsets. Calculate the density mean for each first subset of data to obtain a set of first subset mean values; sort the set of first subset mean values ​​by numerical size and calculate their first overall mean; The first subset average is divided into two sets of averages: the first set contains all first subset averages that are greater than the first total average, and the second set contains all first subset averages that are less than or equal to the first total average. The density of the i-th layer is calculated based on the average value of the first subset of the first group and the average value of the first subset of the second group.

3. The method according to claim 2, characterized in that, The formula for calculating the density of the i-th layer based on the average value of the first subset of the first group and the average value of the first subset of the second group is as follows: Where R is the number of average values ​​of the first subset in the first group. Let be the average of the r-th first subset in the first group, and T be the number of averages of the first subsets in the second group. Let be the average value of the t-th first subset in the second group.

4. The method according to claim 1, characterized in that, The formula for calculating the porosity of the i-th layer in the downhole interlayer is: in, The preset rock skeleton density is the lithology corresponding to the i-th layer of rock. The preset pore fluid density is the formation fluid corresponding to the i-th layer.

5. The method according to claim 1, characterized in that, The process of obtaining the P-wave time difference of the i-th layer in the downhole interlayer includes: Acquire a depth-varying P-wave time difference data sequence obtained from acoustic logging, wherein the P-wave time difference data sequence contains multiple second sampling points, and each second sampling point includes a second depth value and a corresponding P-wave time difference value; Based on the first thickness of the i-th layer in the downhole interlayer, the second sampling points in the P-wave time difference data sequence located within the depth range of the i-th layer are divided into a second initial dataset; The second sampling points in the second initial dataset are sorted in ascending order according to the second depth value, and the second sampling points within the preset length range of the top and bottom ends are removed; Calculate the absolute value of the difference between the longitudinal wave time difference values ​​of two adjacent second sampling points as the second difference value. If the second difference value is greater than the preset second threshold, then the second initial dataset is segmented at the corresponding depth position to obtain multiple consecutive second subset datasets. For each second subset of data, calculate the average P-wave time difference to obtain a set of average values ​​for the second subset; sort the set of average values ​​for the second subset by numerical value and calculate its second overall average value; The average value of the second subset is divided into two groups of average values. The first group contains all the average values ​​of the second subset that are greater than the second total average value, and the second group contains all the average values ​​of the second subset that are less than or equal to the second total average value. The longitudinal wave time difference of the i-th layer is calculated based on the average value of the second subset of the first group and the average value of the second subset of the second group.

6. The method according to claim 5, characterized in that, The formula for calculating the P-wave time difference of the i-th layer based on the average value of the second subset of the first group and the average value of the second subset of the second group is as follows: Where L is the number of values ​​representing the average of the second subset in the first group. Let K be the average of the l-th first subset in the first group, and K be the number of averages of the second subset in the second group. It is the average value of the kth second subset in the second group.

7. The method according to any one of claims 1 to 6, characterized in that, The process of sequentially bonding the core blocks into a single unit according to the vertical order of the rock strata to obtain the interbedded core for the experiment includes: Before bonding, the end faces of each core block that are used to contact each other are subjected to coarse grinding and fine grinding respectively to obtain a flat end face with a preset roughness. Apply adhesive evenly to the bonding surfaces of adjacent core blocks; According to the vertical sequence of the rock strata, core blocks coated with adhesive are stacked vertically to form a core column, and pressure is applied vertically, where vertical is the vertical direction simulating the sedimentation of strata. The core column is placed in a constant temperature environment at a preset temperature and cured for a preset time to allow the adhesive to fully cure, resulting in the structurally complete interlayered core for the experiment.

8. An experimental interbedded rock core, characterized in that, Prepared using the method described in any one of claims 1 to 7, the core blocks comprise multiple core blocks bonded together in the vertical order of the rock strata to be analyzed. Each core block is cut from natural sandstone or natural shale of a single lithology, and the lithology, vertical order, thickness, and physical properties of each core block are respectively matched to the corresponding rock strata to be analyzed in the downhole.

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