A method for determining a representative volume unit of heterogeneous shale and a related device

Abstract

The present application discloses a method for determining a representative volume unit of heterogeneous shale and a related device, which relate to the technical field of oil and gas exploration. A plurality of position points are selected on the vertical surface of a heterogeneous shale sample, and the paleoenvironmental index of each position point is calculated based on an element distribution map. The vertical surface is divided into a plurality of sedimentary phase belts based on the paleoenvironmental index and position information of each position point. The proportion of each sedimentary phase belt is calculated, and a scanning area in the vertical surface is determined based on the proportion of each sedimentary phase belt, and a mineral distribution map corresponding to the scanning area is obtained. An initial area in the scanning area is determined based on the proportion of each sedimentary phase belt, and the initial area is adjusted based on the mineral distribution map to determine the representative volume unit of the heterogeneous shale sample, thereby efficiently determining the representative volume unit of the highly heterogeneous shale.

Description

Technical Field

[0001] The present application relates to the technical field of oil and gas exploration, and in particular to a method for determining a representative volume unit of heterogeneous shale and a related device. Background Art

[0002] Shale refers to laminar clay rock with foliation or bedding structure and easy to break. Its main characteristics are clay-silt grain size (<63μm), easy erosion and strong heterogeneity. At the submillimeter (between 1 and 0.1 mm) to centimeter scale, shales show great differences in vertical mineral composition and pore structure. In order to make the characterization results of heterogeneous shales at the micro-nano scale relevant at the mesoscopic scale, it is necessary to determine representative volume units to achieve macro-micro coupling of heterogeneous shale characterization results.

[0003] Shale has a small particle size and is difficult to observe. A single imaging technology cannot fully and accurately characterize the shale microstructure. For example, the traditional XRD (X-ray diffraction) method of characterizing mineral content requires the shale sample to be crushed and homogenized, which is more susceptible to the macroscopic and microscopic heterogeneity of sedimentary rocks. This may cause useful information to be covered by useless information and cannot fully reflect the true situation of the shale. At this time, the determination of representative volume units is particularly important.

[0004] At present, the representative volume unit is mainly determined by the following two methods: one is to conduct statistical analysis of mineral / pore content based on the grayscale of the image obtained by SEM (Scanning electron microscope) to further determine the representative volume unit; the other is to conduct quantitative analysis of minerals based on AMICS (Automatic Mineral Identification and Characterization System) of scanning electron microscope to further determine the representative volume unit. However, the representative volume units determined by the above two methods are confined to a single thin layer, which is a two-dimensional plane and is not applicable to shales with extremely strong heterogeneity. In addition, when determining the representative volume unit, the initial area is randomly determined, which is highly random. The problem of not being able to determine the representative volume unit based on the initial area may occur, which is inefficient. Therefore, how to efficiently determine the representative volume unit of highly heterogeneous shale is an important part of shale oil and gas reservoir space evaluation. Summary of the invention

[0005] The purpose of the present application is to provide a method for determining a representative volume unit of heterogeneous shale and a related device, which can efficiently determine the representative volume unit of strongly heterogeneous shale.

[0006] To achieve the above objectives, this application provides the following solutions:

[0007] In a first aspect, the present application provides a method for determining a representative volume unit of heterogeneous shale, the method for determining a representative volume unit of heterogeneous shale comprising:

[0008] Obtaining an element distribution map; the element distribution map is obtained by scanning the vertical surface of the heterogeneous shale sample using a micro-area X-ray fluorescence spectrometer, and the element distribution map includes the element type and element content of each scanning point in the vertical surface;

[0009] Selecting a plurality of position points on the vertical surface, calculating the paleoenvironmental index of each of the position points based on the element distribution map, dividing the vertical surface into a plurality of sedimentary facies belts based on the paleoenvironmental index and position information of each of the position points, and calculating the proportion of each of the sedimentary facies belts;

[0010] Determine a scanning area in the vertical surface based on the proportion of each of the sedimentary phase belts, and obtain a mineral distribution map corresponding to the scanning area; the mineral distribution map is obtained by scanning the scanning area using a scanning electron microscope, and the mineral distribution map includes the mineral type and mineral content of each scanning point in the scanning area;

[0011] An initial area in the scanning area is determined based on the proportion of each of the sedimentary facies belts, and the initial area is adjusted based on the mineral distribution map to determine a representative volume unit of the heterogeneous shale sample.

[0012] Optionally, a plurality of position points are selected on the vertical surface, specifically including:

[0013] Acquire an optical image; the optical image is obtained by scanning the vertical surface of the heterogeneous shale sample using a micro-area X-ray fluorescence spectrometer;

[0014] In combination with the optical image and the element distribution map, a plurality of position points are selected on the vertical surface.

[0015] Optionally, the paleoenvironmental index includes paleowater depth index, paleosalinity, paleoclimate index and paleooxidation-reduction index.

[0016] Optionally, the vertical surface is divided into a plurality of sedimentary facies zones based on the paleoenvironmental index and location information of each of the location points, specifically including:

[0017] For each of the location points, determining the environmental type of the location point based on the paleoenvironmental index of the location point;

[0018] Based on the environmental type and location information of each of the location points, the location points with the same environmental type and adjacent to each other are divided into a sedimentary facies belt, so as to divide the vertical surface into several sedimentary facies belts; if the environmental types of two sedimentary facies belts are the same, the two sedimentary facies belts belong to the same sedimentary facies belt.

[0019] Optionally, determining the scanning area in the vertical surface based on the proportion of each of the sedimentary facies belts specifically includes:

[0020] The lateral side length of the scanning area is set to a first preset value, the vertical side length of the scanning area is set to a second preset value, and the position of the scanning area is determined based on the proportion of each of the sedimentary phase belts, so that the area ratio of different sedimentary phase belts in the scanning area is equal to the proportion of each of the sedimentary phase belts, and the scanning area in the vertical surface is determined;

[0021] Determining an initial area in the scanning area based on the proportion of each of the sedimentary facies belts specifically includes:

[0022] The lateral side length of the initial area is set to a first preset value, and the vertical side length of the initial area is set to a third preset value. The position of the initial area is determined based on the proportion of each sedimentary phase belt, so that the length ratio of any vertical side in the initial area in different sedimentary phase belts is equal to the proportion of each sedimentary phase belt, and the initial area in the scanning area is determined; the third preset value is less than the second preset value.

[0023] Optionally, adjusting the initial area based on the mineral distribution map to determine a representative volume unit of the heterogeneous shale sample specifically includes:

[0024] determining a first mineral content of each mineral in the initial area based on the mineral distribution map;

[0025] Adjusting the vertical side length of the initial area to obtain an adjusted area, and determining the second mineral content of each mineral in the adjusted area based on the mineral distribution map;

[0026] Based on the first mineral content and the second mineral content of each mineral, the mineral content change rate of each mineral is calculated; the mineral content change rate is the ratio of the difference and the average value, the difference is the difference between the second mineral content and the first mineral content, and the average value is the average value of the first mineral content and the second mineral content;

[0027] Determine whether the mineral content change rate of each mineral is less than the preset value;

[0028] If yes, then the iteration is terminated, and a representative volume unit of the heterogeneous shale sample is determined based on the adjusted area;

[0029] If not, the iteration continues, the adjusted region is used as the initial region of the next iteration, and the process returns to the step of "adjusting the vertical side length of the initial region to obtain the adjusted region".

[0030] In a second aspect, the present application provides a device for determining a representative volume unit of heterogeneous shale, the device for determining a representative volume unit of heterogeneous shale comprising:

[0031] A first data acquisition module is used to acquire an element distribution map; the element distribution map is obtained by scanning the vertical surface of the heterogeneous shale sample using a micro-area X-ray fluorescence spectrometer, and the element distribution map includes the element type and element content of each scanning point in the vertical surface;

[0032] A proportion calculation module, used for selecting a plurality of position points on the vertical surface, calculating the paleoenvironmental index of each of the position points based on the element distribution map, dividing the vertical surface into a plurality of sedimentary facies belts based on the paleoenvironmental index and position information of each of the position points, and calculating the proportion of each of the sedimentary facies belts;

[0033] A second data acquisition module is used to determine a scanning area in the vertical surface based on the proportion of each of the sedimentary phase belts, and obtain a mineral distribution map corresponding to the scanning area; the mineral distribution map is obtained by scanning the scanning area using a scanning electron microscope, and the mineral distribution map includes the mineral type and mineral content of each scanning point in the scanning area;

[0034] A determination module is used to determine an initial area in the scanning area based on the proportion of each of the sedimentary phase belts, and to adjust the initial area based on the mineral distribution map to determine a representative volume unit of the heterogeneous shale sample.

[0035] In a third aspect, the present application provides a computer device, comprising: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the method for determining a representative volume unit of heterogeneous shale as described in any one of the above.

[0036] In a fourth aspect, the present application provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements any of the above-described methods for determining a representative volume unit of heterogeneous shale.

[0037] In a fifth aspect, the present application provides a computer program product, including a computer program, which, when executed by a processor, implements any of the above-mentioned methods for determining a representative volume unit of heterogeneous shale.

[0038] According to the specific embodiments provided in this application, this application discloses the following technical effects:

[0039] The present application provides a method for determining a representative volume unit of a heterogeneous shale and a related device. A plurality of position points are selected on a vertical surface of a heterogeneous shale sample, and a paleoenvironmental index of each position point is calculated based on an element distribution map. The vertical surface is divided into a plurality of sedimentary phase belts based on the paleoenvironmental index and position information of each position point, and the proportion of each sedimentary phase belt is calculated. A scanning area in the vertical surface is determined based on the proportion of each sedimentary phase belt, and a mineral distribution map corresponding to the scanning area is obtained. An initial area in the scanning area is determined based on the proportion of each sedimentary phase belt, and the initial area is adjusted based on the mineral distribution map to determine the representative volume unit of the heterogeneous shale sample. The present invention determines the initial area based on the proportion of each sedimentary phase belt, thereby avoiding the problem that the representative volume unit may not be determined due to the randomness of the initial area, ensuring that the representative volume unit can be determined, and improving efficiency. In addition, the representative volume unit obtained by the present invention is three-dimensional, thereby avoiding the problem that the determined representative volume unit is a two-dimensional plane and is not applicable to shale with extremely strong heterogeneity, thereby efficiently determining the representative volume unit of the highly heterogeneous shale. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0041] Figure 1 A schematic flow chart of a method for determining a representative volume unit of heterogeneous shale provided in Example 1 of the present application.

[0042] Figure 2 A schematic diagram of the relevant results of the mixed shale 1 of the second section of the Funing Formation in the Subei Basin provided in Example 1 of the present application; Figure 2 A in it is an optical image; Figure 2 B in is the element distribution diagram; Figure 2 C in it is the radar chart for calculating paleoenvironmental index; Figure 2 D in the figure is the proportion of various sedimentary phase belts and mineral distribution map.

[0043] Figure 3 A schematic diagram of the change rate of the mineral content difference of the mixed shale 1 of the second segment of the Funing Formation in the Subei Basin provided in Example 1 of the present application as the SEM-AMICS image field of view increases.

[0044] Figure 4Schematic diagram of the correlation between the mineral content determined by a representative volume unit of the mixed shale 1 of the second segment of the Funing Formation in the Subei Basin provided in Example 1 of the present application and the mineral content determined by XRD.

[0045] Figure 5 A schematic diagram of the relevant results of the mixed shale 2 of the second section of the Funing Formation in the Subei Basin provided in Example 1 of the present application; Figure 5 A in it is an optical image; Figure 5 B in is the element distribution diagram; Figure 5 C in it is the radar chart for calculating paleoenvironmental index; Figure 5 D in the figure is the proportion of various sedimentary phase belts and mineral distribution map.

[0046] Figure 6 A schematic diagram of the change rate of the mineral content difference of the mixed shale 2 of the second segment of the Funing Formation in the Subei Basin provided in Example 1 of the present application as the SEM-AMICS image field of view increases.

[0047] Figure 7 Schematic diagram of the correlation between the mineral content determined by a representative volume unit of the mixed shale 2 of the second section of the Funing Formation in the Subei Basin provided in Example 1 of the present application and the mineral content determined by XRD.

[0048] Figure 8 A schematic diagram of the structure of a computer device provided in Example 3 of the present application. DETAILED DESCRIPTION

[0049] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0050] Example 1

[0051] This embodiment provides a method for determining a representative volume unit of heterogeneous shale. Figure 1 As shown, the method for determining the representative volume unit of heterogeneous shale includes:

[0052] S1: Obtaining an element distribution map; the element distribution map is obtained by scanning the vertical surface of the heterogeneous shale sample using a micro-area X-ray fluorescence spectrometer, and the element distribution map includes the element type and element content of each scanning point in the vertical surface.

[0053] S2: Select multiple location points on the vertical surface, calculate the paleoenvironmental index of each location point based on the element distribution map, and divide the vertical surface into several sedimentary phase belts based on the paleoenvironmental index and location information of each location point, and calculate the proportion of each sedimentary phase belt.

[0054] S3: Determine the scanning area in the vertical surface based on the proportion of each sedimentary phase belt, and obtain a mineral distribution map corresponding to the scanning area; the mineral distribution map is obtained by scanning the scanning area using a scanning electron microscope, and the mineral distribution map includes the mineral type and mineral content of each scanning point in the scanning area.

[0055] S4: Determine an initial area in the scanning area based on the proportion of each of the sedimentary phase belts, and adjust the initial area based on the mineral distribution map to determine a representative volume unit of the heterogeneous shale sample.

[0056] By implementing S1-S4, this embodiment determines the initial area based on the proportion of each sedimentary phase belt, avoiding the problem that the representative volume unit may not be determined due to the randomness of the initial area, ensuring that the representative volume unit can be determined to improve efficiency. In addition, the representative volume unit obtained in this embodiment is three-dimensional, avoiding the problem that the determined representative volume unit is a two-dimensional plane and is not applicable to shale with extremely strong heterogeneity, thereby efficiently determining the representative volume unit of the highly heterogeneous shale.

[0057] Before obtaining the element distribution map and the mineral distribution map, the present embodiment first prepares a heterogeneous shale sample (also called a heterogeneous shale sample) for scanning by a micro-area X-ray fluorescence spectrometer and a heterogeneous shale sample for scanning by a scanning electron microscope, wherein the heterogeneous shale samples required for both scans need to have a flat surface. To achieve this purpose, the present embodiment polishes the heterogeneous shale sample when preparing the heterogeneous shale sample. For the micro-area X-ray fluorescence spectrometer, the heterogeneous shale sample is polished by mechanical polishing, and for the scanning electron microscope, the heterogeneous shale sample is polished by argon ion polishing, that is, the present embodiment prepares a heterogeneous shale sample with a flat surface that is mechanically polished for scanning by a micro-area X-ray fluorescence spectrometer, and prepares a heterogeneous shale sample with a flat surface that is argon ion polished for scanning by a scanning electron microscope.

[0058] In this embodiment, the area of ​​the heterogeneous shale sample used for micro-area XRF scanning does not exceed 200 mm×160 mm, and the area of ​​the heterogeneous shale sample used for SEM-AMICS scanning is 10 mm×10 mm, and the thickness does not exceed 3 mm.

[0059] In S1, the vertical surface of the heterogeneous shale sample is scanned by a micro-area X-ray fluorescence spectrometer, that is, the vertical surface of the heterogeneous shale sample is scanned by a micro-area XRF (X-Ray Fluorescence Spectrometer) to obtain an element distribution map. The element distribution map is a 2D distribution map of different elements, so the element distribution map can be called a 2D element distribution map, including the element type and element content of each scanning point in the vertical surface. Among them, the vertical plane refers to the surface perpendicular to the ground on the heterogeneous shale sample.

[0060] The fusion of optical images and element distribution maps can identify the rock component characteristics and fine sedimentary structures of laminated shale hand specimens or core scales. Therefore, in S2, multiple position points are selected on the vertical surface, specifically including: obtaining an optical image, which is obtained by scanning the vertical surface of the heterogeneous shale sample using a micro-area X-ray fluorescence spectrometer; combining the optical image and the element distribution map, selecting multiple position points on the vertical surface, and the selection principle is to cover areas with different composition and structural characteristics as much as possible.

[0061] When using optical images to identify microfacies features that are difficult to distinguish with the naked eye, the shale is relatively uniform in color, which is not conducive to naked eye identification. Considering that changes in sedimentary structures will cause changes in inorganic geochemical elements, the plane distribution map of inorganic geochemical element intensity (i.e., element distribution map) can be used to identify sedimentary structures, specifically extract element data, calculate paleoenvironmental indexes, further divide sedimentary facies types, divide different sedimentary facies types into zones, and use image processing software to calculate the proportion of various sedimentary facies.

[0062] In this embodiment, the paleoenvironmental index includes paleowater depth index, paleosalinity, paleoclimate index and paleooxidation-reduction index, which are specifically defined as follows:

[0063] (1) Paleobath index

[0064] (Al+Fe) / (Ca+Mg) is the paleo-water depth index, where a high value indicates a deep-water environment and a low value indicates a shallow-water environment. Al represents the aluminum content, Fe represents the iron content, Ca represents the calcium content, and Mg represents the magnesium content. The distinction between high and low values ​​is accomplished by a preset threshold. When the water depth index is greater than the preset threshold, it is a high value, indicating a deep-water environment. When the water depth index is less than or equal to the preset threshold, it is a low value, indicating a shallow-water environment.

[0065] (2) Paleosalinity

[0066] Ca / (Ca+Fe) is the paleo-salinity, Ca / (Ca+Fe) < 0.4 indicates a freshwater environment, and Ca / (Ca+Fe) > 0.6 indicates a saltwater environment. Among them, Ca represents the calcium content, and Fe represents the iron content.

[0067] (3) Paleoclimate index

[0068] The C value is a climate index, C value = Σ(Fe+Mn+Cr+Ni+V+Co) / Σ(Ca+Mg+Sr+Ba+K+Na), C value < 0.2 indicates an arid environment, C value between 0.2 and 0.4 indicates a semi-arid environment, C value between 0.4 and 0.6 indicates a semi-arid-semi-humid environment, C value between 0.6 and 0.8 indicates a semi-humid environment, and C value > 0.8 indicates a humid environment. Among them, Fe represents the iron content, Mn represents the manganese content, Cr represents the chromium content, Ni represents the nickel content, V represents the vanadium content, Co represents the cobalt content, Ca represents the calcium content, Mg represents the magnesium content, Sr represents the strontium content, Ba represents the barium content, K represents the potassium content, and Na represents the sodium content.

[0069] (4) Paleo-redox index

[0070] V / Cr is the paleo-redox index, V / Cr>4.25 indicates a strong reducing environment, 2<V / Cr<4.25 indicates a weak reducing environment, and V / Cr<2 indicates an oxidizing environment. V represents the vanadium content, and Cr represents the chromium content.

[0071] In S2, the paleoenvironmental index of each location point is calculated based on the element distribution map, specifically including: for each location point, the element content of each element at the location point is determined based on the element distribution map, and the content is substituted into the calculation formula of the paleoenvironmental index to obtain the paleoenvironmental index of the location point.

[0072] In S2, the vertical surface is divided into several sedimentary facies belts based on the paleoenvironmental index and location information of each location point, specifically including: for each location point, the environmental type of the location point is determined based on the paleoenvironmental index of the location point; based on the environmental type and location information of each location point, the location points with the same environmental type and adjacent to each other are divided into a sedimentary facies belt, so as to divide the vertical surface into several sedimentary facies belts; if the environmental types of two sedimentary facies belts are the same, then the two sedimentary facies belts belong to the same sedimentary facies belt.

[0073] Among them, for each paleoenvironmental index, the corresponding environment type is determined based on the specific value of the paleoenvironmental index. When the paleoenvironmental index is the paleowater depth index, the environment types include deepwater environment and shallow water environment. When the paleoenvironmental index is the paleosalinity, the environment types include freshwater environment and saltwater environment. When the paleoenvironmental index is the paleoclimate index, the environment types include arid environment, semi-arid environment, semi-arid-semi-humid environment, semi-humid environment and humid environment. When the paleoenvironmental index is the paleo-redox index, the environment types include strong reducing environment, weak reducing environment and oxidizing environment.

[0074] Among them, the adjacent locations with the same environmental type are divided into a sedimentary facies belt, so as to divide the vertical surface into several sedimentary facies belts, specifically including: dividing the adjacent locations with the same environmental type into a sedimentary facies belt, and manually determining the boundaries of each sedimentary facies belt based on the element distribution map to divide the vertical surface into several sedimentary facies belts.

[0075] In S2, the proportion of each sedimentary facies belt is calculated, specifically including: inputting the image of the vertical plane (such as the element distribution map) into the image processing software, drawing the boundaries of each sedimentary facies belt in the image processing software, and selecting grayscale values ​​with large differences to fill different sedimentary facies belts, each sedimentary facies belt corresponds to a grayscale value, and calculating the proportion of each sedimentary facies belt according to the grayscale value of each sedimentary facies belt, and the proportion refers to the proportion of the area of ​​each sedimentary facies belt. The image processing software can be CorelDraw or Adobe Illustrator, etc.

[0076] In S3, the scanning area in the vertical surface is determined based on the proportion of each sedimentary phase belt, specifically including: setting the lateral side length of the scanning area to a first preset value, setting the vertical side length of the scanning area to a second preset value, and determining the position of the scanning area based on the proportion of each sedimentary phase belt, so that the area ratio of different sedimentary phase belts in the scanning area is equal to the proportion of each sedimentary phase belt, and determining the scanning area in the vertical surface. The first preset value may be 500 μm, and the second preset value may be 5000 μm-10000 μm.

[0077] In S3, a scanning area in the vertical surface of the heterogeneous shale sample is scanned using a scanning electron microscope, that is, a SEM-AMICS scan is performed on the scanning area in the vertical surface of the heterogeneous shale sample to obtain a mineral distribution map corresponding to the scanning area, and the mineral distribution map includes the mineral type and mineral content of each scanning point in the scanning area. By setting the scanning area, this embodiment can greatly reduce the time required for scanning and improve efficiency compared to scanning the entire vertical surface of the heterogeneous shale sample.

[0078] Considering that it takes a long time to perform SEM-AMICS scanning on the entire heterogeneous shale sample and the mineral distribution map of the entire heterogeneous shale sample is not required, the present embodiment selects a scanning area for SEM-AMICS scanning, and the lateral side length of the scanning area in the direction parallel to the laminae is 500 μm, and the vertical side length in the direction perpendicular to the laminae is 5000 μm-10000 μm, to obtain a mineral distribution map, which is a 2D mineral distribution map, and the mineral distribution map shows the spatial contact relationship between minerals and minerals, and between minerals and pores.

[0079] In S4, the initial area in the scanning area is determined based on the proportion of each sedimentary facies belt, specifically including: setting the lateral side length of the initial area to a first preset value, setting the vertical side length of the initial area to a third preset value, and determining the position of the initial area based on the proportion of each sedimentary facies belt, so that the length ratio of any vertical side in the initial area in different sedimentary facies belts is equal to the proportion of each sedimentary facies belt, and the initial area in the scanning area is determined, and the third preset value is less than the second preset value.

[0080] The first preset value may be 500 μm, and the third preset value may be a value greater than or equal to 500 μm. The length ratio of any vertical edge in the initial region in different sedimentary facies belts is equal to the proportion of each sedimentary facies belt, which means that the length ratio of a vertical edge in the initial region in different sedimentary facies belts is equal to the proportion of each sedimentary facies belt, and the length ratio refers to the ratio of the lengths of the vertical edges in different sedimentary facies belts.

[0081] It should be noted that, in this embodiment, the vertical direction refers to the direction perpendicular to the lamina, and the transverse direction refers to the direction parallel to the lamina. The vertical and transverse directions are perpendicular to each other, forming a vertical surface.

[0082] In the initial area selected in the element distribution map, because the shale particle size is less than 63μm, the most meaningful resolution in sediment characterization should be much higher than the size of the largest particle in a given core section. Therefore, the lateral side length in the direction parallel to the lamination is set to about 10 times the particle size of the largest mineral particle in the shale. The lateral side length in the direction parallel to the lamination can be 500μm, and the representative length of the lateral side length in the direction parallel to the lamination is obtained. Similarly, the vertical side length in the direction perpendicular to the lamination is set to ≥500μm. The position of the initial area is determined according to the proportion of various sedimentary facies belts. For example, if the inhomogeneous shale sample is divided into two sedimentary facies belts, each of which occupies 50% of the area of ​​the entire sample, then 50% of a vertical side in the direction perpendicular to the lamination is selected in one sedimentary facies belt, and the other 50% is selected in another sedimentary facies belt. At the same time, the initial area is located in the middle of the scanning area as much as possible.

[0083] In S4, the initial area is adjusted based on the mineral distribution map to determine the representative volume unit of the heterogeneous shale sample, specifically including: determining the first mineral content of each mineral in the initial area based on the mineral distribution map; adjusting the vertical side length of the initial area to obtain the adjusted area, and determining the second mineral content of each mineral in the adjusted area based on the mineral distribution map; calculating the mineral content change rate of each mineral based on the first mineral content and the second mineral content of each mineral, the mineral content change rate is the ratio of the difference and the average value, the difference is the difference between the second mineral content and the first mineral content, and the average value is the average value of the first mineral content and the second mineral content; judging whether the mineral content change rate of each mineral is less than a preset value, which may be 3%; if so, ending the iteration and determining the representative volume unit of the heterogeneous shale sample based on the adjusted area; if not, continuing the iteration, taking the adjusted area as the initial area of ​​the next iteration, and returning to the step of "adjusting the vertical side length of the initial area to obtain the adjusted area".

[0084] The vertical side length of the initial region is adjusted to obtain the adjusted region, specifically including: increasing the vertical side length L of the initial region by 100 μm at both ends to obtain the adjusted region.

[0085] Among them, the representative volume unit of the heterogeneous shale sample is determined based on the adjusted area, specifically including: setting the longitudinal side length perpendicular to both the transverse side length and the vertical side length to 500μm, and further determining a three-dimensional area based on the adjusted area and the longitudinal side length, and the three-dimensional area is the representative volume unit of the heterogeneous shale sample. This is because the mineral composition, pore structure, etc. of shale only change significantly in the vertical direction, so this embodiment sets the lengths of the other two mutually perpendicular sides (i.e., the transverse side length and the longitudinal side length) other than the vertical direction to a fixed value, such as 500μm. After determining the vertical side length based on the mineral distribution map, the three-dimensional area can be determined.

[0086] In the mineral distribution map of this embodiment, a horizontal side length of 500 μm × a vertical side length of 500 μm is used as the initial area (also called a basic unit), and the vertical side length L in the direction perpendicular to the lamination increases by 100 μm each time toward both ends. As the vertical side length increases, the change in mineral content in the adjusted area is calculated. If the mineral content does not change significantly with the increase in the length of the vertical side length in the direction perpendicular to the lamination, it is considered that the adjusted area represents a larger-scale sample. At this time, the volume of 500 μm × 500 μm × L μm is the representative volume unit of the heterogeneous shale sample.

[0087] In this embodiment, the obtained representative volume element (RVE) is used as the basic unit, and micro-drilling sampling is performed with a size of n×RVE (n≥1, which is a constant). The powder samples or block samples obtained are used for targeted experiments such as X-ray diffraction, mercury injection experiment, gas adsorption experiment, nuclear magnetic resonance experiment and displacement experiment. The obtained experimental results can be used for in-situ correlation analysis with minerals and organic matter in n×RVE, so that the experimental results are representative at both microscopic and mesoscopic scales.

[0088] Compared with traditional methods, the use of micro-area X-ray fluorescence spectrometer and scanning electron microscope-based mineral characterization automatic quantitative analysis system can efficiently determine the representative volume units of heterogeneous shale lithology, and can expand the representative volume units to a larger scale instead of being limited to a single thin layer. Other targeted experiments can be carried out based on the sampling of representative volume units, and macro-micro matching of characterization results can be achieved in situ.

[0089] In order to more clearly and in detail introduce the method for determining the representative volume unit of heterogeneous shale provided in this embodiment, the following will take the shale sample of the second section of the Funing Formation in the Subei Basin as an example for analysis and explanation:

[0090] Example 1

[0091] Mixed shale 1 of the second section of Funing Formation in Subei Basin was selected to prepare a sample of 1 cm × 1 cm in size. The sample was mechanically polished with sandpaper of 600 to 4000 mesh to obtain a smoother surface. The flat sample was scanned by micro-area XRF with a resolution of 30 μm to obtain an optical image and element distribution map. The optical image is as follows: Figure 2 As shown in A, the element distribution diagram is as follows Figure 2 As shown in B in the figure, the results show that the color of the optical image is relatively uniform, but the element distribution map shows that the sample has different sedimentary phases. In order to determine the type and proportion of the sedimentary phases, 8 locations are selected, such as Figure 2 A and Figure 2 For each point in the figure, the element content data is extracted to calculate the paleoenvironmental index. The calculation results are shown in Figure 1. Figure 2 As shown in C in the figure, the sample is divided into two sedimentary phase belt types based on the calculation results. The proportions of the two sedimentary phase belts calculated by image processing software are 38% and 62%, respectively. Figure 2As shown in D in the figure. On this basis, the horizontal side length in the direction parallel to the laminae is selected as 500 μm, and the vertical side length in the direction perpendicular to the laminae is selected as 5000 μm-10000 μm, which accounts for 38% and 62% in the two sedimentary phase belts respectively. The scanning area (also called representative area) is determined, and the scanning area is scanned by SEM-AMICS to obtain the mineral distribution map of minerals and pores. The mineral distribution map is shown in Figure 2 As shown in D (the far right in D), the mineral distribution map can be used to intuitively and quantitatively determine the mineral type, mineral content, and contact relationship between minerals and minerals, and between minerals and pores of the sample. Taking 500μm×500μm as the initial area, the vertical side length gradually increases by 100μm to both ends, and the change curve of the mineral content difference rate with the measurement area is obtained, as shown in Figure 3 As shown in the figure, it is found that the mineral content difference change rate after 500×4100μm is basically less than 3%. It is believed that this area represents a sample of a larger scale. The volume of this area, 500μm×500μm×4100μm, is the representative volume unit size of the sample. The representative volume unit is determined. Figure 4 As shown, the mineral content determined by the representative volume unit ( Figure 4 The AMICS mineral content in the sample was compared with the mineral content determined by the conventional XRD method ( Figure 4 XRD mineral content in the sample) was analyzed for correlation and R 2 =0.82, indicating that the representative volume unit determined by the method of this embodiment can reflect the mineral composition of the entire sample, and the representative volume unit result can be used to guide the selection of sampling areas for XRD testing or other experiments.

[0092] Example 2

[0093] We selected the mixed shale 2 of the second section of Funing Formation in Subei Basin, prepared a sample of 1 cm × 1 cm, and used sandpaper of 600 to 4000 mesh to mechanically polish the sample to obtain a smoother surface. The flat sample was scanned by micro-area XRF with a resolution of 30 μm to obtain an optical image and element distribution map. The optical image is as follows: Figure 5 As shown in A, the element distribution diagram is as follows Figure 5 As shown in B. The results show that both the optical image and the element distribution map show that the samples have different sedimentary phase zones. In order to determine the type and proportion of sedimentary phase zones, 5 locations were selected, such as Figure 5 A and Figure 5 For each location point, the element content data is extracted to calculate the paleoenvironmental index. The calculation results are as follows: Figure 5 As shown in C in the figure, it is identified that the sample has two types of sedimentary phase belts. Based on the calculation results, the sample is divided into two types of sedimentary phase belts. The image processing software is used to calculate that the two sedimentary phase belts account for 40% and 60% respectively, as shown in Figure 5 As shown in D in the figure. On this basis, the horizontal side length in the direction parallel to the laminae is selected as 500 μm, and the vertical side length in the direction perpendicular to the laminae is selected as 5000 μm-10000 μm, which accounts for 38% and 62% in the two sedimentary phase belts respectively. The scanning area is scanned by SEM-AMICS to obtain the mineral distribution map of minerals and pores, as shown in Figure 5 As shown in D (the far right in D), the mineral distribution map can be used to intuitively and quantitatively determine the mineral type, mineral content, and contact relationship between minerals and minerals, and between minerals and pores of the sample. Taking 500μm×500μm as the initial area, the vertical side length gradually increases by 100μm to both ends, and the change curve of the mineral content difference rate with the measurement area is obtained, as shown in Figure 6 As shown in the figure, it is found that the mineral content difference change rate after 500×4100μm is basically less than 3%. It is believed that this area represents a sample of a larger scale. The volume of this area, 500μm×500μm×4100μm, is the representative volume unit size of the sample. The representative volume unit is determined. Figure 7 As shown, the mineral content determined by the representative volume unit ( Figure 7 The AMICS mineral content in the sample was compared with the mineral content determined by the conventional XRD method ( Figure 7 XRD mineral content in the sample) was analyzed for correlation and R 2 =0.89, which further verifies the validity of the representative volume unit determined by the method of this embodiment.

[0094] This embodiment proposes a method for determining a representative volume unit of heterogeneous shale. The method uses a micro-area X-ray fluorescence spectrometer to perform 2D imaging of heterogeneous shale elements, and uses a mineral characterization automatic quantitative analysis system based on a scanning electron microscope to determine the representative volume unit of heterogeneous shale lithology. The method includes the following steps: select laminar shale samples of different thicknesses in a certain area, perform in-situ micro-area (better than 50μm resolution) XRF scanning on the laminar shale, and obtain an in-situ 2D high-resolution element distribution map of the laminar shale; fuse the optical image and the element distribution map to identify the rock component characteristics and fine sedimentary structures on the scale (mm) of the hand specimen or core of the laminar shale. Based on the element distribution map and element ratio obtained by the micro-area XRF scanning, the sedimentary facies belt is divided in combination with the paleoenvironmental index, and the proportion of various sedimentary facies belts is calculated using image processing software. Select the scanning area for scanning electron microscope imaging and obtain the submicron scale mineral distribution information of shale through AMICS analysis. The side length of the scanning area in the direction parallel to the laminae is set to 500μm, and the side length in the direction perpendicular to the laminae is set to 5000μm-10000μm. The position is determined according to the proportion of each sedimentary phase belt, and a microscopic 2D mineral distribution map that is still representative at the mesoscopic scale is obtained. If the rate of change of the difference in mineral content does not change significantly with the increase in the length in the direction perpendicular to the laminae, the area is considered representative. The volume of the area is 500×500×Lμm 3 The representative volume unit of heterogeneous shale lithology is taken as the basic unit, and other reservoir space characterization or geochemical related experiments are carried out by sampling with nRVE (n≥1) size. This method can efficiently, in situ and quantitatively determine the representative volume unit of heterogeneous shale lithology, which is of great significance for the macro-micro coupling of shale heterogeneity characterization results.

[0095] Example 2

[0096] Based on the same inventive concept, the embodiment of the present application also provides a device for determining a representative volume unit of heterogeneous shale for implementing the method for determining a representative volume unit of heterogeneous shale involved above. The implementation scheme for solving the problem provided by the device is similar to the implementation scheme recorded in the above method, so the specific limitations in the embodiment of the device for determining a representative volume unit of heterogeneous shale provided below can be referred to the limitations of the method for determining a representative volume unit of heterogeneous shale above, and will not be repeated here.

[0097] This embodiment provides a device for determining a representative volume unit of heterogeneous shale, and the device for determining a representative volume unit of heterogeneous shale includes:

[0098] The first data acquisition module is used to obtain an element distribution map; the element distribution map is obtained by scanning the vertical surface of the heterogeneous shale sample using a micro-area X-ray fluorescence spectrometer, and the element distribution map includes the element type and element content of each scanning point in the vertical surface.

[0099] The proportion calculation module is used to select multiple position points on the vertical surface, calculate the paleoenvironmental index of each of the position points based on the element distribution map, and divide the vertical surface into several sedimentary phase belts based on the paleoenvironmental index and position information of each of the position points, and calculate the proportion of each of the sedimentary phase belts.

[0100] The second data acquisition module is used to determine the scanning area in the vertical surface based on the proportion of each sedimentary phase belt, and obtain the mineral distribution map corresponding to the scanning area; the mineral distribution map is obtained by scanning the scanning area using a scanning electron microscope, and the mineral distribution map includes the mineral type and mineral content of each scanning point in the scanning area.

[0101] A determination module is used to determine an initial area in the scanning area based on the proportion of each of the sedimentary phase belts, and to adjust the initial area based on the mineral distribution map to determine a representative volume unit of the heterogeneous shale sample.

[0102] Example 3

[0103] In an exemplary embodiment, a computer device is provided. The computer device may be a server or a terminal. The internal structure diagram thereof may be as follows: Figure 8 As shown. The computer device includes a processor, a memory, an input / output interface (Input / Output, referred to as I / O) and a communication interface. The processor, the memory and the input / output interface are connected through a system bus, and the communication interface is connected to the system bus through the input / output interface. The processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system, a computer program and a database. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The input / output interface of the computer device is used to exchange information between the processor and an external device. The communication interface of the computer device is used to communicate with an external terminal through a network connection. When the computer program is executed by the processor, a method for determining a representative volume unit of heterogeneous shale is implemented.

[0104] Those skilled in the art will understand that Figure 8The structure shown in the figure is only a block diagram of a part of the structure related to the solution of the present application, and does not constitute a limitation on the computer device to which the solution of the present application is applied. The specific computer device may include more or fewer components than those shown in the figure, or combine certain components, or have a different arrangement of components.

[0105] In an exemplary embodiment, a computer device is also provided, including: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the method for determining a representative volume unit of heterogeneous shale described in Example 1.

[0106] Example 4

[0107] An embodiment of the present application provides a computer-readable storage medium having a computer program stored thereon. When the computer program is executed by a processor, the method for determining a representative volume unit of heterogeneous shale described in Embodiment 1 is implemented.

[0108] Example 5

[0109] An embodiment of the present application provides a computer program product, including a computer program, which, when executed by a processor, implements the method for determining a representative volume unit of heterogeneous shale described in Example 1.

[0110] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0111] This article uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and core ideas of this application. At the same time, for those skilled in the art, according to the ideas of this application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A method for determining a representative volume unit of heterogeneous shale, characterized in that: The method for determining the representative volume unit of the heterogeneous shale includes: Obtaining an element distribution map; the element distribution map is obtained by scanning the vertical surface of the heterogeneous shale sample using a micro-area X-ray fluorescence spectrometer, and the element distribution map includes the element type and element content of each scanning point in the vertical surface; Selecting a plurality of position points on the vertical surface, calculating the paleoenvironmental index of each of the position points based on the element distribution map, dividing the vertical surface into a plurality of sedimentary facies belts based on the paleoenvironmental index and position information of each of the position points, and calculating the proportion of each of the sedimentary facies belts; Determine a scanning area in the vertical surface based on the proportion of each of the sedimentary phase belts, and obtain a mineral distribution map corresponding to the scanning area; the mineral distribution map is obtained by scanning the scanning area using a scanning electron microscope, and the mineral distribution map includes the mineral type and mineral content of each scanning point in the scanning area; Determine an initial area in the scanning area based on the proportion of each of the sedimentary facies belts, and adjust the initial area based on the mineral distribution map to determine a representative volume unit of the heterogeneous shale sample; Based on the paleoenvironmental index and location information of each location point, the vertical surface is divided into several sedimentary facies zones, specifically including: For each of the location points, determining the environmental type of the location point based on the paleoenvironmental index of the location point; Based on the environmental type and location information of each of the location points, the location points with the same environmental type and adjacent to each other are divided into a sedimentary facies belt, so as to divide the vertical surface into several sedimentary facies belts; if the environmental types of two sedimentary facies belts are the same, the two sedimentary facies belts belong to the same sedimentary facies belt.

2. The method for determining a representative volume unit of heterogeneous shale according to claim 1, characterized in that: Selecting a plurality of position points on the vertical surface specifically includes: Acquire an optical image; the optical image is obtained by scanning the vertical surface of the heterogeneous shale sample using a micro-area X-ray fluorescence spectrometer; In combination with the optical image and the element distribution map, a plurality of position points are selected on the vertical surface.

3. The method for determining a representative volume unit of heterogeneous shale according to claim 1, characterized in that: The paleoenvironmental indexes include paleowater depth index, paleosalinity, paleoclimate index and paleooxidation-reduction index.

4. The method for determining a representative volume unit of heterogeneous shale according to claim 1, characterized in that: Determining the scanning area in the vertical surface based on the proportion of each of the sedimentary facies belts specifically includes: The lateral side length of the scanning area is set to a first preset value, the vertical side length of the scanning area is set to a second preset value, and the position of the scanning area is determined based on the proportion of each of the sedimentary phase belts, so that the area ratio of different sedimentary phase belts in the scanning area is equal to the proportion of each of the sedimentary phase belts, and the scanning area in the vertical surface is determined; Determining an initial area in the scanning area based on the proportion of each of the sedimentary facies belts specifically includes: The lateral side length of the initial area is set to a first preset value, and the vertical side length of the initial area is set to a third preset value. The position of the initial area is determined based on the proportion of each sedimentary phase belt, so that the length ratio of any vertical side in the initial area in different sedimentary phase belts is equal to the proportion of each sedimentary phase belt, and the initial area in the scanning area is determined; the third preset value is less than the second preset value.

5. The method for determining a representative volume unit of heterogeneous shale according to claim 1, characterized in that: The initial area is adjusted based on the mineral distribution map to determine a representative volume unit of the heterogeneous shale sample, specifically including: determining a first mineral content of each mineral in the initial area based on the mineral distribution map; Adjusting the vertical side length of the initial area to obtain an adjusted area, and determining the second mineral content of each mineral in the adjusted area based on the mineral distribution map; Based on the first mineral content and the second mineral content of each mineral, the mineral content change rate of each mineral is calculated; the mineral content change rate is the ratio of the difference and the average value, the difference is the difference between the second mineral content and the first mineral content, and the average value is the average value of the first mineral content and the second mineral content; Determine whether the mineral content change rate of each mineral is less than the preset value; If yes, then the iteration is terminated, and a representative volume unit of the heterogeneous shale sample is determined based on the adjusted area; If not, continue the iteration, use the adjusted region as the initial region of the next iteration, and return to the step of "adjusting the vertical side length of the initial region to obtain the adjusted region".

6. A device for determining a representative volume unit of heterogeneous shale, characterized in that: The device for determining the representative volume unit of heterogeneous shale comprises: A first data acquisition module is used to acquire an element distribution map; the element distribution map is obtained by scanning the vertical surface of the heterogeneous shale sample using a micro-area X-ray fluorescence spectrometer, and the element distribution map includes the element type and element content of each scanning point in the vertical surface; A proportion calculation module, used for selecting a plurality of position points on the vertical surface, calculating the paleoenvironmental index of each of the position points based on the element distribution map, dividing the vertical surface into a plurality of sedimentary facies belts based on the paleoenvironmental index and position information of each of the position points, and calculating the proportion of each of the sedimentary facies belts; A second data acquisition module is used to determine a scanning area in the vertical surface based on the proportion of each of the sedimentary phase belts, and obtain a mineral distribution map corresponding to the scanning area; the mineral distribution map is obtained by scanning the scanning area using a scanning electron microscope, and the mineral distribution map includes the mineral type and mineral content of each scanning point in the scanning area; A determination module, for determining an initial area in the scanning area based on the proportion of each of the sedimentary facies belts, and adjusting the initial area based on the mineral distribution map to determine a representative volume unit of the heterogeneous shale sample; Based on the paleoenvironmental index and location information of each location point, the vertical surface is divided into several sedimentary facies zones, specifically including: For each of the location points, determining the environmental type of the location point based on the paleoenvironmental index of the location point; Based on the environmental type and location information of each of the location points, the location points with the same environmental type and adjacent to each other are divided into a sedimentary facies belt, so as to divide the vertical surface into several sedimentary facies belts; if the environmental types of two sedimentary facies belts are the same, the two sedimentary facies belts belong to the same sedimentary facies belt.

7. A computer device comprising: A memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the method for determining a representative volume unit of heterogeneous shale according to any one of claims 1 to 5.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the method for determining a representative volume unit of heterogeneous shale according to any one of claims 1 to 5 is implemented.

9. A computer program product, comprising a computer program, characterized in that When the computer program is executed by a processor, the method for determining a representative volume unit of heterogeneous shale according to any one of claims 1 to 5 is implemented.

Images