A method for evaluating lamina structure segmentation and heterogeneity

Abstract

The application discloses a method for lamination structure sectioning and heterogeneity evaluation, wherein the sectioning method comprises the following steps: obtaining an image of different element distribution by scanning a rock sample by using an XRF spectrometer, and selecting an image of a representative element with obvious change as a first image; determining a first lamination division scheme according to the color depth change in the first image; obtaining an image under a laser confocal mode as a second image by scanning by using LSCM; determining a second lamination division scheme according to the light and dark and color change in the second image; obtaining a third lamination division scheme by taking an intersection; and sectioning the rock sample along a parallel distribution direction of the lamination determined according to the third lamination division scheme to obtain single lamination samples corresponding to respective laminations. The application realizes quantitative characterization of millimeter-level lamination structure and corresponding reservoir quality, and provides scientific guidance for effectiveness evaluation of different types of shale reservoirs.

Description

Technical Field

[0001] This invention relates to a method for fine segmentation of laminar structure and evaluation of heterogeneity in fine-grained sediments, belonging to the field of petroleum exploration technology. Background Technology

[0002] Petroleum geologists have conducted extensive and valuable research on the enrichment of organic matter and hydrocarbon generation evolution in fine-grained sediments, the characterization of micro- and nanopore throat systems and reservoir development mechanisms, oil migration and accumulation processes, and the evaluation and prediction of "sweet spots" (Jia Chengzhao, 2018; Liu Bo, 2018; Du Jinhu, 2019; Wu et al., 2019; Zou Caineng et al., 2019; Sun Longde, 2019). A consensus has been reached: the generally well-developed laminar structure in shale leads to reservoir heterogeneity, directly affecting shale hydrocarbon generation, reservoir space, and hydrocarbon content (Wang Guanmin, 2004; Shi Zhensheng, 2020; Xi Kelai, 2020; Hua Ganlin, 2021), and consequently influencing the selection and evaluation of "sweet spots" (Curtis, 2012; Li Jijun, 2015; Wang Yuhua, 2020). The so-called shale gas "sweet spots" refer to areas rich in shale gas that are easy to develop; the areas where "you can get more and better shale gas" are the sweet spots. There are many evaluation criteria for shale gas "sweet spots," such as the total organic carbon (TOC), brittleness, and gas content of shale. These parameters help us determine whether a shale gas exploration area belongs to a "sweet spot."

[0003] Previous studies on shale lamination have primarily focused on macroscopic heterogeneity (Liang Hongwei, 2013), using methods such as rock outcrops, thin section identification, XRD, and SEM, with lithofacies at the meter scale as the unit (Wang Ruifei, 2012). These studies mainly reflect the average values ​​of multiple lamination assemblages (WAGNER T, 2013), neglecting the impact of heterogeneity, especially individual laminations, on shale quality, including comparisons of organic matter abundance, mineral assemblage, and pore structure heterogeneity within individual laminations. Among these, organic-rich laminations are the truly contributing parts to hydrocarbon generation (Chen Jianping, 2013). Interbedded felsic silt laminations and carbonate laminations contribute less to hydrocarbon generation but can serve as hydrocarbon migration channels and reservoir spaces.

[0004] Therefore, strengthening the detailed evaluation of laminar structure, especially the accurate comparison and analysis of single laminar structures, is of great reference value for clarifying the hydrocarbon generation potential of shale, deepening the evaluation of shale heterogeneity, and selecting "sweet spots". Summary of the Invention

[0005] In view of the technical defects and drawbacks existing in the prior art, the embodiments of the present invention provide a method for laminar structure segmentation and heterogeneity evaluation that overcomes or at least partially solves the above problems.

[0006] This invention provides a method for segmenting laminar structures, comprising:

[0007] After scanning the rock sample with an X-ray fluorescence spectrometer, images of the distribution of different elements were obtained. The images of the representative elements with significant changes were selected as the first image.

[0008] The first texture layer division scheme is determined based on the color depth variations in the first image;

[0009] The rock sample was scanned using a laser scanning confocal microscope to obtain an image in laser confocal mode, which was then used as the second image.

[0010] The second texture layer division scheme is determined based on the changes in brightness and color in the second image;

[0011] The intersection of the first and second texture segmentation schemes yields the third texture segmentation scheme; and

[0012] The rock sample is divided along the parallel distribution direction of the layers as determined by the third layer division scheme to obtain individual layer samples corresponding to each layer.

[0013] Another aspect of the present invention provides a method for evaluating heterogeneity, comprising:

[0014] Total organic carbon analysis and rock pyrolysis were performed on each single-layered sample obtained by the above-described method; and

[0015] The organic geochemical characteristics of different laminations were determined based on the analysis results and pyrolysis data.

[0016] Another aspect of the present invention provides a method for evaluating heterogeneity, comprising:

[0017] Each individual lamellar sample obtained by the above method was scanned using FE-SEM, CT, and XRD; and

[0018] The mineral composition of different layers is determined based on the scan results.

[0019] Another aspect of the present invention provides a method for evaluating heterogeneity, comprising:

[0020] A three-dimensional pore model is obtained by CT scanning of each single-layered sample obtained by the above method; nitrogen adsorption experiments are performed on each single-layered sample to obtain nitrogen adsorption data; and the pore structure of the rock sample is determined based on the three-dimensional pore model and the nitrogen adsorption data.

[0021] In another aspect, the present invention provides a method for evaluating the effectiveness of shale reservoirs, comprising: evaluating the effectiveness of the shale reservoir corresponding to the rock sample based on the results of the heterogeneity evaluation obtained by the above method on the rock sample.

[0022] This invention achieves quantitative characterization of millimeter-level laminar structure and corresponding reservoir quality in various aspects, aiming to clarify the microscopic heterogeneity characteristics and main controlling factors of shale hydrocarbon generation potential, mineral composition and reservoir space, and provide scientific guidance for the optimal selection of oil and gas "sweet spots / sections" in shale systems.

[0023] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures described in the written description, claims, and drawings.

[0024] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0025] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0026] Figure 1 A schematic diagram of sample segmentation and preparation methods for rock samples used in experimental analysis;

[0027] Figure 2 This is a flowchart of a layer structure segmentation method provided in an embodiment of the present invention. Detailed Implementation

[0028] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0029] 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 numerals in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples of apparatuses and methods consistent with some aspects of the invention as detailed in the appended claims.

[0030] After research, the inventors have identified two existing technologies that address the aforementioned problems:

[0031] Existing technology one is a method for identifying the lithology of fine-grained sedimentary rocks based on XRF. It uses XRF to quantify minerals in fine-grained sedimentary rock samples and identify different lithologies. The main measurement steps are as follows:

[0032] (1) Based on XRF measured data, establish an equation relating the percentage content of each element in different minerals to the amount of substance of each mineral.

[0033] (2) Establish the equation relationship between the percentage content of different minerals and the amount of substance of each mineral;

[0034] (3) Establish the equation relationship between the percentage content of different minerals and the percentage content of each element in different minerals, and obtain the percentage content of each mineral.

[0035] (4) Establish radar charts based on the percentage content of each mineral in different lithologies, identify lithologies based on the morphology of different radar charts, and complete the identification of fine-grained sedimentary rock lithology based on XRF.

[0036] The drawback of the existing technology is that it only considers lithological classification using XRF elemental data and has not yet achieved high-precision classification of laminae using XRF elemental imaging technology. Furthermore, this technology does not analyze the evolutionary environment, diagenesis, and pore structure of different lithologies.

[0037] Existing technology two is a microscopic quantitative characterization method for organic matter laminae. A cross-section with clearly defined organic matter laminae is selected and polished to obtain a laser ablation target sample. The thickness, concentration, and content of organic matter laminae in the sediment are then quantitatively characterized. The main measurement steps are as follows:

[0038] (1) Cut the sediment into samples of regular shapes;

[0039] (2) Select the cross-section with obvious organic texture characteristics in the sample and polish the cross-section to obtain the laser ablation target sample;

[0040] (3) A combined system consisting of a laser ablation system and an inductively coupled plasma mass spectrometer was used, and the parameters of the combined system were tuned using standard samples;

[0041] (4) Place the laser ablation target sample in the sample cell of the laser ablation system of the combined system, select the area with obvious organic texture characteristics as the scanning area, and adjust the time uniformity of the laser ablation system and the inductively coupled plasma mass spectrometer.

[0042] (5) Set the spot size, scanning speed, single-element residence time of mass spectrometry and the types of nutrient trace elements to be measured, and conduct laser ablation-inductively coupled plasma mass spectrometry experiments to obtain the signal counts of each nutrient trace element.

[0043] (6) Plot a graph with laser ablation time or laser ablation distance as the horizontal axis and the signal count of each nutrient trace element as the vertical axis to determine the effective peak and the range of laser ablation time in the spectrum of each nutrient trace element.

[0044] The drawback of existing technology two is that it focuses primarily on the characteristics of organic matter laminae and does not analyze other types of laminae. Overall, existing research has focused on the characteristics of organic matter laminae, with limited research on other types of laminae. From the perspective of shale oil and gas sweet spot evaluation, felsic silt laminae and carbonate laminae exhibit better reservoir performance compared to organic matter laminae; therefore, more refined quantitative evaluation of different types of laminae is needed.

[0045] Therefore, this embodiment provides a method for fine-grained sedimentary rock lamellar fine-grained segmentation, such as... Figure 2 As shown, it includes the following steps:

[0046] Step 100: After scanning the rock sample with an X-ray fluorescence spectrometer, images of different element distributions are obtained. From these images, images of representative elements with significant changes are selected as the first image.

[0047] The rock sample exhibits a fine-grained, layered sedimentary structure. X-ray fluorescence spectrometry (XRF) is an instrument capable of rapidly and simultaneously determining multiple elements. XRF uses physical principles to detect elements in a substance, enabling both qualitative and quantitative analysis. Specifically, X-rays penetrate the electrons inside atoms, and the outer electrons replenish the characteristic X-rays, generating characteristic X-rays. The intensity of these characteristic X-rays determines the abundance of each element.

[0048] Specifically, a representative full-diameter shale columnar rock sample A can be collected first, with both ends cut flat. A line cut is then made along the direction perpendicular to the striations at approximately one-third of the diameter, yielding a cuboid portion B for XRF spectrometer scanning. The cuboid sample is then placed under an XRF spectrometer for surface scanning to obtain images of the distribution of different elements under XRF, and representative elements with significant variations are selected. Significant variations refer to a large number of gaps between the stripes, making it easy to distinguish individual stripe patterns.

[0049] Step 200: Determine the first texture layer division scheme based on the color depth changes in the first image.

[0050] The variations in color intensity reflect changes in element content. One or more representative elements can be used. When multiple representative elements are selected, their corresponding first images can be overlaid, and the first texture layer division scheme is determined based on the variations in color intensity after overlay. For example, Figure 1 The image to the left of the plus sign shows the first image obtained after selecting Ca and K as representative elements and overlapping them.

[0051] Specifically, the operation of determining the first layer division scheme can be carried out by manually marking on the first image, or other methods can be used.

[0052] Step 300: The rock sample is scanned using a laser scanning confocal microscope to obtain an image in laser confocal mode as a second image.

[0053] The laser scanning confocal microscope is LSCM (Laser Scanning Confocal Microscope). Specifically, the cuboid sample B can be prepared as a thin section and placed under the laser scanning confocal microscope for surface scanning to obtain an image in laser confocal mode as the second image. Step 400: Based on the brightness and color changes in the second image, the second texture segmentation scheme is determined.

[0054] Specifically, determining the second layer segmentation scheme can be done by manually annotating the second image, or it can be done in other ways. For example... Figure 1 The image to the right of the plus sign is shown.

[0055] Step 500: Take the intersection of the first texture partitioning scheme and the second texture partitioning scheme to obtain the third texture partitioning scheme.

[0056] like Figure 1 The image to the right of the plus sign shows the third ridge partitioning scheme obtained after taking the intersection. UA, UB, UC, and UD are symbols used to mark different ridges.

[0057] Step 600: The rock sample is divided along the parallel distribution direction of the layers determined according to the third layer division scheme to obtain single layer samples corresponding to each layer.

[0058] Specifically, based on the final lamellar division scheme, the remaining columnar sample C was traced. Along the parallel lamellar distribution direction, B and C were continuously and densely divided in millimeter increments using wire cutting technology to obtain samples of each individual lamellar layer.

[0059] This completes the fine segmentation of the lamellar structure of the rock sample. This method utilizes LSCM, thin sections, and XRF to divide individual lamellar layers, which are then peeled off one by one using wire cutting. It can be applied to lacustrine shale, transitional marine-continental shale, and marine shale. It breaks through the previous approach of using lamellar assemblage or lithology as units to study the heterogeneity of fine-grained sedimentary rocks, comprehensively utilizing XRF elemental imaging analysis and laser confocal large-area scanning analysis technology to develop a method for fine segmentation and division of single lamellar layers at the millimeter level.

[0060] Subsequently, based on the aforementioned single lamellar sample, the heterogeneity characteristics between lamellar layers can be further analyzed to perform microscopic quantitative characterization of the lamellar layers.

[0061] Therefore, this embodiment also provides a variety of heterogeneity evaluation methods, such as:

[0062] One method for evaluating heterogeneity is as follows: Total Organic Carbon (TOC) analysis and rock pyrolysis are performed on each single-layer sample obtained by the above method, and then the organic geochemical characteristics of different layers are determined based on the analysis results and pyrolysis data.

[0063] Before TOC and rock pyrolysis treatment, each individual lamellar sample can be crushed.

[0064] Another method for evaluating heterogeneity is to perform FE-SEM (Field Emission Scanning Electron Microscopy), CT (Computed Tomography), and XRD (X-Ray Diffraction) scans on each single-layer sample obtained by the above method, and then determine the mineral composition of different layers based on the scan results.

[0065] Before FE-SEM scanning, each individual texture sample can be argon-ion polished and carbon-coated; before CT scanning, each individual texture sample can be laser-cut; and before XRD scanning, each individual texture sample can be pulverized.

[0066] Another method for evaluating heterogeneity is as follows: CT scans are performed on each single-layered sample obtained by the above method to obtain a three-dimensional pore model; nitrogen adsorption experiments are performed on each single-layered sample to obtain nitrogen adsorption data; and the pore structure of the rock sample is determined based on the three-dimensional pore model and the nitrogen adsorption data.

[0067] Before performing a CT scan, each individual layer sample can be laser-cut; before performing a nitrogen adsorption experiment, each individual layer sample can be pulverized.

[0068] The various heterogeneity evaluation methods described above in this embodiment form a complete analytical process when studying the heterogeneity of rock samples. Based on qualitative and quantitative reservoir analysis, it evaluates the hydrocarbon generation potential of different laminae and compares the differences in heterogeneous characteristics such as mineral composition and pore network at the micro- and nano-scale, providing scientific guidance for the effectiveness evaluation of different types of shale reservoirs.

[0069] The following example illustrates this:

[0070] (1) Collect representative full-diameter shale rock samples ( Figure 1 -A), taking a cylindrical sample 20cm long and 10cm in diameter as an example, cut off the uneven ends, and then make a line cut along approximately 1 / 3 of the diameter perpendicular to the striation direction to obtain a cuboid part B approximately 20cm long, 1cm thick, and 7cm wide (see attached diagram). Figure 1 -B), place part B under XRF and use a surface scan mode with a step size of 20μm for the sample;

[0071] (2) Obtain the image of the distribution of different elements in part B under XRF, select the representative elements with obvious changes, and divide the texture according to the color depth of the element content;

[0072] (3) Then, part B is prepared into a rock thin section with a thickness of 0.03 mm, and placed under a laser scanning confocal microscope for surface scanning. The magnification is 100 times to obtain the laminar image in the laser confocal mode. The laminar image is divided according to the changes in brightness and color.

[0073] (4) Combining the two layer division schemes from the second and third steps, optimize and determine the attached layer division scheme. Figure 1 The laminar classification unit in the text marks the single laminar segmentation position of part B and part C;

[0074] (5) Secondary processing of parts B and C: along the parallel texture distribution direction, using wire cutting technology, parts B and C are continuously and densely cut in millimeters, and after single texture separation, a single texture sample is obtained.

[0075] (6) After secondary sampling, the separated single-layer samples are prepared into various sizes for subsequent laboratory testing. The single-layer samples are subjected to argon ion polishing, carbon plating, crushing and laser cutting, etc.

[0076] (7) Divide part B into 3 equal parts along the direction of the vertical lamellar plane; take out one part and divide it into single lamellar planes according to the lamellar plane division scheme. Then prepare each lamellar plane into a common optical thin section D with a size of 1cm*3cm*0.03mm. It is mainly used for optical microscope observation of the planar petrological and mineralogical characteristics of each single lamellar plane.

[0077] (8) For the second sample cut into part B in step (7), samples are continuously taken along the direction perpendicular to the laminae to prepare ordinary optical thin sections E. The thin section size is 3cm*5cm*0.03mm, which is mainly used for optical microscope observation of petrological and mineralogical characteristics in the direction perpendicular to the laminae.

[0078] (9) For the third sample divided into parts B in step (7), continuously sample along the direction perpendicular to the laminae and cut it into relatively flat and appropriately sized 1cm*1cm*0.5cm cubes F for field emission electron microscopy (FE-SEM) observation; fix the cubes to the nail stage with AB glue, and manually polish them with 800-grit, 1000-grit, and 2000-grit sandpaper respectively. Then, use a Laica argon ion polisher to perform circumferential polishing to ensure that the sample surface is flat and smooth before carbon plating. The recommended field emission electron microscopy imaging conditions are: working voltage 2kV, working distance 4.0mm;

[0079] (10) For the remaining sample after the preparation of the thin film in step (7), a cylindrical sample with a diameter of 1 mm and a length of 2 mm is drilled using a micro drill bit; then it is prepared into a small cylinder with a diameter of 65 μm and a length of 200 mm using laser cutting, for nano-CT three-dimensional pore structure scanning; the recommended scanning parameters are: 360° scanning, single angle scanning time of 90 s, and single sample scanning times of 1201 times; after the scanning is completed, the three-dimensional pore model is reconstructed and the porosity is calculated using three-dimensional analysis software;

[0080] (11) Grind each single layer of C into 200 mesh powder, of which 10g is used for XRD (X-ray diffraction), 5g is used for TOC and ROCK-EVAL tests, and 1g is used for low temperature nitrogen adsorption tests.

[0081] (12) The organic geochemical characteristics of different laminations were characterized by TOC and rock pyrolysis data; the mineral composition differences of different laminations were compared by XRD and SEM results; the pore structure of different laminations was analyzed by SEM, nitrogen adsorption and CT results, the quality differences of different laminations were clarified and their heterogeneous characteristics were determined.

[0082] This embodiment is the first to combine high-resolution XRF imaging and large-area laser scanning confocal microscopy for fine segmentation of laminar structures. Based on this, wire cutting technology is used to obtain individual laminae; subsequently, the organic geochemical characteristics, mineral composition, and pore structure of individual laminae are characterized at high resolution, enabling quantitative evaluation of different laminae and effectively improving the accuracy of laminar structure research. This invention can overcome the shortcomings of existing experimental techniques that cannot conduct high-precision single-laminar-layer studies, providing a reference for evaluating the reservoir performance of different types of shale. It can change the traditional research method based on laminar-layer combinations, further advancing the study of shale heterogeneity and providing scientific guidance for clarifying the "source-reservoir" enrichment mechanism of shale strata and the selection of "sweet spots."

[0083] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention 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 of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for segmenting layered structures, characterized in that, include: After scanning the rock sample with an X-ray fluorescence spectrometer, images of the distribution of different elements were obtained. The images of the representative elements with significant changes were selected as the first image. The first texture layer division scheme is determined based on the color depth variations in the first image; The rock sample was scanned using a laser scanning confocal microscope to obtain an image in laser confocal mode, which was then used as the second image. The second texture layer division scheme is determined based on the changes in brightness and color in the second image; The intersection of the first and second texture segmentation schemes yields the third texture segmentation scheme; and The rock sample is divided along the parallel distribution direction of the layers as determined by the third layer division scheme to obtain individual layer samples corresponding to each layer.

2. The method according to claim 1, characterized in that, The process of cutting includes: using wire cutting technology to continuously and densely cut the rock sample in millimeter increments.

3. The method according to claim 1, characterized in that, The scanning of rock samples using an X-ray fluorescence spectrometer includes: The ends of the full-diameter shale columnar rock sample were cut flat, and a cuboid sample was obtained by wire cutting along the direction perpendicular to the laminae at approximately one-third of the diameter; and The cuboid sample was scanned using an X-ray fluorescence spectrometer.

4. The method according to claim 3, characterized in that, The scanning of the rock sample using a laser scanning confocal microscope includes: The cuboid sample was prepared into a thin-film sample; and The thin-section sample was scanned using a laser scanning confocal microscope.

5. A method for evaluating heterogeneity, characterized in that, include: Total organic carbon analysis and rock pyrolysis treatment were performed on each single-layered sample obtained by the method described in any one of claims 1 to 4. as well as The organic geochemical characteristics of different laminations were determined based on the analysis results and pyrolysis data.

6. The method according to claim 5, characterized in that, Prior to the total organic carbon analysis and rock pyrolysis treatment, the process also includes pulverizing the individual lamellar samples.

7. A method for evaluating heterogeneity, characterized in that... include: Each single lamellar sample obtained by the method described in any one of claims 1 to 4 is scanned by FE-SEM, CT, and XRD. as well as The mineral composition of different layers is determined based on the scan results.

8. The method according to claim 7, characterized in that, Prior to the FE-SEM scan, the process also includes argon ion polishing and carbon plating of each individual textured sample.

9. The method according to claim 7, characterized in that, Prior to performing the CT scan, the procedure also includes laser cutting of each individual texture sample.

10. The method according to claim 7, characterized in that, Prior to performing the XRD scan, the process also includes pulverizing each individual lamellar sample.

11. A method for evaluating heterogeneity, characterized in that... include: A three-dimensional pore model is obtained by performing CT scanning on each single-layered sample obtained by the method described in any one of claims 1 to 4. Nitrogen adsorption data were obtained by performing nitrogen adsorption experiments on each of the individual textured samples. as well as The pore structure of the rock sample was determined based on the three-dimensional pore model and the nitrogen adsorption data.

12. The method according to claim 11, characterized in that, Prior to the CT scan, the procedure also includes laser cutting of each individual texture sample.

13. The method according to claim 11, characterized in that, Prior to conducting the nitrogen adsorption experiment, the process also includes pulverizing each individual textured sample.

14. A method for evaluating the effectiveness of shale reservoirs, characterized in that, include: Based on the results of the heterogeneity evaluation of the rock sample obtained by the method described in any one of claims 5 to 13, the effectiveness of the shale reservoir corresponding to the rock sample is evaluated.

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