Shale heterogeneity micro-scale fine characterization method and system

Abstract

The invention discloses a shale heterogeneity micro-scale fine characterization method and a shale heterogeneity micro-scale fine characterization system. The method comprises the following steps: preparing a thin plate sample of a target lamina based on a shale reservoir rock core sample of a to-be-detected developed high-density thin-thin lamina; wherein the target grain layer is a single grain layer or a layer even mainly comprising the single grain layer; the thin plate sample is transversely segmented in the bedding direction of the target lamina to obtain a first sub-thin plate sample, a second sub-thin plate sample and a third sub-thin plate sample, and the total porosity of the target lamina, macroscopic information and microscopic information of organic-inorganic component and aperture structure integration, organic matter abundance and oiliness data are obtained respectively. By means of the method, component-structure-physical property integrated in-situ quantitative and multi-scale imaging analysis of the same sample in the same vision field can be achieved, organic and inorganic components of a single lamina, aperture structure characteristics and differences among different laminas are found out, and effective analysis of the heterogeneity of shale developing high-density millimeter-micron lamina sections is achieved.

Description

Technical Field

[0001] This invention belongs to the field of shale exploration technology, and more specifically, relates to a method and system for fine microscale characterization of shale heterogeneity. Background Technology

[0002] High-quality shale reservoirs are the core of shale oil and gas exploration and development, and reservoir quality evaluation is an integral part of the entire exploration and development process. Shale reservoirs exhibit strong heterogeneity, primarily controlled by lamellar structure and assemblage types, including the organic-inorganic composition and microstructure within the lamellar layers, and the characteristics of lamellar combinations at different scales and of different types. This not only causes significant differences in reservoir quality and hydrocarbon content but also affects the enrichment state and mobility of crude oil, making the prediction of high-quality reservoirs and sweet spots extremely difficult, especially in areas with high-density millimeter- to micrometer-scale thin to ultrathin lamellar segments. Therefore, characterization studies of shale lamellars are particularly important.

[0003] Shale reservoirs generally possess characteristics such as low porosity and permeability, as well as complex composition and structure, making traditional reservoir evaluation experimental techniques not entirely applicable. Currently, scanning electron microscopy, gas (helium) methods, liquid (mercury intrusion porosimetry), and nuclear magnetic resonance (NMR) are mainly used to obtain information such as microscopic pore structure and mineral composition required for shale reservoir evaluation. However, these methods still have many limitations. Among them: 1) The helium injection method mainly detects the effective porosity of samples that are not occupied by fluids and are interconnected. For samples containing fluids (oil, water), the total porosity can only be detected by pretreatment of the fluids (such as washing oil, drying). However, shale reservoirs have always faced the problem of difficult removal of retained fluids. For example, in oil-containing samples, the washing solvent cannot "enter," and even if it is injected, it cannot "exit." The liquid injection method also has similar problems in porosity determination. In particular, these solvents are prone to reacting or adsorbing with organic matter and clay minerals in the sample, resulting in secondary pollution and directly affecting the quality of analysis.

[0004] Nuclear magnetic resonance (NMR) primarily detects the porosity occupied by hydrogen-containing fluids (oil, water). It cannot detect pores not filled by fluid. The total porosity can only be obtained by saturating the sample with a hydrogen-containing fluid and filling all pores. However, fluid saturation still presents the problem of "not being able to get in." High pressure and prolonged immersion can easily damage the sample. Furthermore, the immersion fluid may react or adsorb with kerogen and clay minerals, which can still affect the experimental results.

[0005] Scanning electron microscopy (SEM) can obtain microscopic structural information through high-resolution imaging, but its small field of view always suffers from a lack of representativeness and difficulty in identifying organic matter types. However, the characteristics of organic microscopic components, such as the type, distribution, and porosity of organic matter, have a significant impact on the occurrence, accumulation, and mobility of shale oil and gas. Therefore, two major challenges urgently need to be addressed: first, how to effectively connect the microscopic and macroscopic perspectives, and what technical approach can be used to effectively express the microscopic information obtained from SEM in a macroscopic manner to solve the "representativeness" problem; second, how to combine organic microscopic component analysis under different optical conditions (polarizing, fluorescence) with SEM to achieve in-situ quantitative multi-scale imaging of organic and inorganic composition, pores, and microfractures within a specified region (micro-area).

[0006] Currently, shale reservoir sampling still follows traditional sampling methods and experimental technical standards. For example, standard plunger samples with a diameter of Φ1 inch (25.4 mm) or Φ1.5 inch (38 mm) are collected for property analysis, and large blocks weighing tens of grams are collected for geochemical, thin section, and electron microscopy analysis. For thin-layered to ultra-thin-layered laminae (single laminae thickness <1 cm, mm-μm level laminae), these are all mixed samples, making it difficult to finely characterize the internal composition and fabric of a single laminae, as well as the different laminae structures and types. Therefore, how can we break through traditional thinking and technical standards to collect single-layered samples that do not require oil washing or soaking pretreatment, allow for non-destructive and multiple tests, meet experimental technical conditions, and obtain reliable analytical data? This would enable a multi-scale, multi-type experimental technique for fine characterization of composition, fabric, and properties within the same sample and field of view, providing important evidence for revealing the properties of single laminae, the comparison between different laminae, and the fine characterization of shale reservoirs formed by their combinations.

[0007] The information disclosed in the background section of this invention is intended only to enhance the understanding of the general background of this invention, and should not be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art. Summary of the Invention

[0008] The purpose of this invention is to propose a microscale fine characterization method and system for shale heterogeneity, which can realize in-situ quantitative and multi-scale imaging analysis of composition, structure and physical properties in the same field of view of the same sample, identify the organic and inorganic composition of a single laminae, the pore and fracture structure characteristics and the differences between different laminae, and provide important basis for fine characterization of shale heterogeneity.

[0009] To achieve the above objectives, this invention proposes a method and system for fine microscale characterization of shale heterogeneity.

[0010] According to a first aspect of the present invention, a method for fine microscale characterization of shale heterogeneity is proposed, comprising:

[0011] Thin plate samples of the target lamination were prepared from shale reservoir core samples with high-density thin to ultrathin laminations.

[0012] The target texture is a single texture or a layer pair with a single texture as the main component.

[0013] The thin plate sample is laterally divided along the target lamination direction to obtain a first sub-thin plate sample, a second sub-thin plate sample, and a third sub-thin plate sample.

[0014] Based on the first sub-thin plate sample under its original state, the effective pore volume of high-pressure helium gas and the pore volume of nuclear magnetic fluid are measured to obtain the total porosity of the target texture.

[0015] Based on the second sub-thin plate sample, in-situ micro-region quantitative-imaging analysis was carried out using multi-scale optical and electron microscopy to obtain macroscopic and microscopic information on the organic-inorganic components and pore structure of the target layer.

[0016] Geochemical quantitative analysis was conducted based on the third sub-thin plate sample to obtain data on the organic matter abundance and oil content of the target laminar layer.

[0017] Optionally, the step of measuring the effective pore volume of high-pressure helium and the pore volume of nuclear magnetic fluid based on the first sub-thin plate sample in its original state to obtain the total porosity of the target texture includes:

[0018] The first sub-thin plate sample is pretreated, including drying and isothermal treatment;

[0019] The total volume of the first sub-thin plate sample after pretreatment was determined.

[0020] Based on the pretreated first sub-thin plate sample, porosity analysis was carried out using a high-pressure helium injection method under pressure conditions to obtain the effective pore volume of high-pressure helium.

[0021] The pore volume of the magnetic flux was determined using a two-dimensional nuclear magnetic resonance method based on the first sub-thin plate sample after pretreatment.

[0022] The total porosity of the target texture is calculated based on the pore volume of the nuclear magnetic fluid, the effective pore volume of high-pressure helium, and the total volume.

[0023] Optionally, the in-situ micro-region quantitative-imaging analysis based on the second sub-thin plate sample using multi-scale optical and electron microscopy to obtain integrated macroscopic and microscopic information on the organic-inorganic composition and pore structure of the target laminae includes:

[0024] The second sub-thin plate sample was prepared as a common sample suitable for analysis by polarized fluorescence microscopy and scanning electron microscopy;

[0025] Based on the shared sample and the polarized fluorescence microscope, the structure of the target striations was analyzed in detail, and the target striation measurement area was initially selected.

[0026] The shared sample was subjected to carbon plating treatment to obtain a carbon-plated sample;

[0027] Based on the carbon-coated sample, a full-field scanning electron microscope was used to conduct a quantitative evaluation of minerals and a quantitative analysis of the composition of the initially selected target laminar surface area, thereby quantitatively characterizing the elemental content and mineral composition of the carbon-coated sample.

[0028] Based on the carbon-plated sample, a large field-of-view, high-resolution imaging scan was performed using field emission scanning electron microscopy. Combined with the quantitative analysis results of the composition of the initially selected target striation region, the target striation measurement area was accurately delineated.

[0029] The carbon-plated sample was polished, carbon-removed, and oil-immersed in sequence to obtain an oil-immersed sample;

[0030] Based on the oil-immersed sample, an organic petrological analysis was performed using polarized fluorescence microscopy to finely characterize the organic micro-components of the oil-immersed sample. At the same time, an etching method was used to delineate and mark specific organic and inorganic target areas.

[0031] The oil-immersed sample was polished and carbon-plated sequentially to obtain a secondary carbon-plated sample.

[0032] Based on the secondary carbon-plated sample and the specific organic and inorganic target regions, high-resolution imaging characterization integrating composition and structure was carried out using field emission scanning electron microscopy and focused ion beam scanning electron microscopy to obtain microscopic information on the composition and pore structure of the specific organic and inorganic target regions. The scanning images of the specific organic and inorganic target regions were then stitched together to obtain imaging results with a typical macroscopic field of view.

[0033] High-resolution imaging and two-dimensional nuclear magnetic resonance (NMR) analysis of the shared sample using the low-pressure secondary electron mode of field emission scanning electron microscopy (FET) provide a comprehensive quantitative-imaging characterization of the oil retention state. Optionally, the geochemical quantitative analysis based on the third sub-thin plate sample to obtain organic matter abundance and oil-bearing data of the target laminae includes:

[0034] The third sub-thin plate sample was ground to a particle size of less than 200 μm, and the total organic carbon content and rock pyrolysis parameters of the third sub-thin plate sample were analyzed to quantitatively characterize the organic component characteristics of the target laminar layer.

[0035] Optionally, the thin plate sample has a length of 50-70 mm, a width of 20-25 mm, and a thickness of 4 mm.

[0036] Optionally, the length of the first sub-thin plate sample is 40–60 mm.

[0037] Optionally, the length of both the second and third sub-thin plate samples is 5 mm.

[0038] Optionally, the common sample has a length of 5-7 mm, a width of 4 mm, and a thickness of 5 mm.

[0039] Optionally, the formula for calculating the total porosity is:

[0040] φ t =(V oe +V of ) / V t ×100%;

[0041] Among them, V oe V is the effective pore volume of high-pressure helium gas. of V is the pore volume of the nuclear magnetic fluid. t The total volume of the first sub-thin plate sample is φ. t Total porosity.

[0042] According to a second aspect of the present invention, a fine microscale characterization system for shale heterogeneity is proposed, comprising:

[0043] The preparation module is used to prepare thin-plate samples of the target lamination based on shale reservoir core samples with high-density thin to ultrathin laminations to be tested;

[0044] The target texture is a single texture or a layer pair with a single texture as the main component.

[0045] The segmentation module is used to laterally segment the thin plate sample along the target lamination direction to obtain a first sub-thin plate sample, a second sub-thin plate sample, and a third sub-thin plate sample.

[0046] The joint measurement module is used to measure the effective pore volume of high-pressure helium and the pore volume of nuclear magnetic fluid based on the first sub-thin plate sample in its original state, thereby obtaining the total porosity of the target texture.

[0047] The quantitative imaging analysis module is used to perform in-situ micro-region quantitative imaging analysis based on the second sub-thin plate sample using multi-scale optical and electron microscopy to obtain integrated macroscopic and microscopic information on the organic-inorganic components and pore structure of the target texture.

[0048] The geochemical quantitative analysis module is used to conduct geochemical quantitative analysis based on the third sub-thin plate sample to obtain data on the organic matter abundance and oil content of the target laminar layer.

[0049] The beneficial effects of this invention are as follows:

[0050] 1) For thin- to ultra-thin layered shale reservoirs, single-layer (layer-pair) thin plate samples were prepared. Multi-scale and multi-type experimental techniques were used to carry out in-situ quantitative and high-resolution imaging comprehensive analysis of composition, structure and physical properties in a designated area. This enabled fine characterization of the composition, structure and physical properties inside a single layer in shale reservoirs, as well as different layer structures and their combinations.

[0051] 2) Using the same sample and the same field of view as the main focus, conduct multiple non-destructive tests on the same sample:

[0052] (1) Effective determination of total porosity without oil washing or soaking was achieved. Based on the advantages of helium injection method for determining effective pore volume (i.e., pores not filled by fluid) and nuclear magnetic resonance method for determining pore volume occupied by fluid, a pressure-covered porosity measuring instrument and nuclear magnetic resonance instrument were used to measure the effective pore volume of high-pressure helium gas and the nuclear magnetic fluid pore volume of T2 relaxation spectrum of the sample under the original state. Combined with the total volume of the sample, the total porosity and the original fluid saturation were obtained, solving the problem of "oil washing and soaking".

[0053] (2) Effective integration of microscopic and macroscopic information on organic-inorganic components and pore structure was achieved. Based on the preparation of samples that can be used for both optical and electron microscopy, through optimization of relevant experimental procedures (polishing, oil immersion), and by combining polarized fluorescence microscopy with scanning electron microscopy mineral quantitative evaluation system, field emission scanning electron microscopy and other electron microscopy techniques, in-situ quantitative-multiscale imaging fine characterization of organic matter, minerals, pores, microcracks, etc. in the delineated target area was carried out. Microscopic information on organic-inorganic components and pore structure was obtained, and by stitching together to form a large field of view image, the problem of "representativeness of micro-area samples and identification of organic microscopic components" was solved.

[0054] (3) A quantitative-imaging integrated description of the state of retained oil has been achieved. Under low-pressure and carbon-free conditions, the retained oil film in nanopores can be observed through secondary electron mode using field emission scanning electron microscopy. Combined with the quantitative test of the retained oil content by nuclear magnetic resonance spectroscopy in the same sample, the state of retained oil can be quantitatively-imaging integrated.

[0055] By integrating and analyzing multi-scale and multi-type experimental techniques on the above-mentioned single-layer thin plate samples, the content and distribution of organic and inorganic components, grain size and pore structure, microfracture structural characteristics, and differences between different types of thin-to-ultra-thin layers (layer pairs) of single layers are identified. This enables effective analysis of the heterogeneity of shale with high-density millimeter-to-micrometer-level layered segments, providing important basis and technical support for high-quality reservoir modeling and sweet spot prediction.

[0056] The system of the present invention has other features and advantages that will be apparent from or will be set forth in detail in the accompanying drawings and following detailed description, which together serve to explain the particular principles of the invention. Attached Figure Description

[0057] The above and other objects, features and advantages of the present invention will become more apparent from the accompanying drawings, in which like reference numerals generally denote like parts.

[0058] Figure 1 A flowchart illustrating the steps of a method for fine microscale characterization of shale heterogeneity according to the present invention is shown.

[0059] Figure 2 A schematic diagram of the nuclear magnetic resonance T1-T2 spectrum according to Embodiment 1 of the present invention is shown.

[0060] Figure 3 A schematic diagram of an optical microscope, a field emission scanning electron microscope, and a scanning electron microscope mineral quantitative evaluation system for the target laminar flow measurement area according to Embodiment 1 of the present invention is shown.

[0061] Figure 4 A schematic diagram of the fine microstructure analysis of high-carbon clay texture using field emission scanning electron microscopy according to Embodiment 1 of the present invention is shown.

[0062] Figure 5 A schematic diagram of the organic petrological analysis of high-carbon clay laminae using a polarized fluorescence microscope according to Embodiment 1 of the present invention is shown. Detailed Implementation

[0063] The invention will now be described in more detail with reference to the accompanying drawings. While preferred embodiments of the invention are shown in the drawings, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0064] like Figure 1 As shown, a method for fine microscale characterization of shale heterogeneity according to the present invention includes:

[0065] Thin plate samples of the target lamination were prepared from shale reservoir core samples with high-density thin to ultrathin laminations.

[0066] Among them, the target texture is a single texture or a layered pattern dominated by a single texture;

[0067] The thin plate sample is laterally divided along the target lamination direction to obtain the first sub-thin plate sample, the second sub-thin plate sample and the third sub-thin plate sample;

[0068] Based on the first sub-thin plate sample under the original state, the effective pore volume of high-pressure helium gas and the pore volume of nuclear magnetic fluid are measured to obtain the total porosity of the target texture.

[0069] In-situ micro-region quantitative-imaging analysis was carried out using multi-scale optical and electron microscopy based on the second sub-thin plate sample to obtain macroscopic and microscopic information on the organic-inorganic composition and pore structure of the target layer.

[0070] Geochemical quantitative analysis was conducted based on the third sub-thin plate sample to obtain data on the organic matter abundance and oil content of the target laminar layer.

[0071] Specifically, for shale reservoir core samples with high-density thin to ultrathin laminae to be tested, different types of laminae, and laminae of the same type with different thicknesses and densities, are analyzed based on parameters such as sample hardness and thickness to determine the target laminae for cutting. The target laminae are single laminae or laminae dominated by a single laminae. During the cutting process, cutting is strictly performed along the upper and lower interfaces of the same single laminae or laminae dominated by a single laminae to ensure that the prepared thin plate sample is the target laminae, i.e., the same single laminae or laminae dominated by this laminae. The thin plate sample is cut along its long side. The sample is laterally divided to obtain a first sub-thin plate sample, a second sub-thin plate sample, and a third sub-thin plate sample. The width and thickness of each sub-thin plate sample are the same as those of the thin plate sample, and the sum of the lengths of each sub-thin plate sample is equal to the length of the thin plate sample. The cross-sections of the three sub-thin plate samples are the same field of view of the same laminar layer sample. By measuring the effective pore volume of high-pressure helium and the pore volume of NMR fluid in the original state of the first sub-thin plate sample, the total porosity of the target laminar layer can be obtained, realizing the effective determination of total porosity under conditions of no washing oil and no soaking. Leveraging the advantages of helium injection for determining effective pore volume (i.e., pores not filled by fluid) and nuclear magnetic resonance (NMR) for determining fluid-occupied pore volume, this study employs a pressure-controlled porosity meter and NMR spectrometer to simultaneously measure the effective pore volume under high-pressure helium and the fluid pore volume from the T2 relaxation spectrum of the NMR spectrum. Combined with the total volume of the sample, the total porosity and initial fluid saturation are obtained, solving the challenges of "oil washing and soaking." Furthermore, in-situ micro-area quantitative-imaging analysis is conducted using a second sub-thin plate sample coupled with multi-scale optical and electron microscopy to obtain integrated macroscopic and microscopic information on the organic-inorganic components and pore structure of the target laminae. This achieves effective integration of microscopic and macroscopic information on organic-inorganic components and pore structure. The study integrates optical and electron microscopy (OSM) techniques. Based on the preparation of samples compatible with both optical and electron microscopy, and through optimization of experimental procedures (polishing, oil immersion), it combines polarized fluorescence microscopy with a scanning electron microscope (SEM) mineral quantitative evaluation system and field emission scanning electron microscopy (FETS) to conduct in-situ quantitative-multi-scale imaging characterization of organic matter, minerals, pores, and microcracks within the delineated target area. This yields integrated microscopic information on organic-inorganic components and pore structure, and by stitching together images to form a large field of view, it solves the problem of "representativeness of micro-area samples and identification of organic microscopic components." Geochemical quantitative analysis is conducted using a third-sub-thin plate sample to obtain data on the organic matter abundance and oil content of the target laminae, achieving a comprehensive quantitative-imaging description of the oil retention state. Using the low-pressure, carbon-free conditions of FETS, the oil retention film in nanopores can be observed in secondary electron mode. Combined with the quantitative testing of oil retention content by nuclear magnetic resonance spectroscopy in the same sample, a comprehensive quantitative-imaging characterization of the oil retention state can be achieved.By integrating and analyzing multi-scale and multi-type experimental techniques on the above-mentioned single-layer thin plate samples, the content and distribution of organic and inorganic components, grain size and pore structure, microfracture structural characteristics, and differences between different types of thin-to-ultra-thin layers (layer pairs) of single layers are identified. This enables effective analysis of the heterogeneity of shale with high-density millimeter-to-micrometer-level layered segments, providing important basis and technical support for high-quality reservoir modeling and sweet spot prediction.

[0072] In one example, the total porosity of the target laminar layer is obtained by measuring the effective pore volume of high-pressure helium and the pore volume of nuclear magnetic fluid based on the first sub-thin plate sample in its original state, including:

[0073] The first sub-thin plate sample was pretreated, including drying and isothermal treatment;

[0074] The total volume of the first sub-thin plate sample after pretreatment was determined.

[0075] Based on the pretreated first sub-thin plate sample, porosity analysis was carried out using the high-pressure helium injection method under pressure conditions to obtain the effective pore volume of high-pressure helium.

[0076] The pore volume of the nuclear magnetic fluid was determined using a two-dimensional nuclear magnetic resonance method based on the first sub-thin plate sample that had completed pretreatment.

[0077] The total porosity of the target layer is calculated based on the pore volume of nuclear magnetic fluid, the effective pore volume of high-pressure helium, and the total volume.

[0078] Specifically, firstly, a customized thin-plate sample chamber is used to perform helium porosity analysis on the first sub-thin-plate sample to quantitatively characterize the effective porosity of the target layer. Since conventional helium porosity analysis sample chambers are 1-inch or 1.5-inch plunger sample chambers, which are not suitable for thin-plate samples, this invention customizes a thin-plate sample chamber according to the specifications of the thin-plate sample and applies it to a conventional sample chamber during specific experimental analysis. Then, a nuclear magnetic resonance spectrometer is used to measure the effective pore volume of high-pressure helium and the pore volume of nuclear magnetic fluid on the first sub-thin-plate sample in its original state, thereby obtaining the total porosity of the target layer, realizing the effective determination of total porosity under conditions of no washing or soaking. Based on the advantages of using the helium injection method to determine the effective pore volume (i.e., pores not filled by fluid) and the nuclear magnetic resonance method to determine the pore volume occupied by fluid, this study uses a pressure-controlled porosity meter and a nuclear magnetic resonance spectrometer to jointly measure the effective pore volume of high-pressure helium gas in the original state of the sample and the nuclear magnetic fluid pore volume of the T2 relaxation spectrum. Combined with the total volume of the sample, the total porosity and the original fluid saturation are obtained, thus solving the problem of "washing oil and soaking".

[0079] In one example, in-situ micro-region quantitative-imaging analysis was performed using multi-scale optical and electron microscopy based on a second sub-thin plate sample to obtain integrated macroscopic and microscopic information on the organic-inorganic composition and pore structure of the target laminae, including:

[0080] The second sub-thin plate sample was prepared as a common sample suitable for analysis by polarized fluorescence microscopy and scanning electron microscopy;

[0081] The structure of the target striations was analyzed in detail using a shared sample and a polarized fluorescence microscope, and the target striation measurement area was initially selected.

[0082] The shared sample was subjected to carbon plating treatment to obtain a carbon-plated sample;

[0083] Based on carbon-coated samples, we conducted full-field scanning electron microscopy mineral quantitative evaluation and preliminary target laminar flow determination region composition quantitative analysis to quantitatively characterize the elemental content and mineral composition characteristics of carbon-coated samples.

[0084] Based on the carbon-plated sample, a large field-of-view, high-resolution imaging scan was performed using field emission scanning electron microscopy. Combined with the quantitative analysis results of the composition of the initially selected target striation region, the target striation measurement area was accurately delineated.

[0085] The carbon-plated sample was polished, carbon-removed, and oil-immersed in sequence to obtain an oil-immersed sample.

[0086] Organic petrological analysis based on polarized fluorescence microscopy of oil-immersed samples was carried out to finely characterize the organic micro-components of the oil-immersed samples. At the same time, etching was used to delineate and mark specific organic and inorganic target areas.

[0087] The oil-immersed sample was polished and carbon-plated sequentially to obtain a secondary carbon-plated sample.

[0088] Based on secondary carbon-plated samples and specific organic and inorganic target regions, high-resolution imaging characterization integrating composition and structure was carried out using field emission scanning electron microscopy and focused ion beam scanning electron microscopy. Microscopic information on the composition and pore structure of specific organic and inorganic target regions was obtained, and the scanning images of specific organic and inorganic target regions were stitched together to obtain imaging results of typical macroscopic fields of view.

[0089] Based on the low-pressure secondary electron mode of field emission scanning electron microscopy, a comprehensive analysis of the oil retention characteristics of common samples was performed using high-resolution imaging and two-dimensional nuclear magnetic resonance imaging, which quantitatively and precisely characterized the oil retention state.

[0090] Specifically, the second sub-thin plate sample was first finely ground and argon-ion polished to prepare a high-quality shared sample suitable for microscale fine analysis using polarized fluorescence microscopy and scanning electron microscopy. To ensure the observation of more features of the shale sample, the prepared sample size should be as large as possible but not exceed the sample stage; therefore, the length and width of the sample should be less than 1 cm. To ensure clearer imaging under high-resolution scanning electron microscopy, the width was controlled to 4 mm. Since the scanning electron microscopy sample requires carbon coating and the organic petrology analysis requires sample gelation, the rock and mineral identification was first performed using polarized fluorescence microscopy without carbon coating or oil immersion. The structure of the target laminae was finely analyzed, and the target laminae measurement area was initially selected. Then, the shared sample was carbon-coated to obtain a carbon-coated sample. Full-field scanning electron microscopy mineral quantitative evaluation and component quantitative analysis of the initially selected target laminae measurement area were carried out to quantitatively characterize the elemental content and mineral composition characteristics of the carbon-coated sample. Finally, field emission scanning electron microscopy large-field high-resolution imaging scanning was performed on this carbon-coated sample, combined with... The initial quantitative analysis of the target lamellar region accurately delineates the target lamellar measurement area. The carbon-coated sample is then polished, carbonized, and oil-immersed sequentially to obtain an oil-immersed sample. Based on the oil-immersed sample, polarized back fluorescence microscopy is used for organic petrological analysis to finely characterize the organic micro-components. Simultaneously, etching is used to delineate and mark specific organic and inorganic target regions. The oil-immersed sample is then polished and carbon-coated sequentially to obtain a secondary carbon-coated sample. Based on the secondary carbon-coated sample and the specific organic and inorganic target regions, high-resolution imaging characterization integrating composition and structure is performed using field emission scanning electron microscopy (FEM) and focused ion beam scanning electron microscopy (FIX). This obtains microscopic information on the composition and pore structure of the specific organic and inorganic target regions. The scanned images of the specific organic and inorganic target regions are then stitched together, for example, using MAPS software, to obtain imaging results with a typical macroscopic field of view. Based on the low-voltage secondary electron mode of FEM, a comprehensive analysis of the common sample's high-resolution imaging and two-dimensional nuclear magnetic resonance (NMR) of the retained oil is performed, quantitatively and imaging-based to finely characterize the retained oil's state. This method effectively integrates microscopic and macroscopic information on organic-inorganic components and pore structures. Based on the preparation of samples usable by both optical and electron microscopes, and through optimization of related experimental procedures (polishing, oil immersion), it combines polarized fluorescence microscopy with scanning electron microscopy (SEM) mineral quantitative evaluation systems and field emission scanning electron microscopy (FETS) techniques to conduct in-situ quantitative multi-scale imaging characterization of organic matter, minerals, pores, and microcracks within the delineated target area. This yields integrated microscopic information on organic-inorganic components and pore structures, and by stitching these images together to form a large field-of-view image, it solves the challenge of "representativeness of micro-area samples and identification of organic microscopic components."

[0091] In one example, quantitative geochemical analysis based on a third subplate sample includes:

[0092] The third sub-thin plate sample was ground to a particle size of less than 200 μm. The total organic carbon content and rock pyrolysis parameters of the third sub-thin plate sample were analyzed to quantitatively characterize the organic component characteristics of the target laminae.

[0093] Specifically, after grinding the third sub-thin plate sample to a particle size of less than 200 μm, the total organic carbon content and rock pyrolysis analysis were performed to identify the basic geochemical characteristics of the target laminae within the same field of view of the same sample.

[0094] In one example, the thin plate sample has a length of 50–70 mm, a width of 20–25 mm, and a thickness of 4 mm.

[0095] In one example, the length of the first sub-thin plate sample is 40–60 mm.

[0096] In one example, the lengths of both the second and third sub-thin plate samples are 5 mm.

[0097] In one example, the common sample has a length of 5-7 mm, a width of 4 mm, and a thickness of 5 mm.

[0098] In one example, the formula for calculating total porosity is:

[0099] φ t =(V oe +V of ) / V t ×100%;

[0100] Among them, V oe V is the effective pore volume of high-pressure helium gas. of V is the pore volume of the nuclear magnetic fluid. t φt represents the total volume of the first sub-thin plate sample, and φt represents the total porosity.

[0101] Specifically, the effective porosity of high-pressure helium can be calculated by the effective pore volume of high-pressure helium and the total volume of the first sub-thin plate sample, the porosity of nuclear magnetic fluid can be calculated by the pore volume of nuclear magnetic fluid and the total volume of the first sub-thin plate sample, and then the total porosity can be calculated based on the effective porosity of high-pressure helium and the porosity of nuclear magnetic fluid.

[0102] φ oe =V oe / V t ×100%;

[0103] φ of =V of / V t ×100%;

[0104] φ t =φ oe +φ of ;

[0105] Where, φ oe For high-pressure helium, the effective porosity is φ. of For nuclear magnetic fluid porosity.

[0106] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but this is not intended to limit the invention. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present invention can be combined with each other.

[0107] Example 1

[0108] This embodiment provides a method for fine-scale characterization of shale heterogeneity at the microscale, taking Jurassic continental shale in a basin as an example, including:

[0109] (1) Shale core samples were selected, and for different types of lamellar layers, as well as lamellar layers of the same type but with different thicknesses and densities, and taking into account parameters such as sample hardness and thickness, an imported intelligent low-speed wire cutting machine was used to select the target lamellar layer. Using a thickness of Φ4mm as the standard, the layer was cut along the top interface to prepare rectangular single-layer lamellar samples—thin plate samples. The sample specifications were 4mm thick × 50-70mm long × 20-25mm wide. To ensure the integrity of the prepared samples, imported metal wire was used for cutting, and the sample was cut along the bedding plane.

[0110] (2) The thin plate sample was transversely cut into three parts. The cross-sections of the three parts represent the same field of view of the same layer sample. The thin plate sample was then further wire-cut to obtain samples of different lengths. After cutting, the length of sample ① was 40-60 mm, sample ② was 5 mm, and sample ③ was 5 mm. Since the thin plate sample was made by cutting along the bedding plane, samples ①, ②, and ③ are samples of the same layer or layer combination (layer pair), and are used for integrated analysis of different experimental techniques in subsequent processes.

[0111] (3) Select ① and measure the effective pore volume of high-pressure helium and the pore volume of nuclear magnetic resonance fluid in the original state to obtain the total porosity of the target layer. First, perform sample pretreatment, including drying and isothermal treatment, but do not perform oil washing and soaking (fluid saturation) treatment. Use vernier calipers or 3D scanner to measure the total volume of ① sample. Use the PDP200 overburden rock porosity and permeability analyzer and a customized thin plate sample chamber for helium porosity analysis. Use the porosity measurement technology under overburden conditions to carry out porosity analysis by high-pressure helium injection method to obtain the effective pore volume of high-pressure helium in this layer. Second, use two-dimensional nuclear magnetic resonance technology to measure the pore volume of nuclear magnetic resonance fluid occupied by the stagnant fluid. The total porosity of the target layer is obtained by dividing the sum of the nuclear magnetic resonance fluid pore volume and the effective pore volume of high-pressure helium by the total volume, or by the sum of the porosity of nuclear magnetic resonance fluid and the effective porosity of high-pressure helium in the original state.

[0112] The formula for calculating total porosity is:

[0113] φ t =(V oe +V of ) / V t ×100%;

[0114] Or, φ t =φ oe +φ of ;

[0115] Among them, V oe V is the effective pore volume of high-pressure helium gas. of V is the pore volume of the nuclear magnetic fluid. t The total volume of the first sub-thin plate sample is φ. t For total porosity, φ oe For high-pressure helium, the effective porosity is φ. oe =V oe / V t ×100%, φ of For nuclear magnetic fluid porosity, φ of =V of / V t ×100%.

[0116] (4) The sample ② was finely ground and argon-ion polished to prepare a high-quality sample suitable for both polarized fluorescence microscopy and scanning electron microscopy for fine microscale characterization. The sample dimensions were 5-7 mm long × 4 mm wide × 5 mm thick. To ensure that more features of the shale sample could be observed, the prepared sample size should be as large as possible and not exceed the sample stage. Therefore, the length and width of the sample should be less than 1 cm. To ensure clearer imaging under high-resolution scanning electron microscopy, the width was controlled to 4 mm (i.e., the thickness of the thin plate sample, which is one of the main reasons for determining the lower limit of the thin plate sample thickness; if the thickness is smaller, the observation effect of scanning electron microscopy will be poor).

[0117] (5) The microscale fine characterization sample prepared in sample ② was analyzed using a combination of multi-scale and multi-type experimental techniques. Since scanning electron microscopy samples require carbon plating and organic petrology analysis requires sample gelation, polarized fluorescence microscopy was first used for rock and mineral identification before carbon plating and oil immersion. The structure and texture of the shale sample were finely analyzed, and it was determined that the sample was a gray-black high-carbon clay laminae with clay minerals all having a particle size of less than 10 μm. They generally interacted with organic matter to form flocs, exhibiting a flocculent structure. Most of the felsic detritus had a particle size of 10–40 μm, and the overall structure belonged to a silty mudstone structure with horizontal bedding, such as... Figure 3As shown, high-resolution imaging and two-dimensional nuclear magnetic resonance (NMR) analysis of the oil retention characteristics of uncoated or ultrathinly carbon-coated (<3 nm) samples were performed using the low-pressure secondary electron mode of field emission scanning electron microscopy. This quantitative-imaging approach provided a detailed characterization of the oil retention state.

[0118] (6) Carbon plating is applied to the sample. Based on the carbon-plated sample, a full-field mineral quantitative evaluation and a preliminary target laminar region composition quantitative analysis are carried out using scanning electron microscopy. The elemental content and mineral composition characteristics of the carbon-plated sample are quantitatively and imagingly characterized. Based on the carbon-plated sample, a large-field high-resolution imaging scan of field emission scanning electron microscopy is carried out. The target laminar region is accurately delineated by combining the results of the preliminary target laminar region composition quantitative analysis.

[0119] (7) The carbon-plated sample was polished, carbon-removed and oil-immersed in sequence to obtain an oil-immersed sample; based on the oil-immersed sample, an organic petrological analysis was carried out using a polarized fluorescence microscope to finely characterize the organic micro-components of the oil-immersed sample, and at the same time, an etching method was used to delineate and mark specific organic and inorganic target areas.

[0120] (8) The oil-immersed sample was polished and carbon-coated sequentially to obtain a secondary carbon-coated sample; based on the secondary carbon-coated sample and specific organic and inorganic target regions, high-resolution imaging characterization integrating composition and structure was carried out using field emission scanning electron microscopy and focused ion beam scanning electron microscopy to obtain microscopic information on the composition and pore structure of specific organic and inorganic target regions, such as... Figure 4 As shown, MAPS image stitching software was used to stitch together scanned images of specific organic and inorganic target areas, so that numerous micro-regions (length and width of several μm) could be stitched together into imaging results of a typical macroscopic field of view (length and width >150~200μm), as shown. Figure 5 As shown, the final sample contained an average Al+Na+K content of 15.32%, an average Si content of 28.88%, and an average Ca content of 0.88%. The main minerals were clay minerals, including illite, chlorite, kaolinite, and montmorillonite, with a total content (by area) of approximately 44%. Silt (felsic debris) was the second most abundant mineral, while quartz and feldspar accounted for approximately 41%.

[0122] (9) Sample ③ was ground until the particle size was less than 200 μm. The total organic carbon content and rock pyrolysis parameters of the sample were analyzed using a carbon-sulfur analyzer and a rock pyrolysis analyzer to quantitatively describe the characteristics of the organic components of the sample. The total organic carbon content (TOC) was 1.81%, the residual pyrolysis hydrocarbon (S1) was 0.83 mg / g, the pyrolysis hydrocarbon content (S2) was 1.61 mg / g, and the maximum pyrolysis hydrocarbon content temperature (T) was [not specified]. max The temperature is 477℃.

[0123] (10) Through the integrated analysis of multi-scale and multi-type experimental techniques for single-layer thin plate samples, the content and distribution of organic and inorganic components, grain size and pore structure, microfracture structural characteristics, and differences between different types of thin-to-ultra-thin layers (layer pairs) of single layers are identified. This enables effective analysis of the heterogeneity of shale with high-density millimeter-to-micrometer-level layered segments, providing important basis and technical support for high-quality reservoir modeling and sweet spot prediction.

[0124] Example 2

[0125] This embodiment provides a microscale fine characterization system for shale heterogeneity, including:

[0126] The preparation module is used to prepare thin-plate samples of the target lamination based on shale reservoir core samples with high-density thin to ultrathin laminations to be tested;

[0127] Among them, the target texture is a single texture or a layered pattern dominated by a single texture;

[0128] The segmentation module is used to laterally segment the thin plate sample along the target lamination direction to obtain the first sub-thin plate sample, the second sub-thin plate sample, and the third sub-thin plate sample.

[0129] The physical property analysis module is used to measure the effective pore volume of high-pressure helium and the pore volume of NMR fluid based on the first sub-thin plate sample in its original state, thereby obtaining the total porosity of the target texture.

[0130] The composition-structure imaging analysis module is used to conduct in-situ micro-region quantitative-imaging analysis based on the second sub-thin plate sample using multi-scale optical and electron microscopy, to obtain integrated macroscopic and microscopic information on the organic-inorganic composition and pore structure of the target laminar layer.

[0131] The geochemical quantitative analysis module is used to conduct geochemical quantitative analysis based on the third sub-thin plate sample to obtain data on the organic matter abundance and oil content of the target laminar layer.

[0132] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A method for fine-scale characterization of shale heterogeneity at the microscale, characterized in that, include: Thin plate samples of the target lamination were prepared from shale reservoir core samples with high-density thin to ultrathin laminations. The target texture is a single texture or a layer pair with a single texture as the main component. The thin plate sample is laterally divided along the target lamination direction to obtain a first sub-thin plate sample, a second sub-thin plate sample, and a third sub-thin plate sample. Based on the first sub-thin plate sample under its original state, the effective pore volume of high-pressure helium gas and the pore volume of nuclear magnetic fluid are measured to obtain the total porosity of the target texture. Based on the second sub-thin plate sample, in-situ micro-region quantitative-imaging analysis was carried out using multi-scale optical and electron microscopy to obtain macroscopic and microscopic information on the organic-inorganic components and pore structure of the target layer. Geochemical quantitative analysis was conducted based on the third sub-thin plate sample to obtain data on the organic matter abundance and oil content of the target laminar layer.

2. The method for fine microscale characterization of shale heterogeneity according to claim 1, characterized in that, The method of obtaining the total porosity of the target layer by measuring the effective pore volume of high-pressure helium and the pore volume of nuclear magnetic fluid based on the first sub-thin plate sample in its original state includes: The first sub-thin plate sample is pretreated, including drying and isothermal treatment; The total volume of the first sub-thin plate sample after pretreatment was determined. Based on the pretreated first sub-thin plate sample, porosity analysis was carried out using a high-pressure helium injection method under pressure conditions to obtain the effective pore volume of high-pressure helium. The pore volume of the magnetic flux was determined using a two-dimensional nuclear magnetic resonance method based on the first sub-thin plate sample after pretreatment. The total porosity of the target texture is calculated based on the pore volume of the nuclear magnetic fluid, the effective pore volume of high-pressure helium, and the total volume.

3. The method for fine microscale characterization of shale heterogeneity according to claim 1, characterized in that, The in-situ micro-region quantitative-imaging analysis based on the second sub-thin plate sample using multi-scale optical and electron microscopy to obtain integrated macroscopic and microscopic information on the organic-inorganic composition and pore structure of the target laminae includes: The second sub-thin plate sample was prepared as a common sample suitable for analysis by polarized fluorescence microscopy and scanning electron microscopy; Based on the shared sample and the polarized fluorescence microscope, the structure of the target striations was analyzed in detail, and the target striation measurement area was initially selected. The shared sample was subjected to carbon plating treatment to obtain a carbon-plated sample; Based on the carbon-coated sample, a full-field scanning electron microscope was used to conduct a quantitative evaluation of minerals and a quantitative analysis of the composition of the initially selected target laminar surface area, thereby quantitatively characterizing the elemental content and mineral composition of the carbon-coated sample. Based on the carbon-plated sample, a large field-of-view, high-resolution imaging scan was performed using field emission scanning electron microscopy. Combined with the quantitative analysis results of the composition of the initially selected target striation region, the target striation measurement area was accurately delineated. The carbon-plated sample was polished, carbon-removed, and oil-immersed in sequence to obtain an oil-immersed sample; Based on the oil-immersed sample, an organic petrological analysis was performed using polarized fluorescence microscopy to finely characterize the organic micro-components of the oil-immersed sample. At the same time, an etching method was used to delineate and mark specific organic and inorganic target areas. The oil-immersed sample was polished and carbon-plated sequentially to obtain a secondary carbon-plated sample. Based on the secondary carbon-plated sample and the specific organic and inorganic target regions, high-resolution imaging characterization integrating composition and structure was carried out using field emission scanning electron microscopy and focused ion beam scanning electron microscopy to obtain microscopic information on the composition and pore structure of the specific organic and inorganic target regions. The scanning images of the specific organic and inorganic target regions were then stitched together to obtain imaging results with a typical macroscopic field of view. Based on the low-pressure secondary electron mode of field emission scanning electron microscopy, the common sample is subjected to high-resolution imaging and two-dimensional nuclear magnetic resonance imaging to comprehensively analyze the characteristics of the oil accumulation. The quantitative imaging method provides a fine characterization of the oil accumulation state.

4. The method for fine microscale characterization of shale heterogeneity according to claim 1, characterized in that, The geochemical quantitative analysis based on the third sub-thin plate sample to obtain the organic matter abundance and oil content data of the target laminar layer includes: The third sub-thin plate sample was ground to a particle size of less than 200 μm, and the total organic carbon content and rock pyrolysis parameters of the third sub-thin plate sample were analyzed to quantitatively characterize the organic component characteristics of the target laminar layer.

5. The method for fine microscale characterization of shale heterogeneity according to claim 1, characterized in that, The thin plate sample has a length of 50-70 mm, a width of 20-25 mm, and a thickness of 4 mm.

6. The method for fine microscale characterization of shale heterogeneity according to claim 5, characterized in that, The length of the first sub-thin plate sample is 40-60 mm.

7. The method for fine microscale characterization of shale heterogeneity according to claim 6, characterized in that, The lengths of the second and third sub-thin plate samples are both 5 mm.

8. The method for fine microscale characterization of shale heterogeneity according to claim 3, characterized in that, The common sample has a length of 5-7 mm, a width of 4 mm, and a thickness of 5 mm.

9. The method for fine microscale characterization of shale heterogeneity according to claim 2, characterized in that, The formula for calculating the total porosity is: φ t =(V oe +V of ) / V t ×100%; Among them, V oe V is the effective pore volume of high-pressure helium gas. of V is the pore volume of the nuclear magnetic fluid. t The total volume of the first sub-thin plate sample is φ. t Total porosity.

10. A microscale fine characterization system for shale heterogeneity, characterized in that, include: The preparation module is used to prepare thin-plate samples of the target lamination based on shale reservoir core samples with high-density thin to ultrathin laminations to be tested; The target texture is a single texture or a layer pair with a single texture as the main component. The segmentation module is used to laterally segment the thin plate sample along the target lamination direction to obtain a first sub-thin plate sample, a second sub-thin plate sample, and a third sub-thin plate sample. The joint measurement module is used to measure the effective pore volume of high-pressure helium and the pore volume of nuclear magnetic fluid based on the first sub-thin plate sample in its original state, thereby obtaining the total porosity of the target texture. The quantitative imaging analysis module is used to perform in-situ micro-region quantitative imaging analysis based on the second sub-thin plate sample using multi-scale optical and electron microscopy to obtain integrated macroscopic and microscopic information on the organic-inorganic components and pore structure of the target texture. The geochemical quantitative analysis module is used to conduct geochemical quantitative analysis based on the third sub-thin plate sample to obtain data on the organic matter abundance and oil content of the target laminar layer.

Images