Ex-situ analysis method for microstructure of alumina rock

Abstract

The invention provides an in-situ analysis method for a microstructure of alumina rock. The in-situ analysis method comprises the following steps: manufacturing rock slices; obtaining micron-sized microstructure data under a microscope; obtaining nanoscale microstructure data under a scanning electron microscope; obtaining point, line and surface percentage content analysis data of major elements tested by the X diffraction energy spectrum; the correlation between the composition and distribution of main elements of the soybean oolitic structure and the pore development condition is analyzed in combination with micron-nano data, and meanwhile, the cause of the oolitic structure can be analyzed. The evaluation method can be applied to fine characterization of the characteristics of the alumina rock reservoir, can determine the pore-forming mechanism of the alumina rock reservoir and the main control factors and the distribution rule of the high-quality reservoir, and provides a basis for optimization of a favorable exploration area.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and gas exploration geology, and in particular relates to a bauxite microstructure isotopic analysis method. Background Art

[0002] It is the first time that bauxite has been studied as a natural gas reservoir. Bauxite is a chemical sedimentary rock rich in aluminum, often with a bean-shaped oolitic layer microstructure. The difference in the main elements of the layer structure makes its reservoir performance different. The existing experimental methods have a contradiction between resolution and resolution scale when characterizing the microstructure. It is not possible to characterize the same microstructural features at multiple scales, and is not comprehensive when evaluating the reservoir properties of the microstructure. In order to characterize the microstructure of the sample, some researchers have also reported the use of scanning electron microscopes, microscopes and other technologies for characterization, such as:

[0003] The invention patent with the publication (announcement) number: CN 114910623 A discloses a method for characterizing the multi-dimensional information of the microstructure of metal materials in a high-throughput manner, which is characterized in that the steps of the production process include: (1) sampling and cutting of samples; (2) mechanical grinding and polishing of samples; (3) positioning marks of the area to be tested; (4) corrosion of the polished surface; (5) high-precision information collection of the three-dimensional morphology of the surface; (6) full-domain high-throughput collection of the area to be tested by scanning electron microscopy; (7) test result processing and multi-dimensional information parameter analysis. This method mainly uses a scanning electron microscope to obtain microstructure information, which has the characteristics of high resolution, mainly at the submicron-nanometer level, but the scale represented is small, and the analysis data cannot accurately reflect the overall picture of the analyzed sample, and cannot take into account both resolution and multi-scale, which has limitations.

[0004] The invention patent with authorization announcement number: CN107490503B discloses a sample processing method for in-situ micro-area joint analysis, including the following steps: (1) sample collection; (2) target positioning for microscopic observation to determine the type and stage of diagenesis, and mark the positioning position; (3) sample analysis, and carbon and oxygen isotope analysis of the marked position. This method mainly uses a microscope to obtain microscopic structural information, mainly micron-level images, which cannot reflect the nano- and microscopic structural characteristics of the analyzed sample, and the resolution accuracy is limited.

[0005] Therefore, there is an urgent need to design a method to study the microstructural characteristics of bauxite reservoirs. Summary of the invention

[0006] In view of the defects in the prior art, the present invention aims to establish a bauxite microstructure isotope analysis method through wellhead core rock analysis, so as to provide an effective characterization scheme for bauxite gas reservoir research.

[0007] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0008] The present invention provides a method for isotopic analysis of the microstructure of bauxite, comprising the following steps:

[0009] S1, making rock thin sections;

[0010] S2, rock thin section zoning annotation;

[0011] S3, acquiring micron-scale microstructure images;

[0012] S4, acquiring nanoscale microstructure images;

[0013] S5, obtaining element distribution data of bean ooid structure;

[0014] S6, combining the micron-nano data obtained in steps S3-S5, analyzing the main element composition and distribution of the ooid structure, and its correlation with the pore development.

[0015] As a preferred solution, the method for making rock slices in step S1 is: selecting a part of the bauxite core containing developed ooid structure, cutting a rock sample of 25 mm×25 mm×5 mm or 25 mm×5 mm in diameter, using a casting machine to cast the cut rock sample with epoxy resin, and grinding it into a rock slice with a thickness of 0.03 mm.

[0016] As another preferred embodiment of the present invention, the method for marking the rock slice partitions in step S2 is: drawing grid lines on the surface of the rock slice and marking position numbers in the grids in sequence.

[0017] As another preferred embodiment of the present invention, the method for obtaining the micron-level microstructure image in step S3 is: observing the rock slice marked with the position serial number under a microscope to obtain the micron-level microstructure image and pore development characteristics.

[0018] As another preferred embodiment of the present invention, the method for obtaining the nanoscale microstructure image in step S4 is: after the rock slice is sprayed with a carbon conductive film, it is placed in the sample chamber of a scanning electron microscope for observation, the observation target area is found according to the marked position number, the nanoscale microstructure image is obtained, and an electron microscope photograph is taken at the same time.

[0019] As a further preferred embodiment of the present invention, the method for obtaining the major element data of the bean ooid structure in step S5 is: under a scanning electron microscope, use a matching X-ray diffraction spectrometer to perform point, line and surface element scanning on the bean ooid grain structure from the outer circle to the inner circle to obtain the element distribution data of the bean ooid grain structure.

[0020] Preferably, the specific method of analyzing the main element composition and distribution of the ooid structure in step S6 in combination with the micron-nanoscale data obtained in steps S3-S5 is as follows: through the micron-nanoscale multi-scale microscopic image analysis method of the ooid structure at the same position, combined with X-ray diffraction energy spectrum element analysis, the element composition and distribution of the ooid structure can be identified, and the correlation between the distribution of elements and pore development can be determined.

[0021] A further preferred embodiment is that the main element composition and distribution of the ooid structure in step S6 are as follows: the ooid grain structure has a layered distribution characteristic of Al and Si elements, the core is Si-enriched, and gradually changes to Al-rich and Si-rich layers outwards.

[0022] A further preferred scheme is that there is a good correlation between the distribution of the main elements of the ooid structure and the pore development in the step S6, the Si-rich layer is composed of cryptocrystalline clay minerals, which are dense and non-porous and have no storage properties; the Al-rich layer is composed of well-crystallized diaspore minerals, the minerals are well crystallized and are in the form of microcrystals with obvious dissolution pores, and have storage properties.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The present invention provides an evaluation method for the microstructure of bauxite reservoirs, which includes making rock slices; obtaining micron-level microstructure data under a microscope; obtaining nanometer-level microstructure data under a scanning electron microscope; obtaining point, line, and surface percentage analysis data of major elements tested by X-ray diffraction spectrum; combining micron-nanometer-level data to analyze the correlation between the composition and distribution of the main elements of the oolitic structure and the pore development, and at the same time analyzing the genesis of the oolitic structure, providing an effective characterization scheme for the study of bauxite gas reservoirs. The technology can be applied to the fine characterization of bauxite reservoir characteristics, and can determine the pore formation mechanism of bauxite reservoirs and the main controlling factors and distribution laws of high-quality reservoirs, providing a basis for the optimization of favorable exploration areas.

[0025] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the following is a detailed description of the preferred embodiments of the present invention in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, 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 invention. For ordinary technicians in this field, other design solutions and drawings can be obtained based on these drawings without paying creative work.

[0027] Figure 1It is a flow chart of micron-nano multi-scale isotopic bauxite microstructure evaluation;

[0028] Figure 2 This is the microscopic characteristic diagram of the structure of bauxite bean oolite under a microscope;

[0029] Figure 3 This is the microscopic characteristic picture of the structure of bauxite pea oolite under scanning electron microscope;

[0030] Figure 4 This is the Al element surface distribution characteristic diagram of the oolitic structure of bauxite under scanning electron microscope;

[0031] Figure 5 This is the surface distribution characteristic diagram of Si element in the structure of bauxite pea-shaped oolitic rock under scanning electron microscope;

[0032] Figure 6 This is the characteristic line distribution diagram of Al, Si and O elements in the oolite structure of bauxite.

[0033] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments. DETAILED DESCRIPTION

[0034] The content of the present invention can be further understood by combining the following detailed description of the preferred implementation method of the present invention and the embodiments included. Unless otherwise stated, all technical and scientific terms used in this article have the same meaning as those of ordinary skill in the art to which the present invention belongs. If the definition of a specific term disclosed in the prior art is inconsistent with any definition provided in the present invention, the definition of the term provided in the present invention shall prevail.

[0035] The existing test methods have a contradiction between resolution and resolution scale when characterizing microstructures, and cannot characterize the same microstructure features at multiple scales, and are not comprehensive when evaluating the reservoir properties of the microstructure. In order to solve the above technical problems existing in the prior art, the present invention provides a bauxite microstructure isotopic analysis method, comprising the following steps:

[0036] S1, making rock thin sections;

[0037] S2, rock thin section zoning annotation;

[0038] S3, acquiring micron-scale microstructure images;

[0039] S4, acquiring nanoscale microstructure images;

[0040] S5, obtaining element distribution data of bean ooid grain structure;

[0041] S6, combining the micron-nano data obtained in steps S3-S5, analyzing the main element composition and distribution of the ooid structure, and its correlation with the pore development.

[0042] In a preferred embodiment, the method for making rock slices is: select a part of the bauxite core containing developed oolitic structure, cut a rock sample of 25mm×25mm×5mm or 25mm×5mm in diameter, use a casting machine to cast the cut rock sample with epoxy resin, and grind it into a rock slice with a thickness of 0.03mm.

[0043] In a preferred embodiment, the preferred method for marking the rock slice partitions is: drawing grid lines on the surface of the rock slice, and marking position numbers in the grid in sequence.

[0044] In a preferred embodiment, the preferred method for obtaining micron-level microstructure images is to observe the rock slices marked with position numbers under a microscope to obtain micron-level microstructure images and pore development characteristics.

[0045] In a preferred embodiment, the preferred method for obtaining nanoscale microstructure images is: after spraying a carbon conductive film on a rock slice, place it in a scanning electron microscope sample chamber for observation, find the observation target area according to the marked position number, obtain the nanoscale microstructure image, and take electron microscope photos at the same time.

[0046] In a preferred embodiment, the preferred method for obtaining the major element data of the bean ooid structure is: under a scanning electron microscope, use a matching X-ray diffraction spectrometer to perform point, line, and surface element scanning on the bean ooid grain structure from the outer circle to the inner circle to obtain the element distribution data of the bean ooid grain structure.

[0047] In a preferred embodiment, the specific method for analyzing the main element composition and distribution of the ooid structure in combination with the micron-nanoscale data obtained in steps S3-S5 is as follows: through the micron-nanoscale multi-scale microscopic image analysis method of the ooid structure at the same position, combined with X-ray diffraction energy spectrum element analysis, the element composition and distribution of the ooid structure can be identified, and the correlation between the distribution of elements and pore development can be determined.

[0048] Furthermore, the main element composition and distribution of the ooid structure in step S6 are as follows: the ooid grain structure has a layered distribution characteristic of Al and Si elements, the core is Si-enriched, and gradually changes to Al-rich and Si-rich layers outwards.

[0049] There is a good correlation between the distribution of the main elements of the ooid structure and the pore development in step S6. Specifically, the Si-rich layer is composed of cryptocrystalline clay minerals, which are dense and non-porous and have no storage properties; the Al-rich layer is composed of well-crystallized diaspore minerals, which are well crystallized and present microcrystalline with obvious dissolution pores, and have storage properties.

[0050] In a specific embodiment, the present invention provides a method for isotopic analysis of the microstructure of bauxite, comprising the following steps:

[0051] S1, making rock slices: selecting the part of the bauxite core containing the developed oolitic structure, cutting out centimeter-scale rock samples (preferably with a size of 25 mm×25 mm×5 mm or a diameter of 25 mm×5 mm), casting the rock samples with epoxy resin using a casting machine, and grinding them into rock slices with a thickness of 0.03 mm without covering;

[0052] S2, rock slice zoning and marking: draw 5mm×5mm grid lines on the surface of the rock slice, and mark the position numbers in the grid in sequence;

[0053] S3, obtaining micron-level microstructure images: observe the marked rock slices under a microscope, obtain micron-level microstructure images and pore development characteristics of different partitions, record the position serial numbers of the targets to be observed, and take typical microscopic photos at the same time;

[0054] S4, obtaining nano-scale microstructure images: After the rock slice is sprayed with carbon conductive film, the slice is placed in the sample chamber of the scanning electron microscope for observation. The observation target area is found according to the marked position serial number, and the nano-scale microstructure image is obtained, and a typical electron microscope photo is taken at the same time;

[0055] S5, obtaining the element distribution data of the ooid structure: under a scanning electron microscope, using a matching X-ray diffraction spectrometer to perform point, line and surface element scanning on the ooid structure from the outer circle to the inner circle, the element distribution data of the ooid structure was obtained;

[0056] S6. Combine the micron-nanoscale data obtained in steps S3-S5 to analyze the main element composition and distribution of the ooid structure. The ooid structure has the layered distribution characteristics of Al and Si elements. The core is enriched in Si, and gradually changes into Al-rich and Si-rich layers outward. There is a correlation between the distribution of the main elements in the ooid structure and the pore development. The Si-rich layer is composed of cryptocrystalline clay minerals, which are dense and non-porous and have no storage properties. The Al-rich layer is composed of well-crystallized diaspore minerals. The minerals are well crystallized and are microcrystalline with obvious dissolution pores, which have storage properties.

[0057] The present invention makes rock slices; obtains micron-level microstructure data under a microscope; obtains nanometer-level microstructure data under a scanning electron microscope; obtains point, line, and surface percentage analysis data of major elements tested by X-ray diffraction spectrum; combines micron-nanometer-level data to analyze the correlation between the composition and distribution of the main elements of the oolitic structure and the pore development, and can also analyze the genesis of the oolitic structure, providing an effective characterization scheme for the study of bauxite gas reservoirs. The technology can be applied to the fine characterization of bauxite reservoir characteristics, and can determine the pore formation mechanism of bauxite reservoirs and the main controlling factors and distribution laws of high-quality reservoirs, providing a basis for the optimization of favorable exploration areas.

[0058] The present invention will be further described below in conjunction with embodiments:

[0059] This embodiment relates to a method for isotopic analysis of the microstructure of bauxite. Figure 1 As shown, the specific steps include:

[0060] 1) Rock thin section preparation: Select the part of the bauxite core containing the ooid structure development, cut the rock sample of 25mm×25mm×5mm, use the casting instrument to cast the rock sample with epoxy resin, and grind it into a rock thin section with a thickness of 0.03mm without covering;

[0061] 2) Rock slice zoning and marking: Draw 5mm×5mm grid lines on the surface of the rock slice with a marker pen, and mark the position numbers in the grid in sequence;

[0062] 3) Obtain micron-level microstructure images: Observe the marked rock slices under a microscope to obtain micron-level microstructure images and pore development characteristics, record the position numbers of the targets to be observed, and take typical microscopic photos, such as Figure 2 As shown;

[0063] 4) Obtain nano-scale microstructure images: After the rock slice is sprayed with carbon conductive film, the slice is placed in the SEM sample chamber for observation. The observation target area is found according to the marked position number, and the nano-scale microstructure image is obtained. At the same time, typical SEM photos are taken, such as Figure 3 As shown;

[0064] 5) Obtaining the major element data of the microstructure: Under a scanning electron microscope, use the matching X-ray diffraction spectrometer to perform point, line, and surface element scanning of the oolitic structure from the outer circle to the inner circle, such as Figure 4 , 5 As shown in ,6, the element distribution data of oolite structure were obtained;

[0065] 6) Combining micron-nano data to analyze the composition and distribution of the main elements of the bean oolite structure, the bean oolite grain structure has the characteristics of Al and Si element layer distribution, the core is Si element enriched, and gradually changes to Al-rich and Si-rich layers outward. There is a correlation between the pore development. The Si-rich layer is composed of cryptocrystalline clay minerals, which are dense and non-porous and have no storage properties; the Al-rich layer is composed of well-crystallized diaspore minerals. The minerals are well crystallized and are microcrystalline with obvious dissolution pores, which have storage properties. The origin of the bean oolite structure can be analyzed. The formation of bean oolites is mainly controlled by the desiliconization and aluminum enrichment in the oxidizing environment of the surface period. The silicon element leaching and aluminum element enrichment and purification process form secondary pores.

[0066] This microstructural isotopic analysis method was applied to evaluate the bauxite reservoir.

[0067] The element distribution statistics of the oolitic structure are shown in Table 1. It can be seen from Table 1 that the oolitic structure is mainly composed of Al and Si element layers. In the Al-rich layer, the minerals are well crystallized and are microcrystalline with obvious dissolution pores, which have storage properties; the Si-rich layer is composed of cryptocrystalline minerals, which are dense and non-porous and do not have storage properties ( Figure 2 ). At test points 2 and 4, Al 2 O 3 Content greater than 90%, SiO 2 The content is less than 5%, and the Al / Si value is greater than 10, indicating that the diaspore layer has a dissolution phenomenon, forming intercrystalline dissolution pores; at test points 1, 3, and 5, Al 2 O 3 Content 55%, SiO 2 The content is 44%, and the Al / Si value is close to 1. The clay layer is cryptocrystalline and dense without pores. This indicates that when bauxite is formed into a reservoir, it is due to the differential dissolution of the oolitic structure, which forms structural dissolution. It also reveals that the origin of oolitic is formed by the replacement and superposition of multiple environmental periods. Therefore, the isotopic analysis method of the bauxite microstructure provided by the present invention can be used for the fine characterization of the characteristics of the bauxite reservoir, and can further determine the pore-forming mechanism of the bauxite reservoir and the main controlling factors and distribution laws of the high-quality reservoir, providing a basis for the optimization of favorable exploration areas.

[0068] Table 1 Statistical table of Al and Si element point distribution in the structure of bauxite

[0069] Detection point <![CDATA[Al 2 THE 3 ]]> <![CDATA[SiO 2 ]]> Al / Si illustrate ① 55.49 44.51 1.25 Clay layer ② 97.2 2.80 34.71 Diaspore layer (dissolution) ③ 55.90 44.10 1.27 Clay layer ④ 93.32 6.68 13.97 Diaspore layer (dissolution) ⑤ 54.49 45.51 1.20 Clay layer

[0070] The above description is only a preferred embodiment of the present invention, which is merely illustrative of the present invention and does not limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made by ordinary technicians in this field to the technical solution of the present invention should fall within the scope of protection determined by the claims of the present invention.

Claims

1. A method for isotopic analysis of bauxite microstructure, characterized in that: The method comprises the following steps: S1, making rock thin sections; S2, rock thin section zoning annotation; S3, acquiring micron-scale microstructure images; S4, acquiring nanoscale microstructure images; S5, obtaining element distribution data of bean ooid structure; S6, combining the micron-nano data obtained in steps S3-S5, analyzing the main element composition and distribution of the ooid structure, and its correlation with the pore development.

2. The isotopic analysis method of bauxite microstructure according to claim 1, characterized in that: The method for making rock slices in step S1 is: selecting a part of the bauxite core containing developed ooid structure, cutting a rock sample of 25mm×25mm×5mm or 25mm×5mm in diameter, casting the cut rock sample with epoxy resin using a casting machine, and grinding it into a rock slice with a thickness of 0.03mm.

3. The isotopic analysis method of bauxite microstructure according to claim 1, characterized in that: The method for marking the rock slice partitions in step S2 is: drawing grid lines on the surface of the rock slice and marking position numbers in the grids in sequence.

4. The isotopic analysis method of bauxite microstructure according to claim 1, characterized in that: The method for obtaining the micron-level microstructure image in step S3 is: observing the rock slice marked with the position serial number under a microscope to obtain the micron-level microstructure image and pore development characteristics.

5. The bauxite microstructure isotopic analysis method according to claim 1, characterized in that: The method for obtaining the nano-scale microstructure image in step S4 is: after spraying the carbon conductive film on the rock slice, put it into the scanning electron microscope sample chamber for observation, find the observation target area according to the marked position number, obtain the nano-scale microstructure image, and take electron microscope photos at the same time.

6. The isotopic analysis method of bauxite microstructure according to claim 1, characterized in that: The method for obtaining the major element data of the bean ooid structure in step S5 is: under a scanning electron microscope, using a matching X-ray diffraction spectrometer to perform point, line and surface element scanning on the bean ooid grain structure from the outer circle to the inner circle to obtain the element distribution data of the bean ooid grain structure.

7. The isotopic analysis method of bauxite microstructure according to claim 1, characterized in that: The specific method of analyzing the main element composition and distribution of the ooid structure in step S6 in combination with the micron-nanoscale data obtained in steps S3-S5 is as follows: by using the micron-nanoscale multi-scale microscopic image analysis method of the ooid structure at the same position, combined with X-ray diffraction energy spectrum element analysis, the element composition and distribution of the ooid structure can be identified, and the correlation between the distribution of elements and pore development can be determined.

8. The bauxite microstructure isotopic analysis method according to claim 1, characterized in that: The main element composition and distribution of the ooid structure in step S6 are as follows: the ooid grain structure has the layered distribution characteristics of Al and Si elements, the core is Si-enriched, and gradually changes to Al-rich and Si-rich layers outwards.

9. The isotopic analysis method for bauxite microstructure according to claim 1, characterized in that: There is a good correlation between the distribution of the main elements of the ooid structure and the pore development in step S6, that is, the Si-rich layer is composed of cryptocrystalline clay minerals, which are dense and non-porous and have no storage properties; the Al-rich layer is composed of well-crystallized diaspore minerals, the minerals are well crystallized and are in the form of microcrystals with obvious dissolution pores, and have storage properties.

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