Joint analysis method for organic matter types and micropore development characteristics in rock

Abstract

The invention relates to the technical field of energy exploration analysis, in particular to a conjoint analysis method for organic matter types and micropore development characteristics in rocks, which comprises the following steps: step 1, drying a blocky or granular rock sample, and performing cold inlaying by using epoxy resin mixed with conductive powder to prepare a cylindrical sample; 2, after the cylindrical sample is demolded, first-time mechanical polishing is carried out; 3, marking the surface of the sample by using an etching objective lens when the sample is observed by a microscope; 4, performing secondary mechanical polishing and argon ion polishing on the sample obtained in the step 3; and 5, carrying out rapid positioning observation by using the scanning electron microscope navigation photo and the marked sample photo. The mark etching method is applied to organic matter microscopic observation marking, after the secondary treatment process is completed, various scanning electron microscope analysis can be carried out on the sample, and multi-scale and multi-characteristic analysis technology combination from the micron level to the nanometer level is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of energy exploration and analysis, and in particular to a joint analysis method of organic matter types and micropore development characteristics in rocks. Background Art

[0002] Unconventional oil and gas resources such as shale oil and shale gas are important successor energy sources worldwide. Their huge resource potential may become the main force driving oil production growth in the next 20 years.

[0003] Shale oil and shale gas have the characteristics of self-generation and self-storage. Compared with conventional oil and gas reservoirs, after shale oil and gas are generated from organic-rich mud shale, the pores in the mud shale become its main storage space. Studies have shown that organic pores have better connectivity than pores within mineral particles, and the three-dimensional effective pore network formed by the interconnection of organic particles will have a significant impact on the oil and gas storage capacity and permeability of thermally mature mud shale. Therefore, the fine characterization of organic pores is the key to evaluating the oil and gas storage capacity of mud shale. At the same time, the type of organic matter is one of the important factors affecting the development of organic pores. The microscopic composition of organic matter and the type of asphalt will also have a significant impact on organic pores. For example, type I kerogen has a much higher potential for organic pore development than type III kerogen due to its good oil and gas generation ability. The sapropelite group with strong hydrocarbon generation ability develops abundant organic pores, while the pores in the vitrinite group are less developed. The pore development of asphalt at different evolutionary stages is different. Therefore, it is very important to clarify the type of organic particles while analyzing the development characteristics of organic pores, and then distinguish between the original sedimentary organic pores and the pyrolytic asphalt organic pores after migration, because the final organic pore network and connection path in mudstone mainly depend on the proportion of organic matter distribution in different states.

[0004] At present, the characterization methods of pore types in organic-rich shale can be mainly divided into four categories: imaging method, fluid invasion method, adsorption method, and scattering method. Among them, the imaging method is the only method that can directly observe the development characteristics of micropore size, morphology, and distribution in organic matter in rocks. The existing imaging analysis techniques mainly include field emission scanning electron microscopy (FE-SEM) and focused ion beam scanning electron microscopy (FIB-SEM), which can observe the pore size, morphology, and distribution characteristics in shale samples at the nanoscale, and are one of the effective means to finely characterize the pore characteristics of organic matter. However, the scanning electron microscope observation method has great shortcomings in distinguishing organic matter types. This is mainly because the classification of organic matter types under the scanning electron microscope can only be based on its morphological characteristics. It is difficult to distinguish amorphous sapropel groups, exin groups, and exudate asphalt bodies with similar morphologies, and it is also impossible to distinguish organic matter with different degrees of evolution. Only under an optical microscope can the optical characteristics and fluorescence characteristics of oil-immersion reflected light be used to distinguish them. The existing scanning electron microscope micropore observation method cannot realize the micropore observation of different types of microscopic components and bitumen, which seriously affects the research on the generation and enrichment of oil and gas in shale and the evaluation of storage capacity. Therefore, it is urgent to develop a joint observation and analysis method of optical characteristics and scanning electron microscope characteristics of specific observation targets in rock samples. Summary of the invention

[0005] The purpose of the present invention is to provide a method for jointly analyzing the types of organic matter and micropore development characteristics in rocks, which can solve the above technical problems.

[0006] The present invention provides a method for jointly analyzing the type of organic matter and micropore development characteristics in rocks, comprising the following steps:

[0007] Step 1: After the block or granular rock sample is dried, it is cold-mounted using epoxy resin mixed with conductive powder to make a cylindrical sample;

[0008] Step 2: Demolding the cylindrical sample and performing the first mechanical polishing;

[0009] Step 3: Use the etched objective lens to mark the sample surface when observing the sample under a microscope;

[0010] Step 4: Perform a second mechanical polishing and argon ion polishing on the sample obtained in step 3;

[0011] Step 5: Use the SEM navigation photos and the marked sample photos for quick positioning and observation.

[0012] Preferably, the specific steps of step 1 are as follows: drying the prepared rock blocks and debris for standby use, preparing a cold mounting mold, applying a release agent on the inner surface of the mold, and after the release agent is dried, placing the rock blocks or debris into the cold mounting mold respectively; adding a curing agent to the epoxy resin and mixing evenly, adding the conductive powder to the epoxy resin, stirring evenly, pouring the mixed conductive epoxy resin into the cold mounting mold, standing until solidified, and then demolding to obtain a cylindrical sample for standby use. The mixing ratio of the conductive powder to the epoxy resin and the mixing ratio of the epoxy resin to the curing agent are determined according to the requirements of different product types.

[0013] Preferably, the specific steps of step 2 are as follows: the first step is to grind the rock surface on an automatic grinder using 400 or 600 mesh sandpaper. If it is a granular sample, it is advisable that the exposed edges of the sample are closely connected; the second step is to use 1200 mesh sandpaper to finely grind the surface to reduce the depth of scratches; the third step is to polish the sample surface using alumina polishing liquid and a matching polishing cloth; the fourth step is to polish the sample surface using alumina polishing liquid with a smaller particle size than that in the third step and a matching polishing cloth.

[0014] The third and fourth steps in step 2 are polished using 0.3 μm and 0.05 μm aluminum oxide polishing liquids respectively.

[0015] Preferably, the sample obtained in step 2 has a flat surface under a microscope, preferably with no visible scratches when magnified 500 times.

[0016] Preferably, the specific steps of step 3 are as follows: Under oil-immersion reflected light, observe and analyze the organic matter type according to standard methods to clarify the main organic matter type characteristics in the sample. Select typical organic matter particles and circle the observation target using an etching objective lens.

[0017] Preferably, the lower part of the etching objective lens is a large cylindrical structure, in which a movable steel small cylindrical structure (diameter 2.5mm) is nested, the small cylindrical structure is located on one side of the center point of the large cylindrical structure, and the edge of the small cylindrical structure 0.25mm is a sharpened steel vertex. When the large cylindrical structure is rotated, the small cylindrical structure is driven by the large cylindrical structure and rotates with the large cylindrical structure, and the steel vertex will form a circular notch on the sample with the center point of the large cylindrical structure as the center. When only the small cylinder is rotated, the distance between the steel vertex and the center point of the large cylinder gradually increases to 2.25mm. Therefore, when the large cylinder is rotated, the radius of the etching circle is 0.25mm-2.25mm, and the diameter of the circular notch formed is 0.5mm-4.5mm.

[0018] After completing the microscopic observation of organic particles, clarifying the type of organic matter and its optical characteristics, and completing the etching mark of the particles of interest, it is necessary to remove the surface immersion oil and etching debris, and meet the flatness requirements of SEM observation. The sample surface needs to be mechanically polished and argon ion polished for the second time.

[0019] Preferably, the method for the second mechanical polishing in step 4 is: the chassis speed of the automatic grinder is 160 rpm, the mechanical head speed is 70 rpm, the single-point pressure is 10 N, and polishing is performed for 30-50 seconds under the conditions of 0.05 μm alumina polishing liquid and matching polishing cloth. Then, the sample surface is placed face down in a cutting fixture and bottom surface cutting is performed to ensure that the top and bottom surfaces of the sample are parallel and the height is less than 1 cm.

[0020] Preferably, in order to ensure the observation effect of the scanning electron microscope and remove the mechanical scratches on the surface of the organic matter, argon ion polishing needs to be carried out. The experiment needs to adjust the ion beam voltage and current and set the polishing program to avoid the high temperature of the polishing process from damaging the organic matter on the surface of the sample while achieving a satisfactory polishing effect. The appropriate voltage, polishing time and polishing program can be adjusted according to the hardness and thermal evolution degree of the sample. The argon ion polishing program in step 4 is: a. 4.5kV-6.5kV, 30min-120min; b. 2.5kV-3kV, 10min-15min.

[0021] If the experimental conditions make it impossible to add conductive powder in the cold mounting step, a coating step can be added after the argon ion polishing step. Coating is to meet the conductivity requirements of the sample surface for electron microscope observations such as field emission scanning electron microscopes and focused ion beam scanning electron microscopes. Coating can be carbon or platinum, with a carbon coating thickness of 3nm-5nm and a platinum coating thickness of 2nm-3nm. If it is necessary to conduct energy spectrum analysis with higher requirements for conductivity, the carbon coating thickness should be 8nm-10nm and the platinum coating thickness should be 3nm-5nm.

[0022] Preferably, the specific steps of step 5 are as follows: after completing the above-mentioned sample observation and pretreatment steps, fix the sample on the sample stage according to the operating procedures of the field emission scanning electron microscope, focused ion beam scanning electron microscope or helium ion scanning electron microscope, place it in the sample chamber, rotate the sample to the same angle as when observing under the microscope, and take a navigation photo. When observing under the electron microscope, double-click the mouse to quickly locate the location of the etching mark or the microscope photo, and carry out positioning analysis.

[0023] Beneficial effects:

[0024] The present invention applies the etching marking method to the marking of organic matter microscopic observation. After completing the secondary processing process, the sample can be subjected to a variety of scanning electron microscope analyses, and the marked object can be located and observed for a variety of characteristics, realizing the combination of multi-scale and multi-characteristic analysis technologies from micrometer level to nanometer level. The problem that conventional scanning electron microscope micropore observation cannot determine the parent material type of pore-developing organic matter is solved. Through the technical process of the present invention, on the basis of conducting organic matter type analysis, the micropore development characteristics of each type of organic matter can be located and observed, solving the problem that the type of organic matter cannot be determined in electron microscope observation.

[0025] The combined method of the present invention can realize the observation and analysis of the polished surface of block, granular and powder samples by microscope-scanning electron microscope. In addition to the positioning analysis of organic matter type and micropore characteristics, the combined method can also be applied to other positioning analyses that are not suitable for marking with a pen. The processed samples are not only suitable for scanning electron microscope observation, but also can be used for other rock optical analysis and test projects, such as laser Raman spectroscopy analysis, etc., and can also be used for analysis and testing of various accessories at the scanning electron microscope end, such as scanning electron microscope end energy spectrum, electron probe, cathode luminescence identification, EBSD analysis, secondary ion mass spectrometry, etc. At the same time, the marked samples can still be repeatedly observed and analyzed under the microscope and can be permanently preserved. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0027] Figure 1 It is a schematic diagram of the structure of etching the bottom of the objective lens of the present invention;

[0028] Figure 2 It is a schematic diagram of the structure of the sample cutting fixture of the present invention;

[0029] Figure 3 This is a positioning photograph of the present invention after marking under a microscope and observed under a scanning electron microscope;

[0030] Figure 4 Comparison photos of the same marked area under the reflected light of the microscope of the present invention and the scanning electron microscope;

[0031] Figure 5 Comparison photos of the same area under the fluorescence microscope and scanning electron microscope of the present invention;

[0032] Figure 6 For the present invention Figure 5 Enlarged schematic diagram of the left figure;

[0033] Figure 7 For the present invention Figure 6 The SEM backscatter image corresponding to area 1 in the middle;

[0034] Figure 8 For the present invention Figure 6 The SEM backscatter image corresponding to the middle 2 area;

[0035] Fig. 9 For the present invention Figure 6 The SEM backscatter image corresponding to the middle 3 area;

[0036] Fig.10 For the present invention Figure 6 The SEM backscatter image corresponding to the middle 4 area;

[0037] Fig.11 It is a schematic structural diagram of the etching objective lens used in the present invention.

[0038] Explanation of the reference numerals: 1-large cylindrical structure, 2-small cylindrical structure, 3-apex, 4-movable screw, 5-threaded opening, 6-dial wheel. DETAILED DESCRIPTION

[0039] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0041] In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined. In addition, the terms "installed", "connected" and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal connection of two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0042] In view of the technical defect that it is difficult to determine the type of organic matter in the existing organic micropore imaging analysis method, the present invention, based on in-depth research on the two analysis method processes and sample pretreatment methods, proposes a joint analysis method that uses different pretreatment methods to simultaneously carry out microscopic observation under oil immersion conditions and scanning electron microscope observation under high vacuum conditions. The method has a simple process and reliable results. It is a non-destructive (does not change the sample characteristics and can be repeatedly analyzed and permanently preserved) joint analysis method for positioning organic matter types and micropore development characteristics.

[0043] Example 1

[0044] In order to highlight the applicability of the method to samples, samples of siliceous mudstone, carbonaceous mudstone, and two types of lithology and properties, namely, clastic particles and blocks, were selected for the description of specific embodiments.

[0045] Dry the prepared rock block (single-sided cut flat) and debris for later use. Prepare a cold mounting mold, apply a release agent on the inner surface of the mold, and wait for the release agent to dry. Place the rock block (flat side down) and about 3g of debris into the mold respectively.

[0046] According to the product instructions, mix the curing agent and epoxy resin in a volume ratio of 1:2, add the conductive powder and epoxy resin to the epoxy resin in a weight ratio of 1:1, stir well, introduce the mixed epoxy resin into the cold mounting mold, let it stand for 9 hours, and then demold it for use.

[0047] The demoulded sample was ground and polished according to the following method. After completing step 2 and step 4, the sample was ultrasonically cleaned for 1 minute respectively. The polished sample was placed in a desiccator for later use.

[0048]

[0049] Under a polarized fluorescence microscope, use a 50x oil immersion objective lens to compare the oil immersion reflected light and fluorescence characteristics of the organic matter in the sample to determine the type of organic matter. Select typical organic matter particles or areas of interest and use the etching objective lens to mark them. Select a marking range of 2mm-3mm diameter and etch 25 circles. After marking, wipe off the immersion oil, take a photo of the marked sample, and record the marking order, such as Figure 3 In addition, the uppermost end of the etching objective lens is a threaded opening 5, which is consistent with the threaded opening specification of the common objective lens. When in use, the etching objective lens is installed together with the common objective lens on the objective lens converter. The structural schematic diagram of the etching objective lens is as follows: Fig.11 As shown, when in use, depending on the hardness of the sample, the dial wheel 6 can be rotated fifteen to fifty times to leave a mark of suitable depth. Specifically, the edge of the small cylindrical structure 2 with a diameter of 2.5 mm is a sharpened steel vertex 3 at 0.25 mm. When the large cylindrical structure 1 is rotated, the small cylindrical structure 2 is driven by the large cylindrical structure 1 and rotates with the large cylindrical structure 1. The steel vertex 3 will form a circular mark on the sample with the center point of the large cylindrical structure 1 as the center. The etching objective lens used in the actual operation of this embodiment is Leica Object marker M 25, item number: 11505059.

[0050] The sample is processed for the second time, and the specific process is as follows: a. Secondary polishing: Set the chassis speed of the automatic grinding and polishing machine to 160 rpm, the fixture speed to 70 rpm, the single-point pressure to 10 N, and polish for 30-50 seconds under the conditions of 0.05μm alumina polishing liquid and matching polishing cloth. b. Bottom cutting: Place the sample surface facing down into a special cutting fixture and cut the bottom surface so that the sample meets the requirements of parallel top and bottom surfaces and the height is less than 1cm. Argon ion polishing requires that the bottom and top surfaces of the sample are completely parallel and the thickness is less than 1cm, so the sample needs to be cut for the second time, using the attached Figure 2 The sample cutting fixture in the sample cutting fixture cuts the bottom surface of the sample. Specifically, use Figure 2 The sample cutting fixture is used for secondary cutting. The inner diameter of the fixture is 26mm-28mm, the side wall and bottom thickness is 2mm, the total height is 6mm-8mm, there are three movable screws 4 on the side to fix the sample, and the bottom screw hole is used to fix the fixture. c. Argon ion polishing: The polishing conditions are set to 5.5kV, 40min; 3kV, 15min.

[0051] Fix the sample on the sample stage with conductive glue and place it in the SEM sample chamber. Adjust the sample orientation and take navigation photos. Observe the organic matter particles and areas of interest one by one from low to high magnification using a SEM. Figure 4-10 As shown, it reflects the oil-immersion reflected light and fluorescence characteristics of the sporophyte and asphaltene body and their micropore development characteristics.

[0052] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for jointly analyzing the type of organic matter and micropore development characteristics in rocks, characterized in that: The following steps are involved: Step 1: After the block or granular rock sample is dried, it is cold-mounted using epoxy resin mixed with conductive powder to make a cylindrical sample; Step 2: Demolding the cylindrical sample and performing the first mechanical polishing; Step 3: Use the etched objective lens to mark the sample surface when observing the sample under a microscope; Step 4: Perform a second mechanical polishing and argon ion polishing on the sample obtained in step 3; Step 5: Use the SEM navigation photos and the marked sample photos for quick positioning and observation.

2. The combined analysis method of organic matter type and micropore development characteristics in rock according to claim 1, characterized in that: The specific steps of step 1 are as follows: drying the prepared rock blocks and debris for use, preparing a cold mounting mold, applying a release agent on the inner surface of the mold, and after the release agent is dried, placing the rock blocks or debris into the cold mounting mold respectively; adding a curing agent to the epoxy resin and mixing evenly, adding conductive powder to the epoxy resin, stirring well, pouring the mixed conductive epoxy resin into the cold mounting mold, standing until solidified, and then demolding to obtain a cylindrical sample for use.

3. The combined analysis method of organic matter type and micropore development characteristics in rock according to claim 1, characterized in that: The specific steps of step 2 are as follows: the first step is to grind the rock surface on an automatic grinder using 400 or 600 mesh sandpaper. If it is a granular sample, it is advisable to closely connect the exposed edges of the sample; the second step is to finely grind the surface using 1200 mesh sandpaper to reduce the depth of scratches; the third step is to polish the sample surface using alumina polishing liquid and a matching polishing cloth; the fourth step is to polish the sample surface using alumina polishing liquid with a smaller particle size than that in the third step and a matching polishing cloth.

4. The combined analysis method of organic matter type and micropore development characteristics in rock according to claim 3, characterized in that: The third and fourth steps in step 2 are polished using 0.3 μm and 0.05 μm aluminum oxide polishing liquids respectively.

5. The combined analysis method of organic matter type and micropore development characteristics in rock according to claim 4, characterized in that: The standard of the sample obtained in step 2 is that the surface is flat under a microscope, preferably with no scratches visible at 500 times magnification.

6. The method for jointly analyzing the type of organic matter and micropore development characteristics in rocks according to claim 1, characterized in that: The specific steps of step 3 are as follows: Under oil-immersion reflected light, observe and analyze the organic matter type according to standard methods, clarify the characteristics of the main organic matter types in the sample, select typical organic matter particles, and circle the observation target using an etched objective lens.

7. The method for jointly analyzing the type of organic matter and micropore development characteristics in rocks according to claim 6, characterized in that: The lower part of the etching objective lens is a large cylindrical structure, in which a movable small steel cylindrical structure is embedded. The small cylindrical structure is located on one side of the center point of the large cylindrical structure, and the edge of the small cylindrical structure is a sharpened steel vertex at 0.25 mm.

8. The method for combined analysis of organic matter types and micropore development characteristics in rocks according to claim 1, characterized in that: The method for the second mechanical polishing in step 4 is: the chassis speed of the automatic grinder is 160rpm, the mechanical head speed is 70rpm, the single-point pressure is 10N, and polishing is performed for 30-50 seconds under the conditions of 0.05μm alumina polishing liquid and matching polishing cloth. Then the sample is placed in a cutting fixture with the surface facing down, and the bottom surface is cut so that the top and bottom surfaces of the sample are parallel and the height is less than 1cm.

9. The method for jointly analyzing the type of organic matter and micropore development characteristics in rocks according to claim 1, characterized in that: The argon ion polishing procedures in step 4 are: a. 4.5 kV-6.5 kV, 30 min-120 min; b. 2.5 kV-3 kV, 10 min-15 min.

10. The method for jointly analyzing the type of organic matter and micropore development characteristics in rocks according to claim 1, characterized in that: The specific steps of step 5 are as follows: after completing the above-mentioned sample observation and pretreatment steps, fix the sample on the sample stage according to the operating procedures of the field emission scanning electron microscope, focused ion beam scanning electron microscope or helium ion scanning electron microscope, place it in the sample chamber, rotate the sample to the same angle as when observing under the microscope, and take a navigation photo. When observing under the electron microscope, double-click the mouse to quickly locate the location of the microscope photo and carry out positioning analysis.

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