Iodoform-epoxy resin embedding preparation method for SEM-EDS analysis of coalbed methane reservoir sample

Abstract

The invention discloses an iodoform-epoxy resin embedding preparation method for SEM-EDS analysis of a coalbed methane reservoir sample, and relates to the technical field of reservoir sample detection. The method comprises the following steps: cutting, cleaning and performing low-temperature vacuum drying on a coalbed methane reservoir sample; adding iodoform into the epoxy resin, and fully stirring until the iodoform is completely dissolved to form a uniform and clear mixed solution; then adding a curing agent and stirring at a low speed; after natural and vacuum combined defoaming, embedding and curing the sample; and finally, a flat observation surface is obtained through step-by-step mechanical polishing and argon ion polishing, and sample preparation is completed after conductive treatment. According to the method, iodoform is dissolved firstly, and then the curing agent is added, so that iodoform crystal agglomeration and bubble introduction are effectively avoided, the contrast of the backscattered electron image is remarkably improved, the primary pores and cleat structures of the coal rock are protected, and the EDS quantitative analysis precision is improved; the method is simple in process, controllable in process parameter, good in repeatability, suitable for various samples such as coal rock, coal-containing clastic rock and coal seam dirt band, and capable of providing high-quality sample preparation guarantee for coal bed gas reservoir microcosmic characterization.

Description

Technical Field

[0001] This invention relates to the field of coalbed methane reservoir sample preparation technology, specifically to an iodoform-epoxy resin embedding preparation method suitable for scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and backscattered electron (BSE) imaging analysis of various coalbed methane reservoir samples (coal rock, coal-bearing clastic rock, coal seam interbedded with gangue, etc.). It can be widely used in related experimental detection scenarios such as microstructure characterization of coalbed methane reservoirs, mineral composition analysis, and pore flow characteristic evaluation. Background Technology

[0002] Coalbed methane (CBM) reservoir samples (mainly including coal rock, coal-bearing clastic rocks, and interbedded rock) are the core carriers for studying CBM storage, seepage, and development potential. Their microscopic pore structure (micropores, mesopores, macropores), mineral occurrence state, mineral distribution characteristics, and cleavage and fracture development directly determine the adsorption capacity, seepage efficiency, and development effectiveness of CBM. SEM-EDS detection technology, with its advantages of high resolution and high sensitivity, has become the mainstream method for characterizing the microscopic features of CBM reservoir samples. The quality of sample preparation directly affects the authenticity, accuracy, and reliability of the detection results, and is an important prerequisite for subsequent reservoir evaluation and development scheme optimization.

[0003] Currently, the commonly used preparation processes for SEM-EDS analysis of coalbed methane reservoir samples are direct epoxy resin embedding and mechanical polishing. Some processes add iodoform to improve BSE imaging contrast. However, existing technologies generally have the following prominent technical defects, making it difficult to meet the requirements for accurate detection:

[0004] 1. Poor and unstable contrast enhancement effect: In conventional processes, iodoform is mixed with epoxy resin and curing agent at the same time. Iodoform crystals are difficult to completely dissolve and local crystallization and agglomeration are likely to occur. This leads to blurred boundaries of reservoir sample matrix, pores, resin and minerals in BSE imaging, and the contrast difference is not obvious. It is impossible to clearly distinguish each component, which interferes with microstructure observation and EDS quantitative analysis.

[0005] 2. The original structure of the sample is easily damaged: If the stirring speed and time are not controlled during the stirring process, vigorous stirring will easily introduce a large number of air bubbles. The air bubbles fill the pores of the sample or adhere to the sample surface, which will damage the original pore, cleavage and fracture structure of the coalbed methane reservoir sample, resulting in distorted test data and failure to truly reflect the actual microscopic characteristics of the reservoir.

[0006] 3. Poor adaptability, making it difficult to meet the needs of different types of samples: Coalbed methane reservoir samples are diverse, including soft and fragile loose coal and rock, coal and rock with high clay content, coal and rock cemented with carbonates, and coal seam interbedded with gangue, etc. Existing preparation processes have not optimized parameters for different types of samples, which easily leads to problems such as poor bonding between the embedding layer and the sample, sample falling off, pore collapse, and severe surface scratches, resulting in poor adaptability;

[0007] 4. Poor process controllability and poor repeatability: The existing technology does not clearly define key parameters such as the iodoform addition ratio, stirring time, and curing conditions. The quality of samples prepared by different operators varies greatly, and the repeatability of test results is poor, making it difficult to meet the standardized testing needs of the laboratory.

[0008] 5. Samples are easily oxidized, affecting detection stability: Coalbed methane reservoir samples (especially coal and petrified coal) have high surface activity. During conventional preparation, samples exposed to air are prone to oxidation reactions, which change the surface composition and microstructure of the samples, further interfering with the quality of EDS mineral analysis and SEM imaging.

[0009] Currently, there is a lack of a dedicated preparation method that can simultaneously ensure uniform dispersion of iodoform, preserve the original structure of the sample, prevent crystallization and bubble formation, adapt to various types of coalbed methane reservoir samples, and has controllable and reproducible processes. This method cannot meet the high-precision detection requirements for the microscopic characterization of coalbed methane reservoirs. There is an urgent need to propose a preparation scheme with a complete process, stable results, and wide applicability to solve the many shortcomings of existing technologies. Summary of the Invention

[0010] This invention aims to overcome the technical problems existing in the preparation process of SEM-EDS analysis of coalbed methane reservoir samples, such as uneven iodoform dispersion, crystal agglomeration, bubble introduction, sample structure damage, poor adaptability, poor process controllability, and easy oxidation of samples. It provides an iodoform-epoxy resin embedding preparation method that achieves uniform iodoform dispersion, preserves the original structure of the sample, provides accurate detection results, is adaptable to various types of coalbed methane reservoir samples, and is process-controllable and easy to operate. This improves the accuracy of SEM-EDS characterization of the microscopic features of coalbed methane reservoir samples and provides reliable experimental data support for coalbed methane reservoir evaluation and development scheme optimization.

[0011] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: a method for preparing iodoform-epoxy resin embedding for SEM-EDS analysis of coalbed methane reservoir samples, the complete process flow is as follows: Figure 1 As shown, it includes the following steps:

[0012] Step 1: Sample Pretreatment

[0013] Select representative coalbed methane reservoir samples (coal rock, coal-bearing clastic rock, coal seam interbedded with gangue, etc.), and cut them to the preset size (preferably 5mm×5mm×2mm~8mm×8mm×3mm, which can be adjusted according to the sample type) using a diamond wire cutter; ultrasonically clean the sample surface with anhydrous ethanol for 3~5 minutes to remove surface dust, impurities and oil stains, and avoid impurities interfering with subsequent embedding and detection; after cleaning, place the sample in a vacuum drying oven and vacuum dry at 40~50℃ for 2~4 hours to remove adsorbed water on the sample surface, and at the same time prevent sample oxidation and pore collapse. After drying, take it out and place it in a desiccator for later use to avoid secondary contamination.

[0014] Step 2: Epoxy Resin Pretreatment

[0015] Select transparent epoxy resin (preferably low viscosity epoxy resin with a viscosity of 100~200 mpa.s, which facilitates iodoform dissolution and bubble removal), and place it in a constant temperature environment of 25±2℃ for 30 minutes to eliminate viscosity fluctuations caused by temperature changes; weigh the predetermined mass of epoxy resin and place it in a clean, dry, and impurity-free glass measuring cup. The measuring cup should be cleaned and dried with anhydrous ethanol beforehand to avoid residual impurities affecting the mixing effect, and set aside for later use.

[0016] Step 3: Iodoform dissolution and uniform dispersion

[0017] Add iodoform to the pretreated epoxy resin from step 2. The iodoform content should be 20%–40% of the epoxy resin content (preferably 30%, as this ratio ensures improved BSE imaging contrast while avoiding increased costs and crystallization risks due to excessive iodoform). Use a magnetic stirrer to stir at a constant speed of 150–250 rpm for 15–30 minutes. If stirring manually, do so slowly and at a constant speed, continuously observing the solution state until the iodoform crystals are completely dissolved, forming a uniform, clear, precipitate-free, and crystallization-free yellow transparent mixed solution. Do not add curing agent at this step, as this may cause premature reaction between the curing agent and epoxy resin, leading to incomplete dissolution of iodoform and precipitation / crystallization, affecting dispersion and subsequent embedding quality. Note: Stirring in the dark (iodoform is photosensitive; avoid light exposure to prevent decomposition) can further ensure the stability and uniform dispersion of iodoform. SEM images before and after iodoform dissolution are shown below. Figure 3 As shown.

[0018] Step 4: Mixing, curing, and degassing

[0019] Add a standard ratio of curing agent compatible with epoxy resin to the clear "resin-iodoform" solution obtained in step 3 (the curing agent should be an amine-based curing agent compatible with epoxy resin, and the mass of the curing agent should be 30%~50% of the mass of epoxy resin, preferably 40%. This ratio can ensure the curing strength of the embedded body while avoiding residual bubbles caused by excessively rapid curing). Immediately stir slowly at a low speed, controlling the stirring speed at 100~200 r / min, for 5~10 minutes. During the stirring process, keep the stirring rod rotating at a uniform speed along the wall of the measuring cup to avoid introducing air bubbles through vigorous stirring. After stirring, use a combination of two degassing methods: first, let it stand for 5~10 minutes to naturally remove surface bubbles; then, place the mixed solution in a vacuum degassing chamber and degas for 3~5 minutes under a vacuum of 0.08~0.1 MPa to completely remove residual air bubbles inside the mixed solution, ensuring that the embedded sample is free of bubble defects.

[0020] Step 5: Sample embedding and curing

[0021] Select a silicone or polytetrafluoroethylene mold that matches the sample size. Apply a uniform layer of release agent (preferably silicone-based release agent, as it facilitates subsequent demolding of the embedded body and does not affect sample detection) to the inner wall of the mold. Place the pretreated coalbed methane reservoir sample from step 1 smoothly into the center of the mold, ensuring the sample surface is flat and without tilting. The distance between the sample and the inner wall of the mold should be no less than 2 mm to avoid insufficient sample protection due to an excessively thin embedding layer. Slowly inject the degassed mixed solution from step 4 at a rate of 5-10 mL / min to avoid generating air bubbles. Ensure the mixed solution level is 1-2 mm above the sample surface to guarantee complete sample encapsulation. Select appropriate curing conditions based on the sample type.

[0022] (1) For easily deformable samples such as soft coal and rock, and coal and rock with high clay content: use room temperature curing, and cure at 25±2℃ for 24~48 hours. Slow curing can avoid thermal stress generated during the curing process from damaging the sample structure.

[0023] (2) For samples with high hardness such as coal-bearing clastic rocks and coal seam interbedded with gangue: use constant temperature curing, cure at 60±5℃ for 2~4 hours to shorten the curing time while ensuring the curing strength;

[0024] During the curing process, avoid mold vibration and collision to prevent sample displacement and bubble formation. After curing, remove the embedded body and demold to obtain a complete sample embedded body.

[0025] Step 6: Sample polishing and conductivity treatment

[0026] The solidified embeddings were subjected to progressive mechanical polishing. Wet polishing was used to avoid dust contamination of the sample surface. Three polishing methods were employed:

[0027] (1) Rough polishing: Use 800# sandpaper to polish at a uniform speed to remove burrs and uneven parts on the surface of the embedded body, and polish until the sample surface is initially smooth;

[0028] (2) Medium polishing: Use 1200# and 2000# sandpaper in sequence to gradually refine the surface and remove the scratches left by rough polishing;

[0029] (3) Fine polishing: Use 5000# sandpaper to polish the sample surface at a uniform speed until it is smooth, without scratches or dents, to ensure that the observation surface is flat.

[0030] After mechanical polishing, ion beam polishing is performed using an argon ion polisher with the following parameters: accelerating voltage 5-8 kV, polishing time 10-15 minutes. This further removes polishing scratches from the sample surface, obtaining an atomically smooth observation surface and avoiding interference from scratches on microstructure observation. After polishing, the sample is ultrasonically cleaned in anhydrous ethanol for 1-2 minutes to remove surface polishing dust, and then placed in a vacuum drying oven at 40°C for 30 minutes. After drying, conductivity treatment is performed using a carbon sprayer or a gold sprayer. The carbon spraying thickness is controlled at 10-20 nm (the gold spraying thickness is controlled at 5-10 nm) to avoid excessive coating thickness interfering with EDS mineral analysis. After conductivity treatment, the sample is ready for BSE detection using SEM-EDS technology. Figure 2 ).

[0031] The technical solution adopted in this invention requires control of the following key process parameters:

[0032] (1) Iodoform related parameters

[0033] Iodoform should account for 20% to 40% of the epoxy resin mass. If it is below 20%, the contrast improvement of BSE imaging is not significant, and it is impossible to clearly distinguish the components of the sample. If it is above 40%, iodoform is difficult to dissolve completely, crystallization and agglomeration are likely to occur, and the cost will increase. Stirring time is 15 to 30 minutes, and stirring should be done in the dark to ensure that the iodoform is completely dissolved and evenly dispersed.

[0034] (2) Curing agent related parameters

[0035] The curing agent accounts for 30% to 50% of the epoxy resin mass. If the ratio is too low, the embedded body will not cure sufficiently, resulting in insufficient strength and easy breakage. If the ratio is too high, the curing speed will be too fast, which can easily introduce air bubbles and may cause the embedded body to crack.

[0036] (3) Stirring parameters

[0037] During the iodoform dissolution stage, the stirring speed should be 150~250 r / min to ensure uniform dissolution; during the curing agent mixing stage, the stirring speed should be 100~200 r / min to avoid introducing air bubbles; the stirring time should be strictly controlled to ensure uniform mixing and no air bubbles.

[0038] (4) Curing parameters

[0039] Choose room temperature curing (24~48 hours) or constant temperature curing (60℃, 2~4 hours) depending on the sample type to avoid thermal stress damaging the original structure of the sample.

[0040] (5) Polishing and conductivity parameters

[0041] Argon ion polishing acceleration voltage is 5~8kV, time is 10~15 minutes; carbon or gold spraying thickness is controlled at 5~20nm, balancing conductivity and EDS detection accuracy.

[0042] The core innovation of this invention

[0043] 1. Innovative feeding sequence

[0044] The process employs a two-step method: first, fully dissolve iodoform in epoxy resin until it is homogeneous and clear, and then add a curing agent. This completely avoids local crystallization, agglomeration, and precipitation of iodoform, ensuring uniform contrast and no artifacts in BSE imaging, and preventing interference with EDS quantitative analysis.

[0045] 2. Refinement and standardization of process parameters

[0046] By clearly defining key parameters such as the iodoform addition ratio, stirring speed and time, stirring under light, and vacuum degassing, the problems of violent stirring, numerous bubbles, and structural distortion in traditional sample preparation are solved, thus achieving a controllable sample preparation process and reproducible results.

[0047] 3. Targeted protection of coalbed methane reservoir samples

[0048] In response to the characteristics of coal and rock such as softness, easy collapse, well-developed cleavage, high clay content, and easy oxidation, a combination of "low-temperature vacuum drying, flexible embedding, graded solidification, and low-stress polishing" is adopted to maximize the protection of the original pores, fissures, and cleavage structures.

[0049] 4. Synergistic optimization of imaging and component analysis

[0050] By uniformly dispersing iodoform to enhance backscattered electron contrast and controlling the thickness of carbon / gold spraying, the system achieves both clear SEM morphology and accurate EDS mineral quantification, enabling precise differentiation of coal matrix, minerals, pores, and resin.

[0051] 5. High adaptability to various sample types

[0052] The method can be flexibly adapted to soft coal and rock, high clay coal and rock, carbonate cemented coal and rock, and coal seam interbedded with gangue, forming a standardized and scalable SEM / EDS sample preparation system for coalbed methane reservoirs.

[0053] Compared with the prior art, the present invention has the following significant advantages:

[0054] (1) Iodoform is evenly dispersed, completely eliminating detection artifacts: The innovative process of "dissolving iodoform first and then adding curing agent" is adopted. Combined with light-shielding stirring and precise control of stirring parameters, it ensures that iodoform is completely dissolved and evenly dispersed in epoxy resin, completely avoiding iodoform crystallization and agglomeration. The contrast of BSE imaging is improved by more than 30%, which can clearly distinguish the matrix, pores, resin and various minerals of coalbed methane reservoir samples. There is no local bright spot interference, which significantly improves the accuracy of EDS quantitative analysis and controls the detection error within 0.5%.

[0055] (2) The original structure of the sample is preserved and the test data is true and reliable: Through multi-stage process control such as low temperature vacuum drying, low speed stirring and vacuum degassing, the introduction of air bubbles is reduced and the oxidation of the sample and the collapse of pores and cleavage are avoided. At the same time, the solidification conditions are optimized according to different types of samples to ensure that the embedded layer is tightly bonded to the sample, effectively protecting the original microstructure of easily deformable samples such as soft coal and rock and coal with developed cleavage, and truly reflecting the actual characteristics of coalbed methane reservoirs.

[0056] (3) Strong process controllability and good repeatability: The key process parameters such as the iodoform addition ratio, stirring speed, stirring time, curing conditions, and polishing parameters are clearly defined. At the same time, the adaptation optimization schemes for different types of samples are provided. Operators can operate according to the standard process. The quality difference of samples prepared in different batches is small, and the repeatability of the test results is improved by more than 40%, which meets the standardized testing needs of the laboratory.

[0057] (4) Wide range of applications and strong practicality: It is applicable to SEM-EDS / BSE detection of various samples of coalbed methane reservoirs (soft coal and rock, coal and rock with high clay content, coal and rock with carbonate cementation, coal seam interbedded with gangue, etc.), and can also be extended to the preparation of other tight reservoir samples such as shale and tight sandstone; no complicated equipment is required, only conventional laboratory instruments (magnetic stirrer, vacuum drying oven, polishing machine, etc.), which are easy to operate, cost controllable, and easy to promote and apply.

[0058] (5) Extend sample preservation time and improve detection stability: The embedded sample is tightly wrapped by iodoform-epoxy resin, which can effectively isolate the air and prevent the sample from oxidizing and getting damp. The sample preservation time is extended to more than 6 months, and the sample is not easily damaged or broken during the detection process, which further improves the detection stability and reliability.

[0059] (6) Balancing detection accuracy and operational efficiency: The optimized process flow is reasonable, and the curing time can be flexibly adjusted according to the sample type, which not only ensures the embedding quality and detection accuracy, but also avoids unnecessary time waste, improves sample preparation efficiency, and meets the needs of batch sample detection. Attached Figure Description

[0060] Figure 1The complete process flow diagram of the preparation method of the present invention is shown, clearly marking each step and key parameter, including sample pretreatment, epoxy resin pretreatment, iodoform dissolution, mixing and curing, embedding and curing, polishing and conducting.

[0061] Figure 2 The images show SEM images of coal and rock samples prepared using the method of this invention and conventional methods. The left side shows the conventional method (iodoform crystallization, blurred boundaries), while the right side shows the method of this invention (uniform contrast, clear boundaries).

[0062] Figure 3 The images are SEM images before and after iodoform dissolution. The left side shows the BSE image of the incompletely dissolved iodoform-epoxy resin mixture (with crystals and turbidity), and the right side shows the BSE image of the completely dissolved solution.

[0063] Figure 4 The image shows the SEM image (left) and EDS mineral distribution map (right) of the coal rock sample with high clay content in Example 1.

[0064] Figure 5 The images show the SEM image (left) and EDS mineral distribution map (right) of the soft cleavage coal sample in Example 2. Detailed Implementation

[0065] The present invention will now be described in detail through exemplary embodiments. However, it should be understood that, without further description, the samples, structures, and features of one embodiment may be advantageously incorporated into other embodiments.

[0066] Example 1: Preparation of coal rock samples for coalbed methane with high clay content

[0067] This embodiment focuses on a coalbed methane sample with high clay content (55% clay content, soft texture, and well-developed pores). The specific steps are as follows:

[0068] Sample pretreatment: Select coal and rock samples from this depth range and cut them to 5mm×5mm×2mm using a diamond wire cutter; ultrasonically clean with anhydrous ethanol for 5 minutes to remove surface clay dust and impurities; vacuum dry at 40℃ for 3 hours, and then place them in a desiccator for later use.

[0069] Epoxy resin pretreatment: Select low viscosity epoxy resin (viscosity 150 mpa.s) and place it at a constant temperature of 25℃ for 30 minutes; weigh 100g of epoxy resin and place it in a clean and dry glass measuring cup for later use.

[0070] Iodoform dissolution and dispersion: Add 30g of iodoform to the epoxy resin, use a magnetic stirrer, cover the light, and stir at a constant speed (200r / min) for 20 minutes until a uniform, clear, yellow transparent solution is formed with no crystal residue.

[0071] Mixing, curing and degassing: Add 40g of amine curing agent, stir at low speed (150r / min) for 8 minutes, stir evenly, let stand for 8 minutes, and then place in a vacuum degassing chamber (0.09MPa) for 4 minutes to remove residual bubbles.

[0072] Sample embedding and curing: A silicone mold was selected and a release agent was applied; the pretreated coal and rock sample was placed in the center of the mold, and the mixed solution was slowly poured in, with the liquid level 1.5 mm above the sample surface; the sample was cured at room temperature of 25°C for 36 hours, and a complete embedding body was obtained after demolding.

[0073] Sample polishing and conductivity treatment: Wet polishing was performed step by step using 800#, 1200#, 2000#, and 5000# sandpaper, followed by argon ion polishing (accelerating voltage 6kV, time 15 minutes); ultrasonic cleaning with anhydrous ethanol for 2 minutes, drying at 40℃ for 30 minutes; carbon spraying treatment was performed to achieve a carbon layer thickness of 15nm, completing the preparation.

[0074] Detection results: In BSE imaging, the boundaries of coal matrix (dark gray), pores (light gray), iodoform-epoxy resin (bright yellow), and clay minerals (reddish brown) are clear, with no iodoform crystals, bubbles, or scratch artifacts; EDS quantitative analysis shows that the clay mineral (kaolinite) content is 54.8%, with an error of less than 0.5% compared to the actual sample composition (55%), indicating high quantitative accuracy; the sample pore structure is intact, with no collapse or fragmentation, accurately characterizing the micropore and mineral distribution features of coal and rock with high clay content. Figure 4 The mineral distribution characteristics of clay minerals (kaolinite) and coal matrix are clearly displayed.

[0075] Example 2: Preparation of Coal and Rock Samples with Well-developed Soft Fences

[0076] This embodiment targets coal and rock samples with well-developed cleavage (soft and brittle, with high cleavage density). The specific steps are as follows:

[0077] Sample pretreatment: cut to 5mm×5mm×2mm, ultrasonically cleaned with anhydrous ethanol for 4 minutes; vacuum dried at 35℃ for 4 hours, and then placed in a desiccator for later use.

[0078] Epoxy resin pretreatment: Select low viscosity epoxy resin (viscosity 120 mpa.s) and place it at a constant temperature of 25℃ for 30 minutes; weigh 100g of epoxy resin and place it in a glass measuring cup for later use.

[0079] Iodoform dissolution and dispersion: Add 25g of iodoform, cover with light using a magnetic stirrer, and stir at a constant speed (180r / min) for 25 minutes until completely dissolved, forming a clear yellow solution.

[0080] Mixing, curing and degassing: Add 35g of curing agent, stir at low speed (120r / min) for 7 minutes, let stand for 10 minutes, and then degas under vacuum (0.08MPa) for 5 minutes.

[0081] Sample embedding and curing: Apply release agent to silicone mold, place sample in, and inject mixed solution; cure at room temperature of 25℃ for 48 hours, and demold to obtain embedded body.

[0082] Sample polishing and conductivity treatment: stepwise wet polishing, argon ion polishing (accelerating voltage 5kV, time 12 minutes); ultrasonic cleaning for 1.5 minutes, drying at 40℃ for 30 minutes; gold sputtering treatment, gold layer thickness 8nm, to complete the preparation.

[0083] Test results: The coal and rock cleavage structure is intact, with no collapse, spalling, or bubble defects, and the cleavage boundaries are clearly distinguishable. Figure 5 BSE imaging shows uniform contrast with no local bright spots interfering; EDS analysis can clearly identify the mineral composition around the cleavage, accurately characterize the cleavage development features and microscopic seepage channels, and provide a reliable basis for evaluating the seepage capacity of coalbed methane.

Claims

1. A method for preparing iodoform-epoxy resin embedding for SEM-EDS analysis of coalbed methane reservoir samples, characterized in that, Includes the following steps: (1) Sample pretreatment: Select coalbed methane reservoir samples, cut them to the preset size, and clean them with anhydrous ethanol by ultrasonic cleaning and low-temperature vacuum drying before use; (2) Pretreatment of epoxy resin: Weigh low-viscosity epoxy resin and place it in a clean and dry container for later use; (3) Iodoform dissolution and dispersion: Add iodoform to the epoxy resin and stir until the iodoform is completely dissolved to form a uniform and clear yellow mixed solution. No curing agent is added at this stage. (4) Mixing, curing and degassing: Add curing agent to the above mixed solution, stir at low speed until uniform, and remove air bubbles by natural standing and vacuum degassing; (5) Sample embedding and curing: Place the pretreated sample into the mold, inject the mixed solution, and select room temperature curing or constant temperature curing according to the sample type. After curing, demold to obtain the embedding body; (6) Polishing and conductivity treatment: The embedded body is subjected to step-by-step mechanical polishing and argon ion polishing, and after cleaning and drying, it is subjected to carbon spraying or gold spraying to complete the sample preparation.

2. The method according to claim 1, characterized in that, The sample size in step (1) is 5mm×5mm×2mm~8mm×8mm×3mm; the ultrasonic cleaning time is 3~5 minutes; the low temperature vacuum drying temperature is 35~50℃ and the drying time is 2~4 hours.

3. The method according to claim 1, characterized in that, The iodoform in step (3) is 20% to 40% of the epoxy resin mass; the stirring is done by magnetic stirring or manual stirring, the stirring speed is 150 to 250 r / min, the stirring time is 15 to 30 minutes, and the stirring process is carried out under light-proof conditions.

4. The method according to claim 1, characterized in that, The curing agent mentioned in step (4) is an amine curing agent, and its mass is 30% to 50% of the mass of epoxy resin; after adding the curing agent, the stirring speed is 100 to 200 r / min, and the stirring time is 5 to 10 minutes; the vacuum degree of vacuum degassing is 0.08 to 0.1 MPa, and the degassing time is 3 to 5 minutes.

5. The method according to claim 1, characterized in that, In step (5), during the embedding process, the liquid level of the mixed solution is 1-2 mm higher than the sample surface; the room temperature curing condition is 25±2℃, and the curing time is 24-48 hours; the constant temperature curing condition is 60±5℃, and the curing time is 2-4 hours.

6. The method according to claim 1, characterized in that, In step (6), the progressive mechanical polishing is carried out by wet polishing with 800#, 1200#, 2000# and 5000# sandpaper in sequence; the argon ion polishing acceleration voltage is 5-8kV and the time is 10-15 minutes; the carbon spraying thickness is 10-20nm and the gold spraying thickness is 5-10nm.

7. The method according to claim 1, characterized in that, For soft and fragile coal and rock samples, the cutting size is 5mm×5mm×2mm, the drying temperature is 35~40℃, the iodoform addition ratio is 25%~30%, and the curing is carried out at room temperature for 36~48 hours.

8. The method according to claim 1, characterized in that, For coal and rock samples with high clay content, the ultrasonic cleaning time was extended to 5 minutes, the curing agent ratio was 35% to 40%, and the argon ion polishing time was extended to 15 minutes.

9. The method according to claim 1, characterized in that, For samples of carbonate-cemented coal or coal seam interbedded with gangue, the iodoform addition ratio is 30%–35%, and a constant temperature of 60℃ is used for curing.

10. The method according to any one of claims 1 to 9, characterized in that, The method is applicable to SEM-EDS and BSE imaging analysis of coal, coal-bearing clastic rocks, and coal seam interbedded with gangue, and can be extended to the embedding preparation of shale and tight sandstone reservoir samples.

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