GB/T 18295-2026Microbeam analysis - Scanning electron microscope analysis of sandstone samples from oil and gas reservoirs (English PDF)

5.2 Software

5.2.1 Image Analysis Software It should have functions such as binarization of scanning electron microscope images, extraction of pore structure, and quantitative calculation.

5.2.2 Automated Mineral Analysis Software It should have the following main functions.

a) Control the focused electron beam to scan the sample surface point by point, and control the image acquisition system and the energy dispersive spectrometer system to synchronously acquire backscattered electron images. Image and element data;

b) Based on the atomic number contrast and elemental data obtained at each test point, automatically identify minerals by referring to a standard mineral crystal classification database. phase of matter;

c) Analyze and obtain information such as mineral composition, grain morphology parameters, embedding characteristics and degree of liberation.

5.3 Materials The main materials include.

a) Dichloromethane (analytical grade);

b) Anhydrous ethanol (analytical grade);

c) High-purity nitrogen (purity not less than 99.99%);

d) Conductive adhesive or double-sided conductive tape, etc.;

e) Latex or epoxy resin AB glue, etc.;

f) Ear syringe or compressed air canister;

g) Diamond suspension (coarse particle size 20µm~60µm, medium particle size 3µm~15µm, fine particle size 1µm~ 1.5µm);

h) Carbon rope, carbon rod or gold target (purity not less than 99.99%).

6.2.1 Processing of Natural Cross-Section Specimens

6.2.1.1 Use a crusher or impact hammer to perform primary crushing of the rock sample to obtain blocks with exposed natural fracture surfaces.

6.2.1.2 Select blocks free of cracks or impurities, and process them using a cutting machine, using a flat, fresh cross-section as a reference. The thickness of the processed block should be 5mm~20mm, length/width is 5mm~50mm.

6.2.1.3 Using an ultrasonic cleaner, clean with anhydrous ethanol, and then adhere the processed block to the scanning electron microscope using latex or epoxy resin AB glue. Mirror sample holder.

6.2.1.4 Dry naturally at room temperature for 24 hours, or place in an oven (temperature preferably 40°C~60°C) for at least 2 hours, using a bulb syringe or... Compressed air canisters blow away debris and dust from the surface of the block, keeping the natural cross-section clean and obtaining a natural cross-section sample.

6.2.2 Argon ion beam polishing of sample processing

6.2.2.1 Based on the natural cross-section specimen obtained in 6.2.1.4, the surface is trimmed with a cutting machine and visually parallel to the bottom surface of the sample holder.

Note. For smaller rock fragments, resin inlay is typically used to achieve the dimensions described in

6.2.1.2 before further processing.

6.2.2.2 Using a polishing machine, diamond suspensions of different particle sizes are used for mechanical grinding in sequence, and the surface is smooth and shiny when observed with the naked eye.

6.2.2.3 Dry and clean as per 6.2.1.4.

6.2.2.4 Polishing was performed using an argon ion beam polisher with an accelerating voltage of 1kV~6kV, an incident angle of 2°~8°, and a polishing time of 30min. After 180 minutes, the sample was polished by argon ion beam.

Note. For sandstone samples, the parameters of 5kV acceleration voltage, 2° incident angle and 120min polishing time are usually used.

6.3 Sample Coating Vacuum coating or ion sputtering equipment is used as needed, with carbon rope, carbon rod, or gold target selected for polishing the natural cross-section sample with an argon ion beam. The sample surface should be coated with a carbon or gold conductive film, with a film thickness of 5nm to 20nm. Carbon film is preferred for energy dispersive spectroscopy (EDS). After coating, conductive adhesive or double-sided conductive film should be used. The electrical tape connects the upper surface of the sample to the metal sample holder.

7.5 Mineral composition collection

7.5.1 Parameter Selection Based on the intended use of the component data, refer to Table 2 to set the parameters for the electron microscope and energy dispersive spectroscopy.

7.5.2 Mineral Particle Composition For the target mineral particles in the natural cross-section sample, according to the requirements of

6.3 in GB/T 17359-2023, the sample surface and the instrument electron beam... At a 90° angle, select point analysis or local area scan mode to acquire X-ray energy spectrum, identify the spectral peaks of each element, and obtain the elemental composition.

7.5.3 Mineral distribution on the sample surface For argon ion beam polished samples, automated mineral analysis software is used to control the electron beam for point-by-point scanning (the interval between two points is no greater than...). (10 µm), backscattered electron contrast and elemental information were obtained simultaneously, and the mineral distribution on the sample surface was identified using a mineral classification database. Figure 3 shows an example of obtaining the mineral distribution on the surface of a sandstone argon ion beam polished sample.

a) BSE electron microscope image of sandstone;

b) Elemental distribution image of sandstone;

c) Mineral distribution image of sandstone.

8.1 Pore and throat analysis

8.1.1 Pore Type and Size Measurement Observe the pore characteristics of sandstone, randomly select no fewer than 20 pores, describe the pore types, and Figure 4 shows a schematic diagram of common pore morphological characteristics. Figure. The pore size was measured using an electronic scale conforming to GB/T 27788, and the measurements were marked on the electron microscope image, with the largest pore also marked. Record the gaps.

Note. Common pore types include intergranular pores, intragranular pores, casting pores, intergranular spaces during crystal regeneration, pores within cementitious materials, and dissolution pores.

a) Intergranular porosity

b) Intragranular porosity

c) Cast film porosity

d) Intergranular spaces during crystal regeneration

e) Pores within the cement

f) Dissolution pits

8.1.2 Measurement of Throat Type and Dimensions Observe the characteristics of the larynx, randomly select no less than 20 larynxes, describe the types of larynxes, and Figure 6 shows a schematic diagram of the morphological characteristics of common larynxes. The larynx width is measured using an electronic scale conforming to GB/T 27788 at its narrowest point and marked on the electron microscope image. Identify and record the largest larynx.

Note. Common throat types in sandstone include. constricted throat, necked throat, sheet-like throat, curved sheet-like throat, and bundled tubular throat.

8.1.3 Face Rate Image analysis software capable of binarizing scanning electron microscope images and extracting pore structures was used to analyze the grayscale values of the rock skeleton and pores. To assess the differences in image quality, threshold segmentation and two-dimensional histogram segmentation methods were used to segment the image into different phases. The pore area and the total image area were then calculated. The percentage is used as the face rate. Figure 8 shows an example of phase segmentation and porosity calculation for sandstone samples polished by argon ion beam.

Note. Black represents pores, and blue represents minerals.

8.2 Mineral Analysis

8.2.1 Analysis of cementing materials According to the requirements of GB/T 17361, the type and occurrence of cement should be determined based on mineral morphology and elemental data, as shown in Appendix A. A.1, A.2.

8.2.2 Analysis of post-diagenetic changes

8.2.2.1 Secondary increase Identify the locations of secondary enlargement of quartz and feldspar in the image, determine the degree of enlargement, and annotate and record the findings on the electron microscope image. Appendix B, section B.1.

8.2.2.2 Dissolution and leaching Indicate the locations of leaching and dissolution in the images, mark them on the electron microscope images and record them, see B.2.

8.2.2.3 Transformation and Explanation Indicate the location of the transformation and replacement in the image, mark it on the electron microscope image and record it, see B.3.

8.2.3 Mineral Composition Analysis Based on research needs, the main mineral types, proportions of different minerals, mineral particle morphology, and particle diameter distribution in the samples were analyzed. Take notes. Figure 9 shows examples of the distribution and particle size characteristics of differe...