Method for quantitatively characterizing in-situ pore connectivity of rock sample through scanning electron microscope image
By injecting low-melting alloys under high temperature and high pressure conditions and observing with scanning electron microscope, the problem that existing pore structure connectivity experimental methods cannot provide intuitive visualization and insufficient data reliability is solved, and intuitive visualization and accurate evaluation of pore connectivity of rock samples is achieved.
Patent Information
- Application Number
- CN202311535333.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-11-17
- Publication Date
- 2025-05-20
AI Technical Summary
The existing experimental methods for pore structure connectivity cannot provide intuitive visual results, and the reliability and applicability of the data obtained from the experiment are affected by experimental conditions.
SEM images are used to quantitatively characterize the in-situ pore connectivity of rock samples. By injecting low-melting point alloy under high temperature and high pressure conditions, fluid migration under real formation conditions is simulated, and visualization and accurate evaluation of pore connectivity is achieved through scanning electron microscopy observation and image processing.
The intuitive visualization and accurate evaluation of pore connectivity of rock samples was achieved, comprehensive understanding and accurate evaluation of pore connectivity were improved, and the problems of insufficient visualization of existing methods and data reliability were overcome.
Smart Images
Figure CN120020528A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the field of oil and gas experiments, and specifically to a method for quantitatively characterizing the in-situ pore connectivity of rock samples by scanning electron microscope images. Background Art
[0002] The pore connectivity of rock reservoirs controls the migration and production behavior of oil and gas, and is of great significance in oil and gas exploration and development. It determines the flow capacity of oil and gas in the reservoir, evaluates the effective reserves and production capacity of the reservoir, guides the application of enhanced oil recovery technologies such as water flooding and fracturing, and affects the selection of reservoir development methods. Understanding pore connectivity helps to optimize the development plan and improve the recovery rate. At the same time, it also guides the selection of pore repair technologies to restore or improve the reservoir production capacity. Therefore, the study of reservoir pore connectivity is crucial for the success of exploration and development, provides an important basis for decision-making, improves oil and gas production capacity, and maximizes the utilization of reservoir potential. The strong heterogeneity and a large number of developed nano-scale pore throats in shale and tight sandstone reservoirs make it very difficult to characterize the connectivity of reservoir pore structures.
[0003] Currently, the experimental methods used to characterize the pore structure connectivity include permeability experiments, gas adsorption experiments, and nuclear magnetic resonance experiments. However, these methods have some major defects. First, these experimental methods cannot provide intuitive visualization results, but only numerical data, making it difficult to intuitively understand the pore connectivity situation. Second, there may be differences between the experimental conditions and the real reservoir environment, so the reliability and applicability of the obtained data may be affected. Summary of the Invention
[0004] In order to overcome the deficiencies that the existing experimental methods for pore structure connectivity cannot intuitively express pore connectivity and the reliability of the experimental data is affected by experimental conditions, the present invention provides a method for quantitatively characterizing the in-situ pore connectivity of rock samples by scanning electron microscope images. This method for quantitatively characterizing the in-situ pore connectivity of rock samples by scanning electron microscope images simulates the fluid migration situation under real formation conditions, realizes the visualization of the pore connectivity of rock samples, and then determines the pore connectivity rate, so as to more accurately evaluate the pore connectivity of rocks under real formation conditions.
[0005] The technical solution of the present invention is: a method for quantitatively characterizing the in-situ pore connectivity of rock samples by scanning electron microscope images, including:
[0006] S1. Prepare a rock sample and perform a drying treatment on the rock sample;
[0007] S2. Place the rock sample and a solid alloy together in a high-temperature and high-pressure container, melt the alloy into a liquid state and let it enter the rock sample to obtain a rock sample with the alloy injected;
[0008] S3. Cut and polish the rock sample injected with the alloy, and observe it through a scanning electron microscope. Take SEM photos of the same position in two modes: backscattered electron and secondary electron respectively.
[0009] S4. Extract the ratio of the alloy to the total area in the backscattered electron SEM photo The ratio of the total pores to the total area in the secondary electron SEM photo The connected porosity of the rock sample
[0010] Furthermore, in the step S3, several backscattered electron and secondary electron SEM photos are continuously taken for different parts of the rock sample. After splicing all the backscattered electron SEM photos, a large-scale backscattered electron SEM photo is formed. After splicing all the secondary electron SEM photos, a large-scale secondary electron SEM photo is formed.
[0011] Furthermore, in the step S4, the connected porosity of the rock sample is the average value of the connected porosities of the rock sample obtained from several photos.
[0012] Furthermore, in the step S1, the preparation and drying method of the rock sample is as follows:
[0013] S11. Weigh the core column and cut a cube with a side length of 0.5 - 2 cm 3 perpendicular to the bedding direction of the core column to form a rock sample;
[0014] S12. Place the rock sample in a vacuum drying oven and dry it at 60 - 100 °C for 24 - 48 h.
[0015] Furthermore, the step S2 includes:
[0016] S21. After putting the rock sample and the alloy into a container, evacuate the container;
[0017] S22. Heat the container to melt the alloy into a liquid alloy;
[0018] S23. Pressurize the container to the target pressure to inject the liquid alloy into the rock sample;
[0019] S23. Cool down until the liquid alloy solidifies, and reduce the air pressure in the container to atmospheric pressure.
[0020] Furthermore, the melting point of the alloy in the step S2 is 40 - 80 °C.
[0021] Furthermore, the alloy is composed of tin, bismuth, and lead.
[0022] Furthermore, the temperature of the container after heating in the step S2 is 0 - 200 °C.
[0023] Furthermore, the target pressure in the step S2 is 0 - 200 MPa.
[0024] Further, in the step S3, the rock sample injected with the alloy is cut along the direction perpendicular to the bedding plane, and the cross-section of the rock sample after injecting the alloy is subjected to argon ion polishing treatment.
[0025] The present invention has the following beneficial effects: By adopting the above solution, an in-situ high-temperature and high-pressure low-melting-point alloy injection system is used to simulate the fluid migration situation under real formation conditions, and the alloy is cooled and solidified to facilitate taking scanning electron microscope (SEM) photos, so as to more intuitively observe and calculate the connectivity of the pore structure. By stitching multiple SEM photos to form a large-scale SEM image, image processing can be carried out on samples with a very large field of view to obtain the overall situation of the samples, avoiding the heterogeneity of the samples. At the same time, the backscattered electron mode of the SEM is mainly used to observe the surface composition of the sample, and the low-melting-point alloy can be clearly distinguished. The secondary electron mode is used to observe the surface morphology of the sample, and the pore cracks of the sample can be clearly distinguished. By combining the SEM images and data extraction, and combining the experimental data with the visualization results, the pore connectivity can be more intuitively expressed, improving the comprehensive understanding and accurate evaluation of the pore connectivity. Description of the Drawings
[0026] Figure 1 is the flow chart of the present invention;
[0027] Figure 2 is a backscattered SEM image and the extracted alloy proportion;
[0028] Figure 3 is Figure 2 the secondary electron SEM image taken at the same position and the extracted pore proportion;
[0029] Figure 4 is Figure 2 the energy spectrum analysis diagram of the corresponding sample at EDS Spot 1 in
[0030] Figure 5 is the image after stitching several SEM photos. Detailed Embodiments
[0031] The present invention will be further described below with reference to the drawings:
[0032] As Figure 1 shown, a method for quantitatively characterizing the in-situ pore connectivity of rock samples by SEM images includes:
[0033] S1. Prepare a rock sample and dry the rock sample. Specifically:
[0034] S11. Weigh a certain mass of core column and cut 0.5 - 2 cm along the direction perpendicular to the bedding of the core column 3A cube is formed into a rock sample;
[0035] S12. Place the rock sample in a vacuum drying oven and dry it at 60 - 100 °C for 24 - 48 h. The drying time of the rock sample can be adjusted according to the drying temperature.
[0036] S2. Place the rock sample and the solid alloy together in a high-temperature and high-pressure container, melt the alloy into a liquid state and let it enter the rock sample to obtain a rock sample injected with the alloy. The alloy is composed of tin, bismuth, and lead, with a melting point of 40 - 80 °C. By adjusting the proportion of tin, bismuth, and lead elements in the solid alloy, the melting point of the alloy can be adjusted so that it is in a solid state at room temperature, which is convenient for cutting and observing the rock sample injected with the alloy at room temperature. In addition, because it is in a solid state at room temperature and is not easy to volatilize, it will not affect the health of the operator. The specific steps are as follows:
[0037] S21. After placing the rock sample and the solid alloy in the container, perform a vacuum treatment on the container so that the vacuum degree in the container is 0.05 - 0.1 Pa;
[0038] S22. Heat the container to melt the alloy into a liquid alloy. The temperature after heating is 0 - 200 °C, which is determined according to the melting point of the alloy;
[0039] S23. Pressurize the container to the target pressure. After maintaining the target pressure for a period of time, let the liquid alloy be injected into the rock sample. The target pressure is 0 - 200 MPa, which can be specifically adjusted according to needs. By setting different target temperature and pressure, the in-situ geological environment at different depths in different regions can be simulated. For example, according to needs, select 10 MPa, 50 MPa, 100 MPa, 150 MPa, 200 MPa, etc. as the target pressure to press the liquid alloy into the pore and fracture structure of the rock. The time for maintaining the target pressure can be adjusted according to the magnitude of the target pressure.
[0040] S23. Cool the container until the liquid alloy solidifies and the air pressure in the container drops to atmospheric pressure to obtain a rock sample injected with the alloy.
[0041] S3. Cut the rock sample injected with the alloy along the direction perpendicular to the bedding plane, and perform argon ion polishing treatment on the cross-section of the rock sample injected with the alloy to obtain a smooth and flat surface of the rock sample; through scanning electron microscopy observation, take electron microscope photos of the same position in two modes: backscattering and secondary electrons respectively.
[0042] To avoid the strong inhomogeneity of the sample due to the too small photo size, several backscattered electron and secondary electron SEM photos were continuously taken from different parts of the rock sample. After splicing all the backscattered electron SEM photos, a large-scale backscattered electron SEM photo was formed. After splicing all the secondary electron SEM photos, a large-scale secondary electron SEM photo was formed. The more the number of photos, the stronger the homogeneity of the obtained results.
[0043] S4. Take photos of the cross-section of the rock sample by scanning electron microscopy, and judge by the features with higher gray values and EDS energy spectrum element analysis in it, then the connected pore fracture structure characteristics of the rock sample can be obtained. Extract the ratio of the alloy to the total area in the backscattered electron SEM photo through ImageJ software The ratio of the total pores to the total area in the secondary electron SEM photo Connected porosity of the rock sample Sum and average the η results of all the scanning electron microscopy photos, then the pore connectivity in the large-scale range can be obtained. When η tends to 1, the pore connectivity is better. When η tends to 0, the pore connectivity is worse.
[0044] Example:
[0045] S1. Weigh a certain mass of rock, and cut a cube with a side length of 1 cm along the vertical bedding direction of the rock core column to obtain a rock sample. Place the rock sample in a vacuum drying oven and dry it at 60 °C for 48 h. 3 of the cube, to obtain a rock sample. Place the rock sample in a vacuum drying oven and dry it at 60 °C for 48 h.
[0046] S2. Place the rock sample and the solid alloy in a container, evacuate the container to make the vacuum degree in the container 0.08 Pa; heat the container to 65 °C to melt the solid alloy into a liquid alloy; pressurize the gas pressure in the container to 200 MPa and maintain it for 1 h to inject the liquid alloy into the rock sample; after cooling until the liquid alloy solidifies, reduce the gas pressure in the pressurized container to the atmospheric pressure to obtain the rock sample injected with the alloy.
[0047] S3. Cut the rock sample injected with the alloy along the direction perpendicular to the bedding plane, and perform argon ion polishing treatment on the cross-section of the rock sample injected with the alloy. Observe through scanning electron microscopy and take SEM photos of two modes of backscattered electrons and secondary electrons at the same position respectively. In this experiment, 64 SEM photos were continuously taken horizontally and vertically for splicing.
[0048] S4. As Figure 2 、 3 shown, use ImageJ software to extract the ratio of the alloy and the ratio of the pores through gray scale Pore ratio Then the connected porosity
[0049] By judging with the features of higher gray values in the photos and EDS energy spectrum element analysis, the connected pore fracture structure features of the rock sample can be obtained. Figure 1 The EDS energy spectrum element analysis results at EDS Spot 1 in Figure 4 are shown as follows.
[0050] The 64 photos are stitched together. As shown in Figure 5 the figure, the calculation results of the pore connectivity index of the 64 photos are shown in Table 1-1 and Table 1-2. The sum of the connected porosity η results of the 64 scanning electron microscope photos is averaged to obtain an average connected porosity of the rock sample of 0.225.
[0051] Table 1-1 Calculation results of large-scale stitched scanning electron microscope connectivity
[0052]
[0053] Table 1-2 (continued) Calculation results of large-scale stitched scanning electron microscope connectivity
[0054]
[0055]
Claims
1. A method for quantitatively characterizing in-situ pore connectivity of rock samples using scanning electron microscope images, characterized in that include: S1. Prepare rock samples and dry the rock samples; S2, placing the rock sample and the solid alloy together in a high temperature and high pressure container, so that the alloy melts into a liquid state and enters into the rock sample, thereby obtaining a rock sample injected with the alloy; S3, cutting and polishing the rock sample after alloy injection, and observing it through a scanning electron microscope, taking electron microscope photos of the same position in two modes: backscattering and secondary electron; S4. Extract the ratio of the total area occupied by alloy in the backscattered electron microscope photograph φ1, the ratio of the total area occupied by total pores in the secondary electron microscope photograph φ2, and the connected porosity of the rock sample η = φ1 / φ2.
2. The method for quantitatively characterizing in-situ pore connectivity of rock samples using scanning electron microscope images according to claim 1, characterized in that: In step S3, a number of backscattered electron microscope photographs and secondary electron microscope photographs are taken continuously for different parts of the rock sample, and all the backscattered electron microscope photographs are spliced together to form a large-scale backscattered electron microscope photograph, and all the secondary electron microscope photographs are spliced together to form a large-scale secondary electron microscope photograph.
3. The method for quantitatively characterizing in-situ pore connectivity of rock samples using scanning electron microscope images according to claim 2, characterized in that: In step S4, the connected porosity of the rock sample is the average value of the connected porosity of the rock sample obtained from a plurality of photographs.
4. The method for quantitatively characterizing in-situ pore connectivity of rock samples using scanning electron microscope images according to claim 1, characterized in that: In step S1, the rock sample is prepared and dried by: S11. Weigh the core column and cut 0.5-2 cm along the core column perpendicular to the bedding direction. 3 cubes, forming rock samples; S12. Place the rock sample in a vacuum drying oven and dry it at 60-100°C for 24-48 hours.
5. The method for quantitatively characterizing in-situ pore connectivity of rock samples using scanning electron microscope images according to claim 1, characterized in that: The step S2 comprises: S21, after placing the rock sample and the alloy into the container, evacuate the container; S22, heating the container to melt the alloy into a liquid alloy; S23, pressurizing the container to a target pressure, so that the liquid alloy is injected into the rock sample; S23. Cool down until the liquid alloy solidifies and reduce the gas pressure in the container to atmospheric pressure.
6. The method for quantitatively characterizing in-situ pore connectivity of rock samples using scanning electron microscope images according to claim 5, characterized in that: The melting point of the alloy in step S2 is 40-80°C.
7. The method for quantitatively characterizing in-situ pore connectivity of rock samples using scanning electron microscope images according to claim 6, characterized in that: The alloy consists of tin, bismuth and lead.
8. The method for quantitatively characterizing in-situ pore connectivity of rock samples using scanning electron microscope images according to claim 5, characterized in that: The temperature of the container after heating in step S2 is 0-200°C.
9. The method for quantitatively characterizing in-situ pore connectivity of rock samples using scanning electron microscope images according to claim 5, characterized in that: The target pressure in step S2 is 0 to 200 MPa.
10. The method for quantitatively characterizing in-situ pore connectivity of rock samples using scanning electron microscope images according to claim 1, characterized in that: In the step S3, the rock sample injected with the alloy is cut along a direction perpendicular to the bedding plane, and the cross-section of the rock sample injected with the alloy is subjected to argon ion polishing.