A Uniaxial Compression Experiment with CO2-Bearing Coal Using a Visualized and Constant-Volume Gas-Solid Coupling Test System
June 12th, 2019
This protocol demonstrates how to prepare a briquette sample and conduct a uniaxial compression experiment with a briquette in different CO2 pressures using a visualized and constant-volume gas-solid coupling test system. It also aims to investigate changes in terms of coal’s physical and mechanical properties induced by CO2 adsorption.
This method can help answer key questions in field of carbon dioxide geological sequestration and coalbed methane recovery about the relationship between coal's properties and gas adsorption. The main advantage of this technique is that static and dynamic load can apply on briquette in constant volume state and whole experiment process is visualized by photographic monitoring. There is no particular requirement for the species of the sample, therefore this method can apply to mechanical tests of any porous rock.
To begin, weigh 1000 grams and 300 grams of pulverized coal with a particle size distribution of zero to one millimeter and one to three millimeters respectively. Put them together in a beaker in a mass proportion of 0.76 to 0.24 and use a six millimeter diameter glass rod to mix them well. To prepare the cement, put four grams of sodium humate powder into a beaker and add approximately 96 millimeters of distilled water.
Use a glass rod to stir them and make sure that all sodium humate is well dissolved. Then mix 230 grams of mixed coal powder and 20 grams of sodium humate solution in a beaker. To produce a standard sized briquette coat the inner surface of the shaping tools with lubricating oil.
Assemble tool components Bottom plate, main body and ring and fill the hole with 250 grams of mixed material. Put Press piston on top of the mixed material and place all parts under the Piston of an electrohydraulic servo universal testing machine. Launch the software WinWdw to control the electrohydraulic servo universal testing machine.
In the software, click on force range to set the maximum force to 50 kilonewtons and click on reset to clear the displacement value. Left-click on the option force loading control. Set the moving ratio to 0.1 kilonewtons per second.
Set the target force value at 29.4 kilonewtons and holding time at 900 seconds. Then click on start. After that take out the shaping tools and invert them onto a rubber plate.
Use a rubber hammer to disassemble tool components in the order from the bottom to the top. Put the briquette in a 40 degree Celsius incubator for 48 hours. First, fix the back door of the visualized vessel with high strength bolts.
Connect the computer, data acquisition box and the embedded gas pressure sensor to the back door. To acquire the gas pressure data in the visualized vessel, launch the software Data Acquisition Sensor. On the software, click on start.
Open the valve V1 and close V2, V3 and V4 to vacuum the visualized vessel chamber. After 30 minutes turn off V1 and vacuum pump. Open V2 and the gas tank with helium.
Use the manual pressure reducing valve to adjust the outlet pressure of the gas tank. Carefully observe the gas pressure curve displayed on data acquisition sensor 16. When it reaches about two megapascals turn off V2 and the gas tank.
Then on the computer, launch the software WinWdw to measure the friction force of the loading piston moving downward in the testing machine. In the software, click on force range to set the maximum force to five kilonewtons and click on reset to clear the displacement value. Left-click on the option displacement loading rate and set the moving ratio to one millimeter per minute.
The click on start. Open V4 and discharge helium into the air. Disassemble the back door of the visualized vessel and close V4.Measure the height and diameter of the briquette using a vernier caliper with a precision of 0.02 millimeters.
Weigh the mass of the briquette using an electronic scale with a precision of 0.01 grams. Install the chain roller of the circumferential deformation test apparatus around the middle position of the briquette and fix the clamp holder. Connect the sensor with the data acquisition box through the aviation connector in the visualized vessel and place them under the loading piston.
To ensure the accuracy of the data acquisition, adjust the chain roller and the top surface of the briquette so that they are parallel to the loading piston. Then launch WinWdw to control the universal testing machine. In the software, left-click on the option displacement loading rate.
Set the moving ratio at 10 millimeters per minute. On the remote controller, press the down button for the universal testing machine until the distance left between the piston and the briquette is around one to two millimeters. Then assemble the back door of the visualized vessel.
Vacuum the visualized vessel chamber as previously. Next open V3 and the gas tank of carbon dioxide at purity 99.99%Use the manual pressure reducing value to adjust the outlet pressure of the gas tank. Carefully observe the gas pressure curve displayed in data acquisition sensor 16.
When it gets close enough to the target value, close V3 and the gas tank. After 24 hours of adsorption time the gas pressure curve remains stable and the briquette has reached its adsorption and desorption dynamic equilibrium state. Place a camera with a tripod beside the window of the visualized vessel and adjust the height and angle to ensure that image of the sample is shown in the center of the camera screen.
Start the software SDU Deformation Acquisition v2.0 to monitor the circumferential deformation of the briquette. Click on start. On WinWdw click on new sample and type in the height and diameter of the briquette.
Click on sectional area and then click on confirm. Click on force range to set the maximum force to five kilonewtons and click on reset to clear the displacement value. Left-click on the option displacement loading rate and set the moving ratio at one millimeter per minute.
Click on start to compress the sample. At the same time press the start button on the camera to begin video recording. When the sample totally fails, click on stop and data save in both WinWdw and SDU Deformation Acquisition v2.0.
Then press the start button again on the camera to stop video recording. Open V4 to release carbon dioxide in the vessel chamber and disassemble the back door of the vessel. Disconnect the aviation connectors for the gas pressure sensor and circumferential deformation test apparatus.
Left-click on the option displacement loading rate on WinWdw, set the moving ratio at 10 millimeters per minute. Press the up button on the remote controller of the universal testing machine. When the loading piston of the vessel is around two to three millimeters above the briquette take the briquette out and remove it from the chain roller.
Dismantle the connection tool between the pistons and use a vacuum cleaner to clean the visualized vessel. In this experiment, the isothermal adsorption test proved similar capacity for methane gas adsorption between raw coal and briquette. The strength of the briquette samples used in the test had some fluctuation, but it was rather slight and had little influence on the analysis of the experimental results.
When under different carbon dioxide pressures, ranging from zero to two megapascals, the stress axial strain curves showed obvious compaction, elastic and plastic deformation phases. As the carbon dioxide pressure increased the peak strength of the coal sample decreased, where it showed a nonlinear relationship. The elastic modulus decreased under the carbon dioxide saturated condition and that the relationship between the elastic modulus decreased and the gas pressure was nonlinear as well.
The images obtained through the camera events the fracture's evolution on the sample's surface, under different carbon dioxide pressures. The box counting dimension method was adopted to describe the feature of fractures in failure state under different carbon dioxide pressures. The correlation coefficients between the box number and the side length were all more than 0.95.
The values of the fractal dimension were proportional to those of carbon dioxide pressure and their trend indicated similarity to that of the degree of damage to the coal body. The most important thing is to have a good understanding of test procedure and some experience in experiments of rock mechanics and operation of high-pressure gas. After its improvement, this technique can provide a way for the study of porous media and gas coupling effect under uniaxial or triaxial loading state.
Because high pressure gas tanks are used in this technique, people need to operate carefully during gas filling and releasing.
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Overview
This protocol demonstrates the preparation of a briquette sample and the execution of a uniaxial compression experiment under varying CO2 pressures. It aims to explore the physical and mechanical property changes in coal due to CO2 adsorption.
Key Study Components
Area of Science
- Geological sequestration
- Coalbed methane recovery
- Gas-solid interactions
Background
- This method addresses the relationship between coal properties and gas adsorption.
- Static and dynamic loads can be applied to briquettes in a constant volume state.
- The entire experimental process is visualized through photographic monitoring.
- The method is applicable to any porous rock species.
Purpose of Study
- To investigate the effects of CO2 on coal's physical and mechanical properties.
- To provide insights into carbon dioxide geological sequestration.
- To enhance understanding of coalbed methane recovery processes.
Methods Used
- Weigh 1000 grams of pulverized coal with a particle size of 0-1 mm and 300 grams with a size of 1-3 mm.
- Mix the coal in a beaker in a mass proportion of 0.76 to 0.24.
- Prepare cement by mixing sodium humate powder with distilled water.
- Conduct uniaxial compression experiments under controlled CO2 pressures.
Main Results
- The method allows for the visualization of the experimental process.
- Static and dynamic loads can be effectively applied to the briquette samples.
- Changes in coal properties due to CO2 adsorption were observed.
- The technique is versatile for testing various porous rocks.
Conclusions
- This protocol provides a reliable method for studying coal properties under CO2 conditions.
- It contributes valuable data for carbon sequestration and methane recovery research.
- The experimental setup can be adapted for different sample types.
Frequently Asked Questions
Executive Industry Relevance
This method enables visualization of gas-solid interactions under controlled pressure, supporting mechanistic de-risking in energy-related material science. By quantifying how CO2 adsorption alters mechanical properties such as strength and elastic modulus, it provides predictive confidence for subsurface behavior modeling. The approach aids in evaluating material integrity under multifield coupling conditions relevant to geological storage and resource recovery applications.
Strategic Applications in Biopharma R&D
Early Discovery & Target Validation
- Scientific Value: Enables interrogation of material response to gas adsorption, supporting hypothesis testing on property-gas relationships.
- Operational Value: Provides a reproducible platform for assessing mechanical changes under controlled gas exposure.
Screening & Assay Development
- Scientific Value: Generates quantitative outputs including peak strength, elastic modulus, and fractal dimension for comparative analysis.
- Operational Value: Supports standardization through constant-volume conditions and real-time visualization.
Translational & Preclinical Research
- Scientific Value: Correlates gas pressure with mechanical degradation and fracture evolution, enabling risk-informed extrapolation.
- Operational Value: Facilitates continuity from discovery-scale testing to predictive modeling of subsurface behavior.
Pipeline & Workflow Integration
The method fits within early discovery workflows where material stability under environmental stressors is evaluated prior to downstream application.
- Discovery Biology: Supports hypothesis testing on how gas adsorption influences mechanical integrity of porous matrices.
- Screening: Delivers reproducible, quantitative mechanical readouts under variable gas pressures for comparative screening.
- Analytics: Provides fractal dimension analysis of failure patterns, enabling quantitative characterization of damage evolution.
- Translational Research: Connects lab-scale mechanical response to predictive models of in situ behavior under gas exposure.
- Enterprise Reuse: Offers a reusable platform for studying gas-solid coupling across different porous materials and pressures.
Operational & Enterprise Impact
- Scientific Value: Reduces mechanistic ambiguity by linking gas adsorption to measurable mechanical and structural changes.
- Operational Value: Ensures reproducibility through constant-volume control and real-time monitoring.
- Strategic Value: Improves go/no-go decisions in material selection by predicting behavior under gas-rich conditions.
- Portfolio Impact: Enables risk-adjusted prioritization of materials based on quantified gas-induced degradation.
Implementation Considerations
- Requires expertise in rock mechanics and high-pressure gas handling.
- Needs instrumentation capable of constant-volume control, load application, and real-time imaging.
- Demands standardization of sample preparation to ensure briquette representativeness.
- Involves safety protocols for handling high-pressure CO2 and potential flammable gases.
- Limited by current inability to test with methane due to flammability constraints.
