Analysis of the seepage-diffusion law and transformation mechanism in the CO2 flow adsorption test under various laminae

Physical simulation experiments of CO₂ flow adsorption under various stratigraphies were conducted in the coal seam CO₂ injection project for gas replacement, as CO₂ is in the flow state and the mechanism of CO₂ adsorption in the flow state in the coal seam is still unclear. In the process of CO₂ flow adsorption, the results indicate that seepage in the horizontal stratigraphic direction is predominant, while diffusion in the vertical stratigraphic direction is predominant. The ratio of CO₂ flow adsorption in the horizontal stratigraphic direction is primarily distributed below 50%, and seepage is the dominant process during the CO₂ flow adsorption test. Conversely, the ratio of adsorption in the vertical stratigraphic direction is typically greater than 50%, and diffusion is the dominant process. During the control test, when the outlet was sealed (one-way CO₂ injection without return), the seepage impact diminished while the diffusion effect intensified, resulting in an increase of the saturated CO₂ adsorption quantity to 1.3 to 4.8 times that of the flow adsorption system. In the CO₂ replacement of CH₄ project, when CO₂ penetrates a specific distance, the extraction holes are sealed, thereby prolonging the diffusion period of CO₂ to ensure complete adsorption in competition with CH₄, ultimately enhancing the utilization efficiency of CO₂.