Study of Key Factors for Efficient Coalbed Methane Extraction: Pore Structure, Desorption Rate and Seepage Characteristics

Effective coalbed methane extraction is a key strategy for boosting natural gas production and storage in addition to raising the safety of the production standard of coal mines. In order to examine the effects of important variables such as pore parameters, desorption rate under temperature and pressure conditions, and seepage capacity on coalbed methane production during the coalbed methane extraction process. The low-temperature nitrogen adsorption tests (LTN₂A), methane adsorption/desorption experiments at various temperatures, and the changes in the desorption rate constants, the initial desorption rate, and the desorption rate decay index with temperature and pressure were quantitatively analyzed. And COMSOL software was used to simulate the seepage characteristics of coalbed methane under various reservoir pressures. The results demonstrated that the large interior pore volumes of the samples are beneficial for gas adsorption. Because of its better pore connectivity, the QL sample had a desorption amount that was 55.65% and 48.01% higher at 313.15 and 333.15 K than the WJB sample. The three parameters of <i>k</i>, <i>V</i>₁ and <i>k</i>_<i>t</i> are at a high level with increasing temperature; hence, the desorption rate peaks at 333.15 K and pressures between 1 and 4 MPa. Furthermore, the WJB sample is more sensitive to the temperature than the QL sample. The COMSOL simulation shows that the methane pressure inside the reservoir can be released better when the reservoir pressure is below 10 MPa. The Darcy seepage rate is fast and stable, which is favorable for the seepage of coalbed methane. The findings show a relationship between the desorption and seepage properties of CBM and its pore structure, which may offer empirical and theoretical support for the successful development of the CBM.