Experimental and field verification research on the influence of flow velocity and stress on coalbed methane production

The efficacy of coalbed methane extraction significantly impacts coal mine operations and profitability. To investigate the determinants of this extraction efficacy, we utilized standard core flow velocity stress sensitivity apparatus alongside low-field nuclear magnetic resonance technology. We conducted tests on coal specimens of varying thicknesses to assess quantitatively the extent of damage to the samples, the patterns of permeability and porosity changes, and the effects of stress alterations on permeability. Our findings indicate a direct relationship between the permeability of coal specimens and their thickness. At equivalent flow rates, the velocity sensitivity of thicker coal specimens is notably reduced—by 30.49%—compared to thinner ones. Flow velocity exerts a dual impact on porosity, exhibiting a complex, nonlinear correlation. Net stress demonstrates a heightened sensitivity to the permeability of coal seams, with the stress loading and unloading curves failing to align perfectly. Stress-induced adsorption-desorption processes reveal a pronounced lag effect. Furthermore, dynamic surveillance of bottom hole pressure, water output, and daily gas production from coalbed methane at Wenjiaba Coal Mine revealed that daily gas production initially rises with flow velocity but subsequently declines. It also decreases as bottom hole pressure increases. The observed outcomes closely align with our experimental findings, thereby confirming the validity of our tests. This alignment elucidates the regulatory effects of stress and flow velocity on coalbed methane extraction, offering a theoretical basis for enhancing coalbed methane drainage strategies.