Determination and application of a reasonable drainage rate of coalbed methane in vertical wells in the single-phase flow stage

The determination of a reasonable drainage rate coalbed methane (CBM) in vertical wells the single-phase flow stage can provide maximise transmission water pressure over distance. Based on principle effective stress and Darcy’s law, mathematical model for dynamic changes permeability was established; this basis, relationship between threshold gradient experimentally attained; according to linkage distance pressure, permeability, drop wellbore process, reduction working fluid level taking change into account established. accuracy verified practical data from CBM Daning Block Qinshui Basin, Shanxi Province, China. results show that decreases negative exponential manner with increase time. Different rates were required coal reservoirs different permeabilities; when keeping other conditions constant, larger reservoirs, lower daily drop. research theoretical basis reference system stage.