Mathematical Model for Low-Velocity Flow of Coal Bed Methane in Low-Permeability Reservoirs

A mathematical model for transport of coal bed methane(CBM) was presented, taking into account low-velocity non-Darcy flow behavior and coupling of methane desorption from coal matrix and diffusion from matrix into cleats. Under several simplifying assumptions, a simple calculation method for control area of single wells was proposed. Low-velocity non-Darcy flow behavior was characterized by pseudo threshold pressure gradient (PTPG). Numerical results show that both PTPG and desorption rate have a significant impact on determination of control radius. PTPG has a negative effect on the deployment of the peripheral reserves. Increasing PTPG would result in fewer control area. In the contrast, increasing desorption rate would lead to larger control area. The calculation method would provide engineers a better understanding of development of CBM.