Study on the "Bottle-Neck" Problem of Coalbed Methane Productivity ofHigh-rank Coal Reservoirs

Based on continuous observations of the macrofractures and microfractures and systemic measurements of pores in coal reservoirs, combined with experimental results of stress permeability, methane - water relativepermeability and adsorption-swelling on high-rank coal reservoirs, this paper has analyzed the tertiary seepage characteristics of high-rank coal reservoirs, discussed the coupling effect of effective stress and coal matrix shrinkage on permeability of high-rank coal reservoirs, revealed the bottle-neck phenomenon that the productivity of coalbed methane (CBM)is high in the initial stages and attenuates rapidly after a few months in the course of development using the water drainage and pressure reduction methods, and found out the radical reason that leads to the reduction of methane recovery in high -rank coal reservoirs. Techniques and measures are suggested for developing CBM in high-rank coal reservoirs aiming at the particularity of physical properties of high-rank coal reservoirs.