Sergo Ordzhonikidze Russian State Geological Prospecting University, Moscow, Russia:

M. M. Cherepanskiy, Head of Chair, Doctor of Geologo-Mineralogical Sciences, vodamch@mail.ru

Moscow Division, Gazprom Project Engineering, Moscow, Russia:
V. V. Shishlyaev, Head of Department

In the recent two decades, the methane-bearing coal mines worldwide increasingly often raise a point on the change in the stress state of coal seams during recovery of formation fluids, as well as on the influence of field-geological factors on productivity of holes drilled in methane-bearing coal. Permeability is one of the most variable characteristics of coal seams. Its variation with area, due to rock pressure, deformation characteristics of coal, metamorphic grade and faulting, is an extremely complex pattern which conditions different behavior of drainage zones around a hole. The variation in permeability of coal seams in the course of drilling and operation of methane drainage holes is one of the scantly understood physical processes and, is, thus, of higher concern. This article describes physical models including phenomena of coal matrix shrinkage as well as influence exerted by change in the effective stress on the process of gas recovery from coal during active methane desorption and flow of the formation fluid. The modeling results show that in geological conditions of the Naryk-Ostashkin methane-bearing coal field, methane diffusion has the highest effect on the coal permeability by increasing it. Implementation of mathematical models of change in coal permeability during active processes of methane desorption and fluid flow requires additional information of physical and mechanical properties of coal seams, which needs undertaking full-waveform wide-band acoustic logging using cross-dipole sources.

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