Material-Balance Techniques for Coal-Seam and Devonian Shale Gas Reservoirs With Limited Water Influx

Summary This paper presents the development of two material-balance methods for unconventional gas reservoirs. One method is appropriate for estimating original gas in place; the second is appropriate for making reservoir predictions. These techniques differ from the material-balance methods for conventional gas reservoirs in that the effects of adsorbed gas are included. For estimating original gas in place, the assumption of equilibrium between the free- and adsorbed-gas phases is required. No additional assumptions are required for reservoir predictions.