Simplified Power-Law Model for the Material Balance of Gas Reservoirs Experiencing Water Influx

A simple power-law model is presented for performance of gas reservoirs experiencing water influx using only cumulative production, reservoir pressure, and the gas deviation factor (i.e., the z-factor). The application of the model provides estimation of gas-in-place. The gas material balance relation including ONLY water influx is given in dimensionless form as: pzD=(1−GpD)(1−WeD)  where: pzD=p/zpi/zi WeD=weBWGBgi GpD=GpG The following empirical model is proposed for dimensionless water influx function (WeD): WeD=aGpb+1 Substituting this model into the gas material balance yields: pzD=(1−GpD)(1−aGpb+1) The proposed power-law water influx model was exhaustively validated using the Carter-Tracy and Van Everdingen-Hurst methods to simulate water influx and pressure-cumulative gas production behavior for an unsteady-state water-influx system. The results of these simulation cases were fitted using the proposed (empirical) power-law water influx model and for every case that was tested, the proposed model gave an essentially perfect correlation of the simulated reservoir performance behavior.