This paper presents a new method of estimating drainage area size and shape from production data (bottomhole pressures and flowrates) for gas wells. This method is rigorously based on theory presented earlier for the slightly compressible liquid case and requires a computer program to iterate on gas-in-place until the gas flow and material balance equations are satisfied.
The component equations and analysis technique are strictly applicable only after the initial pressure transient has reached the outer boundary. The gas flow equation that we present is an approximation for variable-rate, post-transient flow, but it has provided excellent results for all of the cases investigated. These results imply, as was also noted for the liquid case, that as long as the changes in flowrate do not dominate the influence of the outer boundary, this method should give acceptable results. Currently, this method is only derived for single-phase gas flow and does not consider the effects of geopressured gas reservoirs or non-darcy flow.