Production decline curves for low-pressure gas reservoirs undergoing simultaneous water production

A family of production decline curves are presented for radial flow geometry with closed outer boundary and with a centrally located well. The formation is fully penetrated by the well and is open to flow in its entirety. The proposed production decline curves are applicable to conventional gas reservoirs which are producing gas and water simultaneously. It is shown that the proposed decline curves exhibit unique characteristics for a variety of reservoir and fluid properties and pressure specifications at the well. The performance of the proposed decline curves were investigated against two different numerical simulators and they were found to be capable of predicting the production of conventional gas reservoirs under two-phase flow conditions with good accuracy. The production decline curves presented in this paper are generated for different ratios of sandface pressure and initial formation pressure and for different reservoir extents. The uniqueness and independency of these curves to PVT data are compromised, as the initial pressure of the reservoir exceeds 2000 psi. The proposed decline curves have the potential of providing a practical tool by which production performance of gas reservoirs under two-phase flow conditions can be predicted for pragmatic purposes without using sophisticated numerical models.