Rate forecasting during boundary-dominated multiphase flow: The rescaled exponential model

Well performance forecasting is an important analytical technique used for field development to guide economic decisions during the life of a reservoir. For the case of dry and liquid-rich gas wells, traditional well performance models are developed based on solving the resultant highly nonlinear gas flow equations via pseudo-pressure and pseudo-time linearization. In this study, we provide a straightforward, density-based alternative to traditional models. We show, as done previously for the case of dry gas wells (. Ayala and Zhang, 2013; Zhang and Ayala, 2014a), that a rescaled exponential model is a rigorous decline solution that can be extended to liquid-rich gas wells producing under constant bottomhole-flowing-pressure (BHP) during boundary-dominated flow (BDF) and multiphase conditions. The proposed multiphase rescaled-exponential model is derived analytically from governing multiphase flow equations; comparisons between numerically simulated results and proposed analytical model for a variety of combinations of reservoir and fluid properties demonstrate that the proposed rescaled-exponential model is a valid and reliable forecast model for constant-BHP liquid-rich gas wells under BDF.