Analysis of Multiphase Reservoir Production From Oil/Water Systems Using Rescaled Exponential Decline Models

In this study, we present an analytical approach based on rescaled exponential models that are able to analyze production data from oil/water systems producing under boundary-dominated flow conditions. The model is derived by coupling two-phase oil/water material balances with multiphase well deliverability equations. Nonlinearities introduced by relative permeability in multiphase oil/water systems are accounted for via depletion-dependent parameters applied to each of the flowing phases. This study shows that S_o–S_w–p relationships based on Muskat's standard assumptions can be successfully deployed to correlate saturation and pressure changes in these two-phase systems without the need for user-provided surface production ratios or well-stream composition information. The validity of the proposed model is verified by closely matching predictions against finely gridded numerical models for cases constrained by both constant and variable bottomhole pressure production. In addition, a straight-line analysis protocol is structured to estimate the original oil and water in place on the basis of available production data using rescaled exponential models. Finally, we explore conditions for validity of the assumptions used in the proposed model, including the S_o–S_w–p formulation, by conducting extensive sensitivity analysis on input parameters.