Screening of Oil Reservoirs for Selecting Candidates of Polymer Injection

Abstract

Polymer flooding has been found to be an excellent method for improving oil recovery from marginal oil reservoirs with intense heterogeneity or high-producing water-oil ratios (WOR). Accurate analysis, however, must be conducted prior to deciding on a polymer flooding operation. Even though the petroleum literature has reported a set of criteria for screening oil reservoirs for polymer flooding and their qualitative analyses, rarely can one find any quantitative analysis outlining the validity of the commonly held views in the petroleum industry. This article presents a quantitative analysis of the performance of an oil reservoir subjected to polymer slug injection. Fluid and rock properties are varied in order to determine the economics of an enhanced oil recovery scheme. The reservoir parameters considered in this analysis are reservoir permeability (230-2300 md), initial water saturation (0.25-0.5), and oil viscosity (25-100 cp). In order to study the role of field operational parameters in determining the success of the polymer slug injection process, polymer viscosity (1.45-9.6 cp), rock adsorption characteristics (10-5 - 10-4 lbm lbm rock), and polymer slug size of a constant concentration (0.1-0.5 PV) are considered. The reservoir performance is represented by the behavior of oil recovery, WOR, and oil production rate. For this study, the detailed reservoir fluid and rock properties were taken from a U.S. prototype (Lower Huntington Beach Garfield zone of California). Detailed analyses indicate that the reservoir permeability is of paramount importance to determining the success of polymer slug injection in an oil reservoir. The analysis of the behavior of sandface pressure for low permeability reservoirs provides interpretation of the plugging effects observed in tight reservoirs. Finally, the numerical model results confirm the widely held view of using 0.70 pore volume injected (that corresponds to a WOR of 15), as a criterion to terminate a polymer slug injection project.