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Abstract

Field-scale applications of chemical flooding become more attractive with higher oil prices. Several pilot and commercial scale chemical floods are currently in operation or design. Economic feasibility of such projects relies on how cost-effectively the remaining oil volume is recovered. Robust design and optimization are essential for technical success and profitability. The main objective in chemical flooding design is to keep the surfactant in Type III near the optimum salinity. Salinity gradient design is a robust design since it can compensate for heterogeneity and reservoir uncertainties and guarantees the surfactant in Type III for a longer time compared to other designs. A comprehensive surfactant phase behavior model is required to take into account the salinity gradient design with all possible phase transitions.

The development discussed in this paper enables accurate modeling and optimization of chemical flooding designs for realistic field-scale projects where a salinity gradient exists naturally or is imposed by design. The parallel processing capability combined with the fully implicit scheme allows high-resolution full field scale chemical flooding simulations. Comprehensive surfactant phase behavior as a function of water salinity has been implemented into a fully implicit and parallel equation of state (EOS) compositional simulator, GPAS. The fully implicit simulation results are validated against an IMPES chemical flooding simulator.

Accurate simulation of chemical processes requires fine grid resolution which adds a large computational overhead for modeling field-scale projects. Our enhanced simulator will allow for high resolution, field-scale design and optimization of chemical flooding projects. This is the first fully implicit, chemical-EOS compositional simulator with a comprehensive surfactant phase behavior that can take into account the effect of salinity and the resulting two or three phase flow with efficient parallel scalability.

Introduction

Chemical flooding is an enhanced oil recovery (EOR) method that can efficiently recover the residual oil saturation by significant reduction of interfacial tension (IFT) between the aqueous and oleic phases. This IFT reduction causes the residual and trapped oil to be mobilized and produced at the production wells. Surfactants also increase oil recovery by solubilization of the oil in the aqueous phase. Normally, a chemical flood consists of few slugs. The first slug contains the aqueous surfactant solution at a desired salinity and polymer for mobility control. The surfactant slug is chased with a polymer drive to maintain the mobility control.