Optimal rate control under geologic uncertainty: water flood and EOR processes

Abstract

Much of the current world oil production comes from mature and partially depleted fields. Increasing the ultimate oil recovery from these fields is critical for meeting growing energy demands in the coming years. Many secondary oil recovery methods have been developed to improve oil recovery after primary depletion. The most widely used is water flooding because it is effective and relatively inexpensive to implement. However, the presence of reservoir heterogeneities, for example high permeability channels, can lead to premature breakthrough and poor sweep efficiency, resulting in reduced oil recovery. One way to improve the sweep efficiency is flood front management via the optimal allocation of production and injection rates. In this paper, we propose an optimal rate control strategy to maximize sweep efficiency and accelerate production during water flooding and EOR processes, in particular, polymer flooding and CO2 injection. We describe our approach and the underlying mathematical formulation, and then we illustrate its power using field-scale examples. We demonstrate the practical feasibility of our method in realistic production scenarios using a 3D synthetic benchmark field example, the Brugge field. We also use stochastic optimization to take geological uncertainty into consideration. The value of using multiple realizations in improving the robustness of the optimization in terms of oil recovery and enhancing NPV is clearly illustrated by the 3D example.