A Numerical Study of Instability Control for the Design of an Optimal Policy of Enhanced Oil Recovery by Tertiary Displacement Processes

Abstract

In this paper, we consider the problem of control of hydrodynamic instability arising in the displacement processes during enhanced oil recovery by SP-flooding (Sur- factant-Polymer). In particular, we consider a flooding process involving displacement of a viscous fluid in porous media by a less viscous fluid containing polymer and surfactant over a finite length which in turn is displaced by a even less viscous fluid such as water. The maximum stabilization capacities of several monotonic and non-monotonic viscous profiles created by non-uniform polymer concentration are studied in the presence of interfacial ten- sions created by surfactants. The study has been carried out numerically to determine and characterize the most optimal viscous profiles of each family. Similarities in optimal mono- tonic viscous profiles of this constant-time injection policy and other injection policies by previousworkersarenoted.Thepresenceofinterfacialinstability(duetoviscosityjump)and layer instability (due to viscosity gradient) in appropriate proportions has been numerically demonstrated to be a necessary condition for monotonic as well as optimal non-monotonic profilesexceptinthelimitingcaseofinfinitetimeinjectioninwhichcasemaximumstabiliza- tion appears to result from pure layer instability. It has also been demonstrated numerically that the optimal non-monotonic viscous profiles can have better stabilization potential than the optimal monotonic profiles. Many other new features of this injection policy which have not been recognized before have been discussed.