Conformance Improvement in Oil Reservoirs by Use of Microemulsions

Abstract

Summary The performance of many improved and enhanced-oil-recovery (EOR) techniques in conventional reservoirs is frequently degraded by conformance problems. The presence of high-permeability streaks or thief layers between injection and production wells typically results in premature water breakthrough, high water cut, and deficient volumetric sweep. As a result, significant oil volumes in the reservoir might not be contacted by the injection fluid. Several conformance-improvement techniques (e.g., foams, gels, resins) have been developed and practiced in improved-oil-recovery operations. Each technique has its own advantages and limitations related to deployment practicality, effectiveness, and durability. In this paper, we introduce a novel conformance-improvement method (CIM) that we consider practical, effective, and durable. The CIM process consists of cyclical injections of pulse slugs of surfactant alternating with brine. The slug compositions are selected on the basis of the rheological behavior of the microemulsion phase. The chemical slugs are configured such that the viscosity of the injected fluids is kept low to preserve injectivity and to ensure the invasion of the conformance agent toward the thief zones. The trailing brine slugs are designed to produce a high-viscosity microemulsion as they mix with the leading surfactant slugs in the reservoir. The proposed process leads to a reduction in the effective mobility of the fluids in the thief layers. As a result, the chase waterflood (WF) would divert into previously uncontacted layers to improve the sweep efficiency. The potential of the proposed CIM in improving oil recovery is demonstrated by various simulations of reservoir cases under waterflooding. We performed various sensitivities to investigate the effectiveness of the proposed process that include well spacing, permeability contrast, size of the thief layers, heterogeneity, and the size of the chemical pulse slugs. Simulations showed that this process is effective in addressing reservoir-conformance issues, and therefore it has the potential to improve the sweep efficiency and the recovery factor (RF) in reservoirs with distinct thief layers. The treatment surfactant volumes are relatively small, which enables this process to be cost-effective.