Enhanced Oil Recovery by Surfactant-Enhanced Volumetric Sweep Efficiency

Abstract

ABSTRACT A new enhanced oil recovery process is proposed for improving volumetric sweep efficiencies in reservoirs. The new process makes use of the chromatographic and phase separation behavior of surfactants to seal off high permeability, low residual oil saturation regions of reservoirs. Though making use of surfactants, the new process is not to be confused with classical (low tension) surfactant flooding, which is designed to enhance oil recovery by reducing oil/water interfacial tensions. In the new process, a sequence of surfactant species is injected into the reservoir. Those injected last are chosen to have higher chromatographic velocities than the former. The species are also chosen so that when they mix in situ, a phase separation occurs, resulting in formation of a pore blocking precipitate or of a high viscosity gel-like coacervate phase. Because the oil recovery mechanism is completely different from that in low tension surfactant flooding, the new process can operate at much lower surfactant concentrations and higher injectivities, greatly reducing the upfront costs of the new process, improving its economic feasibility. Sandpack studies are presented to demonstrate: 1. The process mechanism, 2. The ability of ppm concentrations of surfactant to plug porous media on in situ mixing, 3. The ability of the process to selectively plug high permeability regions, 4. The ability of the process to produce a tertiary oil recovery from a sandpack. Various potential advantages of the new process over other currently developing sweep efficiency enhancement processes are also briefly discussed.