Rheology of Mobility-Control Foams

Abstract

Enhanced oil recovery (EOR) studies have consistently demonstrated the need to mitigate gas channeling in processes involving use of gas to displace crude oil. The use of foam for gas mobility control was first investigated in 1955, and an early field test by Union Oil Co. of California indicated significant merit in the concept. Work was undertaken at New Mexico State U. to provide rheological data of in-situ-generated foam in an attempt to define the mobility-lowering mechanism. A capillary viscometer was constructed to measure the rheological properties of the most promising foams made with commercially available additives. Data collected at different shear rates show that foams are pseudoplastic in nature and several orders of magnitude more viscous, 10 to 100 cp (0.01 to 0.1 Pa·s) than their gas or liquid fractions. Significantly, foam viscosities are generally an inverse function of foam density, which is very advantageous in oil-displacement processes. In areas where gas fingering is pronounced, foam viscosity would be expected to increase with gas saturation and, thereby, would tend to mitigate further gas channeling. The spontaneous generation of a viscous foam phase may also serve to reduce the flowing gas saturation and, thus, lower gas mobility because of the relative permeability effect. This technology is easily adapted to the water-alternating-gas (WAG) process involving CO2 or rich-gas displacement of oil.