Mechanisms of Percolation of Emulsion in Porous Medium and the Application in Tertiary Recovery in Low-Permeability Reservoirs, Ordos Basin, North China

Fengqin Wang¹ and Zhihao Qu^2
1Department of Petroleum Geology, Xi'an Petroleum University, Xi'an, China
²Department of Geology, Northwest University, Xi'an, China

Emulsion is effective in tertiary recovery in low-permeability heterogeneous reservoirs because it can block pore throat to increase sweeping volume and improve water injection effect, and can expel residual oil. This study focuses on microscopic mechanisms of emulsion percolation. In our experiments, the oil-in-water emulsion was a 1:4 mixture of rock wax and water with 2% surfactant, as a shear-thinning liquid containing dispersed oil droplets 9.69 μm in diameter. Cubes (2.5x2.5x0.03 cubic cm) of sandstone cores capable of sustaining 0.2-0.3-MPa pressure and glasses optically-etched 3-40 μm deep to resemble sandstone pore structures with pore throats 6-80 μm wide were experimented.

Heterogeneity of emulsion percolation was caused by pore-throat blocking, pathway changes and unstable flow network. Under great pressure, emulsion flow still behaved non-Newtonian shear-thinning, and was affected by pore structures. Pore throats were blocked by single droplets, random aggregation of multiple droplets, and small dropltets attached to throat walls, which were deformed and flowed through under increased explusion pressure and flow velocity. Residual oil left after water injection was reduced by emulsion throat-blocking and resultant pathway changes. Lateral push and shearing by emulstion also caused residual oil at walls and corners to be torn into small droplets and carried away.

Jurassic medium-to-fine feldspathic quartz sandstone in Ordos Basin is highly heterogeneous with a 0.152-0.0008-md permeabilty, 0.91-3.98 permeability variation coefficient, and 4.85-24.8 permeability maximum-mean ratio. Microscopic experiments showed 6% of residual oil after water injection was recovered by emulsion expulsion, indicating the great potential of this technique in oil recovery in extremely low-permeability reservoirs.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas