Experimental study of the mechanism of nanofluid in enhancing the oil recovery in low permeability reservoirs using microfluidics

Abstract

Due to the low porosity and low permeability in unconventional reservoirs, a large amount of crude oil is trapped in micro-to nano-sized pores and throats, which leads to low oil recovery. Nanofluids have great potential to enhance oil recovery (EOR) in low permeability reservoirs. In this work, the regulating ability of a nanofluid at the oil/water/solid three-phase interface was explored. The results indicated that the nanofluid reduced the oil/water interfacial tension by two orders of magnitude, and the expansion modulus of oil/water interface was increased by 77% at equilibrium. In addition, the solid surface roughness was reduced by 50%, and the three-phase contact angle dropped from 135° (oil-wet) to 48° (water-wet). Combining the displacement experiments using a 2.5D reservoir micromodel and a micro-channel model, the remaining oil mobilization and migration processes in micro-to nano-scale pores and throats were visualized. It was found that the nanofluid dispersed the remaining oil into small oil droplets and displaced them via multiple mechanisms in porous media. Moreover, the high strength interface film formed by the nanofluid inhibited the coalescence of oil droplets and improved the flowing ability. These results help to understand the EOR mechanisms of nanofluids in low permeability reservoirs from a visual perspective.