Formation damage during oil displacement by aqueous SiO2 nanofluids in water-wet/oil-wet glass micromodel porous media

摘要

Formation damage during displacement of dead oil by aqueous silica nanofluids was studied in two identical glass micromodels with water-wet and oil-wet surfaces in the presence and absence of connate water saturation. Nanofluids with different contents of the SiO2 nanoparticles were prepared and their particle size distribution was characterized by dynamic light scattering. The effects of the nanoparticles on the dynamic interfacial tension of the nanofluids-dead oil as well as their effects on the dynamic wettability alteration of glass surfaces were studied. The oil recovery factor increases by the concentration of the nanoparticles up to 0.05 wt% and then decreases due to the aggregation of the nanoparticles. When the surface forces are significantly dominant, the oil recovery factor from the water-wet micromodel is 62 and 42% in the absence and presence of the connate water saturation, respectively. This may be attributed to the destabilization of the nanoparticles by the exposure to the connate water, inferred from the narrow capillary fingers in the displacement patterns. The impact of the connate water saturation on the oil recovery from the oil-wet micromodel is negligible. In addition, when either the nanoparticles become destabilized during the displacement or unstable nanofluids are injected, formation damage occurs in the porous media leading to a significant drop in the sweep efficiency. Results indicate that the ultimate recovery factor decreases significantly after the damage taken place. The damage arises from the adsorption of the asphaltenes onto the nanoparticle-aggregates and deposition over the pores and throats, resulting in an increase in residual oil saturation. Field-emission scanning electron microscopy images illustrate that severe irreversible damage is formed over the water-wet surfaces. However, over the oil-wet surfaces, the damage is found almost reversible. Two schematic representations are proposed for the damage as the interconnected interwoven nanoparticles-asphaltenes aggregates deposited over the surface.