Nanoparticle-enhanced Recovery of Organic Fluids from Porous Rocks

The present work investigates multi-phase fluid transport in porous media at pore-scale. Specifically, we investigate the effect of nano-particles (NPs) aqueous suspensions in remobilisation and recovery of trapped organic fluids from a carbonate rock with a multi-scale pore structure. Our findings have implications for a wide range of applications including: (i) remediation of aquifers contaminated by non-aqueous phase liquids (NAPL) leakage, (ii) oil recovery from hydrocarbon reservoirs, and (iii) storing CO2 in the geological formations. Use of NPs in groundwater remediation has been extensively researched. It has been shown that immiscible displacement of organic fluids from porous media can be enhanced in presence of NPs. The main mechanisms identified are (i) reduction of fluid-fluid interfacial tension (IFT), and (ii) wettability alteration from oil-wet to water-wet or mixed-wet systems. Designing a successful NPs-based organic phase recovery involves deciding on the NPs type, size, concentration, surface and bulk properties, and salinity of the carrier aqueous solution. Using X-ray computed micro-tomography monitored core-flooding experiments, we examined the effect of hydrophilic SiO2 NPs concentration on recovery of a mineral oil from a water-wet dolomite. For details of experimental set-up see Pak et al., (2013). The investigated concentrations were 0.05 and 0.1 wt% and the fluid displacements were performed under capillary dominated flow regime to mimic the flow dynamics of oil reservoirs. The core was initially saturated by water, followed by oil injection and NPs suspension injections. A 3D image was collected after each injection step. Our experiments show oil remobilisation occurs only at the higher NPs concentrations. The pore-scale distribution of the organic and aqueous fluid phases indicate the rock wettability has remained unchanged, i.e. water wet. Instead, we, for the first time, observed an in-situ formation of an oil-in-water emulsion, stabilised by the NPs, consistent with Pickering type emulsions. A reduced IFT, induced by NPs, assisted formation of emulsions through roof-type snap of events. The emulsion is only observed to have formed within the pores with high aspect ratios, i.e. the vugs. Our future experiments will investigate the effect of NPs sizes and surface characteristics on formation of oil/water emulsions and enhancement in organic phase recovery.