Enhancement of capillary imbibition by Gamma-Alumina nanoparticles in carbonate rocks: Underlying mechanisms and scaling analysis

Abstract

Due to the oil-wet nature of carbonate reservoirs, performance of capillary imbibition is relatively weak in these reservoirs. One of the possible solutions to promote capillary imbibition is using nanoparticles (NPs) for wettability alteration purposes. In this study, imbibition efficiency of Gamma-Alumina (Ɣ-Al) NPs with different concentrations was investigated in low permeable, oil-wet carbonate rocks at 80 °C. The underlying mechanisms of Ɣ-Al NPs to enhance imbibition oil recovery were explored by analyzing dynamic contact angle profile, interfacial tension (IFT) of crude oil/Ɣ-Al nanofluid, size distribution of Ɣ-Al NPs and the inverse bond number. Results showed that Ɣ-Al NPs increased oil recovery to as much as 11.5% of the original oil in place (OOIP), while no oil was obtained by water imbibition in the native rock. The increase of Ɣ-Al concentration from 0.01 to 0.3 wt% showed a positive impact on the oil recovery, while further increase to 0.5 wt% provided lower incremental oil. The oil recovery results were consistent with dynamic contact angle profiles in which Ɣ-Al NPs successfully altered rock wettability from oil-wet to more water-wet conditions, but a less water-wetness was obtained for 0.5 wt% Ɣ-Al nanofluid. Also, scanning electron microscopy and energy dispersive X-ray analyses verified that the rock wettability alteration occurs mainly due to the adsorption of Ɣ-Al NPs on the carbonate surface. It was found that Ɣ-Al NPs exhibited a slight reduction in IFT from 15 to 11 mN/m, which provided a weak contribution in the oil recovery. Also, a new scaling equation was proposed to describe capillary imbibition process influenced by rock wettability alteration. The scaling equation successfully captured the oil imbibition recovery with different wettability conditions. This study supports the EOR potential of Ɣ-Al NPs in oil-wet carbonates and also emphasizes the important role of wettability function to upscale capillary imbibition processes from core to field scale.