Abstract
The application of low salinity polymer (LSP) hybrid flooding in sandstone reservoirs has gained significant attention in recent years due to its cost effectiveness and environmentally friendly nature. However, the effects of injection sequence, rock mineralogy, and oil properties on the efficiency of LSP are not well understood, especially in heavy oil. This study therefore aims to investigate these key factors controlling oil recovery during LSP flooding. A total of six core flooding experiments were conducted using both Boise outcrop cores and reservoir cores, which were aged with two different samples of heavy crude oil. The flooding experiments were performed in two different modes, secondary and tertiary recovery, using various slugs of high salinity (HS), high salinity polymer (HSP), low salinity (LS), and LSP solutions for comparative purpose. The pressure drop profile and oil recovery were measured as the injection of fluids progressed through the core. The main finding was that LS flooding did not yield positive results in either secondary or tertiary recovery modes under the experimental conditions for the Boise core. The initial oil-wet wettability state, combined with an increase in pH, did not significantly contribute to oil recovery. In contrast, for the reservoir (MML) core, LS flooding resulted in a significant recovery of 68% of the original oil in place (OOIP) in secondary mode and an additional 8% OOIP in tertiary mode. The presence of dolomite and reactive clay minerals, such as clinochlore and muscovite, facilitated the release of divalent cations (Ca²⁺ and Mg²⁺), which resulted in a low mass action ratio (MAR). Without enough divalent cations to promote the formation of oil-in-water emulsions, oil droplets tend to coalesce, making them more resistant to displacement by the injected water. Thus, low MAR was identified as the major factor driving oil recovery during LS and LSP flooding. Furthermore, this study highlights the effectiveness of LS and LSP flooding for heavy oils with viscosities up to 480 cP, including those with high TAN, aromatic, and resin content. These findings suggest that enhancing interfacial elasticity can significantly improve oil recovery, even in cases where wettability alteration is not a dominant factor. This emphasizes the potential of LS and LSP flooding as effective and widely applicable enhanced oil recovery techniques suitable for various oil types.
