Integral effects of initial fluids configuration and wettability alteration on remaining saturation: characterization with X-ray micro-computed tomography

Abstract

Wettability alteration is the key process in low salinity waterflooding to enhance oil recovery. However, wettability alteration cannot necessarily lead to better oil recovery as other factors such as initial fluids morphology plays critical roles. We used Micro-CT X-ray imaging to investigate the effects of initial water morphology and wettability alteration on final remaining oil saturation and oil ganglia size distribution. The results show that presence of percolating water pathways impedes the oil recovery and oil can be produced mostly from large pores at tertiary mode, whereas the secondary low salinity waterflooding unlocks oil from a much broader range of pores. Moreover, the in-situ contact angles decrease towards less oil-wet regardless of initial water saturation, suggesting that wettability alteration is not dependent on the initial water saturation. We observed that at the end of secondary low salinity waterflooding, larger trapped ganglia were identified which is in agreement with the ganglia mobilisation theory. This work provided novel insights into the source of additional oil recovery during low salinity waterflooding and addressed the unrecognized role of initial fluids morphology in hydrocarbon recovery and multiphase flow.