APPLICATION OF LOW SALINITY HOT WATER INJECTION IN CARBONATES

Abstract

The high efficiency of Low Salinity Water (LSW) injection in carbonates, leading to rock wettability alteration from oil-wet to water-wet and, hence, resulting in better oil displacement, has been confirmed by numerous studies. In recent years, the combination of LSW injection with other Enhanced Oil Recovery (EOR) techniques has been widely discussed to activate the synergistic effects of hybrid EOR methods leading to additional oil recovery. The idea of combining LSW injection with a thermal approach, known as Low Salinity Hot Water (LSHW) injection, is a highly promising hybrid EOR method for heavy oil carbonate formations. In this study, the performance of LSW and hybrid LSHW injection was experimentally evaluated for heavy oil carbonate cores by different measurements of rock-fluid interactions and core flooding experiments. Contact angle measurements were conducted to investigate the optimal dilution of seawater (SW) and evaluate the performance of different variations of Potential Determining Ions (PDIs) concentration on wettability change. Appropriate dilution and ion management were applied to design LSW and engineered water (EW) for oil displacement at different temperatures (from 20°C to 70°C) in order to evaluate the standalone LSW and hybrid LSHW injection performance. The injection of LSW and EW was estimated to be inefficient for heavy oil carbonates, while hybrid LSHW flooding showed a significant increase of oil recovery with the best performance of the brine spiked by PDIs, where 60% and 55% of the residual oil was displaced at 50°C and 70°C, respectively. Moreover, the injection of LSHW directly after SW was found to be more practical than following LSW flooding. The application of the hybrid EOR method activates different mechanisms, such as oil detachment from the rock surface, due to the wettability alteration by EW/LSW and viscosity reduction by the thermal methods. Combined active mechanisms result in better performance, compared to the standalone EOR methods. Rock dissolution and multi-ion exchange by PDIs were identified as the main mechanisms of wettability alteration by EW/LSW via the results of ion chromatography analyses. The synergy between EOR methods affects the active mechanisms of LSW/EW flooding. For example, an increase in temperature showed more active multi-ion exchange and rock dissolution, which resulted in higher oil release from the rock surface.