This document is an expanded abstract.
Summary
Understanding the oil extraction processes at the laboratory scale is critical for designing and implementing the injection fluids to predict the enhanced oil recovery performance at the reservoir scale. Benchtop low-field nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) is a powerful technique to characterize confined fluids in complex rock pore throat networks. The purpose of this study is to study CO2 alternating low-salinity water (LSW) flooding processes with NMR-MRI to efficiently recover the residual oil from carbonate cores. The in situ NMR-MRI results have shown that the LSW with specific ionic strength can improve the recovery of oil from tight carbonate cores. Our ongoing research using low-field NMR-MRI will also provide consistent measurements between laboratory-scale core analysis and ‘‘reservoir-scale’’ well-logging.
Introduction
The idea of injecting low-salinity water (LSW) into petroleum reservoirs has been addressed since the 1960s. Bernard et al., demonstrated that injection of fresh water both in secondary and tertiary modes can increase the oil production from sandstone cores containing clays [1]. In recent years, extensive research has shown that by tuning the salinity and ionic composition of the injected water can improve the oil production [2-3]. However, most of the studies are based on the sandstone reservoirs. Recently, Yousef et al., investigated the potential of using the LSW with specific ionic composition in carbonate reservoirs and owing to rock dissolution mechanism, they achieved 10% increase in oil production during the core flooding experiments [4]. Another report by Puntervold et al. (2015) has reported the mechanism of electrical double layer expansion at the solid liquid interface, which help in improving the production of 25% to 33% original oil in place using LSW with specific SO42- ions composition [5]. The reported results were obtained after spontaneous imbibition and no core flooding experiments were performed. Additionally, different literature has attributed different mechanisms involved in changing the chemical/physical nature of rock surface in the presence of LSW and the mechanisms are well established for the sandstones, but the so called positively charged nature of carbonate rock make the situation very complicated [6]. Thus, there is controversy in the reported literature about the experimental operating conditions, as well as the possible mechanisms involved.
