DefinePK

Abstract

In recent years, numerous studies have confirmed that in certain conditions, low salinity water flooding (LSW) may be more effective than high salinity water flooding (HSW) both in carbonate and sandstone reservoirs. The available data suggests that depending on reservoir conditions, a number of phenomena may be responsible for incremental oil recovery (IOR) during LSW. Wettability alteration, clay swelling, an increase in pH, multi-ion exchange, double layer expansion and fine migration were claimed to be the underlining mechanisms for an increase in oil recovery during LSWF. However, due to a large number of interrelated variables, the ranges of reservoir conditions in which each of these mechanisms is activated has not yet been identified. Thus, additional research is required for a better understanding of the principles and limits of LSWF. However, only a few studies have been conducted on heavy oil displacement. In this paper the higher salinity contrast between injections of reservoir brine followed by injection of fresh water into the cores were tested to define the impact of injecting water salinity on the heavy oil recovery factor. Such extreme salinity contrast of injecting water was used to demonstrate the effect of low salinity water flooding in laboratory experiments and to check the possibility of using low salinity water flooding as an EOR method. As a result, fresh water resulted in 19% of IOR after initial HSW in the preferentially oil-wet sand pack, whereas incremental recovery in the hydrophilic sand totaled only around 4%. In addition, the data collected on the injection pressure change coupled with the analysis of rock mineralogy and the effluent samples suggests that fine migration takes place during the injection of fresh water.