Application of low salinity water injection in heavy oil carbonate reservoirs

Low Salinity Water Injection (LSWI) has received much attention recently as an Enhanced Oil Recovery (EOR) technique. Extensive research programs have been launched to investigate and identify positive effects of LSWI on oil recovery. Experiments have been performed on different formations and crude oils in order to identify the cause of wettability alteration, which is considered as the main reason for the observed additional oil recovery. The majority of the studies reported in the literature have been performed on light oils showing positive results, which represent a significant opportunity for these reservoirs. However, application of LSWI in heavy oils has received much less attention and poses a big challenge, especially in carbonate heavy oil reservoirs. Carbonate reservoirs are generally much more complex than their sandstone counterparts. Further difficulties arise when the reservoir is naturally fractured. These features as well as the oil-wet or mixed-wet conditions that dominate carbonate formations usually result in low recovery factors. The available data suggest that the ultimate recovery factor from these reservoirs is low and in the range of 25 to 45%, depending on the applied method. Although the most widely used method for heavy oil recovery is the thermal processes, non-thermal processes such as gas injection and smart fluids are gaining increasingly more interest amongst operators. In this paper, we present the results of an integrated experimental and simulation study performed in order to explore the potential of using low salinity water as an injection fluid for secondary and tertiary oil recovery from heavy oil carbonate reservoirs. Coreflood experiments were performed to derive measured relative permeability curves. This data were then used to numerically simulate the injection of low salinity water. A systematic sensitivity analysis was then performed to investigate the impact of reservoir parameters on the performance of LSWI in these reservoirs. The parameters considered included: reservoir thickness, well spacing, permeability, heterogeneity, and reservoir pressure. The numerical simulation results confirmed the high potential of LSWI for recovering heavy oils. Oil recoveries of up to 70% (OOIP) were predicted when LSWI was used as secondary recovery, which was consistent with the results from laboratory experiments. On the other hand, high salinity water injection just recovered less than 35%. LSWI as a tertiary recovery method also demonstrated high oil recovery which improves the economics of field applications of waterflooding as less water needs to be injected in the field for achieving the same oil recovery factor when low salinity water is used compared to high salinity water.