An experimental Comparison between Low Salinity water injection in carbonate and Sandston rock

Water flooding has been used for many years to improve oil recovery from reservoirs. In the last decade it has been a growing interest in understanding the low salinity mechanism in sandstone reservoirs which may result in additional oil recovery. Many theories on how low salinity water works have been proposed, but the main mechanism is still debated. Even though many mechanisms have been proposed, none of them have been accepted as the main mechanism behind the low salinity effect. The temperature and the number of divalent cations in the formation water, especially Ca2+ and Mg2+, are also important factors for observing low salinity effect. It is assumed that the low salinity effect is a result of altering the wettability of the rock to a more water-wet condition. The rock becomes more water-wet when organic material is desorbed from the clay surface.In this work the potential of low salinity effect after flooding with seawater and diluted seawater in a sandstone core has been evaluated. The oil recovery by formation water was about 65% of the original oil in place (OOIP). No additional oil recovery was observed after flooding with sea water and 50 times diluted sea water. High temperature and a large concentration of Ca2+ in the initial formation water, may be the main reasons for why no low salinity effect was observed. The carbonate core flood results show that removing NaCl from seawater and diluting the seawater twice and four times yielded about 8% incremental oil. An additional 5% oil recovery was obtained after the subsequent flood of surfactant diluted in low-salinity water. Oil-brine IFT increased with decreasing salinity both in presence and in absence of 1,000-ppm surfactant.

Keywords:

Low Salinity , water injection , carbonate , Sandston