|Institution:||University of Regina|
|Full text PDF:||http://hdl.handle.net/10294/5459|
With the depletion of natural driving forces responsible for pushing the oil from reservoirs and declining oil recovery after the secondary recovery stage, emphasis is now on EOR techniques. Low saline water (LSW) flooding is a type of EOR that has gained immense attention among researchers due to its ease of use, lower cost, and environmentally friendly nature. Previously, researchers have focused on the quantity and compatibility of water to be injected, but recently, it has been recognized that more OOIP can be displaced by decreasing the brine salinity. Though low salinity effects have been seen in various lab-scale core flooding experiments, as well as field pilot projects, the mechanism that actually leads to this enhancement in recovery is still an area of conflict among researchers. This study has been undertaken to investigate low saline flooding in unconsolidated Ottawa sandpack cores with two different crude oils (Weyburn and Pelican) to find the optimum salinity, LSW effective slug size, tertiary recovery by LSW, and underlying mechanisms during LSW flooding by performing unsteady state core flooding experiments. NaCl brine salinity was varied from 500-50,000 PPM during secondary coreflood to first determine the optimum salinity, which was later used in the tertiary recovery stage. By reducing brine salinity from 5,000 PPM to 1,500 PPM, oil recovery increased in the secondary stage and decreased upon reduction to 500 PPM, reaching a peak at 1,500 PPM. A small enhancement in tertiary recovery of 2.24% was observed upon switching to 1,500 PPM NaCl brine after injection of formation brine in the secondary stage for Weyburn oil, though large tertiary recoveries of the order of 9.95% for effective oil viscosity of 4 cP and 7.32% for 29.7 cP were observed for n-dodecane diluted Pelican oil. A LSW slug size of 25% pore volume was found to be effective in producing Weyburn oil in the secondary stage. High recovery obtained in the case of 1,500 PPM NaCl brine was due to the greater water-wet nature of the sandpack, which was later confirmed by the intersection point of kro and krw beyond 0.6.