The Impact of Adding High pH Fluid to Sea Water on The Sandstone Rock Charge During EOR Process

Abstract Many researchers investigated the effect of the ionic strength and the chemistry of the injected water on the oil recovery from sandstone reservoirs. They concluded that as the salinity of the injected water decreased the oil recovery increased. They studied the effect of changing the salinity of the injected water on the zeta potential. The Zeta potential decreased in case of aquifer water compared to the sea water. The new application that we used has the ability to do better than the low salinity water flooding in increasing the oil recovery from sandstone reservoirs without diluting the sea water. Sea water dilution is a costly process, the cost of the new fluid system is low and in terms of recovery it will do better than the low salinity waterflooding. The new EOR fluid system will remove the damage caused by the low salinity water and sea water flooding and also it will prevent the formation damage. In this paper we will study the effect of adding high pH fluid (chelating agent) to sea water on the sandstone rock charge. Zeta potential was measured for Berea sandstone rock with different fluids and different concentrations of the chelating agent which was added to sea water. Also the effect of the chelating agent on the surface tension and oil recovery was evaluated. The results of zeta potential showed that adding high pH chelating agent to sea water decreased the value to -33 mV less than the low salinity water (5,767 ppm) which changed the zeta value to -12mV. In addition, the zeta potential of sandstone rock will be affected by the iron concentration in the fluid. Low salinity water with 1000 ppm iron changed the value to 7 mV. But, in case of adding the chelating agent to the same fluid the effect of iron did not appear and the charge decreased to -24mV. The decrease in zeta potential value indicates more water wet rock surface and in turn, high oil recovery will be achieved. The chelating agent diluted in sea water yielded lower surface tension compared to sea water and low salinity water. The oil recovery increased by 30% after sea waterflooding when we used 5 wt% of Na4EDTA chelating agent diluted from initial concentration of 40 wt% using sea water. The recovery increase can be attributed to the change in the rock surface charge, rock dissolution, IFT reduction mechanisms.