Optimization of chelating agent EOR solutions for carbonate reservoirs

This paper presents a novel approach for optimizing the chemical concentrations for EOR applications in carbonate reservoirs characterized by high salinity and high temperature. The chelating agent fluid systems used in this study were prepared using undiluted seawater. The approach is found to be a cost effective and resulted in very significant incremental oil recovery when applied after the conventional seawater-flooding, and could be used as an alternative to the conventional and low salinity waterflooding. The used chemicals are environmental friendly, stable at high salinity and high temperature and do not required additional chemical additives. A comparison of two chelating agent EOR solutions having concentrations ranging from 3 to 10 wt.% prepared using undiluted Arabian Gulf seawater and used in sequential coreflooding tests to identify the best chelating agent solution and its optimum concentration for getting the highest incremental oil recovery after conventional seawater flooding with a minimum impact on rock integrity. The impact of fluid concentrations and pH on oil recovery and permeability improvements was analyzed, and the productivity index of each solution at the end of each injection sequence has been evaluated. Finally, a chemical cost evaluation study was conducted to identify the optimum chemical concentration that minimize the usage of chelating agents and maximize the oil recovery.