Mixed salt precipitation and water evaporation during smart water alternative CO2 injection in carbonate reservoirs

Abstract

The main objective in this study is to experimentally elucidate the challenges associated with smart water alternating CO2 (smart WAG-CO2) with regard to permeability impairment that occurs due to interaction between injection water-formation water and injection gas-water. For this purpose, static tests including compatibility and zeta potential measurement, and dynamic tests including water, dry and wet CO2 coreflooding experiments are conducted. The findings illustrate that formation scales due to mixing formation water and injection water are mixed-salt with SrSO4 as the dominant scale type. Despite the fact that zeta potential outcomes point up that an increase in sulfate concentration in the injection water advantageously leads to proper potential oil recovery, the coreflooding tests reveal that sulfate ion concentration is the main factor in controlling k/ki ratio; the more the sulfate concentration, the more the level of permeability impairment. During gas injection, evaporation phenomenon was observed, with the evaporation rate being function of core water saturation. In addition, as salinity increases, while evaporation rate is reduced, more salt precipitation occurs in the sample with higher salinity. The results exhibited that initial permeability is more effective than water salinity in changing gas effective permeability. The results of this study can aid the engineers working in upstream sections of petroleum industry to reduce the scale removal expenditures and enhance the smart WAG-CO2 technique.