Hybrid Carbonated Low Salinity Waterflood in Calcite-Cemented Sandstone: Effects of Low pH and Salinity on Oil Production and CO2 Storage

Abstract

Hybrid carbonated low salinity waterflood (CLSWF) introduces synergetic effects of oil viscosity reduction and wettability modification. The technology injecting CO2-saturated low salinity water is a hybrid design of low salinity waterflood (LSWF) and carbonated waterflood (CWF). Coupled with geochemical reaction and equation of state (EOS) modeling, this study proposes compositional simulation of the CLSWF process. In a comparison to LSWF to quantify the synergetic effects, CLSWF introduces enhanced wettability modification effect due to geochemical reactions of ion-exchange and mineral dissolution. The low pH and salinity conditions during CLSWF dissolve significant calcite mineral to increase Ca2+ molality. It results in more cation-exchange and enhances wettability modification following LSWF mechanism. CO2 is transported from CO2-saturated low salinity water to oil during CLSWF. This interphase transport of CO2 reduces oil viscosity improving mobility ratio. As a result, additional oil production with 6% and improved injectivity are observed in CLSWF. In addition, CLSWF introduces CO2 storage effect. Despite of the interphase transport of CO2, significant CO2 is remained in water and captured in reservoir. Therefore, the novel CLSWF is shown to be a promising technology securing both enhanced oil production and CO2 storage.