A Comprehensive Simulation Study of Physicochemical and Geochemical Interactions on Immiscible CO[sub.2]-LSWAG Injection in Carbonates

Low-salinity water-alternating-CO[sub.2] (CO[sub.2] -LSWAG) injection has been widely studied and employed due to its capability to promote enhanced oil recovery (EOR). However, there is no consensus on the dominant mechanisms for oil recovery in carbonates due to the extreme complexity of the oil–brine–rock interactions. This work proposes a comparative investigation of the physicochemical and geochemical effects of continuous CO[sub.2] and CO[sub.2] -LSWAG immiscible injections on oil recovery in a carbonate core. Simulations were carried out using oil PVT properties and relative permeability experimental data from the literature. A comparison of SO[sub.4] [sup.2−] and Mg[sup.2+] as interpolant ions, oil, water and gas production, pressure, and rock and fluid properties along the core and in the effluent was made. The results show a high recovery factor for CO[sub.2] (62%) and CO[sub.2] -LSWAG (85%), even in immiscible conditions. The mineral dissolution and porosity variations were more pronounced for CO[sub.2] -LSWAG than CO[sub.2] . The simulation results showed that Mg[sup.2+] as an interpolant improves oil recovery more than SO[sub.4] [sup.2−] because Mg[sup.2+] concentration in the aqueous phase after LSW injection leads to relative permeability values, which are more favorable.