Improved Oil Recovery Through Eco-Driven CO2 Miscibility Enhancement in Crude Oil: Toward Efficient EOR and Carbon Sequestration

Abstract This study targets lowering the minimum miscibility pressure (MMP) and first-contact miscibility pressure (FCMP) of CO2–oil system to enable miscible/near-miscible CO2 flooding at safer, more practical injection pressures. We evaluate an eco-driven ionic liquid (IL), which is 1-methyl-3-octylimidazolium chloride ([C8mim]Cl), as a low-dosage additive to enhance CO2 miscibility and, in turn, improve oil recovery and CO2 potential storage in carbonate cores. ILs proved their potential to improve CO2 miscibility in crude oil and, due to that, different concentrations (0.25–0.75 wt%) of [C8mim]Cl were screened by vanishing interfacial tension (VIT) at 50 °C to quantify IFT–pressure trends and extract MMP and FCMP with and without [C8mim]Cl. The core flooding procedure used two composite Indiana-limestone plugs representing (a) base case, where secondary seawater injection followed by continuous CO2 injection is attained, (b) IL case, the same sequence but with a 1.5 PV pre-slug of 0.5 wt% [C8mim]Cl in seawater and around thirty hours soak before CO2 injection. VIT screening identified 0.5 wt% as the optimum [C8mim]Cl dose, lowering MMP from 1,642 psi to 1,499 psi and FCMP from 1,976 psi to 1,655 psi. These reductions can be identified in percentages as 8.7% and 16.27%, respectively. In core flooding, the IL pre-slug injected after secondary seawater flooding increased tertiary CO2 recovery from 29.7 % (base) to 39.7 % and raised total recovery from 82 % to 95.2%, corresponding to a 35.9 % improvement in CO2-EOR performance versus the control case. The work introduces a simple, low-dosage, “eco-driven” IL pre-slug strategy that simultaneously reduces both MMP and FCMP and then translates that miscibility benefit into markedly higher core-scale CO2-EOR efficiency in carbonate rock. The integrated VIT-to-core flooding workflow provides a practical screening-to-deployment pathway and demonstrates that 0.5 wt% [C8mim]Cl can unlock near miscible/miscible performance while supporting CO2 sequestration goals.