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

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.