Significant Phase Behavior Changes in Chemically Treated Oil During CO2 Injection

Abstract Carbon Capture, Utilization, and Storage (CCUS) has emerged as a critical strategy for reducing greenhouse gas emissions in response to global climate change. Within the fossil fuel industry, CO2-Enhanced Oil Recovery (CO2-EOR) stands out as a promising dual-purpose technology that not only sequesters CO2 but also improves oil recovery from mature or challenging reservoirs. The success of CO2-EOR largely depends on achieving miscibility between the injected CO2 and the reservoir crude oil, which enables efficient displacement and maximizes hydrocarbon recovery. However, many reservoirs lack the high pressure and temperature conditions necessary for natural miscibility. This study explores a chemical-enhancement approach to improve CO2 miscibility in sub-optimal reservoirs. Specifically, selected oil-based and water-based amphiphilic chemical additives were introduced into a crude oil sample from a reservoir that does not meet miscibility criteria under natural conditions. Through Pressure-Volume-Temperature (PVT) phase behavior experiments, the modified fluids demonstrated significantly reduced saturation pressures and enhanced CO2 solubility. These findings indicate a favorable shift in phase behavior toward miscibility. Complementary slimtube displacement experiments conducted at reservoir conditions further confirmed that the chemically treated fluids exhibit recovery patterns characteristic of near-miscible or fully miscible displacement. The results provide compelling evidence that incorporating tailored chemical additives can effectively enhance CO2-oil interactions, reduce the minimum miscibility pressure (MMP), and extend the technical feasibility of CO2-EOR in reservoirs previously considered unsuitable. This approach offers a cost-effective and scalable solution for improving oil recovery while supporting carbon management goals in various reservoir conditions.