Economic Optimization of Enhanced Oil Recovery and Carbon Storage Using Mixed Dimethyl Ether-Impure CO2 Solvent in a Heterogeneous Reservoir

CO2 is the main solvent used in enhanced oil recovery (EOR). However, its low density and viscosity compared to oil cause a decrease in sweep efficiency. Recently, dimethyl ether (DME), which is more efficient than CO2, has been introduced into the process. DME improves oil recovery by reducing minimum miscible pressure (MMP), interfacial tension (IFT), and oil viscosity. Since DME is an expensive solvent, price reduction and appropriate injection scenarios are needed for economic feasibility. In this study, a compositional model was developed to inject DME with impure CO2 streams, where the CO2 was derived from one of these three purification methods: dehydration, double flash, and distillation. It was assumed that such a mixed solvent was injected into a heterogeneous reservoir where gravity override was maximized. As a result, lower oil recovery is achieved for the higher impurity content of the CO2 stream, lower DME content, and more heterogeneous reservoir. When a high-purity CO2 stream is used, the change in oil recovery according to DME content and heterogeneity of the reservoir is increased. When the lowest-purity CO2 stream is used, the net present value (NPV) is the highest. For a homogeneous reservoir, the NPV is highest for all impure CO2 streams. This optimization indicates a greater impact on revenue from reduced CO2 purchase cost than on profit loss due to reduced oil recovery by impurities. Additional benefits can be expected when considering solvent reuse and carbon capture and storage (CCS) credits.