Effects of CO2-CH4 Co-injection on the Performance of a Coupled Carbon Storage and Enhanced Oil Recovery Process

Abstract:

This study aims at developing compositional simulation models of co-injecting CO₂ and CH₄ during a water-alternating-gas (WAG) process for assessing the efficiency of carbon capture and storage coupled with enhanced oil recovery (CCS-EOR). In this study, the volume of gas injection is fixed at surface conditions for various cases. A three-phase hysteresis and Henry’s models are used to simulate residual and solubility trapping during the WAG process that imbibition and drainage processes occur repeatedly. Since CH₄ is less compressible than CO₂, it occupies more reservoir pore volume and causes high reservoir pressure resulting in improved EOR performance at an early time. However, EOR performance finally becomes lower with CH₄ addition because of reduced miscibility and sweep efficiency, and oil recovery with CH₄ addition is lower than that of CO₂ injection case. Decreased gas displacement and sweep efficiencies cause poor hysteresis effect for residual trapping performance. Although the reduced sweep efficiency, solubility trapping performance does not change because reservoir average pressure with CH₄ addition is greater than that of the CO₂ injection case due to the compressibility effect. To compare the carbon storage efficiency, the index considering global warming potential (GWP) has been compared with various CH₄ concentration models. Because the GWP of CH₄ is about 28 times that of CO₂, the co-injection WAG can further reduce greenhouse gas emissions into the atmosphere compared to the CO₂ WAG. The above results indicate the significance of the integrated analysis for accurate CO₂ sequestration in depleted or depleting hydrocarbon reservoirs under EOR.