A Review of Phase Behavior Mechanisms of CO2 EOR and Storage in Subsurface Formations

Abstract

The emissions of CO2 have been recognized as the main cause of climate change. As an important strategy being used to reduce the CO2 concentration in the atmosphere, carbon capture, utilization and storage (CCUS) has attracted significant attention in recent years. Geological formations, including depleted oil and gas reservoirs and saline aquifers, are popular CO2 storage options. During the process of CO2 storage in subsurface formations, the interactions between CO2 and formation fluids must be considered as they could greatly affect the CO2 trapping mechanisms and CO2 storage capacity. In this paper, we give a brief review of the phase behavior mechanisms associated with CO2 storage in subsurface formations. Two different CO2-storage strategies are considered in this paper: CO2 storage in saline aquifers and CO2 storage in oil reservoirs. Multiphase equilibria, including two-phase, three-phase, and four-phase equilibria, can be observed during CO2 injection into underground formations. Both the experimental and modeling studies on the related phase behavior mechanisms are included in this Review. We also introduce some recently developed robust algorithms for the multiphase equilibria calculations, which could be essential for the design of the CO2 storage process and prediction of CO2 storage capacity.