A systematic review of CO2-enhanced oil recovery mechanisms, technologies, and future prospects

Abstract Anthropogenic CO2 emissions are a key factor in global climate change, necessitating technologies that improve energy security and enable permanent CO2 sequestration. CO2-enhanced oil recovery (CO2-EOR), combined with carbon capture, utilization, and storage (CCUS), offers a strategy to boost hydrocarbon production while reducing atmospheric CO2. However, challenges such as reservoir heterogeneity, early gas breakthrough, and inefficient sweep dynamics hinder its widespread deployment, affecting both economic viability and storage permanence. This comprehensive review, therefore, examines the historical evolution, fundamental mechanisms, and future potential of CO2-EOR. A critical analysis of advanced injection techniques—continuous gas injection (CGI), water-alternating-gas (WAG), and gas-assisted gravity drainage (GAGD)—addresses persistent challenges including gas breakthrough, poor sweep efficiency, and reservoir heterogeneity. The physicochemical mechanisms of CO2-EOR, such as miscibility, capillary effects, and displacement efficiencies, are detailed, with a comparative assessment of horizontal versus vertical flooding approaches. The GAGD process is highlighted as a gravity-dominated alternative, with analysis focused on its underlying mechanisms, operational parameters, and dimensionless governing forces. Furthermore, the integration of CO2-EOR with carbon capture and storage (CCS) is explored as a dual strategy for emission reduction and reservoir revitalization. The review also evaluates economic and environmental criteria for CO2 selection, reservoir complexities, and containment risks. By synthesizing current practices, challenges, and advancements, this work positions CO2-EOR as an essential approach for aligning energy production with decarbonization targets, with its novelty lying in a focused analysis of gravity-stable processes and their integration within the carbon utilization and storage framework.