Direct Flue Gas and CO2 Injection for Simultaneous Energy Recovery and CO2 Sequestration in Ocean: Feasibility Analysis and Perspective

Addressing rising energy demand and making industrial clusters carbon neutral are crucial for sustainable energy transition. Large-scale CO₂ capture from flue gas can be a costly affair, and hence directly injecting flue gas under subsurface offshore reservoirs can be an economical solution. In this pursuit, methane production from natural gas hydrate (NGH) reservoirs using CO₂ sequestration can offer a simultaneous solution for energy transition and achieving net zero. This review delves into the intricate engineering considerations and begins with hydrate thermodynamics and kinetics discussion and subsequently provides a comprehensive analysis of technical factors including porous media characteristics, the state of gas injection, and the assessment of hydrate stability under various conditions of flue gas injection in ocean environments. While the depth required in the ocean for stable CO₂ hydrate formation increases with the decrease in the CO₂ fraction in the flue gas mixture, the depth for hydrate formation in subsea sediments reduces as the CO₂ fraction in the injected flue gas stream decreases. Even though the hydrate formation from flue gas and pure CO₂ in ocean is possible at a depth of 500–2000 m based on CO₂ concentration, which is not necessarily favorable environmentally, the best possible location for flue gas injection (10–20% CO₂) is under seabed sediments where it can form hydrates at a maximum depth of 100–150 m from the seabed. The paper helps in exploring the possibilities of direct flue gas and CO₂ sequestration in the ocean for simultaneous energy production and long-term, large-scale CO₂ sequestration.