Enhanced carbon dioxide sequestration by direct injection of flue gas doped with hydrogen into hydrate reservoir: Possibility of natural gas production

Methane recovery from the natural gas hydrates (NGH) represent the largest source of hydrocarbon energy in the world. However, the existing methods of methane recovery are constrained by low efficiency and ecological impact. One method which can offer methane recovery with simultaneous reduction in atmospheric carbon accumulation is carbon dioxide (CO2) injection into methane (CH4) dominated hydrates. This method may also ensure long term CO2 storage in the cages of recovered methane. However, obtaining huge amount of pure CO2 and its storage stability at real saline conditions of hydrate media are two important aspects for a sustainable methane recovery project. This study focuses on reducing reliance on pure CO2 and therefore, an equivalent flue gas composition of CO2 and nitrogen (N-2, 0-80 mol%) is tested for hydrate potential. The study is an experimental investigation of CO2 hydrate formation (N-2 as binary gas) in common seabed conditions of 2-8 degrees C and 35-75 bar. The inclusion of N-2 was found to depress the conditions of hydrate formation of CO2 and at high N-2 composition [40 mol% for saline water and 45 mol% for fresh water], no hydrates formed. The presence of salt was also found to reduce the amount of gas consumption which inhibited the hydrate formation. Further, the role of hydrogen (H-2) (in minute compositions, 0.1 and 1 mol%) was investigated as a promoter to enhance hydrate formation at unstable conditions (gas mixtures with higher N-2 composition). H-2 showed significant increase in gas consumption by 12-18%. Increasing H-2 composition (from 0.1 to 1 mol%) was able to restore hydrate formation under saline conditions even in the presence of >40 mol% N-2. Based on this study, the use of H-2 is recommended as a promoter to ensure long term storage of CO2 in hydrates with its simultaneous usage for sustainable CH4 production. (C) 2021 Elsevier Ltd. All rights reserved.