Black Sea gas hydrates: safe long terms storage of CO2 with environmentally friendly energy production

Safe long terms storage of CO2 in the form of hydrate with associated energy production from hydrate reservoirs is an attractive concept. We propose a scheme for systematic thermodynamic evaluation of the feasibility of CO2/CH4 swapping. The method is based on 4 criteria: (1) pressure temperature hydrate stability limit projections of in situ hydrates, and hydrate formed from injection gas; (2) Gibbs free energy of in situ hydrates versus Gibbs free energy of hydrates formed from injection gas; (3) energy from the formation of hydrate from injection gas as a heat source for dissociation of in situ hydrates; (4) second law involves a high enough temperature to impose the actual changes in entropy due to the phase transition. The primary mechanism for CH4/CO2 swapping is on nano to meso scale and this latter criterion may not be needed. The distance between the location for formation of hydrate from injection gas (and the released heat) and in situ CH4 hydrate is small. The released natural gas can be cracked to H-2 and CO2 for re-injection to create a cycle with the only export of H-2. The technologies needed in the total cycle are well known and technically feasible. The proposed scheme is demonstrated for the specific conditions of the Black Sea. A mixture consisting of 75 mol% CO2, 24 mol% N-2,N- and 1 mol% CH4 is feasible.

Automated summary

Safe storage of CO2 in the form of hydrate with energy production is an attractive concept. A systematic thermodynamic evaluation scheme based on four criteria is proposed for assessing the feasibility of CO2/CH4 swapping. The scheme is demonstrated for the Black Sea and a specific mixture of CO2, N-2, and CH4 is found to be feasible.