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

Abstract

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 H₂ and CO₂ for re-injection to create a cycle with the only export of H₂. 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, and 1 mol% CH₄ is feasible.