Danube Fan and Nyegga - the largest contrast European gas hydrate deposits for CO2 storing and CH4 and H2 production

Abstract

Huge amounts of hydrocarbons are leaking into the oceans and into air. Methane is a stronger greenhouse gas than CO2. Even though the lifetime of methane in the atmosphere is limited to roughly 7 years there are constant sources of additional methane. Some of these sources are natural gas hydrates that dissociate through inflow of seawater. Other sources of methane fluxes are also controlled by hydrate when the seafloor conditions are inside hydrate formation conditions of temperature and pressure. In this work we propose a new concept which addresses three environmental concerns. Injection of CO2 dominated gas in hydrate filled sediments, and into sediments controlling leakage from conventional sources into seafloor at hydrate forming conditions will contribute in sealing these leakage sources. This can substantially reduce worldwide leakage fluxes of hydrocarbons to the oceans and to air. A critical element of the approach is a thermodynamic analysis that ensures that the injection gas dominates hydrate formation at local sediment conditions. The associated carbon dioxide storage, and related reduction in leakage fluxes of hydrocarbons are two environmental benefits. A third benefit can be gained by adding steam conversion of the hydrocarbons to hydrogen and carbon dioxide (for re-injection). The concept is discussed using geoscience data from the Black Sea and from Nyegga area offshore Norway. We conclude that between 3.4 and 4 mol of hydrogen gas can be produced for every mole of carbon dioxide stored safely in these two regions.