Methane Production from Gas Hydrate Deposits through Injection of Supercritical CO 2

The recovery of natural gas from CH 4 -hydrate deposits in sub-marine and sub-permafrost environments through injection of CO 2 is considered a suitable strategy towards emission-neutral energy production. This study shows that the injection of hot, supercritical CO 2 is particularly promising. The addition of heat triggers the dissociation of CH 4 -hydrate while the CO 2 , once thermally equilibrated, reacts with the pore water and is retained in the reservoir as immobile CO 2 -hydrate. Furthermore, optimal reservoir conditions of pressure and temperature are constrained. Experiments were conducted in a high-pressure flow-through reactor at different sediment temperatures (2 °C, 8 °C, 10 °C) and hydrostatic pressures (8 MPa, 13 MPa). The efficiency of both, CH 4 production and CO 2 retention is best at 8 °C, 13 MPa. Here, both CO 2 - and CH 4 -hydrate as well as mixed hydrates can form. At 2 °C, the production process was less effective due to congestion of transport pathways through the sediment by rapidly forming CO 2 -hydrate. In contrast, at 10 °C CH 4 production suffered from local increases in permeability and fast breakthrough of the injection fluid, thereby confining the accessibility to the CH 4 pool to only the most prominent fluid channels. Mass and volume balancing of the collected gas and fluid stream identified gas mobilization as equally important process parameter in addition to the rates of methane hydrate dissociation and hydrate conversion. Thus, the combination of heat supply and CO 2 injection in one supercritical phase helps to overcome the mass transfer limitations usually observed in experiments with cold liquid or gaseous CO 2 .