An Application of the Results from the Large-Scale Thermal Stimulation Method of Methane Hydrate Dissociation to the Field Tests

Abstract

Methane hydrate formation and the gas recovery from the hydrates using the thermal stimulation method was studied in a large-scale laboratory reactor. A large-scale laboratory reactor (59 L volume) was used in this study. The efficiencies of gas recovery and energy utilization were studied over two different values of initial hydrate saturation (30% and 50%) and three different values of heating rates (20, 50, and 100 W). Results obtained from the tests demonstrate that with the initial hydrate saturation (SH) remaining constant (50% SH); total recovery of methane increases from 40% to 52% to 73% with a heating rate increase from 20 W to 50 W to 100 W. The average thermal efficiency, however, decreases from 86% to 84% to 82% over the same heating rate range. Alternately at a constant heating rate (100 W), total recovery of methane increased from 67% to 74% when an initial hydrate saturation was increased from 30% to 50%. We show that maintaining a constant heating rate throughout the dissociation is not the most efficient procedure. Instead, starting with a low heating rate then increasing it when methane output starts to decrease will be more effective. This suggests that accurate knowledge of the saturation percentage of a chosen hydrate reservoir will enable efficient energy use when recovering methane. We also found that the free water generated during the dissociation and the free water present initially in the reservoir play a major role in carrying the heat front to distant locations in the reservoir hence increasing the gas recovery. We recommend that in the higher hydrate saturation reservoirs, which may lack the free water; the down-hole combustion method will benefit from an injection of hot water in the initial stages, supplying a small amount of heat for the dissociation but providing the free water for convection of heat to the outer regions.