Thermal instability of gas hydrate bearing sediments: Some issues

The overall stability of marine strata holding gas hydrates is dependent on their shear strength characteristics. These characteristics, in turn, are dependent on thermal flux that is imposed for dissociation of the hydrates for the safe and efficient extraction of methane gas from the hydrate bearing sediments. Due to the imposition of thermal flux on these sediments, their fabric structure and pore space hydrate saturation changes, which impacts the overall stability of the sea bed. Estimating stability conditions in such a ‘multiphase and dynamic system’ necessitates collection of undisturbed samples without compromising their in-situ thermodynamic conditions. This is a daunting task given the huge cost of procuring samples and the challenge of maintaining an undisturbed sample with in-situ thermodynamic conditions till it is brought to the laboratory. Synthesizing hydrate bearing sample sediments in laboratory for conducting studies to identify heat migration mechanisms and thermal property measurements and linking them to the shear strength characteristics provides an affordable solution to this problem. With this in view, a critical review of the available literature, dealing with laboratory synthesis of hydrate bearing sediments, their thermal and strength characteristics, the coupled phenomenon of heat and fluid migration, and its impact on the overall stability of marine sediments, has been conducted and presented in this paper. This will facilitate understanding the factors governing and the mechanism of heat transfer in a multiphase system, the changes in the system brought about by the hydrate dissociation front, and the overall impact on the stability of seabed.