Effect of gas hydrates melting on seafloor slope instability

Abstract

We present a theoretical study of the thermodynamic chemical equilibrium of gas hydrate in soil by taking into account the influence of temperature, pressure, pore water chemistry, and the mean pore size distribution. The model uses a new formulation based on the enthalpy form of the law of conservation of energy. The developed model shows that due to a temperature and pressure increase, hydrates may dissociate at the top of the hydrate occurrence zone to ensure a chemical equilibrium with the surrounding bulk water. This original result confirms what has been already shown through experiments. The second part of the paper presents an application of the model through a back-analysis of the giant Storegga Slide on the Norwegian margin. Two of the most important changes during and since the last deglaciation (hydrostatic pressure due to the change of the sea level and the increase of the sea water temperature) were considered in the calculation. Simulation results show that melting of gas hydrate due to the change of the gas solubility can be at the origin of a retrogressive failure initiated at the lower part of the Storegga slope. Once again, the developed model leads to predictions, which are supported by laboratory experiment results, but contradictory to previous interpretations and beliefs considering that hydrate dissociation occurs only at the bottom of the gas hydrate stability zone.

Thermally induced evolution of phase transformations in gas hydrate sediment

“…The dissociation zone extends with time and the strength of the sediment reduces due to the increase of excess pore pressure and the loss of cementation. This may lead to cracks in the base of the structures and overturn of platforms, pipe rupture, and even blowout [7][8][9][10].…”

DEM simulations of methane hydrate exploitation by thermal recovery and depressurization methods

“…where ω is the averaged pure rotation rate; N is the total contact number in the representative volume; the superscript k represents the k th contact; R is the same as that in Eq (3); 1 θ & , 2 θ & are rotational velocities of two contacting particles. The value of APR can be used to indicate not only the energy dissipation, but also the variation of micro structures of soil.…”

“…A methane gas molecule (CH 4 ) can be caged by water molecules under high pressure and low temperature conditions [1][2][3][4]. The aggregation of such cages is an ice-like crystal called methane hydrate (MH) with properties similar to ice [5].…”

Biotechnological aspects of sulfate reduction with methane as electron donor

“…The earth's gas hydrates contain more energy than all other known oil, natural gas and coal reservoirs combined (Kvenvolden 1995). These hydrates are stable at low temperatures (\15°C), high pressures ([5.0 MPa) and in the presence of dissolved CH 4 (Sultan et al 2003), but the hydrates will dissociate when they come in contact with warm fluids or when dissolved CH 4 is depleted (Boetius and Suess 2004). …”