|M.Sc Student||Ziv Charas|
|Subject||The Effect of Particle Migration on the Mechanical Behavior|
of Methane Hydrate Sediment
|Department||Department of Civil and Environmental Engineering||Supervisor||Professor Klar Assaf|
|Full Thesis text - in Hebrew|
Methane hydrate is a solid like ice material which can be found in equilibrium under large stresses and/or low temperatures. The total amount of hydrate in the world is evaluated to be as twice as the sum of fossil energy known today. Therefore both academia and industry consider methane hydrate as a potential energy source for future years, investing significant time and effort into its research, focusing on different methods for gas hydrate extraction and energy production. Recent field experiments, involving the depressurization method for gas hydrate extraction, were prematurely terminated due to excessive sand production. In the depressurization production method the wellbore pressure is reduced, leading to two main field reactions which may be associated with sand migration and production: the first creates a flow gradient towards the borehole which increases the drag force influence on the soil skeleton; the second leads to hydrate dissociation into water and gas. Most of previous research works on the topic of gas hydrate have neglected the sand migration phenomenon.
This thesis offers a hydro-mechanical-thermo-chemical formulation for gas hydrate which includes the sand migration phenomenon. It includes  the influence of shear deformation on the sand production;  criteria for detachment and settling of soil particles;  the strengthening of the soil and limitation of sand migration as function of hydrate saturation.
The formulation was written in a differential form as a C DLL to be incorporated within the finite difference code, FLAC3D. The formulation was verified against previous research works for the case of "no sand migration". A parametric study was performed to evaluate the impact and importance of sand migration, for cases with and without hydrate dissociation.