HR: 10:50h
AN: OS22A-03    [Abstracts]
TI: Grain Scale Study of Hydrate Formation in Sediments From Methane Gas: A Coupled Fluid- Solid Interaction Model
AU: * Juanes, R
EM: juanes@mit.edu
AF: Massachusetts Institute of Technology, Civil and Environmental Engineering 77 Massachusetts Ave. Room 48-319, Cambridge, MA 02139, United States
AU: Jain, A K
EM: akjain@mit.edu
AF: Massachusetts Institute of Technology, Civil and Environmental Engineering 77 Massachusetts Ave. Room 48-319, Cambridge, MA 02139, United States
AB: Ocean sediments bearing methane hydrates exhibit a range of behavior, from cold seeps where solid and gas phases co-exist in the hydrate stability zone (HSZ), to essentially static accumulations where solid and liquid co- exist. This paper and its companion (Behseresht, Prodanovic and Bryant) describe the development and application of models for grain-scale phenomena governing in situ gas-to-hydrate conversion. The motivation is the following hypothesis: as gas phase pore pressure varies, the competition between brine displacement and sediment fracturing determines the extent of conversion of methane gas entering the HSZ to hydrate. Here we present a discrete element method (DEM) to model the strong coupling that takes place between the pore fluids (brine and methane gas) and the mechanical behavior of the sediment. In a discrete element method, each element or grain is an individual entity, identified by its size, mass and moments of inertia. Newton's second law dictates the motion of the assembly of grains. For dry systems, the grain-scale forces are limited to interactions at grain contacts. In contrast, when one or more fluids are present, additional pore-scale forces play a significant role: a set of forces due to pore fluid pressure, and another set due to surface tension between fluids. We develop a self-consistent fluid-solid interaction (FSI) model at the grain scale, in which these additional sets of forces are introduced rigorously. Our computational model captures the two-way coupling between multiphase fluid flow and sediment mechanics, which we validate by means of triaxial laboratory experiments. In particular, this allows us to determine the conditions under which gas invasion fractures the sediment. This determines the distribution of methane gas and hydrate which, in turn, has direct implications on the likelihood that gas and hydrate will co-exist, and on the overall size of the energy resource. Work is under way to couple this grain mechanics model with a capillarity-controlled displacement model, described in the companion paper by Behseresht, Prodanovic and Bryant.
UR: http://www.netl.doe.gov/technologies/oil- gas/FutureSupply/MethaneHydrates/projects/DOEProjects/MH_43 DE: 3004 Gas and hydrate systems
DE: 3021 Marine hydrogeology
DE: 3022 Marine sediments: processes and transport
DE: 3036 Ocean drilling
DE: 5104 Fracture and flow
SC: Ocean Sciences [OS]
MN: 2007 Fall Meeting