A Grain-Scale Coupled Model of Multiphase Fluid Flow and Sediment Mechanics – Application to Methane Hydrates in Natural Systems

Authors: Antone K. Jain and Ruben Juanes

Venue: American Geophysical Union Fall Meeting, San Francisco, CA, December 15-19, 2008 – Special Session H06: Particle Tracking Simulation of Fluid Flow and Mass Transport. http://www.agu.org/meetings/fm08/

Abstract: A discrete element model is presented for the simulation, at the grain scale, of gas migration in brine-saturated deformable media. The model rigorously accounts for the presence of two fluids in the pore space by incorporating grain forces due to pore fluid pressures, and surface tension between fluids. The coupled model permits investigating an essential process that takes place at the base of the hydrate stability zone: the upward migration of methane in its own free gas phase. The ways in which gas migration may take place were elucidated: (1) by capillary invasion in a rigid-like medium; and (2) by initiation and propagation of a fracture. Results indicate that the main factor controlling the mode of gas transport in the sediment is the grain size, and that coarse-grain sediments favor capillary invasion, whereas fracturing dominates in fine-grain media. The results have important implications for understanding hydrates in natural systems. The results predict that, in fine sediments, hydrate will likely form in veins that follow a fracture-network pattern, and the hydrate concentration in this type of accumulations will likely be quite low. In coarse sediments, the buoyant methane gas is likely to invade the pore space more uniformly, in a process akin to invasion percolation, and the overall pore occupancy is likely to be much higher than for a fracture-dominated regime. These implications are consistent with field observations of methane hydrates in natural systems.

Related NETL Project
This presentation is related to the NETL project DE-FC26-06NT43067, “Mechanisms Leading to Co-Existence of Gas and Hydrate in Ocean Sediments." The goal of this project is to quantitatively describe and understand the manner in which methane is transported within the Hydrate Stability Zone (HSZ).

Project Contacts
NETL - Robert Vagnetti (robert.vagnetti@netl.doe.gov or 304 285-1334)
University of Texas at Austin – Steven Bryant (Steven_Bryant@mail.utexas.edu or 512 471-3250)