Conditions under Which Gaseous Methane Will Fracture Ocean Sediments and Penetrate Through the Hydrate Stability Zone: Modeling Multiphase Flow and Sediment Mechanics at the Pore-Scale

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: Two competing processes were simulated, capillary invasion and fracture opening, by which free methane gas penetrates the Hydrate Stability Zone (HSZ). In situ conditions were predicted in which the methane propagates fractures and flows all the way through the HSZ and into the ocean, bypassing hydrate formation. In the fully coupled model, the discrete element method was used to simulate the sediment mechanics, and pore fluid pressures and surface tension between the gas and brine were accounted for by incorporating additional sets of pressure forces and adhesion forces. Results indicate that given enough capillary pressure, the main factor controlling the mode of gas transport is the grain size, and show that coarse-grain sediments favor capillary invasion and widespread hydrate formation, whereas fracturing dominates in fine-grain sediments. The fracturing threshold was calculated as a function of grain size, capillary pressure, and seafloor depth, and place these results in the context of naturally-occurring hydrate 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)