Physics – Geophysics
Scientific paper
Jul 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011georl..3814308h&link_type=abstract
Geophysical Research Letters, Volume 38, Issue 14, CiteID L14308
Physics
Geophysics
Marine Geology And Geophysics: Gas And Hydrate Systems, Marine Geology And Geophysics: Marine Sediments: Processes And Transport, Physical Properties Of Rocks: Fracture And Flow
Scientific paper
It has been suggested that volume expansion caused by hydrate dissociation in sediment pores can result in large overpressure, which in turn may destabilize the sediment and trigger massive submarine landslides. Here, we investigate the pressure evolution during thermally-induced dissociation, by means of a pore-scale model that couples dissociation kinetics, multiphase flow and geomechanics. Dissociation is controlled by a self-preservation mechanism: increasing pore pressure reduces the driving force for dissociation. Hence, the overpressure is constrained by the phase equilibrium pressure, regardless of the kinetic rate of dissociation, heat supply, and sediment permeability. Furthermore, we find that the timescale for buildup of pressure by dissociation is typically much larger than that for its dissipation by drainage. Consequently, the overpressure is controlled by the capillary entry thresholds, which depend on the mode of gas invasion. In low-permeability systems, fracturing is the preferred mechanism, occurring at capillary pressures lower than the entry thresholds in the undeformed sediment. Our results suggest that while large overpressures cannot be sustained by rapid dissociation in natural systems, dissociation can induce important geomechanical effects. Gas migration by fracturing provides a possible link between dissociation, sediment deformation and methane venting.
Holtzman Ran
Juanes Ruben
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