Origin and evolution of fracture‐hosted methane hydrate deposits

Abstract

[1] Fracture-hosted methane hydrate deposits exist at many sites worldwide. These sites often have hydrate present as vein and fracture fill, as well as disseminated through the pore space. We estimate that thousands to millions of years are required to form fracture systems by hydraulic fracturing driven by occlusion of the pore system by hydrate. This time scale is a function of rates of fluid flow and permeability loss. Low-permeability layers in a sedimentary column can reduce this time if the permeability contrast with respect to the surrounding sediments is of order 10 or greater. Additionally, we find that tensile fracturing produced by hydrate heave around hydrate lenses is a viable fracture mechanism over all but the lowermost part of the hydrate stability zone. With our coupled fluid flow-hydrate formation model we assess fracture formation at four well-studied hydrate provinces: Blake Ridge offshore South Carolina, Hydrate Ridge offshore Oregon, Keathley Canyon Block 151 offshore Louisiana, and the Krishna-Godavari Basin offshore India. We conclude that hydraulic fracturing due to pore pressure buildup is reasonable only at Hydrate Ridge and the Krishna-Godavari Basin owing to sediment age constraints, and that hydrate-filled fractures observed at Blake Ridge and Keathley Canyon Block 151 are formed either by hydrate heave or in preexisting fractures. Our findings offer new insight into the processes and time scales associated with fracture-hosted hydrate deposits, which help further our understanding of hydrate systems.Citation: Daigle, H., and B. Dugan (2010), Origin and evolution of fracture-hosted methane hydrate deposits,

X-ray computed-tomography imaging of gas migration in water-saturated sediments: From capillary invasion to conduit opening

“…Our observations also provide critical experimental evidence to explain the means by which gas may transit through the gas hydrate stability zone through new or reactivated pathways within fine grained-sediments [Gorman et al, 2002;Hornbach et al, 2004;Weinberger and Brown, 2006;Daigle and Dugan, 2010].…”

“…[4] These gas invasion phenomena have important implications for understanding hydrates in natural systems (either ocean sediments or permafrost regions) [Hornbach et al, 2004;Weinberger and Brown, 2006;Uchida et al, 2009;Daigle and Dugan, 2010]. They suggest that, in fine sediments, hydrate will likely form as planar, graindisplacing veins, whereas, in coarse sediments, the buoyant methane gas will likely invade the pore space more uniformly and with minimal grain displacement, in a process akin to invasion percolation, causing hydrate in a pore-filling morphology.…”

Mechanisms Leading to Co-Existence of Gas Hydrate in Ocean Sediments [Part 2 of 2]

“…Multiple mechanisms have been proposed for coexistence of free gas and hydrates in the HSZ [Milkov and Xu, 2005;Torres et al, 2005;Ruppel et al, 2005]: (1) regional geotherms, (2) reduction in hydrate stability by salt accumulation, (3) kinetics of hydrate formation, and (4) fast, focused flow of free gas through high-permeability conduits. Evidence of fractures and flow through them at Hydrate Ridge has been inferred from field observations Flemings et al, 2003;Trehu et al, 2004a;Weinberger and Brown, 2006] and modeling studies [Liu and Flemings, 2007;Daigle and Dugan, 2010].…”

“…Previous modeling work has sought to estimate the distribution of hydrates by considering methane transport in the dissolved phase only [Xu and Ruppel, 1999;Buffett and Archer, 2004;Daigle and Dugan, 2010] or as gas flowing by capillary invasion [Liu and Flemings, 2007;Garg et al, 2008;Reagan and Moridis, 2009;Daigle and Dugan, 2010]. These models capture slow processes of pore water flow, heat and salt transport to capture important impacts on hydrate stability and the equilibrium distribution of hydrates [Kowalsky and Moridis, 2007].…”

The potential response of the hydrate reservoir in the South Shetland Margin, Antarctic Peninsula, to ocean warming over the 21st century

“…The generation of vertical hydrofractures can be conservatively estimated when the overpressure exceeds the horizontal effective stress (Aldridge & Haland 1991). We implicitly assume that the maximum principal effective stress is vertical and the intermediate and minimum principal effective stresses are horizontal (e.g., Daigle & Dugan 2010). Here we analyse the likelihood of shallow landslides and vertical fractures to occur in the SSM caused only by hydrate dissociationinduced overpressure over the 21st century.…”