Capillary controls on methane hydrate distribution and fracturing in advective systems

Abstract

[1] We simulate 1-D, steady, advective flow through a layered porous medium to investigate how capillary controls on solubility including the Gibbs-Thomson effect in fine-grained sediments affect methane hydrate distribution in marine sediments. We compute the increase in pore fluid pressure that results from hydrate occluding the pore space and allow fractures to form if the pore fluid pressure exceeds a fracture criterion. We apply this model to Hydrate Ridge and northern Cascadia, two field sites where hydrates have been observed preferentially filling cm-scale, coarse-grained layers. We find that at Hydrate Ridge, hydrate forms in the coarse-grained layers reaching saturation of 90%, creating fractures through intervening fine-grained layers after 2000 years. At northern Cascadia, hydrate forms preferentially in the coarse-grained layers but 2 × 10 5 years are required to develop the observed hydrate saturations (∼20%-60%), suggesting that hydrate formation rates may be enhanced by an additional source of methane such as in situ methanogenesis. We develop expressions to determine the combinations of sediment physical properties and methane supply rates that will result in hydrate-filled coarse-grained layers separated by hydrate-filled fine-grained layers, the conditions necessary to fracture the fine-grained layers, and the conditions that will lead to complete inhibition of hydrate formation as pore space is constricted. This work illustrates how sediment physical properties control hydrate distribution at the pore scale and how hydrate distribution affects fracturing behavior in marine sediments.

Methane Hydrate Formation in Ulleung Basin Under Conditions of Variable Salinity: Reduced Model and Experiments

“…In general, this means that χ max lM can vary in time t; this is allowed in the comprehensive models in Liu and Flemings (2006), Liu and Flemings (2008), Peszyńska et al (2010), and Daigle and Dugan (2011). Further, the depth of points x eq needs not be unique.…”

“…This paper is the first of two in which we present an approximate reduced model of methane hydrate evolution in subsea sediments under conditions of variable salinity. Our two-phase three-component physical model is a simplification of comprehensive models in Liu and Flemings (2008), Garg et al (2008), and Daigle and Dugan (2011) and is simultaneously a significant generalization of the simpler models in Xu and Ruppel (1999), Nimblett and Ruppel (2003), and Torres et al (2004), in which simplified kinetic or even simpler mechanisms for fluid equilibria were assumed. In contrast to Torres et al (2004) and consistently with Liu and Flemings (2008), our model fits in the general framework of multiphase multicomponent models such as those in Lake (1989) and Class et al (2002), and implements bona fide equilibrium phase constraints known from thermodynamics (Sloan and Koh 2008;Davie et al 2004), albeit in an approximate manner.…”

Reduced Numerical Model for Methane Hydrate Formation under Conditions of Variable Salinity. Time-Stepping Variants and Sensitivity

“…In addition, there may be dependence of Equation (3e) on the type of sediment [19,21] but this is out of scope here. In [3] we developed a particular approximation…”

“…In particular, such a model should include geomechanics and pore-scale effects; see, e.g., the conceptual model described in [21]. However, the analysis of such a model is presently out of scope.…”

Gas-In-Place Estimate for Potential Gas Hydrate Concentrated Zone in the Kumano Basin, Nankai Trough Forearc, Japan

“…Short-range migration is the mechanism by which in situ methane produced as a byproduct of microbial metabolism diffuses from one sediment layer to the next. Usually, this means from a fine-grained interval where it is difficult to form hydrates because of the Gibbs-Thomson effect on methane solubility in fine-grain sediments, to an adjacent coarse grain layer with larger pore spaces which act to lower gas solubility, creating a favorable chemical potential scenario that facilitates hydrate nucleation [86]. GH recycling is a second example of a short-range migration mechanism.…”