A mathematical model for the formation and dissociation of methane hydrates in the marine environment

Abstract

[1] To elucidate the geological processes associated with hydrate formation and dissociation in the marine environment under a wide range of conditions, we have developed a one-dimensional numerical computer model (simulator). The numerical model can be used to simulate the following aspects of hydrate formation, decomposition, reformation, and distribution: (1) burial history of deep marine sediments and associated phenomena (e.g., sediment compaction and consequent reduction in sediment porosity and permeability, fluid expulsion, time evolution of temperature and pressure, heat flux), (2) in situ generation of biogenic methane from buried organic carbon and methane solubility in formation brine, (3) methane hydrate formation, decomposition, reformation, and distribution in response to changes in gas concentration, pressure, temperature and fluid salinity (the hydrate formation and decomposition are treated as equilibrium processes), (4) influence of sulfate reduction zone under the seafloor on hydrate formation, (5) possible presence of a free gas zone beneath the gas hydrate stability zone, and (6) multiphase (i.e., liquid brine with dissolved gas, free gas, gas hydrate) flow through a deformable porous matrix. The model provides for a reduction/ increase in permeability due to the formation/decomposition of the gas hydrate. Initial applications of the model to study hydrate distribution at the Blake Ridge (site 997) and Hydrate Ridge (site 1249) are described. Model results are compared with chlorinity, sulfate, and hydrate distribution data.

Estimation of the global amount of submarine gas hydrates formed via microbial methane formation based on numerical reaction-transport modeling and a novel parameterization of Holocene sedimentation

“…Permeability is often correlated to porosity and may further be affected by hydrate content. Garg et al (2008) reported that the size of sediment pores may affect the process of gas hydrate formation. The lithology of the potential hydrate-bearing zone (i.e.…”

“…On a regional scale, numerical modeling is complementing a wealth of observational studies and progressively helps to understand hydrate formation and dissolution processes in important gas hydrate provinces, i.e. Hydrate Ridge, offshore Oregon (Luff and Wallmann, 2003;Torres et al, 2004;Liu and Flemings, 2006;Garg et al, 2008). Global predictions rely on numerical modeling (Buffett and Archer, 2004;Klauda and Sandler, 2005;Archer et al, 2008) and region-by-region extrapolation (i.e.…”

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

“…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.…”

Scaling of transport coefficients of porous media under compaction

“…Notice, here we argue for the importance of the scaling laws for compaction and assess the physical accuracy of models adopted in [6][7][8][9] in this context only. This is the reason, why we readdress the pure Fickian diffusion of aqueous methane and do not consider non-Fickian effects, thermodiffusion and gravitational stratification of the solute, ignored in the existing models of the formation of hydrate deposits, although the importance of non-Fickian effects was shown in [26,27].…”