Both biogenic and thermogenic gases form seafloor gas hydrates. Prolific microbial activity and bacterial mats near gas hydrate mounds show at least an incidental association of the gas hydrates and microbes. Laboratory data indicates more than an incidental association: a synergistic relationship exists between microbes, sediments, and gas hydrates. Commercially available biosurfactants showed significant catalytic effects on hydrate induction times and formation rates. Since gas hydrate formation is an interfacial phenomenon, interactions of anionic biosurfactants and specific porous media surfaces influence hydrate location and form. Bacillus subtilis microbe identified around Gulf of Mexico hydrates was cultured, surfactant extracted, and effects on laboratory gas hydrates demonstrated interactions.
Although extensive laboratory work has been reported on the mechanisms, equilibrium conditions, and kinetics of gas hydrates in liquid water-hydrate-hydrocarbon gas systems, not much progress has been made on defining these phenomena in porous media. Hydrate Formation Mechanisms without Porous Media It is generally accepted that hydrate crystals are initiated in chilled, pressurized, hydrocarbon gas-water systems without porous media by the growth of crystal nuclei until a critical cluster size is reached (Vysniauskas and Bishnoi, 1983). After reaching the critical size, hydrate crystals visibly grow by agglomeration. The nucleation and growth of crystals occur at the gas-water interface where relatively insoluble hydrocarbon gas concentrations in the water are the highest (Sloan, 1998). Typically, when this occurs in a quiescent system, a hydrate film quickly forms across the water surface to impede subsequent hydrate formation (Mori and Mochizuki, 1996; Herri, Gruy and Cournil, 1966). Bishnoi and coworkers (Vysniauskas and Bishnoi, 1983; Vysniauskas and Bishnoi, 1985) developed Equation (1) for hydrate formation rate in a stirred system. The equation applies to vigorous stirring of about 500 rpm where mass-transfer no longer controls or is a significant factor in the rate of gas hydrate formation.