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

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.