Model Simulation for Generation and Migration of Methane Hydrate

Abstract

A one-dimensional numerical simulation model has been developed to forecast the distribution of methane hydrate in the subsurface. The model includes the generation and migration of methane, and the process of methane-hydrate formation after sedimentation. The following processes are consideredfor each cell within the model; 1) Calculation of methane generated within the sediment 2) Process of migration of dissolved methane with compacting water 3) Process of migration of gaseous methane as a separate phase, by buoyancy 4) Evaluation of sealing capacity from the hydrostatic equilibrium equation 5) Calculation of the amount of methane hydrate formation from in-situ temperature and pressure The model will predict the distribution of methane hydrate after applying the above processes for all the sediments. We use this model to simulate the process of methane hydrate formation at ODP Leg 164 Site 997 at Blake Ridge, offshore Atlantic coast of the USA. At this location, the methane hydrate zone indicated by the bottom simulating reflector (BSR) is about 100 m shallower than the base of gas (methane) hydrate stability zone (BGHS) which is calculated from the model using measured temperatures and pressures. To explain this difference, the following hypotheses are proposed; 1) The BSR is a remnant of the past the BGHS that was created when temperature was higher or sea level was lower. 2) Methane hydrate is being generated between the BSR and the BGHS at present. The model simulation indicates that analysis, based not only on present physical conditions but also on the geohistrical time scale, is necessary to explain the present day distribution of methane hydrate.