Effect of Overpressure on Gas Hydrate Distribution
نویسندگان
چکیده
The effect of overpressure on gas hydrate and free gas distribution in marine sediments is studied using a one-dimensional numerical model that couples sedimentation, fluid flow, and gas hydrate formation. Natural gas hydrate systems are often characterized by high sedimentation rates and/or low permeability sediments, which can lead to pore pressure higher than hydrostatic (overpressure). To quantify the relative importance of these two factors, we define a dimensionless sedimentation-compaction group, sc N , that compares the absolute permeability of the sediments to the sedimentation rate. Higher values of sc N mean higher permeability or low sedimentation rate which generally yield hydrostatic pore pressure. Conversely, lower values of sc N generally create pore pressure greater than hydrostatic. Simulation results show that decreasing sc N not only increases pore pressure above hydrostatic values, but also lowers the lithostatic stress gradient and gas hydrate saturation. This occurs because overpressure results in lower effective stress, causing higher porosity and lower bulk density of the sediment. This leads to higher sediment velocity through the gas hydrate stability zone, thereby reducing the mass accumulation of methane and gas hydrate in the pore space. Effect of overpressure on depth of the gas hydrate stability zone is also studied.
منابع مشابه
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