Methane Hydrate Resource Assessment of the U.S. Outer Continental Shelf: Atlantic Margin Model Inputs and Outputs
The Minerals Management Service (MMS) is a U.S. Department of the Interior agency responsible for managing the oil, gas, and mineral resources of the U.S. Outer Continental Shelf (OCS). The MMS is in the process of performing the first comprehensive assessment of potential gas hydrate resources on the OCS since a 1995 assessment led by the United States Geological Survey. An analysis of in-place gas hydrate resources was completed by the MMS in early 2008 for the U.S. Gulf of Mexico, where the mean in-place volume was calculated to exceed 21,000 trillion cubic feet (600 trillion cubic meters). A similar effort is currently underway on the U.S. Atlantic margin.
The Atlantic OCS study area comprises over 500,000 km2 where pressure and temperature conditions provide a stable physical environment for the formation of gas hydrate. Basin-wide interpretations of shallow sand distribution, bathymetry, and sediment isopachs were developed using the MMS proprietary seismic database and provide a spatially-resolvable framework for cell-based modeling. Non-spatial data were derived from available subsurface sources and include distributions of total organic carbon, rock quality, mechanical properties, and gas hydrate saturation.
The Atlantic assessment model structure consists of approximately 24,000 cells that measure 20.90 km2 each. The stochastic FORTRAN-based model incorporates the uncertainty of many input variables through multiple Monte Carlo trial runs, producing a distribution of results where the mean is the expected value. The model methodology is based on mass balance, where inputs include an initial endowment of total organic carbon, a volume of candidate reservoir rock, and a fraction of the rock volume that allows for hydrate concentration.
Input and output data for the Atlantic are spatially referenced and allow for gas hydrate resources to be distributed with reference to underlying geologic features. The largest hydrate concentrations are expected in the Mid- and North Atlantic planning areas, where water depths often exceed 2,000 m, a thick stratigraphic section is available for conversion to biogenic methane, and recent clastic sediment input provides an opportunity for high gas hydrate saturations in sandy reservoirs.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009