Print this pageA Stochastic Model for Assessing In-Place Methane Hydrate Resources
Pulak K. Ray1, John Grace2, Tim Collett3, William Shedd4, and Jesse Hunt4
1 Minerals Management Service, Herndon, VA
2 Earth Science Associates, Long Beach, CA
3 U.S. Geological Survey, Denver, CO
4 Minerals Management Service, U.S. Department of the Interior, New Orleans, LA
An assessment of the amount of methane sequestered in gas hydrates is challenging. Previously, in-place hydrate estimates for any area varied by orders of magnitude. A stochastic methodology for the estimation of gas hydrate volumes in marine environments has been developed at Minerals Management Service (MMS). All key inputs are represented by probability distributions and the resultant estimate of hydrate volumes in-place is also probabilistic.
There are four basic components to the overall hydrate assessment model: 1) Candidate Rock Volume (CRV) Module. Estimates the volume of rock within the hydrate stability zone (HSZ) below the sea floor where the physical and chemical conditions for the formation of hydrates are optimum. The thickness of HSZ is obtained by solving an equation that accounts for pressure, temperature and the impact of proximate salt. CRV is further adjusted for the presence of sulfate reducing bacteria. 2) Hydrocarbon Charge Module. Estimates the volume of available methane from biogenic and thermogenic sources for the formation of hydrates in the CRV. 3) Hydrate Concentration Module. Estimates the volume of methane per unit volume of hydrate saturated CRV, conditional on it being charged. 4) Hydrate Volume Module. Aggregates the distributions on candidate rock volume, charge and concentration to produce distributions of in-place methane hydrate volumes (at standard temperature and pressure).
The model is illustrated with a Gulf of Mexico example, although the same general approach has been modified for the application to the balance of the US Outer Continental Shelf.