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Gas
Hydrate Resource Evaluation Resource Potential of Gas Hydrates
Introduction
The MMS, in conjunction with the United States Geological Survey (USGS) industry, and numerous universities, has invested significant resources to date in an effort to better understand methane hydrates. With the demand for natural gas expected to increase significantly over the next 10 to 20 years, methane gas hydrates, which are likely present on the OCS in significant quantities, may be a potential source to meet both industrial and domestic needs for natural gas. Resource Assessment The MMS is in the process of completing the
first comprehensive assessment of gas hydrate on the OCS since a
1995 assessment published by USGS. The results of the 1995 USGS
assessment are
available online
Background Since very little is known about the capability and reliability of conventional direct-detection technologies as they apply to marine hydrate accumulations, the presence of gas hydrate must be inferred through geologic modeling. Development of the MMS assessment methodology, probabilistic model structure, and underlying framework of input data has been underway for the past several years. The physical model and methodology are updated frequently, and at any time the current model represents our latest understanding of the various physical conditions that affect the volume and distribution of gas hydrate accumulations. Model Summary The modeling methodology and the physical model developed for the OCS gas hydrate assessment are the product of a collaborative body of experts from the MMS, USGS, private industry, academia, and various research institutions. Due to the inherent uncertainties associated with an assessment of undiscovered resources, a stochastic model was developed to sample from distributions of selected input parameters and to provide the results as a probabilistic range. The physical model code is combined in FORTRAN and contains three primary modules:
Each of the primary modules contains a number of
calculations and sub-models where parameters have been derived
from published literature, analogs, and in some cases, expert
judgment. The run order of model version 3.38 is described
in the Flow Diagram
Regional Input Data Input data for each of the four OCS margins will vary according to the amount of local empirical data available. For the Gulf of Mexico, the four primary input grids included bathymetry, top of salt depth, distribution of sandy sediment in the shallow section and location of surficial seismic anomalies. These inputs were generated from seismic data from the GOM that covered 200,000 square miles. The GOM was divided into 202,000 cells of equal size (5,000 ft x 5,000 ft.) and a value generated from each input grid (i.e. water depth, salt depth, and percent) was assigned to every cell. Results The results at this time comprise an analysis of the in-place gas hydrate resources in the Gulf of Mexico (GOM). The estimates presented here only represent in-place resources, and do not include either technically recoverable or economically recoverable resources. The mean in-place estimate for the GOM is 21,444 trillion cubic feet, which includes gas hydrate resources in a variety of sediment hosts and trap types. The fraction of this in-place estimate that can be technically extracted and brought to market will be identified in the next phase of the project. The GOM was chosen as the initial study area due to the relative abundance of empirical data and MMS-controlled proprietary data, both of which are attributable to the mature status of the GOM as a conventional oil and gas province. The model will be modified as necessary to accommodate the parameters unique to the remaining three OCS margins (Atlantic, Pacific, and Alaska). The
complete methodology report
Model Downloads Everything needed to run the model is available for download, including.
An instruction manual is provided in Appendix G of the methodology report. Users are encouraged to develop an input dataset for their area of interest, following the format of the example provided. Each of the model parameters, currently set to reflect physical conditions in the U.S. Gulf of Mexico, should be evaluated for applicability to other study areas. The download files are available to provide interested parities an opportunity to examine the assessment model. The model is current as of February 15, 2008. As work to improve the model and the various physical assumptions continues, the MMS cannot guarantee that the posted model will remain the most current model. The MMS will not provide technical support for the download, modification, or operation of the hydrate assessment model. Future Work The MMS is currently working to modify the preliminary in-place model to incorporate a number of changes, including the addition of a thermogenic gas component and implementation of a technically recoverable module. The modified model will be run on the Atlantic, Alaska, and Pacific region input data as well as on the GOM data. As more data becomes available, an economically recoverable hydrate volume will be generated for all four regions of the OCS. Additional information on the status of MMS gas hydrate research, links of interest, and maps and graphics are available. Privacy | Disclaimers | Accessibility | Topic Index | FOIA Last Updated: 09/04/2008, 07:57 AM
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Gas hydrates are
ice-like crystalline substances occurring in nature where a solid
water lattice accommodates gas molecules (primarily methane, the
major component of natural gas) in a cage-like structure, also
known as clathrate. These form under conditions of relatively high
pressure and low temperatures, such as those found in the shallow
subsurface under many of the world's oceans. One cubic foot of
hydrate at reservoir temperature and pressure yields approximately
160 cubic feet of gas at atmospheric temperature and pressure. The
amount of natural gas in methane hydrate worldwide is estimated to
be far greater than the entire world's conventional natural gas
resources.