Gas Hydrates Resource Assessment
BOEM 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. Ultimately, the final results of the current multi-year effort will provide estimates of the undiscovered in-place, technically recoverable, and economically recoverable gas hydrate resources for each OCS region (Gulf of Mexico, Atlantic, Pacific and Alaska). As of February 2008, only the preliminary in-place results for the Gulf of Mexico have been generated:
MMS Report 2008-004: Preliminary Evaluation of In-Place Gas Hydrate Resources: Gulf of Mexico Outer Continental Shelf
Background
Since relatively 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 BOEM 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 BOEM, 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:
- Charge
- Container
- Concentration
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. The model is currently set to run 1,000 trials per cell.
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 BOEM-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, including preliminary in-place results, is now available.
Future Work
BOEM is currently working to adapt the preliminary in-place model for use on the Atlantic and Pacific OCS; work on the Alaska OCS will follow. Future assessment results will be updated on this page. As more data becomes available, a technically recoverable and economically recoverable hydrate volume will be generated for all four regions of the OCS.