Gas Hydrates

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 deep-water oceans. The amount of natural gas in methane hydrate worldwide is estimated to be far greater than the entire world's conventional natural gas resources. BOEM, in conjunction with our U.S. government partners, industry, and numerous universities, has an ongoing effort to better understand the distribution of methane hydrates on the OCS.

Resources and Publications

The BOEM gas hydrate assessment model was initially developed for the GOM OCS over a period of approximately five years (2003 – 2008). A preliminary assessment of the in-place gas hydrate resources was published in OCS Report MMS 2008-004. This report also included a complete description of the input parameters, methodologies, and modeling approach. The original GOM OCS model structure was modified slightly for the assessment of gas hydrate on the Atlantic and Pacific OCS; the results for all three of these OCS regions are summarized in the “Assessment of In-Place Gas Hydrate Resources of the Lower 48 United States Outer Continental Shelf (BOEM Fact Sheet RED-2012-01).

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Assessment of In-Place Gas Hydrate Resources of the Lower 48 United States
Inplace Gulf of Mexico OCS Hydrates - Report MMS 2008-004-1
MMS Report 2008-004
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BOEM Presentation at the 2012 ESRI Conference
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ICGH 2011
Gulf of Mexico Gas Hydrate Joint Industry Project Leg II_ Walker Ridge 313 Site Summary-1
Gas Hydrate Joint Industry Project Leg II:
Multicomponent and Mutifrequency Seismic for Assessment of Fluid-Gas Expulsion Geology and Gas-Hydrate Deposits_ Gulf of Mexico Hydrates-1
OCS Study BOEMRE Report 2010-046
 

Gas Hydrate Resource Potential in the Terrebonne Basin, Northern Gulf of Mexico, 2011, by Frye, M., Shedd, W., and Boswell, R., Marine and Petroleum Geology, Volume 34 Issue 1, June 2012, pages 150-168.

Abstract - The Terrebonne Basin is a salt-withdrawal mini-basin within the northeast portion of the Walker Ridge protraction area in northern Gulf of Mexico continental slope that contains a thick sequence of upper Pliocene and Pleistocene clastic sediment. Data acquired during the 2009 Gulf of Mexico Gas Hydrate Joint Industry Project Leg II (JIP Leg II) logging-while-drilling (LWD) program confirmed the presence of gas hydrate within a variety of sand and clay units. Integration of the Leg II LWD data with regional seismic mapping allows for the identification of various facies assemblages within the sand units and an initial estimation of the gas hydrate in-place resources throughout the Terrebonne basin. A total of ~4.4 × 109 m3 (1.55 × 1011 ft3) of gas occurs within highly saturated gas hydrate accumulations within channel, proximal levee, and distal levee facies of four primary Lower Pleistocene sand reservoirs. These sand accumulations occur at the base of gas hydrate stability and locally trap additional, unquantified accumulations of free gas. A number of additional thin hydrate-bearing sand units are also observed to occur at shallower depths. Potential recoverable volumes from this accumulation compare favorably with those realized from conventional deep-water gas reservoirs in the vicinity. In addition, Leg II LWD data delineated the occurrence of a stratal-bound occurrence of gas hydrate-filled fractures at low bulk volume saturations within a thick, shallow, and predominantly fine-grained unit. This unit is estimated to contain roughly 17.0 × 109 m3 (5.87 × 1011 ft3) of gas. The areal gas hydrate resource density within the Terrebonne basin is calculated at 1.183 × 109 m3 per km2 where delineated sand reservoirs are present and 0.32 × 109 m3 per km2 where sands are thought to be absent.

Occurrence and Nature of “Bottom Simulating Reflectors” in the Northern Gulf of Mexico, 2011, by Shedd, W., Boswell, R., Frye, M., Godfriaux, p, and Kramer, K., Marine and Petroleum Geology, Volume 34 Issue 1, June 2012, pages 4-30.

Abstract - Subsurface interpretation, utilizing a database of more than 450,000 km2 (175,000 mi2) of three-dimensional (3-D) seismic in the northern Gulf of Mexico (GoM), reveals 145 discrete areas, totaling 4450 km2 (1.1 million acres) where the base of gas hydrate stability (BGHS) can be confidently inferred from seismic data. Unlike many other areas of the world, the majority of these features are not Bottom Simulating Reflectors (BSRs) in the “classic” sense, meaning continuous coherent events that cross-cut primary stratigraphy. Those typical, or continuous BSRs, are noted in only 24% of the features identified within this study. In contrast, the most common seismic manifestation of the BGHS in the GoM (59%) is the discontinuous “BSR”, delineated by widely separated anomalous seismic events that align in general conformance with seafloor bathymetry. A third type of seismic feature, pluming “BSRs”, are continuous events that are not bottom-simulating, but are bowed toward the seafloor and represent areas where large, but areally-limited increases in heat flow (linked to strong vertical fluid flux), perturb the BGHS. The limited nature of continuous BSRs and the relative abundance of discontinuous and pluming forms are attributed to the strong lithologic and structural heterogeneity of the northern GoM basin. This lithologic and structural complexity has served to disrupt and localize regionally pervasive and homogeneous gas flux that is consistent with the formation of large, continuous BSRs noted across other less complex continental margins. The various BSR forms identified in this study are shown to be closely associated (125 of 145) with the occurrence of seafloor amplitude anomalies, which are in turn usually associated with the flanks and crests of salt-cored ridges. These associations are nterpreted to reflect the co-dependence of BSRs and seafloor reflectivity along the migration pathways that typify this geologic setting.

The BOEM gas hydrate resource assessment model for the Pacific OCS is similar to the cell-based, mass balance approach that was initially developed for the 2008 Gulf of Mexico assessment, though a number of fundamental changes were required to reflect the Pacific OCS geologic influence on the gas hydrate petroleum system. The Pacific model employs a depofacies model for prediction of the host lithologic unit, rather than a cell-based deterministic estimate.  The Pacific model introduces limitations based on the age of the underlying crust and the thickness of the sedimentary cover, both of which are partially attributable to the active seafloor spreading that is not present on the Atlantic or GOM OCS.  The Pacific model introduces input variables with a combined spatial/empirical component. The BOEM model predicts the highest density accumulations of gas hydrate in-place will reside in the near-shore basins along the Pacific coast, while opportunities for moderate accumulations are present in sand-rich submarine fan deposits.

Pacific OCS model results are summarized below in BOEM Fact Sheet RED-2012-01.

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Assessment of In-Place Gas Hydrate Resources of the Lower 48 United States

BOEM Fact Sheet RED-2012-01: Assessment of In-Place Gas Hydrate Resources of the Lower 48 United States Outer Continental Shelf

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BOEM Presentation at the 2012 ESRI Conference

Gas Hydrate Resource Assessment of the United States Outer Continental Shelf - BOEM Presentation at the 2012 ESRI Conference in San Diego, California

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ICGH 2011

Gas Hydrate Resource Assessment of the United States Outer Continental Shelf: A Mass Balance Model, 2011, by Frye, M., Schuenemeyer, J., Shedd, W., Piper, K., and Herman, B., Proceedings of the 7th International Conference on Gas Hydrates (ICGH 2011), Edinburgh, Scotland, United Kingdom, July 17-21, 2011

BOEM is currently working to adapt the in-place model for use on the deep-water areas of the Alaska OCS. Future assessment results will be updated as they are published.

BOEM gas hydrate resource assessment model for the Atlantic OCS is similar to the cell-based, mass balance approach that was initially developed for the 2008 Gulf of Mexico assessment. The two most significant changes in modeling approach include the introduction of a Bottom Simulating Reflector (BSR) as a spatial input and the removal of the lateral, or dip-driven, component of the gas migration model. The BOEM model predicts the highest density accumulations of gas hydrate in-place will reside in the central and northern Atlantic OCS, due in large part to the greater likelihood of sandstone reservoirs in the subsurface.

Atlantic OCS model results are summarized below in BOEM Fact Sheet RED-2012-01, and complete reporting on the detail of the Atlantic OCS model is available below in BOEM Report RED 2013-01.

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Gas Hydrate Resource Assessment Atlantic outer Continental Shelf BOEM Report RED 2013-01

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BOEM Fact Sheet RED-2012-01: Assessment of In-Place Gas Hydrate Resources of the Lower 48 United States Outer Continental Shelf

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Gas Hydrate Potential of the Mid Atlantic Outer Continental Shelf, William W. Shedd (MMS, New Orleans, LA) and Deborah R. Hutchinson (USGS, Woods Hole, MA), Published by US Dept of Energy, Fire in the Ice Methane Hydrate Newsletter, Vol. 6 Issue 3, Page 8

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Gas Hydrate Resource Assessment of the United States Outer Continental Shelf: A Mass Balance Model, 2011, by Frye, M., Schuenemeyer, J., Shedd, W., Piper, K., and Herman, B., Proceedings of the 7th International Conference on Gas Hydrates (ICGH 2011), Edinburgh, Scotland, United Kingdom, July 17-21, 2011