Methane Hydrates: an Abundance of Frozen, Clean Energy from the Sea
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The Naval Research Laboratory has developed significant research capabilities related to the study of methane hydrates. Because methane hydrates represent a potential new source of clean energy, international programs to determine the location and concentration of the hydrates within marine sediments have started to accelerate.
Gas hydrates, ice-like mixtures of hydrocarbon gas (mostly methane) and water, are found within arctic permafrost and within ocean sediments located along the margins of most landmasses. Methane hydrates are generated when water and methane lie within a particular pressure-temperature regime. In recent years, scientists have begun to view methane hydrates as a new vast potential fuel reservoir.
The discovery of this reservoir is exciting because the estimated world resources are 300,000 trillion cubic feet of methane, more than 10 times the volume of methane in existing conventional gas reservoirs and twice the total energy contained in all fossil fuel reserves. Given concerns about climate change, the fact that combustion of methane produces significantly less carbon dioxide than does combustions of oil and coal suggests that methane hydrates could play an important role in long-term mitigation of one source of global climate change. There is evidence that methane hydrates may be related to some submarine landslides. While these landslides vary in scale, they can be large enough to damage seafloor cables and pipelines.
Hydrate dissociation and sediment failure occur naturally. If this natural resource is to be exploited, the hydrates must be forced from their stability field (i.e., artificially dissociate the methane hydrates), thus raising the issue of how to engineer systems that avoid environmental damage. There is a great need to understand how hydrates are generated and dissociated naturally so that we can develop systems and procedures that will allow us to safely exploit this research.
Hydrates research at NRL is integrated to take advantage of the wide breadth of capabilities available to the Laboratory. Using information gleaned from this research, NRL scientists hope to address issues such as:
- seafloor instabilities that can lead to slope failures that could adversely impact Navy systems;
- the impact of hydrates on undersea navigation and geoacoustic anomalies; and
- the potential for using methane hydrates in-situ to power Navy systems (such as bottom-mounted sensors) or even to fuel unmanned underwater vehicles.
To achieve these goals, NRL is using a number of unique systems:
Methane sensors. NRL scientists are determining the most important parameters for methane detection at depth; developing a model of the operating environment; and developing protocols for using natural samples/sediment samples to characterize their impact on membrane and sensing systems.
Deep Towed Acoustics/Geophysics System (DTAGS). This multichannel seismic system has proven to be ideal for resolving the depth range where hydrates are found to enable better estimation of the location and concentration of methane hydrates.
Hydrate content and structure. Fine-scale hydrate content and structure is studied in the laboratory and in situ using NMR spectroscopy and imaging. Initial results from this effort are demonstrating the utility of low-field NMR (the NMR logging tool) in quantitatively monitoring hydrate formation in porous media such as sandstone.
Biogenic and thermogenic methane. NRL scientist are combining analysis of methane hydrate content, methane sources, and hydrate structure to determine the parameters that control hydrate formation, composition and dissociation. Using NRL-developed instrumentation and methods, they have examined carbon isotope ratios over a broad array of carbon pools to interpret the biogenic and thermogenic contribution to hydrate content. This analysis is used to trace the cycling of the methane in the sediment and water column. This work addresses hydrate stability, ocean carbon cycling, and global warming.
The integration of these tasks adds immense value to NRL's contribution to the understanding of methane hydrates. To accomplish this, NRL has developed a scheme whereby geophysical, geologic, and bio-geochemical field measurements are collocated using bottom transponders. This allows investigators to relate, for example, sediment structure revealed with seismic data from DTAGS with chemical anomalies in the sediments and leakage of methane into the ocean. By relating the geologic context with detailed measurements of the physical and chemical properties of hydrates and associated sediments, much better models for the process that affect the creation and dissociation of hydrates can be developed. These models will, in turn, allow the Navy and industry to better predict the impact of hydrates on the marine environment.
NRL has established active collaborations with the U.S. Geological Survey, National Energy Technology Laboratory, the Monterey Bay Aquarium Research Institute, the Geological Survey of Canada, The University of Hawaii, Florida State University, Texas A&M University, Japan National Oil Corporation and the University of Bergen, Norway.
About the U.S. Naval Research Laboratory
The U.S. Naval Research Laboratory is the Navy's full-spectrum corporate laboratory, conducting a broadly based multidisciplinary program of scientific research and advanced technological development. The Laboratory, with a total complement of nearly 2,800 personnel, is located in southwest Washington, D.C., with other major sites at the Stennis Space Center, Miss., and Monterey, Calif. NRL has served the Navy and the nation for over 90 years and continues to meet the complex technological challenges of today's world. For more information, visit the NRL homepage or join the conversation on Twitter, Facebook, and YouTube.
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