Gas Hydrates as an Energy Resource, Environmental Hazard, and a Factor in Global Climate Change 2

Gas Hydrates as an Energy Resource, Environmental Hazard, and a Factor in Global Climate Change 2

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Credit:
A.M. Tréhu, G. Bohrmann, F.R. Rack, T.S. Collett, D.S. Goldberg, P.E. Long, A.V. Milkov, M. Riedel, P. Schultheiss, and others/IRIS Consortium

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Gas Hydrates as an Energy Resource, Environmental Hazard, and a Factor in Global Climate Change 1

Description

Seismic reflection cross section of the shallow sea floor collected on the continental slope off of Oregon showing a strong bottom-simulating reflector (BSR) marking the base of the gas hydrate layer and the top of free gas in the sediment pore space. The image also shows a carbonate pinnacle chemically deposited by a fluid seep and a subsurface fault that acts as a conduit for upwards gas migration from deeper sources. Photo shows gas hydrate ice. (Images modified from A.M. Tréhu, G. Bohrmann, F.R. Rack, T.S. Collett, D.S. Goldberg, P.E. Long, A.V. Milkov, M. Riedel, P. Schultheiss, and others, 2004. Three-dimensional distribution of gas hydrate beneath southern Hydrate Ridge: Constraints from ODP Leg 204, Earth and Planetary Science Letters, 222(3–4):845–862, doi:10.1016/j.epsl.2004.03.035.)

At the low temperature and high pressure conditions common in shallow marine sediments and beneath the Arctic permafrost, gas hydrate (an ice-like substance in which molecules of hydrocarbon gases are trapped within cages of water molecules) forms when the gas concentration exceeds saturation. Although estimates of the total mass of methane carbon that resides in this reservoir vary widely, there is general agreement that gas hydrates are common in the sediments on continental margins and must be considered when evaluating the global near-surface carbon budget. In fact, gas hydrates may act as a “carbon capacitor,” trapping and storing methane and thus removing it temporarily from the carbon cycle only to release it suddenly as the environmental parameters that control gas hydrate stability change. Research suggests that such abrupt and massive releases of methane from gas hydrates have occurred in the geologic past. A better understanding of how much gas hydrate is present and how it is distributed in seafloor sediments is needed in order to include this effect in global climate models. International research efforts also are underway to evaluate the potential of gas hydrate as a future hydrocarbon source and as an environmental hazard.

Because gas hydrates are not stable at Earth’s surface unless the temperature is below ~ -60oC, remote-sensing techniques are essential for understanding the distribution and dynamics of gas hydrates. The base of the gas hydrate stability zone is often marked by a characteristic seismic reflection, providing an effective tool for large-scale mapping of gas hydrate distribution. High-resolution 3D seismic reflection data image the plumbing system that feeds gas hydrate deposits and are used to guide sampling and longterm monitoring efforts. Waveform modeling can be used to identify local concentrations of gas hydrate. Temporal changes in gas hydrates caused by naturally episodic fluid flow, climate change, or extraction as an energy resource can be monitored through repeated (4D) seismic reflection imaging.

Date Taken: February 18, 2009
Photographer / Contributor: A.M. Tréhu, G. Bohrmann, F.R. Rack, T.S. Collett, D.S. Goldberg, P.E. Long, A.V. Milkov, M. Riedel, P. Schultheiss, and others, 2004.

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Seismological_Grand_Challenges, Long_Range_Science_Plan,

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