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Critically pressured free-gas reservoirs below gas-hydrate provinces

Nature volume 427, pages 142–144 (2004)Cite this article

Abstract

Palaeoceanographic data have been used to suggest that methane hydrates play a significant role in global climate change. The mechanism by which methane is released during periods of global warming is, however, poorly understood1. In particular, the size and role of the free-gas zone below gas-hydrate provinces remain relatively unconstrained, largely because the base of the free-gas zone is not a phase boundary and has thus defied systematic description. Here we evaluate the possibility that the maximum thickness of an interconnected free-gas zone is mechanically regulated by valving caused by fault slip in overlying sediments2. Our results suggest that a critical gas column exists below most hydrate provinces in basin settings, implying that these provinces are poised for mechanical failure and are therefore highly sensitive to changes in ambient conditions3. We estimate that the global free-gas reservoir may contain from one-sixth to two-thirds of the total methane trapped in hydrate4. If gas accumulations are critically thick along passive continental slopes, we calculate that a 5 °C temperature increase at the sea floor could result in a release of ∼2,000 Gt of methane from the free-gas zone, offering a mechanism for rapid methane release during global warming events.

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Figure 1: Cross-section cartoon of a normal fault in a basin.
Figure 2: Gas column thickness required for fault reactivation (grey) at the Blake ridge.
Figure 3: Depth from sea floor to BSR (m) versus gas column thickness.

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Acknowledgements

We thank J. Dickens, P. Flemings and A. Milkov for discussions. This work was funded jointly by the US National Science Foundation and the US Department of Energy.

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  1. Department of Geology and Geophysics, University of Wyoming, Laramie, Wyoming, 82071, USA

    Matthew J. Hornbach, Demian M. Saffer & W. Steven Holbrook

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  3. W. Steven Holbrook
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Correspondence to Matthew J. Hornbach.

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Hornbach, M., Saffer, D. & Steven Holbrook, W. Critically pressured free-gas reservoirs below gas-hydrate provinces. Nature 427, 142–144 (2004). https://doi.org/10.1038/nature02172

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