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Published December 15, 2020 | Supplemental Material + Published
Journal Article Open

Crustal fingering facilitates free-gas methane migration through the hydrate stability zone


Widespread seafloor methane venting has been reported in many regions of the world oceans in the past decade. Identifying and quantifying where and how much methane is being released into the ocean remains a major challenge and a critical gap in assessing the global carbon budget and predicting future climate [C. Ruppel, J. D. Kessler. Rev. Geophys. 55, 126–168 (2017)]. Methane hydrate (CH₄⋅5.75H₂O) is an ice-like solid that forms from methane–water mixture under elevated-pressure and low-temperature conditions typical of the deep marine settings (>600-m depth), often referred to as the hydrate stability zone (HSZ). Wide-ranging field evidence indicates that methane seepage often coexists with hydrate-bearing sediments within the HSZ, suggesting that hydrate formation may play an important role during the gas-migration process. At a depth that is too shallow for hydrate formation, existing theories suggest that gas migration occurs via capillary invasion and/or initiation and propagation of fractures (Fig. 1). Within the HSZ, however, a theoretical mechanism that addresses the way in which hydrate formation participates in the gas-percolation process is missing. Here, we study, experimentally and computationally, the mechanics of gas percolation under hydrate-forming conditions. We uncover a phenomenon—crustal fingering—and demonstrate how it may control methane-gas migration in ocean sediments within the HSZ.

Additional Information

© 2020 National Academy of Sciences. Published under the PNAS license. Edited by David A. Weitz, Harvard University, Cambridge, MA, and approved November 3, 2020 (received for review May 30, 2020). PNAS first published November 30, 2020. We thank Carolyn Ruppel and William Waite from the US Geological Survey; Peter Flemings, Kehua You, and Dylan Meyer from the University of Texas at Austin; Gareth Crutchley from GEOMAR Helmholtz Centre for Ocean Research Kiel for insightful discussions; and David Santillán (Technical University of Madrid) and Ehsan Haghigat (MIT) for help with the code development. This work was supported in part by the US Department of Energy Grants DE-SC0018357 and DE-FE0013999. X.F. was supported by the Miller Fellowship. J.J.-M. was supported by Swiss Federal Institute of Aquatic Science and Technology and Guest Scientist status from Los Alamos National Laboratory. J.J.-M., J.W.C., T.P.N., and H.V. were supported by US Department of Energy Basic Energy Science Program Grant LANLE3W1. L.C.-F. was supported by Spanish Ministry of Economy and Competitiveness Grants RYC-2012-11704 and CTM2014-54312-P. L.C.-F. and R.J. were supported by MIT International Science and Technology Initiatives, through a Seed Fund grant. Data Availability: All study data are included in the article and SI Appendix. X.F. and J.J.-M. contributed equally to this work. Author contributions: X.F., J.J.-M., T.P.N., J.W.C., L.C.-F., and R.J. designed research; X.F., J.J.-M., T.P.N., J.W.C., and H.V. performed research; X.F. and J.J.-M. analyzed data; and X.F., J.J.-M., J.W.C., L.C.-F., and R.J. wrote the paper. The authors declare no competing interest. This article is a PNAS Direct Submission. This article contains supporting information online at https://www.pnas.org/lookup/suppl/doi:10.1073/pnas.2011064117/-/DCSupplemental.

Attached Files

Published - 31660.full.pdf

Supplemental Material - pnas.2011064117.sapp.pdf

Supplemental Material - pnas.2011064117.sm01.m4v

Supplemental Material - pnas.2011064117.sm02.m4v

Supplemental Material - pnas.2011064117.sm03.m4v

Supplemental Material - pnas.2011064117.sm04.m4v


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