|Mapping Permafrost and Gas Hydrate using Marine Controlled Source Electromagnetic Methods (CSEM)
||Last Reviewed 12/11/2014
The objective of this project is to develop and test a towed electromagnetic source and receiver system suitable for deployment from small coastal vessels to map near-surface electrical structure in shallow water. The system will be used to collect permafrost data in the shallow water of the U.S. Beaufort Inner Shelf at locations coincident with seismic lines collected by the U.S. Geological Survey (USGS). The electromagnetic data will be used to identify the geometry, extent, and physical properties of permafrost and any associated gas hydrate in order to provide a baseline for future studies of the effects of any climate-driven dissociation of permafrost and hydrate. Results will be used to expand the geological and geographical applications of marine electromagnetic methods, and provide a geophysical tool to complement the seismic methods currently being used.
The Regents of the University of California - San Diego, Scripps Institute of Oceanography, La Jolla, CA 92093
United States Geological Survey (USGS), Wood Hole, MA 02543
Permafrost underlies an estimated 20 percent of the land area in the northern hemisphere and often contains associated methane hydrate. Numerous studies have indicated that permafrost and hydrate are actively thawing in many high latitude and high elevation areas in response to warming climate and rising sea levels. Such thawing has clear consequences for the integrity of energy infrastructure in the Arctic, can lead to profound changes in arctic hydrology and ecology, and can increase methane emissions through the dissociation of methane hydrates or by microbial processes accessing organic carbon that has been trapped in permafrost. There has, however, been significant debate over the offshore extent of subsea permafrost.
Our knowledge of subseafloor geology relies largely on seismic data and cores/well logs obtained from vertical boreholes. Borehole data are immensely valuable (both in terms of dollar cost and scientific worth), but provide information only about discrete locations in close to one (vertical) dimension. Seismic data are inherently biased toward impedance contrasts, rather than bulk sediment properties. In the context of mapping offshore permafrost and shallow hydrate, seismic methods can identify the top of frozen sediment through the identification of high amplitude reflections and high velocity refractors. However, simple 2-D seismic surveys do little to elucidate the bulk properties—particularly the thickness—of the frozen layers. However, permafrost and gas hydrate are both electrically resistive, making electromagnetic (EM) methods a complementary geophysical approach to seismic methods for studying these geologic features. Deep ocean EM methods for mapping gas hydrate have been developed by both academia and industry, but the deep ocean techniques and equipment are not directly applicable to the shallow-water, near-shore permafrost environment. The project addresses this problem by designing, building, and testing an EM system designed for use in very shallow water, and using it to not only provide insight into the extent of offshore permafrost, but also collect baseline data that will prove invaluable for future studies of permafrost degradation.
The project will exploit the close association of hydrate and permafrost at high latitudes and, in particular, their common response to changing climate. By using a second geophysical method to supplement seismic data, researchers will be able to better map the current extent of permafrost and thus better understand the impact of past sea level rise on the hydrate stability field, as well as provide a critical baseline for studies targeting the effects of current climate change.
Accomplishments (most recent listed first)
- The research team collected 100 line km of CSEM data offshore Prudhoe Bay in July 2014
- Researchers tested the new EM transmitter and receiver system in San Diego Bay.
- Researchers constructed and tested the electromagnetic transmitter.
- Researchers finalized the design of the electromagnetic transmitter and receiver systems for use in shallow water. The new equipment will be used to carry out a pilot study to map the contemporary state of the permafrost on part of the U.S. Beaufort inner shelf.
Current Status (December 2014)
The Scripps research team conducted fieldwork offshore Prudhoe Bay from July 15 through 21. Although sea ice had not retreated past the expected boundary of marine permafrost, the team successfully collected more than 100 line km of CSEM resistivity data from the west edge of Prudhoe Bay to 50 km east of Prudhoe Bay. Initial processing of the data resulted in apparent resistivity pseudosections showing near seafloor resistivities consistent with water-saturated sediments, increasing at depth to resistivities consistent with permafrost. There is considerable lateral variation in apparent resistivity, indicative of structure in the permafrost. During the next quarter, the team will invert the towed receiver data and begin to incorporate data from the seafloor instruments.
Project Start: October 1, 2012
Project End: September 30, 2016
Project Cost Information:
Phase 1 - DOE Contribution: $121,473, Performer Contribution: $59,598
Phase 2 - DOE Contribution: $187,695, Performer Contribution: $39,598
Phase 3 - DOE Contribution: $197,852, Performer Contribution: $39,598
Phase 4 - DOE Contribution: $92,270, Performer Contribution: $42,058
Planned Total Funding - DOE Contribution: $599,290, Performer Contribution: $180,852
NETL – Skip Pratt (firstname.lastname@example.org or 304-285-4396)
University of California – San Diego, Scripps Institute of Oceanography – Steve Constable (email@example.com (858-534-2409)
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Quarterly Research Performance Progress Report [PDF- 15.3MB] July - September, 2014
Quarterly Research Performance Progress Report [PDF- 3.29MB] April - June, 2014
Quarterly Research Performance Progress Report [PDF- 346KB] January - March, 2014
Quarterly Research Performance Progress Report [PDF-897KB] October - December, 2013
Quarterly Research Performance Progress Report [PDF- 1.73MB] July - September, 2013
Quarterly Research Performance Progress Report [PDF- 472KB] April - June, 2013
Quarterly Research Performance Progress Report [PDF- 238KB] January - March, 2013
Quarterly Research Performance Progress Report [PDF- 238KB] October - December, 2012