DE-FE0010144

Goal
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.

Performer
The Regents of the University of California - San Diego, Scripps Institute of Oceanography, La Jolla, CA 92093

Collaborators
United States Geological Survey (USGS), Wood Hole, MA 02543

Background
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.

Impact
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
New project awarded on October 1, 2012

Current Status (November 2012)
The researchers will design, build, and test a Controlled Source Electromagnetic system. The design will be based on existing equipment, which will be modified as needed to adapt it to small vessel operations in shallow water. Researchers will build a towed array of at least four electric field receivers with transmitter receiver offsets of up to 500 m, along with at least two receivers capable of being moored on the shallow sea floor. UCSD researchers will collaborate with USGS scientists to design the surveys using existing seismic data as a guide. The survey of Harrison Bay, Alaska is planned for the summer of 2014, with a survey of Camden Bay, Alaska to follow in the summer of 2015.

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

Contact Information:
NETL – Skip Pratt (skip.pratt@netl.doe.gov or 304-285-4396)
University of California – San Diego, Scripps Institute of Oceanography – Steve Constable (sconstable@ucsd.edu or (858-534-2409)
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