SUGAR – Submarine Gas Hydrate Deposits

Begin of project: July 1, 2008

End of project: April 1, 2011

Status of project: December 1, 2009

Subproject A2.2. Controlled Source Electromagnetic (CSEM) for Gas Hydrate Evaluation and Quantification

Coordination: Dr. Katrin Schwalenberg (BGR, Hannover)
Co-Workers: Dr. Martin Engels (BGR, Hannover), Joachim Deppe (BGR, Hannover)

SUGAR (Submarine Gas Hydrate Reservoirs) is a joint research project funded by two German ministries (BMWi, BMBF) and German industry with about 30 partners. The overall goal is to develop technologies and knowhow to produce natural gas from marine methane hydrates and to securely store carbon dioxide as CO₂ hydrate within the hydrate stability zone. This also includes the identification and assessment of suitable gas hydrate reservoirs with geophysical equipment.

The aim of SUGAR subproject A2.2 is the assessment of submarine gas hydrate deposits with active marine electromagnetic methods. The assessment of suitable gas hydrate occurrences as a potential energy reservoir and as a deposit for the secure CO₂ sequestration demands area-wide studies of the entire gas hydrate stability zone (GHSZ). Open questions of particular importance are: How are gas hydrates distributed through the sediment section and what are the local concentrations? CSEM is a qualified method to sense the complete depth range of the GHSZ. The electrical conductivity or resistivity derived from CSEM data is a clear indicator where gas hydrates have formed in sufficient quantities. Gas hydrates are electrical insulating and replace the conductive pore fluid or parts of the sediment matrix. As a consequence the bulk resistivity of the gas hydrate formation will be enhanced. This has been observed using a bottom-towed electrical dipole-dipole system (Edwards, 1997, Yuan and Edwards, 2000) off the coast lines of Canada and New Zealand (Schwalenberg et al., 2005, 2009a, b).

Methods
BGR Hannover is building a new bottom-towed CSEM system – HYDRA - that is in particular sensitive to the first few hundred meters below the seafloor. The system consists of multiple, cable-linked, electrical receiving dipoles at fixed offsets behind a transmitter dipole (see Figure). The instrument is connected to the coaxial tow cable and dragged on the seafloor along profiles behind the ship. The coax cable also transmits the source signal from the shipboard current transmitter to the transmitter dipole on the seafloor. The “pig” is a heavy plough that keeps the array on the seafloor and contains the control unit and other devices. To perform a local 3D study of a gas hydrate target IFM-Geomar’s marine magnetotelluric (MT) receivers are modified to be used as broadband receiver stations for active source measurements.

Sketch of HYDRA - the bottom-towed, electrical, multi-receiver-system developed at BGR, and IFM-Geomar’s broadband, electromagnetic seafloor receiver nodes Source: BGR

Project Website: http://www.sugar-projekt.de

Literature:

• Edwards, R.N: On the resource evaluation of marine gas hydrate deposits using a seafloor transient electric dipole-dipole method”, Geophysics, 62, 63-74, 1997.
• Schwalenberg, K., Willoughby, E., Mir, R., and Edwards, N., 2005, Marine gas hydrate electromagnetic signatures in Cascadia and their correlation with seismic blank zones. First Break, 23
• Schwalenberg, K., Haeckel, M., Poort, J., Jegen, M., 2009. Evaluation of gas hydrate deposits in an active seep area using marine controlled source electromagnetics: Results from Opouawe Bank, Hikurangi Margin, New Zealand. Marine Geology, doi:10.1016/j.margeo/2009.07.006.
• Schwalenberg, K.,Wood,W.T., Pecher, I.A., Hamdan, L.J., Henrys, S.A., Jegen, M.D., Coffin,R.B. Preliminary interpretation of electromagnetic, heat flow, seismic, and geochemical data for gas hydrate distribution across the Porangahau Ridge, New Zealand. Marine Geology, in print.
• Yuan, J. and Edwards, R.N.: The assessment of marine hydrates through electrical remote sounding: Hydrate without a BSR? Geophysical Research Letters, 27, 16, 2397-2400, 2000.

Partner:

Project Partner: Dr. Marion Jegen (IFM-Geomar, Kiel)

Promotion / document number:

Sponsored by BMBF Grant No. 03G0688A