HR: 0800h
AN: GP41B-0873 [Abstracts]
TI: Marine Controlled Source EM Methods: Equipment, Methodology, and Results
AU: * Constable, S
EM: sconstable@ucsd.edu
AF: Scripps Institution of Oceanography, MC 0225, La Jolla, CA 92093-0225
United States
AU: Behrens, J
EM: jbehrens@ucsd.edu
AF: Scripps Institution of Oceanography, MC 0225, La Jolla, CA 92093-0225
United States
AU: Key, K
EM: kkey@ucsd.edu
AF: Scripps Institution of Oceanography, MC 0225, La Jolla, CA 92093-0225
United States
AB:
The marine CSEM method has become an important tool for academia and the petroleum industry. Commercially viable seafloor
receivers were developed for marine MT exploration over the last decade, but progress in CSEM transmitter design is still at
an early stage. We have developed 200~A and 500~A transmitters (Scripps Undersea Electromagnetic Source Instrument, or
SUESI-200/500) which operate within the 30~kVA power limitations of academic tow cables. This is done by careful control of
antenna impedance (resistance and inductance) and power efficiency. Electrode impedance is largely a function of length,
rather than surface area or diameter. The antenna can be made neutrally buoyant by balancing the weight of an aluminum
conductor with a thick plastic jacket. Telemetry for control, navigation, and monitoring is overlaid on high voltage power
transmission down coaxial tow cables, as an alternative to fiber optic telemetry, allowing use with winches and cables of
opportunity. The CSEM noise floor determines the source--receiver ranges, and thus the investigation depths, that can be
achieved, and depends on frequency, dipole moment, receiver noise, magnetotelluric interference, and stack time. For typical
values, this is 10-15~VA-1m-2. We present examples of data from a sub-salt hydrocarbon prospect in the Gulf
of Mexico, and an academic project over the magma chambers of the East Pacific Rise.
UR: http://marineemlab.ucsd.edu
DE: 0925 Magnetic and electrical methods (5109)
DE: 3006 Marine electromagnetics
DE: 3094 Instruments and techniques
SC: Geomagnetism and Paleomagnetism [GP]
MN: Fall Meeting 2005