Publications

A towed streamer electromagnetic acquisition system has been under development since 2004. The goal was to build a system that is loosely based on the layout of 2D marine seismic acquisition systems with comparable acquisition speed, dense sampling, real time quality control of source signal and receiver data, and ability to do on-board processing. Further it facilitates simultaneous acquisition of 2D seismic from the same vessel. In October 2012 an acquisition campaign over a series of known fields in the Norwegian sector of the North Sea was conducted with the first commercial version of the towed streamer EM system. The 800 m long bi-pole source is towed at 10 m and it is powered by a 1,500 ampere source-signal. The EM streamer has effectively 26 offsets from 0 - 7,700 m and it is towed at a depth of 50 - 100 m. Currently the acquisition system is limited to 400 m water depth. Following our noise attenuation processing, the signal-to-noise is comparable to conventional controlled source EM (CSEM) systems. One of the most challenging targets was the Alvheim Boa Field, which was successfully detected, although it is a medium sized oil and gas field located 2,100 m below mudline. With conventional processing the target response is 7-8 % above background. With an uncertainty of 3%, this is recognized as a weak but true anomaly. With the recently introduced optimized synthetic aperture processing, where the sensitivity is increased by focusing the radiated source energy on the target, the anomaly increased to 200 % above background. Other weaker anomalies in the vicinity of the target are also attenuated, due to the focusing effect of the source energy on the designated target.