oa Application of synthetic aperture concepts to Towed Streamer EM data

In October 2012 a series of known oil & gas fields in the North Sea were surveyed with the newly developed towed streamer EM system. This is the first commercial Controlled Source EM (CSEM) system where both source and receivers are towed in a similar fashion as 2D seismic, and the technology is also combinable with 2D seismic facilitating simultaneous acquisition from one vessel. One of the selected targets was an average size oil & gas field located 2,100 m below mudline, where approximately half of the recoverable oil has been produced, but with the gas cap still intact. The source was towed at 10 m and the 8,700 m long EM streamer was towed at a depth of 50 m. The resulting electric field was measured at 23 offsets ranging from 0 to 7,700 m. The towing speed was 4 kn, and the water depth was 110 - 125 m in the survey area. The rich sampling makes the towed streamer EM acquisition technology ideal for the recently introduced synthetic aperture processing. The accuracy in the frequency responses enabled the detection of the depocenter of the reservoir with a signal strength only 7-8% above background with an uncertainty of 5% in a non-optimized synthetic aperture processing. The improved sensitivity provided by optimized synthetic aperture processing increased the signal above background to 200%. Further, by focusing the energy on the target it will also de-emphasize the strength of the anomalies of no interest located in proximity to the reservoir under evaluation.