Optimized Synthetic Aperture Sensitivity Enhancement of a Deep EM Marine Target

In October 2012 the Alvheim-Boa Field was surveyed as part of a North Sea acquisition campaign with the newly developed Towed Streamer EM System to provide resistivity estimates over a number of known oil and gas fields. The Alvheim-Boa field is medium sized, located 2,100m below the sea-floor, and half of the recoverable oil has already been produced but the gas cap is intact. The resulting maximum anomaly above background following conventional processing is 7-8 %. The anomaly is recognized as originating in the reservoir based on the following facts: The peak anomaly coincides with the maximum reservoir thickness in the Boa Field; the peak appears at the same location on both survey lines; the anomaly is only detected by the lowest frequencies and the longest offsets indicating a deep origin; and the uncertainty in the long offset data is less than 3 %. The optimized synthetic aperture processing is a way to focus the radiated energy from the source bi-pole towards the target of interest. This resulted in an increase in the maximum anomaly to 200 % above background. An additional strong advantage of the target focusing ability is that other nearby minor anomalies of no interest where de-emphasized.