Rapid Imaging of Towed Streamer EM Data Using the Optimal Synthetic Aperture Method

Abstract

The mainstream approach to the interpretation of towed streamer electromagnetic (EM) data is based on 2.5-D and/or 3-D inversions of the observed data into the resistivity models of the subsurface formations. However, the rigorous 3-D and even 2.5-D inversions require large amounts of computational power and time. The synthetic aperture (SA) method is one of the key techniques in remote sensing using radio frequency signals. During recent years, this method was also applied to low-frequency EM fields used for geophysical exploration. This letter demonstrates that the concept of the SA EM method can be extended for rapid imaging of the large volumes of towed streamer EM data. We introduce a notion of virtual receivers, which complement the actual receivers in the construction of the SA for the towed streamer data. A numerical study demonstrates that this method increases the EM response from potential subsurface targets and opens a possibility for on-board real-time imaging of EM data during a survey. The method is illustrated by the imaging of towed streamer EM data acquired over the Troll oil and gas fields in the North Sea. Remarkably, the imaging of the entire towed streamer EM survey requires just a few seconds of computation time on a desktop PC. This result is significant, because it opens a possibility for real-time imaging of the towed streamer EM survey data.