Advanced 3D imaging of complex geoelectrical structures using towed streamer EM data

Abstract

Summary The towed streamer EM system makes it possible to collect EM data with a high production rate and over very large survey areas. At the same time, 3D inversion of towed streamer EM data remains a very challenging problem because of the huge number of transmitter positions of the moving towed streamer EM system, and, correspondingly, the huge number of forward and inverse problems needed to be solved for every transmitter position over the large areas of the survey. We overcome this problem by exploiting the fact that a towed streamer EM system's sensitivity domain is significantly smaller than the area of the towed streamer EM survey. We have introduced the concept of a moving sensitivity domain, originally developed for airborne EM surveys, for interpretation of marine EM survey data as well, which makes it possible to invert the entire towed streamer EM surveys with no approximations into high-resolution 3D geoelectrical seabottom models. In order to improve the accuracy and reliability of the anisotropic 3D inversion results, we have developed 3D inversion method, which takes into account: 1) the variable background, 2) an a priori model constructed by anisotropic 1D inversion results, seismic data, and well-log data, and 3) bathymetry. We have applied our this method to the anisotropic 3D inversion of towed streamer EM data from the Mariner field in the North Sea. The results show that our method can recover a more reliable and reasonable 3D geoelectrical model, and the technology has proven to be fast and efficient for large amounts of towed streamer EM data in a complex geological setting.