Anisotropic 3D inversion of towed-streamer electromagnetic data: Case study from the Troll West Oil Province

Abstract

One of the critical problems in the interpretation of marine controlled-source electromagnetic geophysical data is taking into account the anisotropy of the rock formations. We evaluated a 3D anisotropic inversion method based on the integral equation method. We applied this method to the full 3D anisotropic inversion of towed-streamer electromagnetic (EM) data. 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 has become 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 overcame 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. This approach makes it possible to invert entire towed-streamer EM surveys with no approximations into high-resolution 3D geoelectrical sea-bottom models. We present an actual case study for the 3D anisotropic inversion of towed-streamer EM data from the Troll field in the North Sea.