3D inversion of marine magnetotelluric data on massively parallel computer

Abstract

Three‐dimensional (3D) magnetotelluric (MT) inversion is an emerging technique for offshore hydrocarbon (HC) exploration. Hydrocarbon‐bearing formations typically have a resistivity much higher than those of conductive sea‐bottom sediments, which makes an EM method an effective HC exploration technique. In this paper we introduce a new approach to 3D inversion of MT data for offshore HC exploration based on the integral equation method. The Tikhonov regularization and physical constraint have been used to obtain a stable and reasonable solution of the inverse problem. The method is implemented in a fully parallel computer code. For numerical experiments we simulate complex and commonly occurring offshore geological synthetic models. We also conduct the inversion of the Gemini Prospect MT data collected by the Scripps Institution of Oceanography (SIO) in the Gulf of Mexico. The inversion domain was discretized into 2.5 M cells. It took 16 hours to complete 51 iterations on the 832 processor cluster with the final misfit between the observed and predicted data of 7.7%. The inversion results reveal a resistive salt structure which is confirmed by a comparison with the seismic data. These inversion results demonstrate that we can map resistive geoelectrical structures, like salt domes or HC reservoirs, with reasonable accuracy using 3D inversion of the marine MT data.