Rigorous 3-D inversion of marine CSEM data based on the integral equation method

Marine controlled source electromagnetic (MCSEM) surveys have become an important part of offshore petroleum exploration. In this paper we present a new approach to 3-D inversion of MCSEM data. It is based on rigorous integral equation (IE) forward modeling and a new IE representation of the sensitivity (Frechet derivative matrix) of observed data to variations in sea-bottom conductivity. This approach requires just one forward modeling on every iteration of the regularized gradient type inversion algorithm, which speeds up the computations significantly. We also use a regularized focusing inversion method, which provides a sharp boundary image of the petroleum reservoir. The methodology is tested on a 3-D inversion of the synthetic EM data representing typical MCSEM surveys conducted for offshore petroleum exploration.