Sensitivity study of three-dimensional marine controlled-source electromagnetic method

The marine controlled-source electromagnetic (CSEM) method is of increasing importance as a powerful geophysical tool in hydrocarbon exploration. Related to this, three-dimensional (3-D) forward modeling provides an effective method for marine CSEM survey planning and sensitivity analysis (Fréchet derivative). To further evaluate the feasibility of this measurement system as well as its resolution capabilities, we carried out a 3-D sensitivity distribution experiment. The sensitivity calculation used in this work is based on reciprocity theorem and directly affects the accuracy and efficiency of the inversion computation process. This is also a key problem in Gauss-Newton type inversion algorithms. Thus, we analyze the sensitivity distribution of the electric field for both a homogeneous half-space and resistors embedded in conductive sediments. To illustrate the potential of this approach in a 3-D survey, we then adopt a series of simple numerical models to simulate hydrocarbon reservoirs in real situations across a typical suite of configurations. We show that the sensitivity simulation can enhance our understanding of sensitivity characteristics. Indeed, via comparisons and the analysis of sensitivity distributions, we demonstrate the feasibility of this approach for the detection of hydrocarbon reservoirs, and provide additional information for planning and designing marine CSEM surveys.