Cross-well electromagnetic imaging in three dimensions

In this paper, we develop a new technique for 3D cross-well electromagnetic tomography, based on an EM borehole survey consisting of a moving vertical magnetic dipole transmitter, located in one or several boreholes, and a tri-axial induction receiver, located in the other boreholes. The method is based on the LQL approximation for forward modelling, which results in a fast inversion scheme. The method incorporates both a smooth regularized inversion, which generates a smooth image of the inverted resistivity, and a focusing regularized inversion, producing a sharp focused image of the geoelectrical target. The practical application of the method to synthetic data demonstrates its ability to recover the resistivity, location, and shape of resistive and conductive rock formations.