The study of diffusion effects in RIM tomographic imaging

Abstract

To date, the standard method of producing images from medium-frequency RIM measurements is to use a straight-ray tomographic reconstruction algorithm. In constrast, conventional inversion methods for low-frequency EM measurements are commonly described in terms of secondary fields, produced by eddy currents in a conductive body, and are often carried out by a combination of forward modelling and regularized inversion. These two approaches differ considerably, which brings rise to many questions on the validity of applying straight-ray tomography to RIM data. In the past, this has been justified by the success of the empirical results but work is ongoing to provide a firm theoretical basis for the RIM method and to produce more accurate transmission tomography algorithms which go beyond the straight-ray approximation. Using numerical modelling results, this paper examines the validity of applying a straight-ray tomographic reconstruction algorithm to medium-frequency EM data. Rock conductivities are varied in the examples. The paper also looks at one of the approaches being studied which will hopefully lead to a more accurate transmission tomography algorithm.