Effect of steel-cased wells on hydrocarbon detection based on controlled source electromagnetic diffusion process

In controlled source electromagnetic (CSEM) modeling with well casings, it is common to assume that the current is flowing vertically in each casing, due to the large conductivity contrast between casings and their host media. This assumption makes the integration of the tensor Green's function relating the induced fields to source currents simple, since only the z-z component of the tensor needs to be considered. However, in practice, it can be improper to neglect the horizontal current effects in the casing without a close examination.