Limitation of well velocity surveys in highly deviated wells drilled parallel to bedding

A highly deviated near-horizontal well that has been drilled parallel to the bedding of a slightly dipping porous layer is considered. Even though the differences in depths between successive geophone locations may be well defined, it is shown that no reservoir interval velocity can be extracted from a vertical-incidence velocity survey in this case. This paper also deals with the more general case of a deviated well drilled beneath the layer interface of the two-layer model.