The representation of a wellbore in a reservoir simulation model has led to over prediction of productivity index and deliverability of horizontal wells. Recent experience with horizontal wells has revealed that in many circumstances (oil production wells), the inflow performance of horizontal wells and hence their deliverability may be affected by pressure drop along the wellbore. This effect has serious implications on perforated well length because the productivity index is no longer directly proportional to the well length.
Although pressure variation along horizontal wellbores has been reported by some authors:  and confirmed by production logging: , there still remains the problem of calculating it in a reservoir simulation model. In this paper we describe the equations on which the wellbore pressure drop model is based and present an outline of a novel computational method which solves these equations. The ease with which the wellbore model can be coupled to an existing reservoir simulator is demonstrated.
Altough little dat is available to us, the model is tested for plausibility against production data from a horizontal well. The results indicate that wellbore parameters such as well length, diameter and perforated interval have the most significant effect on the level of pressure drop in the wellbore. The consequences of ignoring this wellbore pressure drop is to over predict the well deliverability. It is also shown the wellbore pressure drop increases dramatically with increase in reservoir productivity.