Abstract
Horizontal wells are reviving many marginal oil fields through accelerated oil production. In some fields, a single horizontal well produces as much as all the vertical wells put together. While there are prolific results as far as the profitability of the operation is concerned, there are other pertinent questions that arise. Does the vertical well flow pattern suffer as a result of horizontal well production? Does the ultimate oil recovery increase as a result of horizontal well operation? Given a pattern of vertical wells, can a horizontal well location be so chosen that the total oil production (and recovery) is maximized? These are the questions this paper attempts to address.
The results show that horizontal wells do indeed capture the oil in the drainage area of vertical wells. The extent of this "loss" depends on several factors. These include direction and allocation of the horizontal well within the drainage area, position of the horizontal well between the vertical boundaries, permeability anisotropy, net pay thickness, and oil viscosity. For a given pattern, there is a horizontal well configuration that maximizes the total production rate. The question of ultimate oil recovery is quite complex, and it may be said that in light oil reservoirs a horizontal well would tend to increase the ultimate oil recovery. Although it is concluded that, each of these factors ascribes to significant effects, it is the location of horizontal well that warrant the greatest effect on overall performance of vertical well.
