How New Horizontal Wells Affect the Performance of Existing Vertical Wells

SHIRIF, EZEDDIN, U. of Alberta

Horizontal wells are reviving many marginal oilfields through accelerated oil production. In some fields, a single horizontal well produces as much as all the vertical wells put together. There are important 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, in the context of heavy oil reservoirs.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 heavy 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 the horizontal well and oil viscosity that warrant the greatest concern about overall performance of vertical well.

AAPG Search and Discovery Article #90911©2000 AAPG Pacific Section and Western Region Society of Petroleum Engineers, Long Beach, California