In 1993, an aggressive horizontal well drilling program started in a Heavy Oil Field, located in the eastern part of Venezuela. The crude oil is characterized by low gravity (8 degree API). The main objective of this program is to improve oil recovery and control water invasion. This paper presents the numerical simulation of the first three horizontal wells in the reentry program and sensitivity analysis considering some parameters, such as vertical/horizontal permeability anisotropy, sand thickness, horizontal length, well-bore diameter, number of branches, angles between branches, and friction effects for cold and hot production. A pseudo-compositional and fully implicit 3-D thermal simulator was used to obtain all the results presented in this study. The numerical simulation includes the vertical and horizontal history match and the forecast of oil well production performance. Sink-source and well-bore discretization were used as methods for the horizontal well representation. Simulation results show that a horizontal well reduces water invasion. It also indicates that the optimum horizontal well length for the Jobo area is 800 to 1200 feet. The vertical/horizontal permeability effect is important only for some speecific values of the sand thickness and the horizontal length of the well. The well-bore diameter recommended to drill the horizontal wells is seven inches. In addition, drilling of branches at some angles is an option for improving horizontal well production. The sensitivity analysis, using the well-bore discretization option, reveals that friction has an important effect on the well oil production. The friction effect is more important when the horizontal well length is increased and in some cases it can reduce the cold oil production around 50
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