TABLE OF CONTENTS This chapter presents the practical reservoir engineering equations that are designed to predict the performance of vertical and horizontal oil wells. The chapter also describes some of the factors that are governing the flow of fluids from the formation to the wellbore and how these factors may affect the production performance of the well. The analysis of the production performance is essentially based on the following fluid and well characteristics:
Fluid PVT properties
Relative permeability data
Inflow-performance-relationship (IPR)
A commonly used measure of the ability of the well to produce is the Productivity Index. Defined by the symbol J, the productivity index is the ratio of the total liquid flow rate to the pressure drawdown. For a water-free oil production, the productivity index is given by:
where Q o = oil flow rate, STB/day
J = productivity index, STB/day/psi
pr = volumetric average drainage area pressure (static pressure)
pwf = bottom-hole flowing pressure
?p = drawdown, psi
The productivity index is generally measured during a production test on the well. The well is shut-in until the static reservoir pressure is reached. The well is then allowed to produce at a constant flow rate of Q and a stabilized bottom-hole flow pressure of pwf. Since a stabilized pressure at surface does not necessarily indicate a stabilized pwf, the bottom-hole flowing pressure should be recorded continuously from the time the well is to flow. The productivity index is then calculated...
