Page 333 - Principles of Applied Reservoir Simulation 2E

Chapter 31

31.1 Productivity Index

Productivity index (PI) is defined as the ratio of rate Q to pressure drop
AP, or PI = £?/AP, where AP ~ P e- P w, P e = average reservoir pressure, and
P w = wellbore bottomhole pressure BHP. From Darcy's Law for radial oil flow
we can write PI as
_
PI = (31.1)
AP " Mo[H'A,) + S\

The meaning and units of all terms are given as follows:
= oil viscosity (cp)
\i 0
= oil FVF (RB/STB)
B 0
r e = drainage radius (ft)
= wellbore radius (ft)
r w
S = skin
K e = effective permeability (md) = k ro K abs
= relative permeability to oil
k ro
K ahs = absolute permeability (md)
= net thickness (ft)
h net
Q 0 = oil rate (STB/D)

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