TABLE OF CONTENTS Determination of the flow capacity of a gas well requires a relationship between the inflow gas rate and the sand-face pressure or flowing bottom-hole pressure. This inflow performance relationship may be established by the proper solution of Darcy's equation. Solution of Darcy's Law depends on the conditions of the flow existing in the reservoir or the flow regime.
When a gas well is first produced after being shut-in for a period of time, the gas flow in the reservoir follows an unsteady-state behavior until the pressure drops at the drainage boundary of the well. Then the flow behavior passes through a short transition period, after which it attains a steady-state or semisteady (pseudosteady)-state condition. The objective of this chapter is to describe the empirical as well as analytical expressions that can be used to establish the inflow performance relationships under the pseudosteady-state flow condition.
The exact solution to the differential form of Darcy's equation for compressible fluids under the pseudosteady-state flow condition was given previously by Equation 6-150 as:
where Q g = gas flow rate, Mscf/day
k = permeability, md
= average reservoir real gas pseudo-pressure, psi 2/cp
T = temperature, R
s = skin factor
h = thickness
r e = drainage radius
r w = wellbore radius
The productivity index J for a gas well can be written analogous to that for oil wells as:
or
with the absolute open flow potential (AOF), i.e., maximum gas flow...
