Page 317 - Principles of Applied Reservoir Simulation 2E

302 Principles of Applied Reservoir Simulation

Once Z is known, the gas formation volume factor is easily determined for a
given temperature and pressure using the real gas law.
The isothermal gas compressibility c is obtained from Eq. (28,2) as
1 1 1 BZ
=
c (28.3)
"a P.
where P c is the critical pressure (psia).
Real gas viscosities are computed using the method described in Govier
[1975]. This method is a computerized version of the Carr, Kobayashi, and
Burrows [1954] hydrocarbon gas viscosity determination procedure.

Pseudo-Pressure Calculations
Pseudo-pressures are defined by

iK/0 = 2/ ^-dP' (28.4)
P e » gZ
where
1
P - dummy integration variable with pressure units (psia)
= reference pressure = 14.7 psia
P 0
P = specified pressure (psia)
|l g = gas viscosity (cp)
Z = gas compressibility factor

The pseudo-pressure t|f (P) is often written as m(P). Since \l g and Z depend
on P', evaluation of Eq. (28.4) is accomplished by numerical integration using
the trapezoidal rule and a user-specified pressure increment AP' ~ dP'.

Gas Property Description
Four different gas property descriptions may be specified. Their descrip-
tions and control parameter (KODEA) values follow:

KODEA GAS DESCRIPTION
] Sweet gas: input 12 component mole fractions as
0.0.0. 1.0 0. 0. 0. 0. 0. 0. 0.