Page 235 - Principles of Applied Reservoir Simulation 2E

220 Principles of Applied Reservoir Simulation

is the oil pressure gradient and Az is the height of the oil column. An
where J 0
estimate of average oil pressure gradient for the oil column is found by averaging
the pressure gradient at surface and reservoir conditions:
4 Approximate pressure gradient at surface conditions:
p = 46.244 A ~~ 0.321
ft 3 ft

where oil density at surface conditions (p s) is 46.244 Ibm/SCF.
Approximate pressure gradient at reservoir conditions:

p = £i * 34.3 A « 0.238 £™
ft 3 ft
# 0
where oil FVF (B 0) at bottomhole conditions is 1.3482 RB/STB.

The resulting FBHP for use in WINB4D is

l
FBHP = /2 0.321 . -, 0.238 x 9500ft « 2660psia
ft ft

A more accurate estimate can be obtained from wellbore correlations or nodal
analysis as discussed by such authors as Brown and Lea [1985].

Well Block Pressure from PBU
In Chapter 1 7 we saw that a pressure correction was needed to properly
relate the pressure buildup (PBU) curve to simulator well block pressures. To
illustrate this correction, suppose a well is in a block with grid dimensions Ax
= 200 ft and Ajy = 200 ft. We want to compare the simulator well block pressure
with a pressure from a PBU. Peaceman [1978, 1983] showed that shut-in
pressure P ws of the actual well should equal the simulator well block pressure
P 0 at a shut-in time A/, given by

K