Page 263 - Fundamentals of Reservoir Engineering

OILWELL TESTING 200

EXERCISE 7.6 HORNER PRESSURE BUILDUP ANALYSIS, INFINITE
RESERVOIR CASE

A discovery well is produced for a period of approximately 100 hours prior to closure
for an initial pressure buildup survey. The production data and estimated reservoir and
fluid properties are listed below

q = 123 stb/d = 0.2
φ
= 500 stb = 1 cp
N p µ
h = 20 ft B oi = 1.22 rb/stb

-6
= 0.3 ft c = 20×10 /psi
r w
A ≈ 300 acres = (c o S o +c w +S w +c )
f
and the pressures recorded during the test are listed in table 7.5.

1) What is the initial reservoir pressure?

2) If the well is completed across the entire formation thickness, calculate the effective
permeability.

3) Calculate the value of the mechanical skin factor.

4) What is the additional pressure drop in the wellbore due to the skin?

5) If it is initially assumed that the well is draining from the centre of a circle, is it valid
*
to equate p i to p ?
Closed-in time Wellbore pressure Closed-in time Wellbore pressure
∆t (hrs) (psi) ∆t (hrs) (psi)
0.0 4506 (p wf )
0.5 4675 3.0 4763
0.66 4705 4.0 4766
1.0 4733 6.0 4770
1.5 4750 8.0 4773
2.0 4757 10.0 4775
2.5 4761 12.0 4777
TABLE 7.5

EXERCISE 7.6 SOLUTION

1) The effective flowing time is

N 500
t = p × 24 = × 24 = 97.6 hrs
q final 123

t +∆ t
Points on the Horner build up plot of p ws versus log are listed in table 7.6.
t ∆