Page 201 - Well Control for Completions and Interventions

194 Well Control for Completions and Interventions

Example calculation:
Well depth: 10,000 ft TVD.

Bottom hole temperature: 260 F.
Ambient temperature (surface): 80 F.

Reservoir pressure: 4690 psi.
Required overbalance: 250 psi.
Using Eq. (5.1), calculate the required density under surface conditions.
Density ðppgÞ 5 ð4690 1 250Þ=ð0:052 3 10; 000Þ 5 9:5 ppg. The expan-
24
sion coefficient for a 9.49 NaCl brine will be used: 2.543 10 (Table 5.2).
Next, calculate the average temperature in the wellbore.

Surface temp 1 bottom hole temperature
2
60 1 260
5 160 F

2
The temperature adjusted brine weight becomes:

1
ρ 5 9:52 2 5 9:277 ppg:
T
1 2 ð160 2 70Þ0:000254
The temperature adjusted brine weight is adjusted for pressure using
Eq. (5.2).
BHP using the corrected brine density of 9.277 ppg is:

10; 000 3 0:052 3 9:277 5 4824 psi
Average wellbore pressure (between TD and surface) is therefore
4824/2 5 2412 psi.
The pressure correction is:

1

ρ 5 9:227 2 2 5 9:27 ppg:
p
1 1 2412Þ0:00000198
ð
This would, by convention, be rounded up to 9.3 ppg.
A slightly different method is used by Tetra and illustrated in their
“Engineered Solution Guide for Clear Brines.” First, a density correction
is calculated.

αðBHT 2 surfÞ
C t 5 (5.4)
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