Page 202 - Well Control for Completions and Interventions

Completion, Workover, and Intervention Fluids 195

where:
C t 5 average temperature correction in ppg,

α 5 expansion factor in lb/gal/100 F (from Table 5.4),

surf 5 ambient (surface) temperature F, and
BHT 5 bottom hole temperature ( F).

A pressure correction is obtained from the equation:
βðBHPÞ
C p 5 (5.5)
2000
where:
C p 5 average pressure correction in ppg,
β 5 compression factor in lb/gal/1000 psi (Table 5.4), and
BHP 5 bottom hole pressure in psi.
Brine density corrected for both pressure and temperature is then
obtained:

d c 5 d u 1 C t 2 C p
where:
d c 5 corrected density (temperature and pressure) in ppg,
d u 5 uncorrected density in ppg,
C t 5 average temperature correction in ppg (Eq. (5.4)), and
C p 5 average pressure correction in ppg (Eq. (5.5)).
Example calculation (using the same data as the previous example):
Well depth 10,000 ft TVD.
o
Bottom hole temperature 260 F
o
Ambient temperature (surface) 80 F
Reservoir pressure 4690 psi.
Required overbalance 250 psi.
The brine density will be as before, 9.5 ppg. The expansion and com-
pression factors for a 9.5 ppg NaCl will be used (Table 5.4).
Density loss (ppg) is:

0:386 ð260 2 80Þ
C t 5 5 0:3474 ppg
200
To calculate the density increase, bottom hole pressure using an uncor-
rected brine weight must be calculated, 9.5 3 0.0523 10,000 5 4940 psi;
the same as reservoir pressure 1 overbalance:

0:0188ð4940Þ
C p 5 5 0:0463 ppg
2000