Page 40 - Well Control for Completions and Interventions

32 Well Control for Completions and Interventions

Where SG 5 density of gas; D 5 depth (feet); 28812.47 is a product of
multiplying together; 53.34 (constant); 558.6 degree Rankin; 0.967 Z
factor (compressibility).
For SI units the following values were used in the formula:
SG 3 D
Correction factor5e 8765:275 (1.10)
For SI units the following values were used in the formula:
Where SG 5 density of gas; D 5 depth (m); 8765.275 is a product of

multiplying together; 29.24 (constant); 310 Kelvin; 0.967 Z factor
(compressibility).
Alternative formulas for gas pressure at depth are:

SITHP Depth
ð
BHP 5 SITP 1 2:5Þ (1.11)
100 1000
This is a “drillers” estimation that includes an approximate 30 psi over-
balance. It underestimates pressure in deep wells with high density gas.
An alternative (more accurate) equation is:
SITP 1
5 (1.12)
BHP 2:718 0:000034 3 SG 3 Depth
If the gas SG, the gas compressibility (Z) factor, and the average
wellbore temperature are known, a more accurate determination of
bottom-hole pressure can be calculated from:

0:01877 3 SG 3 D
SITP 3 e Z 3 T (1.13)
Where SG 5 gas specific gravity (dimensionless); D 5 depth in feet;
Z 5 gas correction factor (compressibility); T 5 temp in Rankin
( F 1 460); e 5 exponential (approximately 2.718).

Example: Calculate the bottom-hole pressure in a gas well using the
following data:

SITHP: 2500 psi
Well depth: 9000 ft TVD
Gas gravity: 0.80
Average temperature 190 F

Gas Z factor 0.96