Page 30 - Well Control for Completions and Interventions

24 Well Control for Completions and Interventions

Figure 1.11 The pressure exerted by 1 ft of liquid over an area of 1 in. 2
2 2
Converting the area of the cube’s base from ft to in , the weight
acting on each square inch is:

7:48
5 0:051944-0:052
144
The gradient of a 1 ppg fluid is therefore 0.052 psi/ft (Fig. 1.11).
It can also be derived by dimensional analyses. One US gallon con-
3
tains 231 in. .
lb 2
1 3
psi 1ft in 231
1 5 3 3 5 19:250000 lbs=gallon
ft 12in psi 1 US gallons
1=19:25 5 0:0519-0:052:

Although it is more accurate to divide fluid weight (ppg) by 19.25 to
obtain the gradient, this is rarely done. The factor 0.052 is widely used,
and the conversion factor is listed in all well control manuals and text
books. The magnitude of the error when using 0.052 is approximately
0.1%.

SI units: To convert density to a pressure gradient:
Fluid density in kg=m 3
Pressure gradient ðkPa=mÞ 5
102 (1.6)
3
Pressure gradient ðkPa=mÞ 5 Kg=m 3 0:00981