Page 42 - Air and gas Drilling Field Guide 3rd Edition

2.3 Comparison of Mud and Air Drilling 33

In USCS units, in the mud drilling example, the specific weight of the drilling
3
mud in the annulus of the drill collars is 75 lb/ft . Using this value in Equation
(2-2), the density of the drilling mud is
75:0
r ¼
m
32:2
2
¼ 2:33 lb sec =ft 4
r m
or
3
¼ 2:33 slugs=ft :
r m
The average velocity of the drilling mud at this position is approximately 2.0 ft/
sec. Substituting these values into Equation (2-1), the kinetic energy per unit
volume for the drilling mud example is
1 2
KE m ¼ ð2:33Þð2:0Þ
2
3
KE m ¼ 4:7lb ft=ft :
In SI units, in the mud drilling example, the density of the drilling mud in the
3
annulus of the drill collars is 12,001 kg/m . Also, the approximate velocity just
above the drill collars is 0.61 m/sec. Using these values in Equation (2-1), the
kinetic energy per unit volume for the mud example is
1 2
KE m ¼ ð1201Þð0:61Þ
2
3
KE m ¼ 233:4N m=m :
In USCS units, in the air drilling example, the specific weight of the com-
3
pressed air in the annulus just above the drill collars is 0.632 lb/ft . Using this
value in Equation (2-2), the density of the compressed air is
0:632
r ¼
a
32:2
2
r ¼ 0:0196lb sec =ft 4
a
or
3
r ¼ 0:0196 slugs=ft :
a
The average velocity of the compressed air at this position is approximately
21.1 ft/sec. Substituting these values into Equation (2-1), the kinetic energy per
unit volume for the drilling mud example is
1 2
KE a ¼ ð0:0196Þð21:1Þ
2
3
KE a ¼ 4:4lb ft=ft :
In SI units, in the compressed air example, the density of the air in the annulus
3
of the drill collars is 10.1 kg/m . Also, the approximate velocity of the air flow