Page 48 - Air and Gas Drilling Manual

.
ρ
32 2
.
ρ a = 0 688 lb − sec 2 Chapter 1: Introduction 1-25
.
= 0 0214
a
ft 4
The average velocity at this position is approximately 30 ft/sec. Using these
values in Equation 1-1, the kinetic energy per unit volume for the air drilling
example becomes
KE a = 1 (0 0214 ) (30 0 . ) 2
.
2
ft − lb
.
KE = 96
a 3
ft
The kinetic energy per unit volume values of the two example flows (drilling
mud and compressed air) are nearly the same at the position in the annulus where it
would be expected that the rock cuttings carrying capacity of the fluids are a
minimum. The flow kinetic energy per unit volume of the mud drilling fluid does
not change as the drilling mud flows to the surface in the annulus (uniform cross-
sectional area). The flow kinetic energy per unit volume of the compressed air on
the other hand increases exponentially as it seeks atmospheric conditions at the exit
to the annulus. This is because the compressed air has stored internal energy and as
it starts up the annulus and resistance to flow decreases (i.e., lower hydrostatic head)
this internal energy is converted to velocity.
References

1. Marcus, R. D., et al., Pneumatic Conveying of Solids, Chapman and Hall, 1990.
2. Singer, C., et al., A History of Technology, Vol. 4, Oxford Press, 1958.
3. Singer, C., et al., A History of Technology, Vol. 5, Oxford Press, 1958.

4. Singer, C., et al., A History of Technology, Vol. 6, Oxford Press, 1958.

5. Personal communication with H. J. Gruy, February 5, 1997.
6. API Recommended Practice for Drill Stem Design and Operating Limits, API
RP7G, 16th Edition, August 1998.

7. Roscoe Moss Company, Handbook of Ground Water Development, Wiley, 1990.
8. Burghardt, M. D., Engineering Thermodynamics with Applications, Harper and
Row, 1982.