Page 43 - Air and gas Drilling Field Guide 3rd Edition

34 CHAPTER 2 Air and Gas Versus Mud

just above the drill collars is 6.43 m/sec. Using these values in Equation (2-1), the
kinetic energy per unit volume for the mud example is
1 2
KE a ¼ ð10:1Þð6:43Þ
2
3
KE a ¼ 209N m=m :
The kinetic energy per unit volume values in the two flow examples (drilling
mud and compressed air) are similar in magnitude at the critical position in the
annulus where it would be expected that the rock cutting carrying capacity of
the drilling fluids is 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 (assuming a uniform cross-sectional area in the annulus). The flow
kinetic energy per unit volume of the compressed air, however, increases dramat-
ically as it seeks atmospheric conditions at the exit to the annulus. This is because
the compressed air has stored internal energy (from the compression process)
and as it starts up the annulus and resistance to flow decreases (i.e., lower hydro-
static head), this internal energy is converted to velocity. This kinetic energy
per unit volume is a critical factor in assuring proper borehole cleaning drill bit-
generated rock cuttings of both a mud-drilled and an air-drilled borehole.

REFERENCES
1. Marcus, R. D., Leung, L. S., Klinzing, G. E., and Rizk, F., Pneumatic Conveying of Solids,
Chapman and Hall, 1990.
2. Singer, C., Holmyard, E. J., Hall, A. R., and Williams, T. I., A History of Technology, Vol. 4,
Oxford Press, 1958.
3. Singer, C., Holmyard, E. J., Hall, A. R., and Williams, T. I., A History of Technology, Vol. 5,
Oxford Press, 1958.
4. Singer, C., Holmyard, E. J., Hall, A. R., and Williams, T. I., A History of Technology, Vol. 6,
Oxford Press, 1958.
5. H. J. Gruy, Personal communication, February 5, 1997.
6. API Recommended Practice for Drill Stem Design and Operating Limits, API RP 7G, 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.
9. API Specifications for the Internal-Combustion Reciprocating Engines for Oil-Field Service,
API Std. 7B-11C, Ninth Edition, 1994.
10. Angel, R. R., “Volumetric Requirements for Air or Gas Drilling,” Petroleum Transactions,
AIME, Vol. 210, 1957.