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Gas Drilling Operations 163

required for a flammable mixture (GRI, 1997), these facts are seldom
considered when designing air drilling operations. This is mostly because
downhole conditions are very hard to predict. The best practice is to
avoid using air as a drilling fluid whenever hydrocarbon-bearing zones
are drilled. If air has to be utilized, use misting/foaming to reduce mud
rings and thus the potential for fires or explosions.
Thorough training of the drilling crew is essential for safe gas drilling
operations. Personnel safety training and detailed, written gas drilling
procedures are required. An emergency backup escape route is imperative
in the event that the wind changes direction. Gas detection, fire extin-
guishing, and other equipment should be placed at strategic locations.

SUMMARY

This chapter introduced operating procedures in gas drilling to
reduce operation complications and outlined measures to avoid gas
drilling problems. Possible problems include borehole instability, mud
rings, water loading, bit balling, crooked holes, corrosion, and downhole
fires and explosions. An inadequate gas injection rate is recognized as the
leading cause of all of these problems. Overinjection of gas and small bit
orifices are believed to be responsible for bit balling with ice or hydrates,
wellbore washouts, and crooked holes. Thorough training of the drilling
crew is essential for safe gas drilling operations.

REFERENCES
Gas Research Institute (GRI), 1997. Underbalanced Drilling Manual. Gas Research Institute
Publication, Chicago.
Guo, B., Ghalambor, A., 2002. Gas Volume Requirements for Underbalanced Drilling of
Deviated Holes. PennWell Books.
Guo, B., Ghalambor, A., 2005. Natural Gas Engineering Handbook. Gulf Publishing
Company.
Guo, B., Yao, Y., Ai, C., 2008. Liquid carrying capacity of gas in underbalanced drilling.
Paper SPE 113972, Proceedings of the SPE Western Regional Meeting, March 31–
April 2, Los Angeles.
Hallman, J.H., Cook, I., Muqeem, M.A., Jarrett, C.M., Shammari, H.A., 2007. Fluid
customization and equipment optimization enable safe and successful underbalanced
drilling of high-H2S horizontal wells in Saudi Arabia. Paper SPE 108332, Proceed-
ings of the IADC/SPE Managed Pressure Drilling and Underbalanced Operations
Conference and Exhibition, March 28–29, Galveston.
Turner, R.G., Hubbard, M.G., Dukler, A.E., 1969. Analysis and prediction of minimum
flow rate for the continuous removal of liquids from gas wells. J. Pet. Technol.,
Trans. AIME 246, 1475–1482.