Page 18 - Air and gas Drilling Field Guide 3rd Edition

CHAPTER

2
Air and Gas Versus Mud

This engineering practice monograph has been prepared for petroleum and related
drilling and completion engineers and technicians who work in modern rotary
drilling operations. This book derives and illustrates engineering calculation tech-
niques associated with air and gas drilling technology. This book has been written
in consistent units to ease application in either USCS or SI. Also, field unit equation
use has been minimized in the text. Chapter 1 and Appendix A give definitions of
important units and constants and useful conversions for both USCS and SI.
Air and gas drilling technology is the utilization of compressed air or other gases as
a rotary drilling circulating fluid to carry the rock cuttings to the surface that are gen-
erated at the bottom of the well by the advance of the drill bit. The compressed air or
other gas (e.g., nitrogen or natural gas) can be used also or can be injected into the
well with incompressible fluids such as fresh water, formation water, formation oil,
or drilling mud. There are three distinct operational applications for this technology:
air or gas drilling operations (using only compressed air or other gas as the circulating
fluid), aerated drilling operations (using compressed air or other gas mixed with an
incompressible fluid), and stable foam drilling operations (using compressed air or
other gas with an incompressible fluid to create a continuous foam circulating fluid).
In the past, air and gas drilling methods have been a small segment of the petro-
leum deposit recovery drilling industry. Currently, air and gas drilling methods that
utilize compressed air (or other gases), aerated fluids, or foam fluids comprise about
20 to 30% of all operations. There are two separate and unique reasons for utilizing
air and gas drilling methods in modern oil and gas deposit recovery operations.
These are:
Performance Drilling: Drilling formations above a potential producing
formation to generally take advantage of increased rates of penetration of
these drilling methods.
Underbalanced Drilling: Drilling of potential producing formations using
annulus bottom hole pressures that are below the formation pore pressure.
This reduces or eliminates formation damage that could affect follow-on
production.
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