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CHAPTER SIX

Gas Compressors

Contents
6.1 Introduction 119
6.2 Gas Flow Mechanics 119
6.2.1 Gas Flow in Vertical Holes 120
6.2.2 Gas Flow in Deviated Holes 125
6.2.3 Gas Flow through the Bit 127
6.3 Gas Injection Rate Requirements 128
6.3.1 Criteria for Hole Cleaning 128
6.3.2 Corrections for Site Pressure, Temperature, and Humidity 135
6.4 Gas Injection Pressure Requirements 138
6.5 Horsepower Requirements 142
Summary 144

6.1 INTRODUCTION
Compressors are used to provide pressurized gas in air and gas drilling
operations. Portable compressors were first utilized in the late 1880s in the
mining industry to drill boreholes (Singer, 1958a). Deep petroleum and nat-
ural wells were drilled utilizing portable air compressors in the 1920s (Singer,
1958b). The more popular use of air as a circulating drilling fluid began in
the early 1950s (Martin, 1952). By the late 1970s, it was estimated that air
and gas technology was being used on about 10% of the deep wells drilled
and completed (Lyons et al., 2001; GRI, 1997). This chapter addresses the
technical issues involved in selecting gas compressors, including volumetric
requirements, pressure requirements, and power requirements.

6.2 GAS FLOW MECHANICS
The gases used in air and gas drilling include air, natural gas, and
nitrogen. Gas drilling becomes mist or unstable foam drilling when water
and foaming agents are added to the stream of injection gas to increase the
cuttings-carrying capacity of the gas. The liquid phase volume is less than
3% in the system. The study of the hydraulics of gas carrying solid particles

Applied Drilling Circulation Systems. DOI: 10.1016/B978-0-12-381957-4.00006-1
© 2011 Elsevier Inc. All rights reserved. 119