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Gas Compressors 135

parameters (e.g., the shape and size of the particles) have hindered its
practical application.
Schoeppel and Spare (1967) reported that the gas flow rate values
obtained from the minimum kinetic energy criterion were at least 25%
below the actual field’s needs. This motivated numerous investigators to
develop more accurate models to determine the minimum required gas
injection rate for gas drilling. These models include those presented by
Capes and Nakamura (1973), Sharma and Crowe (1977), Ikoku and col-
leagues (1980), Machado and Ikoku (1982), Mitchell (1983), Puon and
Ameri (1984), Sharma and Chowdry (1984), Wolcott and Sharma (1986),
Adewumi and Tian (1989), Tian and Adewumi (1991), and Supon and
Adewumi (1991).
Guo and colleagues (1994) performed a comparison of results from
model calculations and field experience. The comparison showed that
among these models, only the result given by Angel’s model obtained
from the minimum kinetic energy criterion has a trend consistent with
field experience, although Angel’s model provides lower estimates for the
minimum volumetric gas requirements. Guo and colleagues found that
Angel’s charts give values lower than field requirements because Wey-
mouth’s friction derived for flow in smooth pipes was used in Angel’s
calculations for flow in rough wellbores.
Guo and colleagues incorporated Nikuradse’s (1933) friction factor
correlation for rough boreholes into Angel’s analysis. This improvement
made Angel’s approach as far as field experience the best. Guo and col-
leagues also introduced various hole inclinations into the analysis and
used the concept of the kinetic energy index as an indicator for hole
cleaning. The kinetic energy index is defined as the kinetic energy of the
3
in situ gas divided by the minimum required kinetic energy (3 ft-lb/ft ).
Guo and Ghalambor (2002) generated correlations and engineering
charts for determining the air and gas flow rates required for hole clean-
ing using the minimum kinetic energy criterion. Lyons and colleagues
(2009) coded the minimum kinetic energy criterion in their MathCad
programs.

6.3.2 Corrections for Site Pressure, Temperature,
and Humidity

When a compressor is operated at surface locations above sea level, the volu-
metric air flow rate intake is the actual cubic feet per minute (acf/min), not
the standard cubic feet per minute (scf/min). The ambient pressure and