Page 179 - Air and Gas Drilling Manual

,
= 1 695 lb/ft abs
The actual atmospheric temperature of the air at the drilling location, T at (that will be
used by the compressor), is
t P at = 70˚F 2 Chapter 5: Shallow Well Drilling Applications 5-21
at
.
T at = t at + 459 67
o
T at = 529 67 R
.
Thus, P g and T g become
P = P at = 1 695 lb/ft abs
2
,
g
T = T at = 529 67 R
o
.
g
Using Equation 4-11, the specific weight of the gas entering the compressor is
(1 695, ) (1 0. )
γ =
g
(53 36. ) (529 67. )
γ g = 0 0600 lb/ft 3
.
Note the above specific weight value can also be obtained from Figure D-4 in
Appendix D.
The approximate minimum volumetric flow rate for this illustrative example
adjusted for the actual atmospheric conditions at the drilling location can be
determined by equating the weight rate of flow of the air at the two atmospheric
conditions. This reduces to
 0 0763. 
q g = 378 
 0 0600.
q g = 481 acfm

The above volumetric flow rate is the adjusted minimum value for the atmospheric
conditions at this drilling location (6,000 ft above sea level).
Illustrative Example 5.3a Determine the direct circulation minimum
volumetric flow rate of air required to drill a 6 1/4 inch openhole borehole (6 1/4
inch drill bit diameter) and a drill string composed of 240 ft of 4 3/4 inch by 1 1/2
inch drill collars (see Table B-1) above the drill bit and API 2 7/8 inch, 6.85 lb/ft