Page 336 - Air and Gas Drilling Manual

Using Equation 4-11, the specific weight of the gas entering the compressor is
)
(1 827,
) (1 0.
γ
=
)
g
(53 36. ) (519 67. Chapter 8: Air, Gas, and Unstable Foam Drilling 8-19
γ g = 0 0659 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 = 1 588 8 .
,
 0 0659 
.
,
q g = 1 840 acfm
The above volumetric flow rate is the adjusted minimum value for the atmospheric
conditions at this drilling location (4,000 ft above sea level).
8.3 Injection Pressure and Selection of Compressor Equipment
The planning process given in Section 8.1 requires that the borehole
requirements be compared to the capabilities of the compressor units available.
Specifically, these comparisons are made between: a) the borehole volumetric flow
rate and the compressor volumetric flow rate capability, b) the borehole injection
pressure (using the compressor volumetric flow rate) and the pressure capability of
the compressor, and c) the horsepower required by the compressor and the input
capability of the prime mover. This will be demonstrated in the examples that
follow.

8.3.1 Selection of Compressor Equipment
The volumetric flow rate capabilities of the available compressor units must be
compared with the approximate minimum volumetric flow rate required by the
geometric configuration of the well and the anticipated parameters of the drilling
operation.
Illustrative Example 8.3a describes the implementation of the basic planning
step No. 8 given in Section 8.1.

Illustrative Example 8.3a Select the appropriate compressor system for the
direct circulation drilling operations data given in Illustrative Example 8.2a. The
selection of the appropriate compressor will be made from the example compressor
systems listed in Section 4.7 of Chapter 4. In Illustrative Example 8.2a it was
found that the drilling location adjusted minimum volumetric flow rate of air for the