Page 420 - Air and Gas Drilling Manual

9-24 Air and Gas Drilling Manual
7,000 ft to 10,000 ft and determine the derated power available from the prime
mover.
General Data
The solution to a full friction aerated drilling problem must be carried out by
trial and error. The trial and error technique requires the selection of the magnitude
of the volumetric flow rate of the compressed air, q g, that will result in a bottomhole
pressure in the annulus of 3,500 psig. This trial and error technique further requires
that the upper limit pressures in each depth interval be selected so that the overall
interval integrals are satisfied. The trial and error q g that will satisfy these
limitations is
,
q 1 168 acfm
g
The volumetric flow rate of the compressed air, Q g, in consistent units is
1 168
,
Q g
60
3
Q g 19 47 ft /sec
.
Table 4-1 gives an average atmospheric pressure of 12.685 psia for a surface
location of 4,000 ft above sea level (mid latitudes North America) (also see
Appendix D). The actual atmospheric pressure for the air at the drilling location
(that will be used by the compressor), P at, is

p at 12 685 psia
.
P p 144
at at
2
P at 1 826 6 lb/ft abs
,
.
The actual atmospheric temperature of the air at the drilling location (that will be
used by the compressor), T at, is
t at 60˚F

.
T t 459 67
at at
T at 519 67.˚R

Thus, P g and T g become
2
P g P at 1 826 6 lb/ft abs
,
.