Page 494 - Air and Gas Drilling Manual

Chapter 10: Stable Foam drilling 10-19
example, the volumetric flow rate of the incompressible fluid will be sought.
Therefore, the trial and error process requires the selection of the magnitude of the
volumetric flow rate of the incompressible fluid (water and surfactant), q w, required
to yield a minimum kinetic energy per unit volume in the annulus of approximately
3
3.0 ft-lb/ft . Also, the minimum annulus foam quality must be greater than 0.60.
This trial and error technique further requires that the upper limit pressures in each depth
interval of the annulus be selected so that the overall interval integrals are satisfied.
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 at p 144
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 60˚F
at
T at t at 459 67
.
T 519 67˚R
.
at
Thus, P g and T g become
2
P g P at 1 826 6 lb/ft abs
,
.
T g T at 519 67˚R
.
Using Equation 4-11, the specific weight of the gas entering the compressor is
0
1
(,827 ) ( . )
1
g
(53 .36 ) (519 . )
67
3
0 0659 lb/ft
.
g
Note the above specific weight value can also be obtained from Figure D-4 in
Appendix D.