Page 217 - Air and Gas Drilling Manual

P
at
at
,
P
= 2 116 lb/ft abs
at = p 144 2 Chapter 5: Shallow Well Drilling Applications 5-59
The atmospheric temperature of the gas (air) that will flow into any compressor, T at,
that will supply the drilling operation is
o
t = 60 F
at
T at = t at + 459 67
.
o
T = 519 67 R
.
at
Thus, P g and T g become
P = P = 2 116 lb/ft abs
2
,
g at
T = T = 519 67 R
o
.
g at
Using Equation 4-11, the specific weight of the gas entering the compressor is
2
(,116 ) ( . )
0
1
γ =
g
67
(53 .36 ) (519 . )
γ = 0 0763 lb/ft 3
.
g
To determine the minimum volumetric flow rate of air at API standard
conditions, it is necessary to select (by trial and error) a volumetric flow rate, q g
3
(scfm), that will give a kinetic energy per unit volume of 3.0 ft-lb/ft in the annulus
at the bottom of 1,000 ft depth of the borehole. Kinetic energy per unit volume
should be a minimum at the bottom of the annulus. The volumetric flow rate
selected (trial and error) is (at API standard conditions)
.
q g = 472 2 scfm
The value of Q g is
q g
Q =
g
60
3
Q = 787 ft /sec
.
g