Page 326 - Air and Gas Drilling Manual

The atmospheric temperature of the air that flows into the compressor, T at, that will
supply the drilling operation is
o
t at = 60 F Chapter 8: Air, Gas, and Unstable Foam Drilling 8-9
.
T at = t at + 459 67
o
T = 519 67 R
.
at
where t at is atmospheric temperature (˚F),
T at is absolute atmospheric temperature (˚R).
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
2
where P g is the gas pressure (lb/ft , abs),
T g is the absolute gas temperature (˚R).
Using Equation 4-11, the specific weight of the gas entering the compressor is
(,116 ) ( . )
2
1
0
γ =
g
(53 .36 ) (519 . )
67
γ = 0 0763 lb/ft 3
.
g
3
where γ g is the specific weight of the gas (lb/ft ),
R is the gas constant for API standard conditions air (53.36 ft-lb/lb-˚R),
S g is the specific gravity of the particular gas used (for API standard
conditions
air S g = 1.0).
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 the 10,000 ft depth 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 = 1 588 8 scfm
,
.
g
where q g is the gas volumetric flow rate in the circulation system (scfm or acfm).
The value of Q g is