Page 182 - Air and Gas Drilling Manual

5-24 Air and Gas Drilling Manual
Also determine the injection pressure, the input power required by the compressor,
and the derated output power available from the prime mover while drilling at 1,200 ft.
a) Sullair Model 840 Rotary Screw Compressor
A candidate compressor is the integrated system on-board the portable Tamrock
Driltech Model D25K drilling rig (see Figure 4-19). The on-board primary
compressor is a Sullair Model 840, two-stage, oil flooded, rotary helical lobe (screw)
type. This compressor is powered by a Caterpillar Model 3406, diesel fuel,
turbocharged prime mover capable of a 400 peak horsepower at the operating speed
of 1,800 rpm (see Figure 4-20). The compressor is capable of producing a
volumetric flow rate of 840 scfm and a fixed pressure of 340 psig at API standard
conditions. This drilling rig is capable of drilling to about 1,000 ft of vertical depth
so it can probably be used for drilling to 1,200 ft with a light weight drill string
(check drill string weight against hoisting capability). Even though this drilling rig
and its integrated Sullair rotary screw compressor are to be placed at the 6,000 ft
surface elevation drilling location, the compressor will still produce the same
volumetric flow rate as at sea level conditions. The actual volumetric flow rate of
this compressor at the 6,000 ft surface elevation is 840 acfm (see Chapter 4). This
volumetric flow rate is greater than the required adjusted minimum volumetric flow
rate of 481 acfm (factor of safety of 1.75). Therefore, this compressor unit is capable
of producing the volumetric flow rate to drill the borehole.
A comparison must also be made between the injection pressure required to drill
this borehole and the pressure capability of the selected compressor system. The
injection pressure is obtained by a sequence of calculation steps that determine the
bottomhole pressure in the annulus, the pressure at the bottom of the inside of the
drill string, and then the injection pressure (upstream through the circulation
system). In these calculations, the actual volumetric flow rate into the compressor is
840 acfm. Also, in these calculations, the actual atmospheric conditions at the
drilling location will be used (i.e., 11.769 psia and 70˚F) (see Table 4.1 or
Appendix D). The atmospheric pressure of the air, P at, entering the compressor is
.
p at = 11 769 psia
P = p 144
at at
2
P at = 1 695 lb/ft abs
,
The atmospheric temperature of the air, T at, entering the compressor is

o
t at = 70 F
T at = t at + 459 67
.
o
T = 529 67 R
.
at