Page 31 - Air and Gas Drilling Manual

1-8 Air and Gas Drilling Manual
the inside of the borehole. At the surface the drilling fluid (water) from the annulus
with entrained cuttings is returned to the pit where the rock cuttings are allowed to
settle out to the bottom. The pumps on single drilling rigs are small positive
displacement reciprocating piston or centrifugal type.

Figure 1-6: Direct circulation mud system.

Figure 1-7 shows a detailed schematic of a direct circulation compressed air
drilling system that would be used on a typical double or triple drilling rig. Direct
circulation requires that atmospheric air be compressed by the compressor and then
forced through the standpipe on the mast, through the rotary hose, through the
swivel and down the inside of the kelly, down the inside of the drill pipe and drill
collars, through the drill bit (at the bottom of the borehole) into the annulus space
between the outside of the drill string and the inside of the borehole. The
compressed air entrains the rock bit cuttings and then flows with the cuttings up the
annulus to the surface where the compressed air with the entrained cuttings exit the
circulation system via the blooey line. The compressed air and cuttings exit the
blooey line into a large pit dug into the ground surface (burn pit). These pits are
lined with an impermeable plastic liner.