STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

Air and Gas Drilling 845
The booster, which can compress air coming from the primary compressors
to higher levels (i.e., on the order of 1,000 psig or higher), is always a pistontype
compressor capable of variable volumetric flow and variable pressure output.
The volumetric rate of flow requirements for air drilling operations and
unstable foam drilling operations are quite large, on the order of 1,000 actual
cfm to possibly as high as 4,000 actual cfm.
For stable foam drilling operations, much less volumetric rate of air flow is
needed (Le., usually less than 500 actual cfm). Also, the compressor should be
capable of variable volumetric rate of flow and variable output pressure. The
back pressure must be continuously adjusted to maintain a continuous column
of stable foam in the annulus. This continuous adjustment of back pressure
requires, therefore, continuous adjustment of input volumetric rate of airflow
and output pressure (also, water and surfactant must be adjusted).
For aerated mud drilling operations, the compressor should also be capable
of variable volumetric rate of airflow and variable output pressure. Again, as
drilling progresses, the input volume of compressed air and the output pressure
are continuously adjusted.
Chemical (and Water) Tank and Pump. The pump injects water, liquid foamers
and chemical corrosion inhibitors into the high-pressure air (or gas) line after
compression of the air and prior to the standpipe.
Solids Injector. This is used to inject hole-drying powder into the wellbore to
dry water seeping into the borehole from water-bearing formations.
Rotating Kelly Packer (Rotatlng Head). Figure 4-187 shows the details of a
rotating head, This surface equipment is critical and is also a unique piece of
moving seal here
gas or air
down thru kelly
Figure 4-1 87. Rotating head.