Page 378 - Air and Gas Drilling Manual

Chapter 8: Air, Gas, and Unstable Foam Drilling 8-61
8.5 Water Injection
Water is injected into the volumetric flow rate of air (or other gases) flowing
from the compressors to the top of the inside of the drill string for three important
reasons. These reasons are
• Saturate the air or other gas with water vapor at bottomhole annulus pressure
and temperature conditions.
• Eliminate the stickiness of the small rock cuttings flour generated by the
advance of the drill bit,
• Assist in suppressing the combustion of the mixture of produced
hydrocarbons and oxygen rich air.
Figure 8-13 shows the typical “mist” pump. The figure shows a typical stand-
alone skid mounted positive displacement duplex liquid pump driven with a
Caterpillar Model 3304, diesel fueled, naturally aspirated, prime mover. This pump
forces liquid into the pressurized air flow line from the compressors to the standpipe
on the drill rig (see Figure 2-1).

Figure 8-13: Liquid “mist” pump for air (or natural gas) drilling operations.
The liquid pump draws its water from a liquid tank (located at the left back end
to the skid mounted unit shown in Figure 8-13). Often other additives are mixed in
the suction tank. These are typically corrosion inhibitors, polymer, and a foamer
[13]. Table 8-2 gives the approximate volume mix of these additives.
Table 8-2: Typical approximate additives volumes per 20 bbls of water for unstable foam
drilling (actual commercial product volumes may vary).

Additives Volume per 20 bbls of Water
Foamer 4.2 to 8.4 gals
Polymer 1 to 2 quarts
Corrosion Inhibitor 0.5 gals