Page 58 - Air and Gas Drilling Manual

2-8 Air and Gas Drilling Manual
2.3 Wellhead Equipment
All air and gas drilling operations require the use of a rotating head (or similar
air or gas flow diverter) which is installed below the rotary table. The blowout
preventer (BOP) stack is always used when subsurface overpressured dangerous gases
or fluids might be encountered while drilling (i.e., oil and natural gas drilling
operations, and geothermal drilling operations). Figure 2-7 shows schematics of
three typical wellhead assemblies for double and triple drilling rigs set up for air and
gas drilling operations to recover oil and natural gas, or geothermal fluids [6].

Figure 2-7: Typical wellhead assemblies for an air and gas drilling operation (G denotes a
rotating head, A denotes an annular blowout preventer, R denotes pipe or blind rams, and
S denotes the drilling spool).
2.3.1 Rotating Head
The rotating head or a similar air flow diverter was developed for use in air and
gas drilling operations to keep air or gas with entrained rock cuttings from flowing
to the drilling rig floor through the rotary table kelly bushings. Diverting this
drilling fluid flow from the drilling rig floor is mandatory for all air and gas drilling
operations. Even on small drilling rigs the air exiting the annulus (direct
circulation) must be diverted in order to provide a safe work space for the rig
operators. These diverter devices were developed with the introduction of air and gas
drilling operations in the early 1930’s.
The right side of the rotating heads shown in Figure 2-7 shows the vent to the
blooey line. Figure 2-8 shows a low pressure rotating head. This rotating head is
capable of diverting a 500 psig air or gas flow while rotating at 100 rpm (and 1,000
psig with no rotation). This rotating head is made up (via the flange fitting on the
bottom of the head) to the top of a BOP stack or the top of a casing spool and
casing. The BOP stack is incorporated in the wellhead assembly when overpressured
dangerous gases or fluids may be encountered in the drilling operation