Page 55 - Air and gas Drilling Field Guide 3rd Edition

46 CHAPTER 3 Surface Equipment

locked. This secures the rotating head for drilling operations. The drill pipe can
be lowered into the well through the rotating head as the drill bit is advanced.
The kelly drive (together with the kelly bushing) fits snugly around the kelly
and allows the internal rotating sections of the head to rotate with the rotation
of the drill string. If it is anticipated that a well will be making large volumes of
natural gas, the bottom hole assembly of the drill string is designed to allow the
stripper rubber to be stripped over the drill collars to the drill bit.
Procedures for placing the drill string into a well and removing it from the
well must be followed carefully when a well is making natural gas or geothermal
steam or hot water (or any other dangerous gases or fluids). There are other
operations performed by a drilling rig that involve use of the rotating head that
must be carried out carefully if a well is making gas or geothermal steam (e.g.,
placing a casing string or a liner string in a well).
Figure 3-10 shows a cutaway view of a typical rotating head and shows the
rotating head in the drilling position with the kelly inside the head. The kelly
drive section has a kelly bushing, which can be changed to accommodate various
kelly designs. The spindle subassembly rotates with the drill string. The spindle
housing subassembly (which does not rotate) is seated into the main body hous-
ing of the head and seals to prevent air or gas from passing to the rig floor. The
stripper rubber (flexible packer) diverts the air or gas with entrained rock cut-
tings to the outlet (to the blooey line). The flexible stripper rubber is forced
by air (or gas) flow pressure against the outer surface of the kelly or drill pipe.
There are other seals between the rotating assembly and the spindle housing.
Together all these sealing agents divert the air or gas flow (with entrained rock
cuttings) to the blooey line, away from passage to the rig floor (see Figure 3-10).
Although the rotating head was originally developed for air and gas drilling
operations, this device was adapted for use in geothermal drilling operations
and later for use in underbalanced drilling operations to recover oil and natural
gas. These recent applications have encouraged the development of rotating
heads capable of operating at higher pressures and temperatures. These high
pressure heads are used in underbalanced drilling operations where lightweight
drilling mud (or other drilling fluids) is used to drill through pressured oil or nat-
ural gas rock formations. The lightweight drilling mud (or other drilling fluids)
allows oil and gas to flow into the well bore as the drill bit advances into the rock
formation. When these reservoir fluids are circulated to the surface they impose
high pressures on the wellhead equipment. These high pressure rotating heads
are capable of operating at pressures up to approximately 1500 psig (1035
2
N/cm gauge)(while rotating the drill string at about 100 rpm) and up to approx-
2
imately 3000 psig (2070 N/cm gauge)(for the nonrotating drill string). The high
temperature rotating heads are generally used in geothermal drilling operations.
Most of these heads can operate with steam and hot water flows at temperatures

up to about 500 F(260 F).
Rotating heads are also used in air and gas drilling operations where subsur-
face high overpressured oil, natural gas, or geothermal fluids are not expected.