Page 75 - Drilling Technology in Nontechnical Language

66 Drilling Technology in Nontechnical Language Second Edition

Running and cementing surface casing

Now 26" (660 mm) diameter surface hole has been drilled below the

conductor to a depth that gives sufficient formation strength to contain
any likely overpressures if a kick occurs in the next hole section. Casing is
cemented in place with the casing shoe in this strong formation.

Once the cement is hard, the top joint of casing is unscrewed. The
surface casing connection just above the conductor top is left a little less
tight, and now it can be unscrewed by turning the top joint of casing,
which is sticking up above the rotary table. Once this is out of the well,
the diverter is removed from the conductor, leaving the top of the surface
casing exposed. If for some reason the surface casing cannot be unscrewed,
or if the connector is in the wrong place, the diverter can be lifted slightly.
This will allow the rig welder to cut the casing above the connection with
an acetylene torch. The diverter cannot be removed until this top joint of
casing is out.
At the top of the surface casing now is either a thread or a cut end. A
special piece of equipment, a casinghead housing (CHH), is screwed onto
the thread, or there is also a weld-on type of CHH that can be attached to

the surface casing by welding (fig. 3–17). The CHH has a flange on top

that is used to attach the blowout preventer. Also, the weight of the next
casing will be supported by a hanger sitting inside the top of this spool.
Figure 3–17 shows the CHH made up on top of the surface casing. Note
also the plates below the CHH, which sit on top of the conductor and so
transmit loads from the CHH to the conductor. This is also illustrated in

the middle photograph in figure 3–5. The valve shown on the right of the
picture allows fluids to be pumped into the well or released from the well.

Any pressure inside this space can be monitored with a pressure gauge.
Once the CHH is in place (whether a screw-on or a weld-on type), the
blowout preventer can be positioned and attached to the top of the CHH.
The blowout preventer equipment and control system must be tested to
ensure that everything works. It is also vital to pressure test the entire BOP
and each part of it to ensure that it will hold the pressure that it should.
BOP systems come in standard pressure ratings of 2,000 psi (13.7 kPa),
3,000 psi (20.7 kPa), 5,000 psi (34.4 kPa), 10,000 psi (68.9 kPa), and 15,000
psi (103 kPa). BOPs also come in different sizes, the size being the nominal
inside diameter of the BOP.

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