Page 83 - Drilling Technology in Nontechnical Language

74 Drilling Technology in Nontechnical Language Second Edition

Running and cementing the rst intermediate casing
If there were any hole problems while logging, the drilling BHA and
drill bit last used may be used to go to the bottom of the hole and back. This
can check if there is any debris on bottom (rock material that remained in
the hole or cavings that have come from an unstable formation since the last
trip out). The action of a round trip with a bit and BHA can be beneficial. If

there are any tight spots while tripping in (places that require some force to
pass), the driller can start pumping mud and rotating the drillstring to ream
out the tight spots that might otherwise cause a problem when running the
casing. This round trip is called a check trip.
On some operations, the rig crew run in with the casing themselves. On
other operations, a specialist contractor will send out people and equipment
to work with the rig crews to run the casing into the well.

As with surface casing, a float shoe is screwed onto the bottom of the

casing. After two joints of casing (about 80 ft, or 24 m) is run a float collar.
A float collar is similar to a float shoe, except it has a thread at the bottom

end so that casing can be run underneath it. This gives two float valves in
the casing string, so that if one fails, the other acts as a back up.
The casing is run into the well. During running, the crew will put
a hose into the casing every two or three joints and fill it up with mud

(because the float valves on the bottom prevent mud from entering the

casing at the bottom). Now the casing outside diameter is smaller than
the drill bit, but it is much less flexible than the drilling assembly. It is

possible to have problems running casing into the hole because of this
and because of the large surface area of the casing compared to the drill
string. If there is a part of the hole that is enlarged and this is just above a
different rock formation that is in gauge, there will be a “ledge” in the hole.

The casing might hit this ledge, and it might be difficult to pass through
it. There is a better chance of getting stuck with casing because it is very
large and rigid when compared to the drillstring.
Once all the casing is in the well, a casing hanger is screwed onto the top
joint of casing. This has a cone-shaped profile that fits into the casinghead

housing on top of the surface casing. Figure 3–21 shows the situation
before the intermediate casing has been lowered down so that the casing
hanger lands inside the casinghead housing.

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