Page 207 - Drilling Technology in Nontechnical Language

198 Drilling Technology in Nontechnical Language Second Edition

The casing is lowered into the drilled hole and cement is placed between
the cement and the hole. The cement has to support the casing (the physical
loads) without long-term deterioration. It has to protect the casing from
corrosion due to salt water within the formations around it.

The cement must also prevent formation fluids and gases from moving
up the annulus outside of the casing, which could be anything from
inconvenient to disastrous.
Cement is also used for other purposes during drilling a well. It may
seal off zones that allow mud to leak into the formation. It is used to
abandon a well by sealing the wellbore to prevent fluids and gases from

migrating to the surface. It is often used to seal off the lower part of the
well and allow a new hole to be drilled away from the old wellbore.
Casing and cementing will be described so as to impart an understanding
of the importance of the casing and cement, how these things are designed,
and how they are placed in the well.

Casing Types

Casing provides different functions during drilling, completing,
producing, and abandoning a well. In a deeper well, there may be half a
dozen different kinds of casing used to perform the necessary functions at
different stages of drilling and completing the well.

Conductor pipe

The first casing is usually called the conductor. It may be driven into

the ground with a pile driver or it may be cemented inside a drilled hole.
The conductor is not set deep into the ground, so there is no strength to hold
formation pressures in the event of a kick. The purposes of the conductor
are to accomplish the following:

▪ Conduct drilling fluid returns back up to the rig during
drilling surface hole so that a closed circulation system can
be established. A closed circulation system is desirable so that
mud returns can be treated, drilled solids removed, and the mud

reused. (An open circulating system is where the fluid returns
from the well are lost, for instance into the sea.)

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