Page 226 - Drilling Technology in Nontechnical Language

Chapter 9 – CASING AND CEMENTING 217

Clearly, cementing against massive salts is a complex problem if the
well is to meet its long-term objectives. The success of this cement job
starts when drilling through the salt (minimizing leached washouts). Good
planning, expert involvement, and attention to every detail, including

slurry and spacer design, rig equipment, downhole casing configuration,
and cement job supervision and quality control, are vital.

Running and Cementing Casing

After drilling and logging a hole section, casing is lowered into the
well. It is cemented in place by pumping cement down the inside, where it
exits at the bottom of the casing and comes back up the annulus.
Casing usually comes in lengths of around 40 ft. A special valve called

a float shoe is screwed on the bottom joint of the casing. This is made of
cement with a plastic valve in the middle, so that it is all drillable with

normal drill bits (fig. 9–9). The valve allows fluids to be pumped down
through it but does not allow fluids to flow the other way. This keeps the

cement slurry in place once pumping stops. Without the float valve, the

higher hydrostatic pressure in the annulus would force cement to come
back up inside the casing once pressure is released at the surface after
cementing. Pressure in the annulus is higher because cement slurry in the
annulus is denser than the mud inside the casing.

Fig. 9–9. A oat shoe screwed onto 30" casing

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