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Chapter 9 – CASING AND CEMENTING 221

line up with the threads on the female end (top of the previous joint). The
connection can be rotated but the threads become damaged and will not
fully make up, so it has to be unscrewed again. The threads may be so
badly damaged that both of the casing joints have to be taken off again and
replaced. It is not an easy job to run big casings!
Large surface casings do not use the cement plug system. One reason
for this is that a large surface hole can become highly enlarged, and it
is uncertain how big it really is. These casings are normally cemented
all the way up to the surface or seabed. If top and bottom cement plugs
are used, the volume of cement has to be known in advance, but for a
surface casing, this is not known. The solution is to pump cement until
cement returns are seen back at the surface, and then mud can be pumped
behind to complete the job. The technique is called stinger cementing and

is shown in figure 9–13.

Fig. 9–13. Stinger cement job

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