Page 246 - Drilling Technology in Nontechnical Language

Chapter 10 – EVALUATION 237

Explosive sidewall coring

A tool is run in the hole on wireline that incorporates hardened hollow

steel bullets inside a long steel carrier (fig. 10–5). The bullets are secured
to the carrier with two wires. After placing the bullet at the correct depth
for a sample, an explosive charge drives the bullet into the wall. The carrier
is pulled up on its cable, and this exerts a pull on the wires holding the
bullet. With a bit of luck, the bullet will have penetrated to the right depth,
the wires will not break, and the bullet and sample will be recovered.
The bullet must be selected for the hardness of formation to be sampled.
The wrong choice may lead to the bullet bouncing off the wall (no sample
recovered) or overpenetrating (the wire will break before the bullet can be
pulled out of the wall).

Fig. 10–5. Explosive sidewall core bullet
Courtesy of Schlumberger.

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