The CST chronological sample taker acquires sidewall cores using a series of core recovery bullets fired into the formation. Various bullet designs are available, corresponding to the degree of formation consolidation.
This percussion-type gun is accurately depth positioned by using a spontaneous potential or gamma ray log. A surface-controlled, electrically ignited powder charge fires a hollow cylindrical bullet into the formation at each sample depth.
Each bullet is attached by two retaining wires to the gun; these are used to retrieve the bullet and core. The wires have a breaking strength of approximately 1,800 lbf to release the gun from the core bullet, which prevents a stuck core resulting in a stuck CST sample taker.
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