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→Special coring
A heavy duty core barrel should be considered when cutting long lengths of relatively homogeneous formations or when anticipating higher than normal torque loads. This system can also be especially attractive when rig time is the largest component of the coring expense.
A heavy duty core barrel should be considered when cutting long lengths of relatively homogeneous formations or when anticipating higher than normal torque loads. This system can also be especially attractive when rig time is the largest component of the coring expense.
[[file:conventional-coring_fig2.png|thumb|{{figure number|2}}Sponge-lined coring system. © DBS, a Baroid Company.]]
The precursor of today's heavy duty core barrels is the marine core barrel. This tool was developed to be stronger than conventional systems for use in offshore settings. The marine barrel increases the margin of safety against tool failure, but is restricted to cutting a 3-in.-diameter core.
The precursor of today's heavy duty core barrels is the marine core barrel. This tool was developed to be stronger than conventional systems for use in offshore settings. The marine barrel increases the margin of safety against tool failure, but is restricted to cutting a 3-in.-diameter core.
Attempts have been made to use core barrel liners to cut naturally fractured rock. Unfortunately, shards of core often cut into the relatively soft liner material, causing the core barrel to jam.
Attempts have been made to use core barrel liners to cut naturally fractured rock. Unfortunately, shards of core often cut into the relatively soft liner material, causing the core barrel to jam.
===Sponge-lined coring system===
===Sponge-lined coring system===