一种锥型，通常是圆头引导器形状的器件，一般出现在套管柱的最下端。
A tapered, often bullet-nosed piece of equipment often found on the bottom of a casing string.
后者在其中心有一圆柱形沟槽，这样能生成整体芯在钻孔作业过程中引导钻头。
The latter has a cylindrical groove at its center, thus generating a solid core, which guides the tool as it proceeds during the drilling operation.
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