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The eccentric or underreaming bits has proven to be highly successful in drilling ahead of pipe or casing in caving formations. This enables drilling operations to proceed without the hazards of caving walls. The casing is lowered as the drilling progresses. There is adequate room for couplings to pass through the underdug hole if the bit is kept properly dressed. This bit must drill its own hole and underdig at the same time. It cannot be used to underream holes that have been drilled unless the hole below the casing is filled with material as hard as the wall to be drilled. Concrete is generally used for this purpose.
Where drive pipe
is used, this underdigger will enable you to land the pipe where you
desire. The drive pipe will go much easier and will pass through compact
formations or shells where normally it would be impossible to go. In
hard formations the drilling speed is about half that of a regular
pattern bit. A tight line should be used and the tools made to reach
out.
Approximate Weight & Length Table
NOTE: While actual weights will vary only slightly from the ones shown, the length will vary depending on joint size. Lengths shown in the table are for bits having standard joints for hole size shown.
The spudding bit is characterized by its flat, thin body section.
This bit is used for starting holes in soft formations such as sand and clay. It is also used where a regular bit of suitable diameter would make the tool string to heavy for the machine.