In conventional drilling applications, hole enlargement is generally performed after the pilot hole is drilled. Typical applications are gas storage, coalbed methane, gravel packing work overs, or contingency hole enlargement operations
In these applications the enlarged hole size is anywhere between 1.5 to 2 times the pilot hole (for instance 6” x 12 ¼" or 8 ½" x 16”), and for this reason they are also called jumbo hole enlargement operations.
Jumbo hole enlargement operations have extremely fast penetration rates – 5 to 10 times faster than drilling with the pilot bit. Therefore, the customer decision to enlarge is centered on the well economics – the round trip cost versus the risk of remedial jobs due to the need of a jumbo opening ratio.