Houston-based drilling contractor Rowan of Houston completed the deepest large-diameter hole ever drilled with a down hole hammer and bit – drilling an amazing 3,896 feet – for a gas storage well in Tioga, Pa., that had been constructed by NE Market Hub. A number of other parties also assisted with the project to ensure the completion of the wells in a safe and efficient manner, including technical consultants Al Owings, Tom Weller and Jim Browning from Continuous Operations Incorporated (COI) of Houston, Bill Lahew from Numa distributor Bill’s Bit Service of Smithfield, Pa., Tom Siguaw from Market Hub Partners, and Numa regional manager Carl Chidester.

The Numa polycrystalline diamond (PCD) carbide bit was chosen because it was specially designed for oil and gas drilling applications consisting of highly abrasive and medium hard rock formations. The PCD bits allow operators to run DTH products longer and deeper.

A hole this deep required a large volume of air to efficiently clean the hole. Weatherford Inc. from Houston was contracted to supply and service more than 13,000 cfm of deliverable air from many different compressors, which were run behind five two-stage boosters. Since such a large air volume could not be run totally through the hammer, a ported sub with two 1-inch-diameter holes was run directly above the hammer that was fitted with a 3⁄4-inch choke for the 28-inch bit, and a 5⁄8-inch choke for the 24-inch bit. When the drilling of the 28-inch hole began, airflow monitors showed that the actual air volumes were between 10,000 cfm and 10,500 cfmgoing down the hole. Drilling pressures ran between 590 psi to 630 psi.

The project employed a telescopic drilling process with holes reducing in size from 39 inches to 24 inches. At the outset, a Numa Champion RC300 hammer was fitted with a 39-inch bit and drilled the first 80 feet of the hole. A 34-inch bit was installed in the RC300 hammer to drill down to 753 feet, where a conventional DTH hammer was used to complete the second and third phases of the drilling.

The reverse circulation (RC) drilling method provides an environmentally sensitive operation that can eliminate traditional hole-cleaning problems. Reverse circulation drilling utilizes dual-wall drill pipe and high pressure air to efficiently clean the hole. The principles of RC drilling and dual wall pipe are fairly simple. Air is forced down the annular space between the outer and inner pipe, and is exhausted out the outer edge of the RC bit. All cuttings and down-hole samples then are forced (vacuumed) back up through the center of the bit and inner pipe (collection tube) to be safely collected and discarded at the surface. With this method, no foam is required to clean the hole, and lubricants are not free to contaminate the formation.

The second phase utilized a Numa Champion 240 hammer with a PCD carbide bit to drill a 28-inch-diameter hole to install 26-inch diameter casing. During this phase, the hammer and bit drilled through a formation consisting of shale, sandstone and limestone to a depth of 2,272 feet. The hole was drilled dry, so cleaning this large-diameter hole at this depth was no problem.

For the third phase, a 24-inch PCD carbide bit was installed in the Champion 240 hammer, and the choke size was changed from 3⁄4-inch to 5⁄8-inch. The hammer and bit were tripped in the 2,272 feet hole, and continued drilling without incident through additional layers of shale, sandstone and limestone to install the 20-inch casing to a total depth of 3,896 feet.

Once reaching 3,896 feet, Federal Energy Regulatory Committee requirements dictated that the drilling be switched from DTH to fluid and a roller bit. The hammer was tripped out of the hole, and a 24-inch roller bit was tripped in. Drilling continued until a total depth of 5,996 feet was reached.