A Boart Longyear drilling team recently completed a ventilation shaft for an underground longwall coal mine in Wyoming.

Guiding a 60-inch bit through a challenging formation that includes two aquifers, the drillers reached a depth of 550 feet. The task was completed earlier than expected, in four weeks, despite delays in project startup.

“What our team accomplished was absolutely remarkable,” says Jason Lam, U.S. and Mexico territory contract manager at Boart Longyear. “Drilling such a large-diameter hole through loss circulation formations in a single pass – and in less than a month and a half – is something few companies are capable of performing.”

The job was completed using a dual-tube flooded reverse-circulation drilling technique. It was key to the drillers’ success because it allowed the massive bit to penetrate loss circulation zones that prohibit the use of a more traditional raised bore drilling rig. The technique pumps air through the outer tube and forces mud and cuttings upward through the inner tube, preventing them from plugging porous rock formations.

The Boart Longyear Salt Lake City Rotary Drilling Services team worked around the clock, rotating three-member crews. They used a LM 200 top head drive rig fitted with stabilizers and the 60-inch bit. To minimize the chances of causing mine entry collapse, the borehole was drilled off to the side of the mine tunnel and a 54-inch casing with ½- inch wall thickness was installed and cemented in place. Underground mine crews then mined over and punched through the concrete to open up the shaft.

Boart Longyear, based in Salt Lake City, touts itself as the world’s leading provider of drilling services and equipment, and performance tooling for the mining industry. The company has more than 9,000 employees worldwide, manufactures equipment in six global factories, and sells to customers in more than 100 countries. For more information, go to www.boartlongyear.com.