Boart Longyear rises to the challenge

A Boart Longyear team has risen to the challenge of boring a ventilation shaft for an underground longwall coal mine in south west Wyoming.

Task

Guide a 60 in. bit to a depth of 550 ft through a challenging geological formation that included two aquifers – all in just over four weeks.

Not only was the task completed, but it was completed several das ahead of the deadline despite project start-up delays.

Key to success

The dual-tube flooded reverse-circulation drilling technique, which allowed the extraordinary bit to penetrate loss circulation zones that precluded the use of a more traditional raised bore 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.

Working around the clock in rotating, three-member crews, the Boart Longyear Salt Lake City Rotary Drilling Services team utilised a LM^TM200 top head drive rig fitted with stabilisers and the massive bit. To minimise the risk of a mine entry collapse, the borehole was drilled to the side of the mine tunnel and a 54 in. casing with 0.5 in. wall thickness was installed and cemented in place. Underground mine crews then mined over and punched through the concrete to open up the shaft.

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

Adapted from a press release by Emma McAleavey.

Read the article online at: https://www.worldcoal.com/coal/26022015/boart-longyear-case-study-1978/