Rock In Colorado Challenges HDD Contractors

September 2012, Vol. 67 No. 9

Patience and technique resulted in steady progress with no setbacks. As the pilot hole began its build toward the exit, penetration slowed. The decision was made to trip and change bits. After consideration, Jim decided to return to the bottom with the new bit, but without the addition of a motor. Again, the choice was the right one, as the driller worked the new bit through the trouble and back into the original pilot hole until reaching bottom. The same technique was continued until cobble and boulders were encountered at the exit side, sooner and deeper than expected. This discovery would increase the difficulty, as well as the risk, during the reaming process. The pilot bit was on line and just short of exit when a wire-line short interrupted communications with the magnetic steering tool. The last joint was slowly rotated into the pre-constructed exit pit confirming the accuracy of the DataTraX guidance system being used.

A 24-inch, TCI RockReamer was attached at the exit and pulled back towards the rig. Jim watched and listened as the tool worked its way down through the soil and boulders. Unsure and worried, he ordered the tool pushed back to surface. After studying the situation, he sent Matt and Israel back to the yard with a plan. Back-reaming would involve more Brotherton tricks of the trade.

Fighting round
"You have to fight round with round. Too many edges; there was too much space for cobble and rock to slide between the cutters. This buildup of cuttings and loose rock would damage the tool and drill string, while leaving us with an inferior hole that could cause trouble during pullback," Jim explained, "I needed this tool to grind everything and let nothing slide by."

The two worked through the night. They used a ¾-inch wall, 18-inch diameter casing to craft a protective shield that was placed around the tool, with very close tolerances between cutters. The fitted armor left no room for anything to slide between the cutters and forced anything loose in the hole to stay ahead of the cutters. At sunrise the next morning, the Brotherton’s customized tool was returned to the rig site, ready to resume reaming operations.