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Taking Water Pipe HDD To Extremes
“Extreme elevation changes set this project apart from other projects,” Bell continued. “The first bore dropped 1,500 feet from starting to exit point. That is the biggest elevation change we have ever encountered on a conventional directional drilling installation. In addition to elevation changes, the second bore had a sharp right turn and multiple direction changes.”
Bell said the park service had been considering ways to replace the old pipe for some time, and there had been discussions about whether the work could be done by directional drilling. One plan was to drill a portion of the route and use open-cut construction for another segment. Laney devoted several months planning and engineering to the project.
The HDD unit used was a Laney-manufactured LDD 753 powered by dual Caterpillar diesel engines, each developing 550 horsepower. The machine produces 683,000 pounds of pullback. The fluid system was a Laney designed and built Dragon tank with M-I Swaco shakers.
The first bore was 5,244 feet from the top down to the exit point at a grade that reach 45 degrees in some places. It followed the path of the park’s main road which led up to the drill unit’s location. The pilot hole was drilled with a 9 7/8-inch roller cone TCI bit and six-inch mud motor rented from J.T. Miller Inc. A Laney owned and operated Tensteer wireline system guidance system and rented SlimDril Drillguide GST gyroscopic tool were used to guide the bore.
“Environmental restrictions prohibited us from clearing any land in the park, and there were areas where we were unable to layout a True Tracker grid for the wireline system,” Bell said. “In those situations, we used gyroscopic guidance.”
The pilot hose was completed in approximately six weeks through interbedded layers of sandstone, claystone and shale. The pilot hole was completed in approximately six weeks.
Laying out and welding the six-inch stainless steel pipe in preparation for pullback was a challenge for Triad personnel.
“Pipe stringing and welding was restricted to a winding dirt trail and only minimal disturbance of the terrain was allowed,” said Bell. “The job required several weeks. As the string was laid out, temperature changes would actually move the pipe when it heated and expanded a problem because there was so little space. When the pipe cooled, it would contract.”
Prior to pullback, the pilot hole was reamed to a 17 1/2-inch hole with a TCI hole opener and then swabbed to ensure the hole quality.