Thermal Grout, HDD Make 6,200-Foot Electrical Transmission Installation Possible

By Jeff Griffin, Senior Editor | December 2012, Vol. 67 No. 12

Throughout the drilling process, SEDD monitored operations, including drill times, pull and push pressures, rotary torque, rpm, differential, soils removed, drilling fluid pressures and other fluid data, and gallons per minute being pumped. Disposal of drill cuttings, spoils and displaced drilling fluid complied with applicable regulations, permits and other project requirements.

SEDD completed the reaming operation in two ream passes -- a 36-inch diameter ream pass, followed by a 48-inch ream pass. The reaming strategy was subject to change depending on the types of soil encountered when drilling the pilot hole and earlier ream pass. The 48-inch ream pass was followed by a mud or swab pass immediately prior to pulling in the 36-inch steel casing. The drill stem was connected to the pulling assembly consisting of a tapered ball reamer, swivel, shackle and pulling head. Once started, the pullback operation was a continuous operation until completion.

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“Pullback installation of the 36-inch steel casing was successful, albeit longer in duration than anticipated,” said Olson. “We had estimated about 20 continuous hours to install the casing as compared to the 68 continuous hours it actually required. The challenges faced were apparent after the initial pullback attempt.”

Challenging geology
The geological formation constantly allowed the drill stem to become key-seated in the bottom of the borehole, creating a challenge to keep the reamer, which is located directly in front of the pulling assembly, from rotating freely as required.

“In order to overcome these challenges during the pullback,” Olson continued, “SEDD delayed pumping ballast water during the initial stages of the pullback in an effort to use the buoyancy forces on the 36-inch steel casing to assist with the rotation of the reamer. We also used a pneumatic hammer located at the north end of the pipeline to assist in breaking the frictional forces throughout the pullback.”

Fabrication of steel casing and HDPE conduits that would go in the casing were performed concurrently with drilling operations.

The HDPE fusion and lay-down area was along right-of-way and adjacent to the 36-inch steel pipe fabrication area.