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Two Platforms, Two Shore Approaches, Two Lines And A Hurricane
At 2,955 feet, the south shore crossings were the shortest of the project and the first to be completed. They were also the only non-intersect crossings. The entry points were in a high-security area next to the DVP power plant, and HDD took place with an American Augers 70,000 pounds/pullback-drill spread on land and a 330-drill spread on the marine platform.
But there were some complications even here. For one, the south shore crossing included the 45-degree bend, which wouldn't have been a concern for the conventional open-cut dredged crossings envisioned when the ROW was acquired. But the ROW is only 120-feet wide, and since two lines were being installed offset 20-feet from each other, staying within ROW was a concern for an HDD crossing. To make it as easy as possible, Mears used a 'racecar' alignment.
"Basically, we started the drill path curve well before the bend, just like a racecar uses the full width of a track to start turning before it gets to curves," explains Denis Doherty of Haley & Aldrich, who was part of the Mears design team, "This allowed us to use flatter radiuses and avoid any issues in that area."
Steering for the crossing was done with a standard Para-Track II guidance system and 12-inch casing was installed along the first 270-feet of the curved bore path to allow enough push force to advance the bottom hole assembly along the bore path. Due to environmental concerns, downhole pressures were monitored closely to avoid inadvertent returns of drilling fluid. Drilling got off to a good start with a successful crossing and no release of fluid.
Divers helped to complete the initial phase of the first crossing by fastening a crane line to the drill string so that the string could be lifted onto the south platform. Then, the platform-based 330-drill spread worked in tandem with the shore-based 70,000 pound drill rig spread to ream the pilot hole to a final diameter of 22 inches.
The product pipes were welded and coated as needed onshore within the power plant staging area. Pulling the product was complicated by the need to keep the main power plant road open at all times. Tie-in welds were performed during the pullback operation and both pipes were supported over the road as needed during pullback. The first crossing of the project, from south shore to south platform, was completed successfully on April 12, 2011.