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Intersection Beneath The Mississippi: 7,700-Foot Bore Generates Many Challenges For Ranger
A 9 7/8-inch mill tooth bit from Southeast Bit Co. was used. Steering was done by Horizontal Technology Inc. using a Tensor steering tool. On the entry side, water for drilling fluid came from the river. Water for the exit point drill unit was hauled from a fire hydrant about three-miles away. Fluid returns were maintained during the entire path of the hole with no inadvertent returns.
Drilling and intersection of the pilot holes required six days, plus two survey days. Intersection of the two bores deep under the river was a challenging part of the project.
“After several calculations by GEOEngineers using soil data and pressure models, a distance from each drill rig was determined to be the best place to attempt the intersect,” Simon said. “This predetermined distance of plus or minus 200 feet was the best area for which calculated pressures and allowable pressures were close to the same. The intent was to not let the calculated pressure exceed the allowable pressure.”
To establish the exact point of intersection, a grid had to be established above on the river’s surface. Tug boats towed two, 150- by 60-foot barges with 50-foot spuds into a position above the insect point. A Tru-Tracker grid system was set up on one barge to assist with the intersect by verifying that data from the wireless system was not being affected by magnetic forces of the earth or other forms of interference.
Horizontal Technology steering technicians on each drill rig were in constant communication and the drill bit of the entry-side machine was guided into the hole of the other drill unit 150-feet below. The exit side drill bit then was tripped back to the rig as the entry drill bit pushed across the already drilled hole. Intersection of the holes was completed in six days.
Marine activity delays added almost four days to the job, said Simon.
“Work was delayed two days because of dense fog on the river,” he explained. “As the tugs were mobilizing the barges, tug captains were unable to move because of very low visibility. There were two more delay days because the wrong size spuds were sent to the location, making it impossible to spud down due to depth of mud line and water current.”
In preparation for installation, the 12-inch carbon steel pipe lined with HDPE was assembled using a new type of connector that does not require flanges, said Rod Thibodeaux, Boardwalk Louisiana Midstream engineering manager.