Frequent Challenges For Winter Ocean Drilling In Maine

By Jeff Griffin, Senior Editor | June 2012, Vol. 67 No. 6

“We have worked with Sargent on many occasions,” Kelly said. “The previous year we had completed another shore approach project with Sargent which won a Build Maine Award from the Associated General Contractors of Maine. So the two companies had an experienced team in place well-suited to the Northport project.”

Ultimately, it was decided to use HDD on the project.

“Sargent,” Kelly said, “entrusted a great deal to our team, and we moved forward together to tackle one of the most challenging projects we’ve faced.”

To launch the HDD segment of the installation, the ETTI crew used a Ditch Witch JT8020 HDD unit powered by a 275-horsepower liquid-cooled diesel engine. The machine develops 80,000 pounds of pullback, 10,000 foot pounds of torque and spindle speeds to 210 rpm. The HDD portion of the project was 250-feet long under the ocean floor.

The drill unit was set up in a position extremely close to the point reached by high tides.

“Cold temperatures -- the low-to-mid- 20s in the day and single numbers at night -- required that drill steel pipe had to be protected from drill fluid freezing and splitting the pipe,” Kelly said. “This was accomplished with antifreeze and thermal blankets.”

Kelly called subsurface conditions “brutal.”

“Eighty percent of the drill was through heavy cobble and massive boulders,” he said. “The pilot hole was made with a five-inch Railhead Incredibit which fractures rock in a random elliptical pattern, ‘dancing’ in the hole to produce a larger-diameter bore than that of other bits of comparable size. On this project, the five-inch tool produced a 10-inch diameter hole. We tracked the drill head using a Ditch Witch 752 tracking system operated from a boat. A Ditch Witch FM50 fluid mixing system was used. The pilot hole was completed in a two-day period, working from 4 a.m. until dark.”

After the pilot hole was complete, construction divers, working from barges, changed out the downhole tools, using air bags to float them into position.

Floating pipe

The most complex part of the project was floating pipe into the water, positioning it, sinking the pipe in the correct position, and then connecting it to the drill string for pullback.