It’s like a word problem. You know the one: Two trains on the same trackleave at different times, one from the north and one from the south, where willthey intersect? For Michels Directional Crossings Co., that was the questionabout the two drill bits it used during a record horizontal directional drilling(HDD) project in Canada last year. Success hinged on where the two bits met inthe middle.
In the Canadian province of Quebec, in the French-speaking city ofTrois-Rivieres, 88 miles northeast of Montreal on the banks of the St. LawrenceSeaway, Michels used a relatively new method in HDD — the intersect method — tocomplete a drill of more than 7,400 ft during the harsh winter months.
Trois-Rivieres, founded in 1634, is a leading worldwide production center forthe pulp and paper industry. The city sits on the St. Lawrence River and at themouth of the Saint-Maurice River and has a population of more than 137,500people.
The purpose of the project was to connect utility transmission linesbelonging to Trans Quebec and Maritime (TQM) Pipeline to an industrial powergrid. The new pipeline will supply natural gas to a 550-megawatt cogenerationplant being built by Trans Canada Energy. Michels worked as prime contractor forproject owner Gaz Metro, a natural gas supplier in Quebec, which also will usethe lines for local distribution.
Michels set an industry record for 20-in. diameter steel pipe at 7,456 ft,according to Michels design engineer Gregory Goral, who helped develop thepre-design drawings. The length of the drill surpassed the company’s previousmark for a single drill length of 6,580 ft.
The distance was too long for one drill rig, Goral says. After a certainpoint, a single rig would no longer have the horsepower needed to provide thethrust and rotary torque required to cross the entire span through solid rock.Michels decided to use the intersect method, a newer process the company hadsuccessfully used before on other projects, but none nearing this extreme of alength.
The intersect method employs two drill rigs that start from opposite ends ofthe project site and meet somewhere in the middle. In effect, one drill providesthe pilot bore for the other.
One of the most difficult aspects encountered during the planning of theproject was determining where the drills would meet, Goral says. The companyfactored in equipment capabilities, production time and length to determine thejuncture.
“It took probably 400 to 500 ft to perform the intersect,” says Goral,explaining that one pilot hole had to be directed and drilled into the other asthe drill bits converged. Michels monitored the progress using a secondarytracking system, which normally involves a guide wire laid along the ground topick up a signal from the pilot bit.
However, ice and river traffic did not allow the wire to be laid across thesurface of the river, says project director Mike Prior, vice president andgeneral manager of Michels Directional Crossings Co.-Canada. Instead, thecompany used a coil in a non-metallic vessel to pick up the signal and determinethe position of the drill head.
The company also tried using a helicopter to track the progress, but thepropeller blades interfered with the signal, Goral says.
The Michels crew started drilling Feb. 15, 2005, from the north bank of theSt. Lawrence. The company used a Michels Atlas 840, an 840,000-lb rig, and aMichels Hercules 1200, a 1.2 million-lb rig, to drill 160 ft below ground level,beneath the riverbed, starting with a 9 7/8-in. diameter pilot bore.
“The vast majority of the drill was mainly drilled through bedrock thatranged in compression strength from 3,000 to 8,000 psi,” Goral says. In additionto the shale bedrock there was solid limestone.
The bedrock on the north side was approximately 100 ft below the surface.Michels installed 400 ft of steel conductor casing and used a telescoping methodto drive the casing into the overlying soils. The diameter of the casingdescended from 42 in. to 36 in. to 20 in. The bedrock on the south side wasright at the surface and required only 40 to 50 ft of casing.
With the 840,000-lb rig set up on the north side of the St. Lawrence, thecrews drilled more than 4,800 ft until it reached the hole drilled from thesouth side.
Before the crews could begin drilling from the south side, Ganotec, the pipesupport contractor hired by Gaz Metro, had to build a jetty out into the waterto provide ground access to an island where the 1.2 million-lb rig was thenstaged. The drilling began Feb. 23, 2005.
The machine drilled approximately 3,375 ft toward the north site. The boreserved as a pilot hole for the intersecting drill. The intersect procedure wascompleted March 8, 2005.
After the initial bore was complete, Michels reamed the hole to approximately30 in., Prior says. The entry and exit points were opened to 32 in.
Michels began and completed pipe pullback on May 5, 2005.
Not for Camping
At the north and southjobsites, Michels built large, hangar-sized tents to enclose the area where thedrilling took place, serving the crews, the machinery and the surroundingcommunity.
The tents protected the workers and machinery from the extreme cold, whichGoral says got as low as -45 F.
These tents also mitigated noise disturbances to nearby communities on thenorth side, Goral says.
Talking the Talk
Another obstacle forMichels was overcoming a language barrier. The English-speaking Michels crew andthe French-speaking Ganotec and Gaz Metro crew met weekly during the project todiscuss the progress.
With the help of translators, the two companies were able to communicate withno problems, Prior says. During the project, some Michels employees even tookthe time to learn some French.
Bradley Kramer is assistant editor for Trenchless Technology.