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River crossing requires innovative HDD work.

The successful installation of three separate horizontal directionally drilled (HDD) crossings by Mears/HDD LLC clearly demonstrates the challenges contractors face almost on a daily basis.

All three crossings were completed as part Of a project to replace a portion of an existing liquids pipe owned by Olympic Pipe Line, and operated by BP Pipelines, North America. Olympic's 400-mile interstate pipeline system includes 12-inch, 14-inch, 16-inch and 20-inch pipelines. The pipeline runs along a 299-mile corridor from Blaine, WA, to Portland, OR. The system transports gasoline, diesel, and jet fuel. This fuel originates at four Puget Sound refineries, two in Whatcom County and two in Skagit County, and is delivered to Seattle's Harbor Island, Seattle-Tacoma International Airport, Olympia and Vancouver, Washington and Portland, OR.

The three HDD crossings completed in 2004 for Olympic are near Arlington and Everett, WA. The Ebey Island and the South Ebey Slough crossings had drilled lengths of 5,700 feet and 1,400 feet, respectively. Crews installed a 20-inch pipeline at these locations. While the two proved difficult they were nowhere near as complicated as the Stillaguamish River crossing that called for a 16-inch diameter pipeline to be installed at a depth of 180 feet below the river bed.

From the outset everyone involved knew the Stillaguamish River crossing presented a special challenge. Two years earlier, difficult soil conditions prevented another drilling contractor from completing this crossing.

Mears Vice President Nell Smith said that although the Stillaguamish River crossing was only 3,340 feet in length, it was the most technically demanding of the three. Not only is the river system extremely ecologically sensitive it is well known for its excellent Chinook Salmon runs and fishing is also great for steelhead and trout as well. Therefore, any type of construction project in and around the Stillaguamish must take into consideration not only the environmental issues, but the fall and summer Chinook Salmon runs as well.

Smith said this project had to follow strict parameters. The permits, obtained by Olympic Pipe Line clearly defined the date work would be halted to accommodate the salmon runs, regardless of the stage of project completion.

Continuing, he noted that all of the contractors invited to bid on the project had to provide detailed plans as to how the bores would be completed, along with an estimate of the anticipated cost. All were also required to give a presentation outlining their respective plans. The Mears plan was selected.

Special tools

Mears Project Manager Jim Ellis gives part of the credit for the selection to the fact that the Mears plan called for the use of a downhole pressure monitoring device that would allow the annular pressure to be monitored at all times.

"Our plan was to use a downhole monitoring devise so that we could watch our annular pressure and compare the readings to the calculated pressures that the over-burben could withstand. That, along with a recorder that was installed on the two rigs we were mobilizing to the site would allow us to constantly monitor and record a number of parameters, including torque, push, pull, mud volumes and mud loss in the mud tanks, to name a few. In addition, the system transmitted the recorded data to the web via a satellite link every 15 minutes which allowed off-site personnel to monitor the drilling activities.

"Fortunately," Ellis said, "we selected a mud product supplied by MI Swaco called Drilplex that is designed to reduce pressure buildup. Normally, when you are using a standard extended bentonite and water mixture the resulting high gel strengths can cause increased annular pressure.

"Instead, the Drilplex, which is a rheology modifier, decreased the gel strength and lessened the opportunity for crews to pressure up the formation and create or cause an inadvertent fracture."

There is a substantial difference in elevation between the two ends of the crossing. At the lower elevation, on the south side of the river, was an agricultural area where a potato field was located. It was at this location that the Mears 660 rig was set up to begin the pilot bore. The north side of the river, where the pipeline right-of-way and the exit location for the bore were located, is adjacent to a residential area. Here, the riverbank drops approximately 100 feet from grade to the water line.

Ellis said, "It was evident from the start that the river crossing posed special challenges for the HDD contractor. I believe the client fully understood the complexities as well, given the difficulties the first contractor experienced."

Drilling begins

With the Mears 660 rig located at the lower elevation (on the south side of the river) crews started the pilot hole bore on July 13 using a 9 7/8-inch mill tooth bit. Initially a mud motor was used. Despite some early success with the mud motor, crews found it impossible to maintain directional control through the first gravel and cobble that was encountered.

After exploring several options, a decision was made to use a jet to allow the crew to drill ahead and negotiate the first of the three gravel/cobble formations that was encountered some 100 feet into bore.

In order to save that portion of the hole that had been successfully completed, a decision was made to run a temporary 12-inch steel casing. After the casing was installed, the drillstring was tripped back out of the hole to change back to the motor assembly and allow drilling of the pilot hole to continue.

Ellis said that despite encountering a cobble/gravel formations below the planned exit location that significantly slowed drilling operations, the bore's pilot hole was completed on August 2.

"Once we were able to complete the pilot bore, the 660 rig was moved to the higher elevation on the north side of the river to allow crews to set up the 160 rig on the south end," he explained.

A short time later crews were able to begin pre-reaming operations. "We started the cut from the south side with an 18-inch diameter hole opener," Ellis explained. "The 18-inch reamer was successfully pulled all the way through the bore.

"Next, a 26-inch reamer was connected. When crews attempted to pull it through the bore the drillpipe broke about 300 feet short of the exit location where the 25-foot thick cobble/gravel formation was encountered.

"At that point we had no idea why the drillpipe had parted."

Smith explained that the Mears crew and officials at the site felt confident that the pipe itself was not a factor because the breaks were occurring in the heaviest portion of the tool joint, an area where breaks traditionally do not occur.

After experiencing three pipe failures during this reaming operation, a survey probe was run from the north end of the bore to see where the pipe was laying in the hole.

He said, "It was at this point that we were able to determine that as the drillpipe was rotating in the thick cobble/gravel formation it caused the pipe to deviate from the originally drilled bore profile and rise as much as 10 feet outside the bore path. This was imposing so much stress on the pipe that it finally failed."

350-gmp of water flows into bore

Next, the crew managed to run the drill pipe through the bore. However, at some time during the process a perched water table was disturbed in the highest gravel and cobble formation, causing water to freely flow through the drilled hole down to the rig site at the south end of the site.

According to Smith, this occurred near the end of the work day and the crew was not aware of the problem until they arrived the following morning to find the lower elevation of the site flooded and water running out of the bore at a rate of some 350 gpm.

"Then we had the problem of what to do since we couldn't continue with a hole in that condition," Smith said.

He noted that when the perched water table was snagged and flooding occurred on the south end of the project one of the first options considered was to hammer in a steel casing to isolate the gravel layer at the top end of the bore. The problem with that was that Olympic was absolutely against having a casing around the pipeline.

"There was a risk that if a casing was installed it may not be possible to get it out and, for corrosion concerns, Olympic could not allow the pipeline to remain housed within a casing," he said, "so we were looking for something different."

That's when Mears superintendents on the project, along with other Olympic and Mears personnel, made a decision to call on Halliburton to use oil field technology to cement the hole.

"What Halliburton did was to direct our crew to go in and push pipe to just below the interface of the lower portion of the gravel/cobble formation," Ellis said. "Next, they pumped cement into the hole to provide a plug that would seal the bore.

"Although they were successful in reducing the flow of water, everyone was not convinced that the drillpipe could safely pass through the gravel formation at the north end. The project team agreed on a grouting plan in order to further seal the perched water table and to solidify the gravel layer. At that point, Northwest Cascade Inc. was called in to install 126 vertical pressure grout wells in a predetermined pattern."

While these two efforts worked to sufficiently dry up the hole, on the very next pass the drillpipe twisted off again.

"We were able to recover the drill pipe but it was clear that these challenging subsurface conditions called for further measures," Ellis said.

At that time, Mears approached officials with Olympic with the idea of installing a small diameter casing. "The idea was to get the drillpipe in, make sure it was in the correct location and then run a small diameter casing down over it in the top few hundred feet of the bore," he said. "This would allow the crew to pull a final ream pass across and make sure the bore was open. At the same time, since the casing would not be rotating, it would hold the drillpipe in place and prevent any deviation outside the bore."

Ultimately, the client agreed and the crew was able to pull the reamer successfully. Next, the cutter was taken back to the south end and the crew hooked onto a 160 ft long dummy pipeline section. The dummy section was pulled up to the casing, the casing was removed and then the dummy pipe pulled out of the hole at the north end. Olympic's representatives inspected the dummy section for damage.

As soon as the dummy section was pulled the casing was reinstalled (and surveyed to ensure it remained in the correct position) in preparation for the final line pull-in.

While this work progressed, crews with Snelson Companies Inc. were busy stringing and welding the pipe. Due to limited space, the pipe was welded up in two strings.

On Oct. 5, Mears' crew hooked onto the pipe and pulled it the entire 3,396 foot length of the bore in less than eleven hours (which included stopping for a tie-in weld and its field coating) successfully completing the crossing.

Smith said, "The job took two and a half months and was completed just 10 days before the scheduled permit termination date of Oct. 15, which coincided with the impending salmon run."

Both Ellis and Smith agreed that this was one of the most challenging HDD projects either of them has been involved in and that its success was due to capitalizing on the experience within the Mears organization and the cooperation of the project team.

Rita Tubb * Managing Editor
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Author:Tubb, Rita
Publication:Underground Construction
Geographic Code:1USA
Date:Sep 1, 2005
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