Engineering Demands at the Colville River.

Getting oil from the Alpine project to the trans-Alaska oil pipeline in an environmentally friendly way was difficult with a mile-wide river in the way.

The pressure couldn't have been greater. In March 1998, nearing the end of what would be the shortest season on record for North Slope oil field construction, managers of Arco Alaska Inc.'s headliner Alpine development were just a touch nervous.

That's because a key element of that $1 billion developing field-construction of an underground river crossing by means of a drilling technique new to the North Slope-wasn't proving up.

Crews had failed five times to bore a 4,500-foot hole underneath the Colville River in attempts to create a mini-transportation tunnel designed to carry crude oil from the remote oil field to existing North Slope pipeline structures.

Designers were scratching their heads trying to figure out how to apply this technology, called horizontal directional drilling, to Arctic conditions. Drillers from Outside were still coping with the operating changes required by the cold environment.

And time was quickly running out for that winter construction season, the only time that crews are permitted to work on the fragile North Slope tundra, protected by a deep layer of frost and ice.

Fast-track to the present Representatives from Arco Alaska and the project's designer, Michael Baker Jr. Inc., are just a touch nervous again. But for an entirely different reason-they're awaiting a decision as to whether this same Colville River crossing project, now nearly complete, will win a national engineering achievement award.

Already, the project's design has been selected by the Alaska section of the American Society of Civil Engineers for a state award. It was also named an outstanding project in the organization's western zone, according to Howard Thomas, past president of the Alaska section.

"Uniqueness was a big reason for the Colville project's selection for the state award," he said. "This directionally drilled river crossing was the first of its kind in the arctic and in permafrost."

Even Alaska Coy. Tony Knowles got on the bandwagon of praise for the project. In a supportive letter submitted to the national engineering organization, Knowles lauded the environmental attributes of the design and the new technology of boring under the river, as compared to more conventional bridge construction or trenching through the riverbed.

"The goal of the project was to leave behind nothing but the pipeline. The design engineers took great efforts to minimize human disruption of the environment," he wrote. "I am impressed by this extraordinary engineering accomplishment ...."

Considering HDD 

Known as HDD in the industry, the technology involves a drill stem that can be precisely steered, tracked and directed in all three dimensions. Targets can be hit within three feet, even after boring through lengths of up to 6,000 feet. Pipelines then run underneath (instead of over or through) a natural barrier, such as a river.

The technology is used for pipeline construction outside of Alaska, in areas where soil conditions are amenable to horizontal drilling and the necessary specialized equipment operates with ease in moderate temperatures.

"Elsewhere in the world, this technique is commonplace and preferred," said Martin Thurlow, Arco Alaska's project manager for Alpine. "It works best in silts and clays. It doesn't work well in gravel and probably can't be made to work in cobbles."

Unknown was how horizontal directional drilling would work in permafrost, the perpetually frozen layer of earth found throughout much of Alaska, particularly on the oil-rich North Slope.

Horizontal directional drilling in permafrost was always considered infeasible, recalls John Swanson, vice president of Alaska operations for Michael Baker Jr. Inc., the engineering firm that designed Arco's Alpine project.

That is until Arco Alaska decided to try that technology as a means for providing pipeline access across the Colville River to the North Slope's most western field, Alpine.

"The idea was in the back of everyone's head that maybe we could try this," Swanson said. "The first thing that really hit us was that environmentally, everything else was going to tear up the countryside, except for the directional drilling, and the costs appeared to be half (of building a bridge or digging a trench).

"It became a point where we asked, 'What can we do to make this technology work?'"

Preliminary studies and engineering models showed that the technology could work, despite the layer of gravel beneath the Colville riverbed and concerns about how the hot crude carried in the pipeline would affect permafrost surrounding the line.

Proving the technology on a large scale became the next step.

"We almost had no choice. The Colville River presented an immense obstacle," Thurlow said.

Nearly a mile wide at its narrowest point, the Colville provided a substantial barrier to accessing Arco's western oil field.

Spring breakup, with substantial runoff from the Brooks Range roaring through the Slope to the Beaufort Sea, includes icebergs and large sheets of ice flows, Thurlow said.

"The result is that building any kind of bridge would be challenging and unbelievably expensive," he added. "So HDD was the best choice from a cost and environmental perspective.

"We just had to make it work. If it didn't, then the entire project was in jeopardy," he said.

Making it Work

The first season of horizontal directional drilling on the North Slope was chalked up to a learning experience, filled with more than a few tense moments, Thurlow said.

For starters, support construction crews were late to the field because an unusually mild November and December kept ground too soft for work. The frost line didn't drop below the required level considered safe for work on the tundra until the very end of 1997.

While construction crews from Houston Contracting in Fairbanks hastened to build ice roads and start preparing the pipelines that would eventually be pulled through the tunnel under the river, Outside workers traveled north with the specialized drill equipment to begin their first Arctic winter season.

Horizontal Drilling Inc., a Houstonbased firm, won the bid to try the new technology on the North Slope. And initially, problems came from a specialized blend of drilling fluid called mud.

Drill mud is a watery substance injected into the bore hole to keep the drill bit cool, to circulate out cuttings and, if necessary, to inject special chemicals if problems develop down the hole, such as a freezeup.

Because of concerns with working in frozen ground, Arco and its designers came up with a variety of mud mixtures to keep the flow from freezing up. "We looked at freeze depressants and temperature control as possibilities but probably outsmarted ourselves," Thurlow said.

A special mixture was concocted that would lower the freezing point of the mud. But that chemical leached into the soils and melted the permafrost around the hole, he explained. "The result was that the holes kept collapsing and were lost when the drill pipe became stuck."

Finally, crews started using a conventional mud mixture, without the special freeze depressant chemicals. Success came, just at the end of the spring 1998 season, as the first of four planned holes was finally bored out.

"It did, however, prove the feasibility of the concept and gave us a wealth of experience with which to go away and plan for our second attempt nine months later," Thurlow said.

During the second construction season at Alpine, which ended in the spring of 1999, drillers reverted to a conventional mud system, similar to that used in other parts of the world.

"The result was three new holes, all completed with almost no problems, fin time," Thurlow said.

Construction crews were able to pull through the four lines, and start hooking up the system that will carry crude oil from Alpine to Kuparuk, where it will eventually feed into the trans-Alaska oil pipeline. The project is scheduled to be producing later this year, after the final construction and installation of operating equipment.

During both construction seasons, drillers lost some of the drilling mud mixture in the bore holes, particularly in the thawed zone under the active river channel. Subsequently, Arco conducted water monitoring to make sure the drilling fluids didn't reach the surface.

"We knew that we were drilling with something close to river water anyway, so there was not impact risk," Thurlow said.

News of that drilling mud loss unnecessarily alarmed a number of people, Swanson noted.

"It's the uncertainty of not knowing where exactly the material is," he said. "We were able to prove to agencies that no material ever migrated into the water. That was one of our last stumbling blocks."

Future Use

In addition to the professional recognition the project has received, the Colville River crossing proves that oil field development can be improved, from an environmental and expense perspective.

Thurlow estimates the savings over conventional bridge building to be as much as $150 million.

The other alternative, digging a trench across the river during winter, would have required that the active channel be diverted so the bed could dry up. "That's not an easy thing to do. Environmentally, it's the least friendly method--it's more the brute force, or sledgehammer technology," he said.

Swanson sees horizontal directional drilling techniques being applied to other remote oil field developments. "As we move further west and east on the North Slope, it has good applications," he said.