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Gravel use presents technical challenges Oil industry, regulators join forces to meet challenges on Alaska’s North Slope, convert abandoned mines into fish, waterfowl habitat Rose Ragsdale For Petroleum News
Among the most visible and enduring signs of the oil industry’s presence on the North Slope are the gravel roads, pads and airstrips scattered across the tundra. While these piles of pulverized rock from ancient rivers appear to be as ordinary at the gravel roads and structures crisscrossing other populated areas of Alaska, they actually have evolved and challenged the oil industry for the past 30 years.
Gravel is abundant on the North Slope. Industry officials say the entire region is undermined by about 2,000 feet of frozen gravel and sand once you get below 18 inches of organic soils, lichens, sedges and various Arctic grasses.
No one knows how much gravel has been mined on the North Slope, but educated guesses put the amount in excess of 40 million cubic yards, covering roughly 10,000 acres.
That may sound like a lot, but it’s actually a fraction of 1 percent of the entire 15-million-acre central North Slope and less than 3 percent of the operating oil fields, said Bill Streiver, environmental studies leader for BP Exploration (Alaska) Inc.
Put in perspective, gravel infrastructure on the North Slope covers roughly twice the acreage occupied by Atlanta International Airport. Moreover, these pads, roads and airstrips are scattered across an expanse the size of West Virginia.
In the 1970s, gravel seemed to be the answer for building and maintaining oil field facilities in a frozen land of harsh weather and harsher conditions.
But gravel, abundant and benign, still presented technical challenges to North Slope oil field operators.
ARCO Alaska Inc., for example, soon faced a learning curve in road-grading technology.
The gravel, initially mined from the bottom of riverbeds, was rounded rock that did not compact well and over time, loosely compacted gravel would fall apart, creating cracks and fissures in the roads, according Jim Weeks, a top ARCO executive on the North Slope in the 1970s and 1980s.
One innovative ARCO employee thought the roads would compact and hold their shape better if the gravel was more angular, Weeks said in a recent interview.
“So we bought a gravel crusher, crushed the native gravel and no more problems,” Weeks recalled.
Riverbed gravel becomes problem More questions about gravel use arose in the 1980s.
Regulators became concerned about the impact of gravel mining in riverbeds on Arctic fish populations though the actual excavation occurred in winter.
“It soon became obvious that there was a hydrological impact to rivers from this practice,” said William Morris, a biologist with the Division of Habitat Restoration of the Alaska Department of Natural Resources. “During breakup, isolated pools would be left behind in gravel-scraped areas, creating a problem with fish entrapment.”
Though the ultimate impact of the riverbed mining was debatable, Streiver said the industry switched to land-based gravel mining in the 1980s.
“In the short term when we were out there digging up the gravel in the rivers, it wasn’t good for any fish. But if you made the river deeper, it might be better for certain species,” he said.
Morris said the industry’s extensive use of water taken from deep pools in the rivers in winter to build ice roads and pads also had a potentially harmful effect on fish over-wintering habitat, and could even result in fish kills.
Fish habitat is extremely limited in the Arctic, especially in winter where temperatures typically drop to minus 60 Fahrenheit and up to six feet of water in most rivers, lakes and ponds freezes solid.
In summer and winter, the industry also encountered problems with actually sucking fish out of the water with water and gravel, Morris said.
To avoid these potential environmental hazards, the oil companies stopped taking water from the rivers in winter and started using intake screens when they pumped out water in summer. These changes reduced hazards to fish significantly, Morris said.
Gravel mines become fish habitat Land-based gravel mining, meanwhile, brought new challenges when all of the gravel was removed from a pit.
BP’s Streiver said DNR biologists, then a part of Alaska Fish and Game, hit upon the “clever idea” of converting the gravel pits into additional fish habitat.
Today, the oil industry partners with state biologists to do just that.
“We had figured out the basics by 2000,” Morris said. “One of the things that turned out to be fairly important is how close to the shore a gravel mine site is. If it’s too close, it backfills with seawater and becomes useless as fish habitat.
“We also figured out that if you put the gravel mine near a river, chances are very good that a lot of fish will find the pit once it is rehabilitated. In those pits located a great distance from a river or creek, the wait likely will be longer,” he said.
Still, the wait can be worth it.
One gravel pit in the Kuparuk River field took more than 20 years for fish to find it. “Broad whitefish now use the pit as winter habitat, and to a lesser extent, other species of whitefish use it also,” Morris said.
In all, eight gravel mines have been rehabilitated and connected to stream channels on the North Slope. Of the larger older sites, Morris said a majority have been rehabilitated for fish habitat.
He said some of the larger sites that are not feasible for fish will be reclaimed eventually for waterfowl habitat. State regulators plan to build islands within them for waterfowl nesting areas far enough from shore to deter predators such as Arctic foxes.
DNR biologists also figured out that getting the oil field contractors to contour the sides of a mine to create shallow shelves on the sides of the pit after gravel mining ends at a site improves the quality of the resulting fish habitat.
Ideally, the pits-turned-fish-ponds range from 25-30 feet up to 60 feet deep and in total area from 15-20 acres to well over 100 acres.
“The big thing for fish is deepwater habitat,” Morris said. “In the Arctic, freezing limits over-wintering habitat. There is very limited liquid water on the slope in winter.”
More sources of water The gravel mines-turned-ponds also provide the industry with water in summer for remote camps and for keeping down dust on the roads. In winter, they help greatly with ice road and ice pad construction.
“It’s a win-win for the environment,” Morris said.
The ponds are able to provide ample water for industry uses because of the low density of fish populations on the slope.
“When spring breakup comes, ponds and lakes on the North Slope fill almost instantaneously, so water removed during the winter for ice road and pad construction is hardly missed,” Morris said.
Having the rehabilitated gravel mines allows even more fresh water to be stored over the summer, he added.
Today, rehabilitation happens concurrently with the gravel mining. The approach was successful when gravel was mined to build both the Northstar and Badami fields, officials say.
“The Northstar gravel pit near the Lower Kuparuk River was designed to mesh with the river so you wouldn’t know it was there, and that’s actually the case,” Morris said.
Less gravel mining needed Meanwhile, a trend nationwide toward minimizing industry’s impact on the environment has brought other changes to gravel use on the North Slope. In 30 years, the industry has succeeded in reducing the amount of tundra its operations affect by more than two-thirds.
“With drilling pads now about 20 percent of the size they were in the 1970s and directional drilling enabling industry to produce more oil from fewer pads, less gravel is needed,” Streiver said.
BP spokesman Daren Beaudo said the next evolution in oil field design will require even less grave. The new 120-million-barrel offshore Liberty field, for example, is being developed from an existing satellite development pad at the Endicott field “that is being augment with a little more gravel.”
“We’re eliminating need for a new separate production facility, albeit a small one like at Northstar,” Beaudo said. “We’ll also be able to eliminate a sub-sea pipeline and drill ostensibly from onshore at a distance of eight miles.”
Streiver said BP also won’t need a gravel road. “Prior to going to extended reach drilling at Liberty, the project would have required a gravel road,” he said.
The operators are also picking up gravel.
“We have a program where we go out to old abandoned drill pads, pick up the gravel and rehabilitate the sites by doing things like planting native Arctic grasses,” Streiver said.
If the reclaimed gravel is contaminated, the operator follows regulatory guidelines to dispose of it. But if the gravel is clean, the company uses it a new location.
So far, BP has reclaimed gravel from old exploration sites and three airstrips west of the Kuparuk River.
“We’ve also picked up parts of production pads and a man camp,” Streiver said. “In a couple of cases, we’ve also picked up gravel berms around the old reserve pits that we had for mud and cuttings in the 1970s.
“In a way, what we’re doing with the gravel mines is an extension of this idea that you minimize your footprint and where you can’t minimize your footprint, you look for ways to restore the area once you’re done,” he added.
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