A cross-agency team that includes the Bureau of Land Management, the U.S. Geological Survey and the Alaska Department of Natural Resource will drill a test well at Franklin Bluffs in the central North Slope this summer using a lightweight drilling rig. The drilling forms part of a multi-year project to investigate coalbed methane as an alternative to diesel fuel as an energy source in rural Alaska.
“This will be the first coalbed methane test on the North Slope … specifically drilled for coalbed methane,” Charly Barker, senior research geologist at USGS, told Petroleum News.
The team has already investigated the potential for coalbed methane at Chignik on the Alaska Peninsula and at Fort Yukon in the eastern interior of Alaska. Although the other target area for investigation is Wainwright on the Chukchi Sea coast, the team is first going to drill the Franklin Bluffs test well.
We want to do some test drilling for coalbed methane in a permafrost area that’s easily accessible before doing the Wainwright investigation, USGS drilling supervisor Art Clark said. The Franklin Bluffs well has multiple objectives, including drill testing in the permafrost, coalbed methane testing in permafrost and subsurface stratigraphic studies, Clark explained.
The team is using the CS 1000 drilling rig that it bought last year for its coalbed methane investigation at Fort Yukon. Although the Fort Yukon well encountered some thick coal seams, the gas content and permeability of the coal both turned out to be too low for practical gas production. However, the drilling rig proved very successful, USGS geologist Beth MacLean said — the well drilled to a depth of 2,287 feet.
“We’re not sure what the depth capacity of this equipment is,” Clark said, “We’re thinking it’s going to be around 3,000 feet … it’s really small … it’s all engine and hydraulics.”
The rig weighs just 10,000 pounds and breaks down into components, Clark said.
Franklin Bluffs
The Franklin Bluffs drilling site is on an old construction pad just off the Haul Road, 40 miles south of Deadhorse.
“We want to know whether we can go in through the permafrost and continue down another 1,000 to 1,500 feet without the permafrost causing problems,” Barker said.
“We’re trying to do this while we’re still in a place that’s fairly accessible and easy to work out of, like Deadhorse,” he said.
The well will penetrate Tertiary rocks of the Camden basin. There is potentially up to 175 feet of coal so we’re looking at drilling as deep as 3,000 feet and coring as many of the major coal beds as we can, Clark said.
The state geological survey will also take drill cores to evaluate the subsurface stratigraphy — the well location is close to a seismic line, although the nearest existing well is about six miles away.
The team plans to do the drilling between mid-July and mid-August.
Permafrost and coalbed methane
The coalbed methane investigation at Franklin Bluffs will focus on the extent to which permafrost impacts the gas and its production.
“We’re going to look at the depth and character of the permafrost. We’re going to look at coal and coal gas, how it’s affected by permafrost,” Clark said.
The team particularly wants to find out whether the permafrost has caused the gas to escape from the coal. Other drilling on the Slope has shown that the gas content of coal tends to drop or is missing altogether in the permafrost, perhaps because the gas has leaked through fractures caused by expanding ice. The Franklin Bluffs investigation will test this hypothesis and perhaps shed light on whether this type of gas loss is likely to pervade permafrost areas.
“If we can substantiate this in one well it would have a major impact on the resources of coalbed methane because we could lose the first 1,000 to 2,000 feet of coalbed (methane) across the North Slope,” Barker said.
The prime drilling depth for coalbed methane on the Slope extends down to 3,000 to 4,000 feet, so losses in the permafrost could represent about half of the total resource.
“It’s an enormous resource lost — several trillions of cubic feet,” Barker said.
Drill rig testing
The relative ease of transportation of the lightweight rig that the team is using raises some intriguing questions about potential uses of this type of rig on the Slope for relatively low cost exploration or development. So a prime objective of the Franklin Bluffs well is to test the operation of the rig in deep permafrost.
“In this geologic setting how does (the rig do), what depth can we get — that will give us a better idea of what we can do with it later on down the road,” Clark said.
There’s also a question regarding how long a hole in the permafrost will remain stable and how long the hole will remain open.
“Most oil and gas rigs when they drill they’ll case off the permafrost and then continue drilling,” Clark said. “… We’re not going to case off our permafrost.”
However, the team will closely monitor mud temperatures, to see how these relate to ice, core and hole stability and to determine whether technology such as mud coolers is needed for this type of permafrost drilling.
Intriguingly, the well will penetrate the same Sagavanirktok formation that contains gas hydrates further north. So, although the team does not expect to find gas hydrates at Franklin Bluffs, the drilling tests should provide invaluable insights into the potential use of a lightweight rig for gas hydrate work.
“One of the things that’s being kicked around is can we use this equipment or similar equipment to do gas hydrate exploration,” Clark said. “… The gas hydrate people … are very interested in this hole.”
Wainwright
The test drilling at Franklin Bluffs is setting the stage for the Wainwright investigation — the team hopes to drill for coalbed methane in Wainwright in the summer of 2006 but still needs to find a substantial part of the funding for that project. The drilling will penetrate coal-bearing Cretaceous rocks down to 2,500 feet directly below the village.
What we’re trying to do in Wainwright is answer all the questions relating to coalbed methane in that environment — the geology, the gas content of the coal and the quality of the underground water, Clark said. The team is also going to test a new coalbed methane production technique involving the use of two wells. One of the wells will reduce the subsurface water pressure by pumping out water, so that the reduced pressure releases gas in the other well.
“We want to see if we can produce relatively freshwater through permafrost, a frozen zone, without losing the well or (running into) other problems,” Clark said. “… We’re not sure that anyone’s tried to do coalbed methane in high Alpine settings.”
Water disposal presents particular issues for coalbed methane production in a permafrost area because water will not dissipate or evaporate at the surface — excess water will need to be re-injected deep underground below the permafrost.
“We want to determine how much water would have to be produced to get the gas out and what’s the quality of that water,” Clark said.
Meantime the team is forging ahead with its plans for Franklin Bluffs this summer.
“The rig is at Fort Yukon now and its coming down on the barge in the next couple of weeks and then we’re going to pick it up in Nenana,” Clark said.
