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Coalbed methane drilling completed Core drilling identifies gas in buried coal seams, initial results show low saturation and ‘clean’ water content Patricia Liles Petroleum News Contributing Writer
A team of state, federal and university researchers in mid-September successfully completed a 2,287-foot core hole to assess the potential of tapping coalbed methane as a power-producing energy source in the eastern Interior village of Fort Yukon, Alaska.
Drill crews punched through two sections or layers of coal, using a core rig owned by the state of Alaska. Researchers collected coal samples of the two and one-half inch diameter core and have been monitoring and measuring the amount of gas contained in the deeply-buried lignite coal.
“There is gas there,” said Charley Barker, research geologist for the U.S. Geological Survey and a member of the research collaboration. “You can light the gas with a match.”
Whether that coalbed methane can be produced economically, replacing 360,000 gallons of diesel fuel burned annually in the village’s electric power plant, has yet to be determined.
The group’s final conclusions and an accompanying report on the $1.6 million research project should be completed in about a year, according to Brent Sheets, Arctic Energy Office representative for the U.S. Department of Energy, which contributed about $1 million for the multi-year research project.
This November, the various players plan to meet and discuss preliminary results from this fall and to decide on plans for next year — whether drilling will continue at Fort Yukon or whether the drill rig will be moved to another remote village site to test for coalbed methane resources.
Fort Yukon is one of about 40 remote villages in Alaska located on or near known coal resources. Two other communities, Wainwright on the North Slope and Chignik on the Alaska Peninsula, are also high priority targets for the coalbed methane exploration program. Initial tests show low saturation Early indications show the coalbed methane gas contained in the Fort Yukon lignite coal contains low saturation levels, which means that to produce the energy source, substantial water pumping would be required.
“Some (samples) measure up to 50 percent saturation, but on average, it’s 25 percent,” Barker said, during a Sept. 21 teleconference interview from his Denver office.
Coalbed methane gas will typically flow freely from buried coal seams which measure 100 percent saturation, Barker said. As the saturation percentage goes down, more water must be removed from the coal formation to liberate the gas. “The pressure at that depth, it’s a lot of water,” he said.
Offsetting the low saturation rate is some good news. Initial hydrological tests also conducted this fall indicate that the water contained in the coal formation, which would have to be removed to produce gas, is relatively “clean” water.
“It’s not saline or salty water,” Sheets said. “It’s like fresh water and it could be used.” Two zones of coal identified Drilling this year identified two zones of coal at the test or observation drill hole about a mile east of Fort Yukon. The drilling site was selected based on a previous, unrelated, drill hole completed 10 years ago, which unexpectedly encountered gassy core samples at a depth of 1,280 feet.
This fall, the research team re-entered that old drill hole and began collecting core samples where the previous drilling stopped.
The first zone of coal begins at 1,256 feet, ending at 1,316 feet, according to Barker. The next 16 feet contain a carbonaceous coaly-shale mixture, still capable of containing methane gas, he said. Below that is another 10 feet of the soft brown lignite coal, typical at Fort Yukon.
The second, deeper zone of coal is a thinner swath stretching 21 feet, beginning at 1,900 feet and ending at 1,921 feet. Researchers had expected that deeper zone of coal to be thicker and at a shallower level, based on results from a seismic survey conducted around Fort Yukon in 2001. Clean coal found Analysis of coal samples collected 10 years ago shows that the Fort Yukon coal has a high moisture content and relatively low energy value, Barker said. But it’s considered high quality for its ultra-low sulfur content, some of the lowest he’s tested. “It’s extremely clean coal.”
Fort Yukon coal tests 0.03 percent sulfur, compared to 0.2 percent typically found in coal currently mined in Healy, Alaska, which is also considered low sulfur coal, Barker said.
This summer’s research project kicked off with drilling on Aug. 21. The on-site work wrapped up Sept. 12 and the state-owned drill rig was winterized and stored at Fort Yukon.
State geologists from the Alaska Division of Geophysical and Geological Surveys also participated in the project this summer. Federal funding from the Bureau of Land Management allowed the state to purchase the slim-hole Christiansen CS 1000 P6L core rig and accessory equipment, totaling $267,344.
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