Powder River Basin
The Powder River Basin is a geologic structural basin in southeast Montana and northeast Wyoming, about 120 miles (190 km) east to west and 200 miles (320 km) north to south, known for its coal deposits. The region supplies about 40 percent of coal in the United States. It is both a topographic drainage and geologic structural basin. The basin is so named because it is drained by the Powder River, although it is also drained in part by the Cheyenne River, Tongue River, Bighorn River, Little Missouri River, Platte River, and their tributaries.
While the Powder River Basin is unified geologically, residents of areas distant from the Powder River proper do not think of themselves as living in a single geographic region. For example, residents of the Crow Reservation in the Big Horn River watershed, or of Sheridan in the Tongue River watershed, would locate the Powder River Basin as the region east of the Big Horn Mountains, using a definition based on watershed and topography.
Major cities in the area include Gillette and Sheridan, Wyoming and Miles City, Montana. Outside of these main towns, the area is very sparsely populated and is known for its rolling grasslands and semiarid climate. It is the single largest source of coal mined in the United States, and contains one of the largest deposits of coal in the world. Most of the active coal mining in the Powder River Basin actually takes place in drainages of the Cheyenne River. Because of the Powder River Basin, Wyoming has been the top coal-producing state in the United States since 1988. In 2007, the Powder River Basin alone produced 436 million short tons (396 million tonnes) of coal, more than twice the production of second-place West Virginia, and more than the entire Appalachian region. The Powder River Basin is the largest coal producing region in the United States. The Black Thunder Coal Mine is one of the most productive coal mines in the United States; in 2006 this single mine produced 84 million metric tons of coal, more than any state except Wyoming, West Virginia, and Kentucky. The region is also a major producer of natural gas through a process called coal-bed methane extraction. Underground coal seams are dewatered through pumping, which reduces pressure and releases trapped gases up to the well head.
The coal beds of the region began to form about 60 million years ago when the land began rising from a shallow sea. The rise of the Black Hills uplift on the east and the Hartville uplift on the southeast side of the basin created the present outline of the Powder River Basin.
When the coal beds were forming, the climate in the area was subtropical, averaging about 120 inches (3,048.00 mm) of rainfall a year. For some 25 million years, the basin floor was covered with lakes and swamps. Because of the large area of the swamps, the organic material accumulated into peat bogs instead of being washed to the sea. Periodically the layers of peat were covered with sediments washed in from nearby mountains. Eventually the climate became drier and cooler. The basin filled with sediment and buried the peat under thousands of feet, compressing the layers of peat and forming coal. Over the last several million years, much of the overlying sediment has eroded away, leaving the coal seams near the surface.
Powder River Basin coal is classified as "sub-bituminous" and contains an average of approximately 8,500 btu/lb, with low SO2. Contrast this with eastern, Appalachian bituminous coal containing an average of 12,500 btu/lb and high SO2. PRB coal was essentially worthless until air pollution emissions from power plants became a concern. A coal-fired plant designed to burn Appalachian coal must be modified to remove SO2 at a cost estimated in 1999 to be around $113 per ton of SO2 removal if it switches to burning PRB coal, and $322 per ton of SO2 removal by installing scrubbers.
The Powder River Basin is the largest coal mining region in the United States, but most of the coal is buried too deeply to be economically accessible. The Powder River Basin coal beds are shaped like elongated bowls and as mines expand from east to west in the Powder River Basin, they will be going "down the sides of the bowl." This means that the overburden (rock lying over the coal) will increase as will the stripping ratio (the ratio of rock that needs to be moved to get to a ton of coal).
The United States Geological Survey (USGS) has conducted a series of studies on the economic accessibility of coal in the major coal producing regions of the country. The studies have typically found that only a small fraction of the coal will be economically accessible at the current price of $10.47/ton. In August 2008, the USGS issued an updated assessment of coal in the Powder River Basin. After considering stripping ratios and production costs, the USGS concluded that at the time of the economic evaluation, only 6 percent of the original resource, or 10.1 billion short tons of coal, was currently economically recoverable. At a price of $60/ton, roughly half (48%) of the coal is economic to produce.
Presently the approximately 15 mines in the Powder River Basin are working in areas where the stripping ratio is between 1:1 (i.e. one ton of rock for one ton of coal) and 3:1. As the mines expand the stripping ratio will increase. As more rock needs to be moved (using large electrically powered draglines and diesel and electric mining trucks) the production cost will also increase.
The United States uses about 1 billion tons of coal a year, with about 40 percent of the coal currently coming from the Powder River Basin. The amount of coal coming from the Powder River Basin has been increasing over the last 20 years.
Increasing the price paid for coal can increase the amount of economically recoverable coal, but increasing the price of coal will also increase the production cost for the coal. In addition, because coal is a solid, not a liquid, it cannot be produced from many scattered wells as oil and gas can be. Rather, coal has to be produced from mines that expand slowly by moving massive quantities of overburden.
The mines in the Powder River Basin typically have less than 20 years of life remaining. Almost all of the coal in the Powder River Basin is federally owned and further mine expansions will require a series of federal and state approvals, as well as large investments in additional mine equipment to begin the excavations.
The majority of the coal mined in the Powder River Basin is part of the Fort Union Formation (Paleocene), with the low sulfur and ash content of the coal in the region making it very desirable. Coal supplies about half of the United States' electricity supplies, with the Powder River Basin mines supplying around 40 percent of the coal that fuels those stations, mainly to the east of the Rocky Mountains, for generating electricity.
Coal mining companies currently operating in the Powder River Basin
Southern Powder River Basin
- Alpha Natural Resources (Belle Ayr Mine, Eagle Butte Mine)
- Arch Coal (Black Thunder Mine, Coal Creek Mine)
- Black Hills Corporation/Wyodak Resources Development (Wyodak Mine)
- Cloud Peak Energy (Antelope Mine, Cordero Rojo Mine)
- Kiewit Corporation (Buckskin Mine)
- Peabody Energy (North Antelope Rochelle Mine, Caballo Mine, Rawhide Mine)
- Western Fuels Association (Dry Fork Mine)
Northern Powder River Basin
- Ambre Energy/Cloud Peak Energy (Decker Mine)
- Cloud Peak Energy (Spring Creek)
- Westmoreland Coal Company (Absaloka Mine, Rosebud Mine)
Power plants fueled from Powder River Basin coal
The Powder River Basin also contains major deposits of petroleum, including the giant Salt Creek Oil Field. The oil and gas are produced from rocks ranging from Pennsylvanian to Tertiary, but most comes from sandstones in the thick section of Cretaceous rocks.
The Bell Creek Field is a Lower Cretaceous stratigraphic trap in the Muddy Sandstone. Discovered in 1967 by the Exeter Drilling Co. No. 33-1 Federal-McCarrell well, which found 27 feet of pay at a depth of 4500 ft.
Recent controversy surrounds the extensive coalbed methane extraction in the region. In the last decade, nearly 7000 such wells have been drilled. An extensive network of gas pipeplines connecting these wells has been built, along with a series of pressurization plants, as well as power lines to provide electricity to operate the system. In addition, thousands of miles of new access roads have been constructed.
Extracting the gas requires that water be pumped to the surface to release gas trapped in the coal seam. While some of the water is successfully utilized in agriculture production such as livestock water and crop irrigation, some waters are naturally high in salinity and sodium adsorption ratio. There has been controversy on how to best manage these saline waters.
In 2007, Powder River Basin coalbed field produced 442 billion cubic feet of gas, making the field the 3rd largest source of natural gas in the United States.
The region also contains major deposits of uranium, contained in sandstones. (See Uranium mining in Wyoming). The Wasatch Formation (Eocene) contains the uranium ore "roll front" type deposits found in the Pumpkin Buttes District. Cameco Corporation subsidiary Power Resources Inc. operates uranium mines in the basin.
In Spring 2005, coal extracted from the mines would retail at the mines for around $5 a ton. However, power stations and plants in the eastern United States were paying over $30 a ton – the difference caused by the cost of transportation. (In October 2008, the mine-mouth price of Powder River Basin coal was closer to $15 per ton.) To transport coal from the basin, there is a joint railway line owned by the BNSF Railway and the Union Pacific Railroad running the length of the southern section of the Powder River Basin, including the climb over Crawford Hill, Nebraska. A third railroad, the Dakota, Minnesota and Eastern Railroad, faced strong resistance from many parties for its attempts to extend its rail line into the coal mining area, but while the plan was eventually approved by regulating authorities, the project was abandoned after the railroad was purchased by the Canadian Pacific Railway.
Originally a single track Burlington Northern Railway line built in stages from 1972 to 1979, the rail line ran south from Donkey Junction in the north 13 miles (21 km) to Caballo, Wyoming; and then for 103 miles (166 km) to Shawnee in Converse County. The Chicago and North Western Railway ran close to the northern section, as did the Union Pacific at Caballo.
Having already formed the Western Railroad to distribute the coal, in 1982 C&NW and the UP formed Western Railroad Properties, Inc. (WRPI), to acquire half interest in the Burlington Northern coal line from Shawnee Junction to Coal Creek Junction. On December 15, 1986 WPRI purchased 11 miles (18 km) more of BN line from Coal Creek Junction to East Caballo Junction. Beginning June 27, 1983 WPRI constructed six miles (10 km) of new railroad from Shawnee Junction. to Shawnee, rebuilt 45 miles (72 km) of C&NW line from Shawnee to Crandall and 56 miles (90 km) of new railroad from Crandall to Joyce, Nebraska. The first commercial train ran on August 16, 1984.
By 1985, the line was single track for almost its entire length, and it was handling 19 million tons of coal. The implementation of the second stage of the Clean Air Act (1990) caused demand for clean coal to rise quickly. The C&NW struggled to upgrade capacity to dual track, resulting in numerous failures on the line in 1994, and eventually Union Pacific's purchase of C&NW in 1995. The UP spent 855 million dollars over the next five years expanding capacity over its entire network to handle coal shipments from the PRB. By 2005 the Joint Line capacity had grown to handle an all-time record 325 million tons, and was either dual or three track capacity for its entire length.
Due to various trackage and locomotive failures on the Joint Line in late 2004 and early 2005, the line failed to deliver the amount of contracted coal supplies, and electricity rates increased by 15 percent. Coal customers threatened to evaluate alternate sources of energy and transportation, including the Arkansas Electric Cooperative Corporation. As a result, the 280-mile (450 km) expansion of the Dakota, Minnesota and Eastern Railroad line was approved by the Surface Transportation Board. In 2006 UP and BNSF announced a $100 million investment to provide three track capacity for the entire length of the Joint Line plus a fourth track added over the steepest sections, including Logan Hill. These improvements will enable the Joint Line to handle over 400 million tons of coal.
Presently more than eighty train loads of coal, which vary in size from 125 to 150 cars, are shipped from southern PRB mines each day. In 2006, Union Pacific set a record by hauling 194 million tons of coal – an 8% increase compared with 2005 tonnage. The company achieved this by increasing train size, with trains averaging more than 15,000 tons, a 200-ton weight increase compared with fourth-quarter 2005’s average.
According to the BNSF 2008 Annual Report, the quadruple track project was completed.
In 2009, the America’s Power Factuality Tour stopped at the Powder River Basin to report on its role in generating electricity in the US.
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- Railroad Battle Brewing
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- Western, Burlington Northern and Union Pacific railroads Railway Age – October 1994
- UP will expand PRB coal lines Railway Age – Nov, 1996
- UP, BNSF Announce Southern Powder River Basin Joint Line $100 Million Capacity Expansion Plan
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- Bell Creek CO2 Development Update
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- Wyoming coal mining
- Geological history
- USGS Open-File Report on impacts of CBM development in the region
- Assessment of Coal Geology, Resources, and Reserves in the Montana Powder River Basin United States Geological Survey