Why hasn't coalbed methane been produced before?
What is the current level of coalbed methane activity in Wyoming?
How is coalbed methane produced?
How much coalbed methane is there?
How long can a coalbed methane well produce?
How much coalbed methane can be produced?
How thick should a coal bed be for a viable coalbed methane target?
Who owns the coalbed methane?
Who owns the coal?
Which has priority, coal mining or coalbed methane development?
How does the surface landowner keep his rights if he does not own or lease the minerals?
COALBED METHANE IN WYOMING
By Rodney H. De Bruin, Robert M. Lyman,
Richard W. Jones, and Lance W. Cook
Why hasn't coalbed methane been produced before?
Coals with coalbed methane of thermogenic origin in Wyoming analogous to coals being produced in the San Juan Basin, New Mexico and the Black Warrior Basin, Alabama are certainly present in Wyoming, but are poorly documented and mostly unexplored. Before the current high level of activity, it appeared that many Wyoming coals were either too deep or not of sufficient thickness to be economically viable at the time.
Although Wyoming coal fields contain large coal resources in numerous thick beds, the shallow depths and immature (low rank) coals were once considered too low in gas content to be economically produced using conventional coalbed methane production methods. These methods had worked well in higher rank, higher yield coals (those with higher gas contents, e.g., on the order of 350 cubic feet of gas per ton of coal) but met with no success in the Powder River Coal Field (Shirley, 2000). One of the main reasons for the acceleration in the number of wells and corresponding production in the Powder River Coal Field was the development of a new production technique in which wells are completed open hole (see section on production below). Renewed interest in coalbed methane has expanded to most of the other Wyoming coal fields. This interest is mainly due to spillover from success in the Powder River Coal Field and to increased exploration for more conventional (thermogenic) coalbed methane targets. (TOP of page)
What is the current level of coalbed methane activity in Wyoming?
The coalbed methane play in the Powder River Coal Field is currently the most active gas play in the United States. In December, 1999, monthly production had reached 6.75 billion cubic feet from 1412 producing wells, with 907 shut-in wells awaiting pipeline connections. Production reached nearly 64 billion cubic feet of gas in 1999 (Figure 6). There are currently 72 drilling rigs (Front cover) at work in this play.
Future production in the Powder River Coal Field is expected to increase even more. Drilling on federal land, which had slowed because of a moratorium on permitting, will increase because an environmental impact statement has been completed which allows development to proceed. Recent completion of several new pipelines has added nearly a billion cubic feet per day of new capacity out of the basin.
There are a number of ongoing exploration projects in various other parts of the state, but development of new coalbed methane fields outside the Powder River Coal Field has not yet occurred.(TOP of page)
How is coalbed methane produced?
In the Powder River Coal Field, coalbed methane wells are completed open hole. Using this method, casing is set to the top of the target coal bed and the underlying target zone is under-reamed and cleaned out with a fresh-water flush. A downhole submersible pump produces water up the tubing; gas separates from the water and is produced up the annulus (Figure 7).
Natural gas and water produced at individual wells (Figure 8) are piped to a metering facility (Figure 9), where the amount of production from each well is recorded. The methane then flows to a compressor station (Figure 10), where the gas is compressed for shipment in a pipeline. The water goes to a central discharge point at a drainage or impoundment.
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How much coalbed methane is there?
The amount of coalbed methane present in Wyoming coals depends upon the tonnage of coal and the amount of gas present in each ton of coal (gas content). After the total gas in place is estimated, recoverable resources are estimated based on geologic and economic factors. Total recoverable gas resources from coal beds in all Wyoming coal fields (Table 2) is estimated at 16.74 trillion cubic feet (TCF). This total alone is over three TCF more than wyoming's proved reserves of 13.65 TCF of dry natural gas in traditional natural gas fields and represents nearly 15 years of state production at current rates. The estimated recoverable gas resources total for coal beds is also about 70% of the cumulative total natural gas production from Wyoming through 1999. The Powder River Coal Field alone accounts for about 61% of the state's total resources of coalbed methane. From these comparisons, it is obvious that coalbed methane will be an important resource in Wyoming for many years.
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How long can a coalbed methane well produce?
The life of a coalbed methane well depends on the distance from its neighboring wells (spacing of the well field), how wells communicate with each other in the subsurface, and the amount of gas available to each well. These and other factors for Wyoming low rank coals are not entirely understood and are still being studied. Most of the producers in the Powder River Coal Field expect that a coalbed methane well can produce for 10 to 12 years. As a coal bed in the original production zone is drained of its methane, the well often can be reworked to produce gas from lower coal beds. Depending on the situation, multiple coal beds could extend the life of a well site by 10 to 30 years.
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How much coalbed methane can be produced?
In general, coalbed methane wells go through three stages during their production cycle (Figure 11). During the dewatering stage, the amount of water produced initially exceeds that of gas, but with continued production, the volume of water continues to decrease as the volume of methane increases. A stable production stage is reached with maximum methane produced and water production becomes stable. During the decline stage, the amount of methane produced continues to decline until it becomes uneconomic to continue production. For the Powder River Coal Field coal beds, usually after several months of dewatering, the average production reaches about 160,000 cubic feet (or 160 MCF) of gas per day and 400 barrels (42 gallons per barrel) of water per day. Conservative estimates place the amount of coalbed methane available per well at 400 million cubic feet (or 400 MMCF). Current production cycles have not continued long enough to construct adequate decline curves. (TOP of page)
How thick should a coal bed be for a viable coalbed methane target?
The coal thickness required for coalbed methane depends on the gas content, which is related to the rank and maturation of the coal. Higher rank coals 10 feet thick have been exploited, but usually the target coals must be at least 20 feet thick. In the Powder River Coal Field, where the gas content per ton of coal is low, some wells produce from 30-foot-thick coals; most exploration targets are aimed at coals at least 40 feet thick. This extra thickness beyond 30 feet may be necessary to ensure economical operation of the coalbed methane well.
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Who owns the coalbed methane?
Both the land surface (surface estate) and the resources below the surface (mineral estate) can be owned and are considered property. The mineral estate can be owned in total (all minerals) or can be owned by specific mineral commodity (e.g., oil and gas estate, coal estate). Coalbed methane is considered natural gas and is part of the oil and gas estate.
Where one party owns both the surface and mineral estates, the land is said to be owned in fee simple. Homesteaders in Wyoming had the option of acquiring both estates, although many chose only to claim the surface estate (reserving the mineral estate to the federal government). To help finance construction of the transcontinental railroad, to give the builders of the railroad some financial incentives, and to assist in opening the developing nation to rail transportation, almost half of the mineral and surface estate was given to the railroads in select areas of Wyoming. In southern Wyoming, this area is called the Union Pacific land grant, and it includes a 20-mile-wide strip of land on both the north and south sides of the railroad route.
In much of Wyoming, the owner of the mineral rights is often different than the surface owner. It is common in Wyoming for the surface estate to be owned by private individuals and the mineral estate to be owned by the federal government (and leased to private individuals or companies). State lands are usually underlain by state-owned minerals. The U.S. Supreme Court ruled in 1999 that the owner of the oil and gas estate rather than the owner of the coal estate owns the coalbed methane. The mineral owner has rights to access and develop their minerals, and under the law, surface owners are entitled to compensation for damages to their property due to mineral extraction.
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Who owns the coal?
Coal in Wyoming is owned by the private, state, and federal sectors. The coal portion of the mineral estate in the early 1900s was reserved over vast areas by the federal government and can be leased by those wishing to develop the coal reserves. The State of Wyoming was given the coal under state lands ceded by the federal government. (TOP of page)
Which has priority, coal mining or coalbed methane development?
This depends on the owner of the mineral estate. A private mineral owner determines the priority of development, whereas for state-owned or federally owned coal, the one with the first lease (based on issuance date) generally has priority for development. Currently neither mining nor coalbed methane development has specific priority, and the State of Wyoming is encouraging joint cooperation between the two industries. wyoming's Congressional Delegation is currently looking at ways to help arbitrate conflicts between both industries, but at this time nothing firm has been resolved. (TOP of page)
How does the surface landowner keep his rights if he does not own or lease the minerals?
Landowner rights are preserved regardless of whether or not they participate in coalbed methane development of the mineral estate. Regulatory bodies are empowered to shut down coalbed methane operators and individual wells if their activities are irresponsible or damaging to the surface. The landowner can negotiate with the coalbed methane producer to be compensated for damage to or the loss of use of his land. Most of the coalbed methane operators are willing to work with the landowners to avoid conflicts, but when this fails, state and federal regulators can help resolve these matters.
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Figure 6. Yearly production and number of producing wells for coalbed methane in the
Powder River Basin, Wyoming. 1989-1999. Source: Wyoming Oil and Gas Conservation Commission production reports, 1989 through 1999.
Figure 7. Schematic diagram showing open-hole completion technique for a typical coalbed methane well.Modified from diagram furnished by the Wyoming State Engineer's Office.
Photograph by Rodney H. De Bruin.
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