Unconventional resources such as coalbed methane will become progressively more important worldwide as population continues to grow at an unprecedented – and possibly unsustainable – rate.
As a result, coalbed methane and other unconventional resources undoubtedly will play an important role in supplying energy needs to both economically developed and emerging nations worldwide in the foreseeable future.
Preliminary worldwide coalbed methane resources are estimated to range between 5,800 and 24,215 Tcf (164 to 686 Tm3).
The largest potential resources, which also have the largest degree of uncertainty, are in the Former Soviet Union with 4,000 to 16,116 Tcf (113 to 456Tm3). North America ranges between 951 to 4,383 Tcf (27 to 124 Tm3), whereas South America and Europe range from 15 to 32 Tcf (42 to 91 Bm3) and 161 to 269 Tcf (4.6 to 7.6 Tm3), respectively. Africa ranges between 27 to 55 Tcf (760 to 1,557 Bm3), and the Middle East has no coalbed methane resources. The Asia Pacific region, which includes China, ranges from 646 to 3,360 Tcf (18 to 95 Tm3).
The rate of coalbed methane resource development within individual countries will be highly variable due to local economic factors and government energy priorities and policies.
The United States remains the world leader in coalbed gas exploration, booked reserves and production, although coalbed methane production is expanding internationally – particularly in Canada and Australia, and commercial production from India will undoubtedly accelerate in the near future.
In North America, there is commercial coalbed gas production or exploration in approximately 12 U.S. and several Canadian basins. Coalbed methane now represents 9 percent of 2006 dry-gas production and 9 percent of proved dry-gas reserves in the United States, with the major producing areas located in the San Juan, Powder River, Black Warrior, Raton, Central Appalachian and Uinta (Ferron and Book Cliffs) basins.
Coalbed Methane Reserves (U.S.)
Figure 2
Other U.S. areas with significant exploration or production are the Cherokee, Arkoma, Illinois, Hanna, Gulf Coast and Greater Green River basins.
Annual coalbed methane production in the United States continues to increase, but not as rapidly as in previous years. The annual 2006 coalbed methane production was up slightly (1,758 Bcf; 49.8 Bm3) from 2005 coalbed methane production, which was 1,732 Bcf (49.0 Bm3) from an estimated 54,000 wells (figure 1).
Coalbed methane reserves decreased slightly from 19.892 Tcf (563.3 Bm3) in 2004 to 19.620 Tcf (555.6 Bm3) in 2006, representing a decrease of only 72 Bcf (7.7 Bm3) (figure 2).
There are two important facts to remember:
- Demand for natural gas in the United States is expected to increase 50 percent over the next 20 years as additional co-generation power plants and natural gas electric power generation facilities are constructed.
- The global demand for energy will continue to increase regardless of the current economic downturn as the middle classes of emerging economies such as China and India continue to expand.
Therefore, development of unconventional resources such as coalbed methane and gas shales worldwide is critical for economic stability and continued growth.
Enhanced coalbed methane recovery using sequestered greenhouse gases (carbon dioxide) and microbial conversion of the coal and sorbed gases into methane may represent a solution to solving energy and environmental objectives simultaneously and development of these technologies is accelerating to meet global demand.
From Hazard To Resource
Coal mine explosions have been known for centuries, and the gas associated with coal mining operations always has been of major concern.
However, despite the early failures to recognize coal gas as beneficial rather than simply a mining hazard, Scotsman William Murdoch was the first to recognize the usefulness of coal gas as an illuminant in the late 1700s. Coal gas remained an important illuminating source for the world until it was replaced by electricity.
The first true coalbed methane production in North America is harder to pinpoint, but it probably occurred in West Virginia, Ohio, Oklahoma and other locations in the early 1920s and the 1930s. The early discoveries were serendipitous and tapped into water-free coal beds on structural highs.
These early wells were clearly targeted at coal seams, and it appears that at least one operator may have applied the same exploration strategy in Ohio and West Virginia.
The Big Run Field in West Virginia was developed in 1932 and produced over 2 bcf (56MMm3) of coalbed methane from 25 or 30 wells, and apparently there are several other fields that also produced coalbed methane. The Excello Shale gas play in Oklahoma also tapped into a thin coal seam surrounded by carbonaceous shale, so it too can be considered an early coalbed methane play.
The first coalbed methane wells in the San Juan Basin were drilled by Stanolind (Amoco) in the 1950s along the Ignacio Anticline and did not produce significant amounts of water because the coals were structurally high. Phillips Petroleum also drilled and completed wells in Fruitland coal seams during this time period, and the San Juan 32-7 #6-17 well, completed in 1953, has been producing gas for more than 50 years with minimal decline in reservoir pressure.
The first attempt at dewatering coal seams to produce methane was performed by Amoco in 1977 at the Cahn Gas Com #1 well in the Cedar Hill Field. The IP for the test wells was only 100 Mcfd (2,832 m3d) with 100 Bbl (15.9 m3) of water, but this production soon increased to more than 1 Mmcfd (28.2 Mmm3d) by 1979, and the modern era of coalbed methane exploration and development was started.
– ANDREW R. SCOTT