Information on coalbed methane and CBM drilling
What is coalbed methane or CBM?
The main component of natural gas is methane. Coalbed methane (CBM) is simply the natural gas found in coal seams. With CBM drilling, wells are drilled into coal seams in much the same way as a typical gas well, but there is a major difference. CBM is considered an “unconventional gas” as coalbed methane production differs from that of conventional natural gas. Conventional natural gas is found in fairly distinct pockets or reservoirs, and a well must be drilled into a specific reservoir where natural gas has accumulated. Coalbed methane is produced by drilling wells into underlying coal seams across a wide expanse of land so that methane can “drain” to the wells.
How was coalbed methane formed?
Coalbed methane was created through a natural process that started millions of years ago in swampy areas that covered Western Canada and parts of the United States. Layers of sand and clay gradually covered the remains of dead plants. Eventually, the organic matter was buried so deep that naturally occurring heat and pressure transformed it into coal. When depth and pressure are combined, coal generates methane gas, which is stored within the microscopic structure of the coal itself.
How is CBM produced?
Coalbed methane production involves drilling standard vertical or horizontal wells and employing special completion techniques to allow it to “drain” to the well. Methane is stored in the molecular structure of the coal and once pressure is released in a coal seam, the gas detaches from the coal and migrates through natural fractures in the coal, called cleats. The coalbed methane gas molecules flow through this natural fracture system to the wellbore.
Coalbed methane supply
In the U.S. some 10 per cent of the country’s natural gas supply comes from CBM. In Canada, the industry is much younger with the first pilot CBM drilling taking place about 10 years ago. Today, CBM accounts for about 1 per cent of Canada’s annual coalbed methane production. Most of that natural gas supply comes from the Horseshoe Canyon coals in Alberta, which is the most well understood and technologically advanced of the CBM plays.
Horseshoe Canyon coal trend.
The Canadian industry drills 1,500 to 2,000 wells per year into the Horseshoe Canyon coals in Alberta. Since 2001, the industry has created 14,000 CBM drilling wells into the coal trend, which is now producing some 700 MMcf/d to Canada’s natural gas supply. Still, there are large amounts of untapped potential. The Horseshoe Canyon covers about 32,000 sections or 20 million acres in central Alberta and has an estimated 36 trillion cubic feet of resource potential.
See more information on CBM production.