Production profile: coalbed methane


CBM is an unconventional source of natural gas produced from coal seams. Gas is often dissolved in naturally occurring groundwater. CBM wells are typically less than 1000 meters total depth. In this article I will try to introduce you some numbers connected with CBM.
Extraction of coalbed methane grew out of venting methane from coal seams. Some coal seams have been noticed as dangerous and filled with gas so as a safety measure, wells were drilled from the surface into the seams to drive off the methane before mining. Typical CBM wells are drilled quickly. Often a well can be drilled and completed in less than 48 hours. Drilling penetration rates and final well construction details can vary greatly between different CBM fields.

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To extract methane wells are drilled into coal seams and groundwater is pumped out, which is necessary as the water removal reduces the pressure and allows methane release from the coal. Coal seams are traditionally accessed using a single vertical well. Extracting the gas begins with drilling well 300-1500 meters deep. The top section of the well is cased with steel and cement to prevent the loss of water on any aquifers. The coal seams are than stimulated to open the pores within the coal. This releases the pressure within the coalbed and allows the gas and water to flow into the well. The coal resource remains undamaged. The gas and water rise to the surface through separate pipes. The water is transported through underground pipes to a container for reduce and recycling. The gas is piped to processing facility to be compressed and dehydrated.
Coalbed Methane Drilling is performed with rotary and core drilling equipment. Rotary rigs are used to drill and set casing for production wells, and, along with core drills, are used to drill long directionally-drilled holes into coal seams from which coal-bed methane gas is extracted. Due to the occurrence of gas, blow-out preventers are often needed.

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Coalbed methane as a natural gas resource was approved by US government in late 1970’s. The US Department of Energy funded researches in the area of unconventional gas sources, including coalbed methane. Estimated reserves are about 7500 trillion cubic feet globally with more than 700 tr. cubic feet in the US alone.
CBM extraction in US is currently expanding in the northeast Wyoming and southeast Montana, 7% of the natural gas production comes from CBM extraction. According to the CBM Association of Alabama 13% of the land in 48 United States has coal under it and large part of this coal contains methane. Most CBM production came from the Rocky Mountain states of Colorado, Wyoming, and New Mexico.
In Australia, commercial CBM extraction was started in 1996 in the Bowen Basin, Queensland. As of 2013, coal seam gas made up about ten percent of Australia’s gas production. According to reserves are estimated to 33 trillion cubic feet. as of January 2012.
In Canada, British Columbia have approximately 90 trillion cubic feet of coalbed methane. The only province with commercial coalbed methane wells is Alberta.
Kazakhstan could witness the development of a large coalbed methane (CBM) sector over the coming decades, according to industry professionals. Preliminary research suggests there may be as much as 900 billion m3 of gas in Kazakhstan’s main coalfields – 85% of all reserves in Kazakhstan.

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About author

Agata Gruszczak

Editor in YoungPetro, fourth year student of Mining and Geology at the Faculty of Drilling, Oil and Gas at AGH University of Science and Technology, member of AGH UST Student Chapter. Interested in enhanced oil recovery and unconventional resources. Keen on Scandinavian culture, reading fantastic literature.

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