The Origins and Production of Coal Bed Methane Gas

Coal Bed Methane (CBM), also known as Coal Seam Methane, is a natural gas which is trapped in an underground coal seam. The majority of all natural gas used for heating or electricity production is Methane gas. The gas trapped in the coal seams in Wyoming’s Powder River Basin (WPRB) are thought to be of biogenic origin from bacteria generating gas, and has created tremendous supplies of methane gas within the coal seams over time. It's estimated that WPRB contains approximately 25 Tcf (trillion cubic feet) of recoverable methane gas. As of December 2008 approximately 3 Tcf (trillion cubic feet) had been produced, less than 14 percent of the total estimated reserves, leaving huge reserves of recoverable CBM still in place.

Coal Bed Methane exploration and production is occurring in CBM wells in the Powder River Basin and Tongue River Basin of Wyoming and Montana, Marcellus Shale Gas Wells in the Appalachian Basin, CBM gas wells in the Black Warrior Basin, CBM gas wells in the Raton Basin of Colorado, CBM gas wells in the San Juan Basin of Northern New Mexico, as well as other Coal Bed Methane gas production in Queensland Australia. Canada is expected to have the second largest reserves of Coal Bed Gas next to the USA. Below is a map of the Coal Bed Methane regions of the Western United States.

Gas producing coal seams in the WPRB lie at depths ranging from 250 feet to around 3,000 feet. Typically a water well type drilling rig (truck mounted) is used to drill these shallow gas wells.

The drilling and completion of a Coal Bed Methane Well.

1. A well bore is drilled into the top 2 to 5 feet of the coal seam. Steel casing is set into the well bore and the casing is cemented to the land surface. The coal seam is then drilled out and a geophysical log is run to confirm the penetrated coal zone. An under reaming tool is then used to expose the coal to the bore hole based on the log. The well bore may also be drilled completely through the target coal seam, and casing is then run to the bottom of the bore hole and cemented. A perforating tool is then utilized to shoot holes through the steel casing and cement adjacent to the coal.
2. An electric submersible pump is set in the well just above the exposed coal or in the coal seam. Water is then pumped out of the well bore to reduce the hydraulic head pressure. The water is pumped through a riser pipe attached to the top of the pump and up to the land surface where it is discharged either on the ground, to impoundments or to treatment facilities, or with the ARID System re-injected at low pressure into another shallower aquifer. The reduction of the water pressure in the coal seam allows the gas to be liberated and with the water the gas moves toward the well bore.
3. The liberated gas collects inside the casing above the pumping water level at which the pump maintains the fluid level for optimal gas production and flows to the top of the well under pressure, or with the ARID System, through a riser pipe and out the well head. The gas is piped to a gas compressor site and ultimately delivered into a gas sales line.