 |
||||
|
||||
|
|
|||
 |
||||
| Overview Regulatory Issues Solutions Impoundment Irrigation Treatment |
Coal Bed Methane (CBM) is methane gas which is trapped in a coal body. The gas trapped in the coal seams is thought to be of biogenic origin, (from bacteria generating gas), and has created tremendous supplies of methane gas within the coals over time. It's estimated that Wyoming's Powder River Basin (WPRB) contains approximately 25 TCF (Trillion Cubic Feet) of recoverable methane gas. As of October 2005 only 876 Million MCF (MMCF) had been produced, less than 10 percent of the total estimated reserves, leaving huge reserves of recoverable CBM still in place.  There are several major coal seams that produce gas in the WPRB and 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. There are two basic completion methods used for CBM wells. Under the first method, a CBM 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. An electric submersible pump is set in the well just above the exposed coal. Water is then pumped out of the well bore and discharged to the surface. The reduction of the water pressure in the coal (hydraulic head) allows the gas to be liberated from within the coal seam. 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. The liberated gas collects inside the casing above the pumping water level, (level at which the pump maintains the fluid level for optimal gas production) and flows to the top of the well under pressure. The gas is gathered (piped) to a gas compressor site and ultimately delivered into a gas sales line The second method of CBM well completion is similar to conventional oil and gas drilling. The well bore is drilled completely through the target coal seam, casing is 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. A pump is installed and water is pumped from the well which allows the gas to be released. |
|||
 | ||||
 |
||||
