Trident Exploration operates a significant portion of a Mannville-age coalbed methane field near Ft. Assiniboine, Alberta, Canada. This presently is the only commercial Mannville project in Alberta and currently produces about 90mmcf/d. The Mannville coals are wet and artificial lift is extensively used to dewater the coal seam. Well design has evolved throughout the project, starting with vertical wells and then progressing to horizontal and multilateral wells. Each design change has allowed significant production increases, but has also added to the challenge of economically lifting water. Electric submersible pumps and beam pumps are typically used. Rod driven PCPs were used in early stages of the project with limited success. A PCP driven by a downhole motor, or ESPCP, has successfully operated through a 6 month trial period. The ESPCP has shown potential to deal with problems caused by well design and problems inherent with CBM production.
The Corbett Creek project is a wet coalbed methane development located near Fort Assiniboine, Alberta, Canada. Current CBM production is about 90 mmcf/d (2500 e3m3/d). The target formation is the upper Mannville coals, which exist over a broad area across central and southern Alberta. It is estimated that these coals contain more than 360 TCF (10.1 × 1012 m3) of gas (1). Water saturation, gas content, depth, and other properties vary widely throughout the Mannville coals. In the Corbett area, the coal is from 840m to 1100m vertical depth. Two seams are targeted, one being an average of 3m thick and the other 2m thick. Seams are separated by 5m to 10m. Water is removed from the coal seams to reduce bottom hole pressure to a critical point where gas will begin to desorb from the coal. The greater the differential between the desorption pressure and the bottom hole pressure, the greater the amount of gas that will desorb.
A pilot project was started in 2000 by Trinity Energy with three evaluation wells. Five more vertical wells were drilled over the next two years to continue evaluation of the area. Trident acquired the properties in 2002 and continued expanding the pilot by drilling 35 more vertical wells over the next two years.
Horizontal drilling was introduced in 2004 to improve water inflow, accelerate dewatering and decrease the amount of time to initial gas production. Surface footprint was also significantly reduced. Results proved successful and 40 horizontal wells were drilled over the next two years. In July 2005, Trident and partner Nexen announced Corbett was the first commercial Mannville project in Alberta.
In 2006, the multilateral well design was introduced to reduce drilling and artificial lift costs. One multilateral well replaced 3 or 4 single leg horizontals. Multiple seams could be drilled from one well. Gas rates per well also significantly increased and allowed some wells to free flow after an initial dewatering phase. (See CIPC Paper 2008–200 "Economics of Mannville CBM Development: Drilling & Production Innovation at Corbett Creek" by John Cockbill for more detail.)
