Authors B.A. Johnson, Nexen
Source Canadian Unconventional Resources and International Petroleum Conference, 19-21 October 2010, Calgary, Alberta, CanadaCopyright 2010. Society of Petroleum Engineers
In developing the Doris Mannville Coal Bed Methane (CBM) gas field near FortAssiniboine, Alberta, the Nexen exploitation team encountered many unforeseen artificial lift challenges using Electric Submersible Pumps (ESPs). High failure rates and short pump run timesmade forecasting of production volumes and reserves difficult, while high operating costs driven primarily by downhole servicing reduced the economic viability of the project.
Theroot cause of the high pump failure rate was attributed in most part to the unanticipated volume of produced coal fines and reservoir solids in the produced water stream. Theproduction of these solids, coupled with lower than expected water production rates, led to a re-evaluation of the field’s artificial lift strategy. Following a thorough artificial liftevaluation, a change from an ESP to a reciprocating rod pump (Pump Jack) system was initiated.
The largest anticipated benefit of reciprocating rod pumping systems over ESP artificiallift systems were:
• Increased minimum flow path area through the system, reducing the frequency of solids plugging, leading to longer pump run times.
• Reduced well servicingcosts with reciprocating rod pumps through elimination of services required solely by ESPs.
• Elimination of pump failures due strictly to electrical shortages by changing from anelectrical/mechanical (ESP) to a straight mechanical (Pump Jack) downhole system.
• Improved operating efficiency by matching artificial lift design with actual water production rates.