Dynamic Annular Pressure Control (DAPC) is a new technology that allows accurate control of downhole pressure in a well. DAPC was used in conjunction with Coiled Tubing Drilling (CTD) on the Gannet GA-03 well between February and April 2005. This report describes the selection, design, testing and field performance of the recent DAPC-CTD Gannet project.

The original horizontal wells in the Gannet Alpha reservoir were positioned in the middle of the 53ft oil rim. Upward migration of the oil rim, due to gas production, meant that it had moved beyond the reach of the original horizontal wells. As a result, these had watered out, and many of the wells had been shut in for several years.

A review of the reservoir model in 2000 revealed that much of the migrated oil, some 25-35% of the STOIIP, was stranded and would be lost forever unless infill drilling was performed.

Re-instatement of the drilling rig was considered uneconomic and CTD was selected as a lower cost, technically feasible option, though Shell's history with CTD showed mixed success, indeed a five well campaign in 1999 was cancelled after catastrophic failures in the first two wells. The primary issue in these wells was associated with managing the downhole pressure to find a balance between wellbore stability and differential sticking. The main subsurface challenges on the Gannet are the same and as such overcoming these hurdles was of prime importance.

CTD and DAPC offered a novel solution, and this report details the development of the Gannet CTD project through feasibility, concept selection, detailed design, and successful execution.

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