When Petronas Carigali, the national oil company of Malaysia, planned the development of its platform EWDP-A offshore Sabah, they did so on the basis of using coiled tubing for any thru-tubing workover operations which were needed while the drilling rig was still in place. In this way the drilling rig could be fully utilized for drilling operations, thus maximizing the efficiency of, and minimizing the total time for, the development. Well EW 117 was completed on this platform as a level 6 Multilateral in July 2000 with dual 3-1/2" tubing strings accessing two laterals with measured depths of 14,910ft. and 15,236ft., respectively. The clean-out and perforation operations commenced with coiled tubing with the rig assisting. However, due to a combination of the tortuosity and the lengthy horizontal sections of the laterals, it was not possible to reach bottom with coiled tubing because of the high frictional forces encountered.

After consideration of several alternatives a feasibility study was undertaken to explore the possibility of using a Hydraulic Workover (Snubbing) unit to perform the -thru-tubing operations concurrent with the continuing drilling activity. The study concluded that, with some custom designed handling equipment, a special tapered workstring and strict adherence to a permissible concurrent activity matrix, this approach was indeed feasible. The operation was performed in February 2001 and the well made available for production by the beginning of March. Throughout the workover operation the drilling rig sequence remained in accordance with plans, apart from a period of 14 hours downtime while moving the Snubbing unit into its working location.

This paper will review the problem encountered, the motive forces applicable, the feasibility study and the resultant custom designed equipment and workover operation. It will discuss on the integrated team approach and detailed planning, in which active participation from Petronas Carigali, the drilling contractor and several service companies resulted in a successful operation.

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