Recently, a solution has been developed to provide for milling of nipple profiles and other downhole hardware with electric wireline. A new milling bit and milling system for the wireline miller enables nipple profiles to be opened up in diameter to allow larger intervention products to be deployed, e.g. straddle packers and insert valves. Extensive testing was conducted prior to the introduction of this service to optimize the weight on bit and torque. The result was the development of a unique version of the hydraulic stroking tool to be combined with the milling tool to provide the controlled weight on bit.
A major benefit of using the wireline milling system is the ability to provide precision milling without mobilizing coiled tubing (CT) or heavy surface equipment for circulating and handling fluids. Thus, there is no risk of damaging the reservoir from the circulating fluids. In addition, this kind of intervention can be performed more cost-effectively, involving less people, less heavy lifts and therefore, reduced HSE risks.
The world's first milling of a nipple profile on wireline took place in Indonesia where the wireline miller was mobilized to enlarge the nipple profiles in 10 wells. The entire operation was performed in 20 operating days and well kills were prevented, which would have been necessary if executing the operation with a conventional method, such as on CT. Major benefits included minimal reduction in production levels, precision milling with zero cuttings left in hole and no labour-intensive requirement for CT or heavy surface equipment.
As of December 2009, the ID of twenty (20) Super 13 Chrome nipples have been enlarged for one operator, without a miss-run related to the new milling system.
This paper will discuss the technical aspects of this new milling system as well as present the field performance gained to date through a field test and two case histories.