A revolutionary drilling technique has emerged allowing drilling with electric wireline utilising metal machining technology in combination with field proven Well Tractor technology.

As the Well Tractor technology evolved and confidence was gained during the past several years, the application of a cost efficient method for milling of specific downhole hardware (i.e. valves, plugs etc.) as an alternative to existing methods has emerged. The technology is specifically needed on offshore installations where the logistical limitations are high. The article will describe the actual operation and the process of developing the technology.

The first ever operation involving the milling of a blocked borehole on wireline was conducted in late 2003 in an oil producer on a North Sea platform. A single plate isolation valve was stuck in closed position and it was imperative to get the oil producing well on-stream at short notice. During the tests leading up to the actual operation, the concept had been tested onshore in a test-loop with an estimated drilling time of 35 minutes to drill an 80 mm (3.15") hole trough a 2 cm (0.79") thick "super chrome" single flapper. The total operational time in the well for the entire milling operation was 11.5 hours from rig-up to rig down while the milling itself only took 7 minutes. During this operation all milled material was retrieved and the challenges of controlling stalling and actual control of the retrieval of the milled out plate were met. The development of wireline drilling used the Well Tractor features to achieve Weight On Bit and reactive torque control, while the limited total power available was addressed by designing specific bits for specific applications based on an approach of "surgical" intervention. The added advantage is that the risk of getting stuck by wedging the BHA in the object or in cuttings has been virtually eliminated by targeting a well defined area within the object itself.

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