Milling interventions can resolve a variety of issues related to downhole restrictions, and these extend beyond remediation of typical scale buildup. One such problem or challenge is that of downhole hardware becoming stuck or no longer functioning properly.

In early 2020, a North Sea operator experienced a significant increase in water cut from a horizontal producer and needed to investigate. Production logging found no evidence of scale, but the run did reveal a half-open formation isolation valve. An additional caliper log showed the valve had a clean shifting profile, but, after a failed open-close operation, the operator decided to mill the valve to make further logging and water shut off possible.

The e-line toolstring consisted of a tractor and a milling tool with a specialized milling bit. The function of the tractor was twofold, providing conveyance to target depth as well as countering the torque of the milling tool during the operation. A Power Suction Tool was also included as a contingency for potential fishing of milled hardware/debris. During the run, after tagging the valve, hardware milling was carried out in two three-hour stages. The valve was completely milled through, collected as two pieces (half-moons) in a single run.

The operation resulted in the removal of the restriction and enabled access to the section of the well below the isolation valve. With the operation requiring just 8.5 hours, the solution provided significant time and cost savings to the operator.

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