Full isolation valve milled in the North Sea

A client in the North Sea was unable to cycle open an isolation valve (IV). A previous attempt to open the valve had been made by a mechanical solution provider but had not been successful. Welltec® was brought in to shift open the valve using its Well Key®. The client also requested a milling solution as a contingency.

Welltec performed a systems integration test (SIT) and found that the ball valve could be milled in one run using a double metal matrix compound (MMC) mill bit, with a main core and a pilot drill core. Welltec qualified this milling solution with the client and was subsequently mobilized to perform the job.

A total of nine runs were performed, with the final two runs devoted to milling the ball valve.

The first run, with a toolstring comprised of a release device, Well Tractor®, Well Stroker®, and Well Key, confirmed that the IV assembly was blocked by either geometry or debris. The Well Cleaner® Power Suction Tool recovered o-rings and grease debris during the second run, and the ball valve was tagged. Over the next five runs, the client and Welltec attempted several toolstring configurations, attempting to shift the ball valve, but only managed partial movement. It was assumed that the sleeve was damaged. It was decided to close the valve entirely to prepare it for milling.

During the final two runs, the Well Miller®, equipped with the double MMC with a main core and pilot drill core, was used to mill through the upper half of the ball valve. Although the pilot bit engaged the lower half of the ball during the same run, the main core bit did not break through. The toolstring was pulled to surface for inspection. The main mill bit was found to be partially worn, so it was swapped out and the toolstring run back in hole. Once the pilot mill was engaged, milling commenced. After two hours of effective milling, the Well Miller succeeded in breaking through the lower half of the valve.

Welltec met the challenge posed by the client to develop a contingency milling technique, successfully evaluated it during a SIT, and executed during the operation. Typically, if mechanical interventions fail to open IVs, coiled tubing or drilling rigs must be called in. These heavier solutions result in significant costs to the client and added time to account for mobilization and operation.

Moreover, adding heavier equipment and more personnel raises safety risks. By adding the milling contingency, Welltec made the operation more cost effective for the client while reducing operational time and mitigating risk to all personnel involved. The client was extremely pleased with Welltec’s solution and performance.

This opportunity enabled Welltec to improve its milling and clean-out capabilities. The double MMC milling technique adds to a growing array of IV contingency solutions that Welltec now offers.