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Abstract An oil-producing subsea well located offshore Congo was equipped with an inoperable subsea vertical xmas tree (XT), in specific the production master gate valve in the vertical bore stuck at 55% to 65% open following the measurement of the valve stub. The inoperability of the valve actuators resulted in the temporary closure of the oil-producing well in 2017, as it was defined necessary by the operator well integrity policy, for this reason, the XT had to be replaced using a rigless light well intervention (RLWI), due to water depth of 800meter. In order to do so, temporary plugs needed to be run in hole to provide temporary barriers and allow the XT tree change-out to be completed. To achieve such an objective the partially open gate valve had to be milled out. The operator issued a challenge to the oilfield services industry to present a solution to mill the partially open gate valve via RLWI vessel. The supplier responded with a solution that could mill the gate valve in a single run, including recovery of the milled coupon. In addition, the solution would ensure that all the operational well barriers remained free from obstruction in the event of the milling toolstring becoming stuck, with fishing contingencies also in place. The resulting solution utilized a wireline-deployed milling toolstring equipped with a fully automated milling stroker, a metal matrix compound (MMC) core bit with an eccentric spear mechanism, shearable spacers, and contingency featuring an electric release fishing tool (ERFT). The benefits of this solution related to several areas; the surface read-out system allowed precise control of the milling BHA. The partially open gate valve was successfully milled through, and the coupon recovered to the surface on a single run, with a total milling time of 14 hours and 40 minutes. This paper discusses the challenges and solutions related to milling a partially open gate valve on a closed oil-producing subsea well using an RLWI vessel offshore Congo. It covers the project scope, solution design, planning, equipment preparation, job execution, and provides estimates of risk and cost reduction to as well the added production level resulting from this operation.
Ndjawe et al. (Tue,) studied this question.