Case History: Innovative Milling Operation of Stuck Wellhead Tubing Master Valve using Coiled Tubing at South Ghawar Field, Saudi Arabia

Abstract

Milling a stuck partially opened wellhead tubing master valve (TMV) becomes inevitable to access the wellbore if all repairing attempts had failed. Typically, the milling can be accomplished by utilizing a milling machine, mounted on a wellhead, equipped with motors and special mills. In this case history, CT was selected to fully satisfy standard well control requirements. Different sizes of mills were utilized to provide access through the double disc gate valve to facilitate setting downhole barriers to replace the defective TMV with a new one safely and successfully. The post-job visual inspection of the milled bore showed regular cut of this gate valve. This paper highlights the extensive planning and preparation work performed to execute the job safely and successfully. The paper will also focus on the thorough risk assessment procedure and contingency plans to ensure all well control requirements are fully covered. This unique operation has showed that milling TMV using CT is proved to be a viable option addressing well control issues while performing the milling operation. The paper will also present many lessons learned to be applied in future similar jobs.