Electric-Line Milling Operation on Tree Master Valve of a High Surface Pressure Well Enables Well Control

Abstract

This paper presents the success story of an innovative milling operation on a stuck-closed tubing master valve performed with electric line technologies. This field application has resulted in restoration of well accessibility, enabled well control, and saved costs related to rig intervention. The paper also documents lessons learned and recommends proper operational procedures related to future similar rigless operations, specifically with regards to well control and barrier philosophy. A stuck-closed surface valve in a live well is treated with extra caution as it presents a serious and challenging well control issue. Such a situation often calls for immediate intervention to restore well accessibility and reestablish well integrity barriers. The stringent well control requirements of the oilfield operator make the operational design and corresponding job execution even more challenging. In this case, Well-A is a land based vertical oil well on which the master gate valve was stuck and non-functional in the closed position. The pressure bellow the valve was last measured to be 1200 psi, a relatively high shut-in wellhead pressure compared to other offset producers in the same field. The wellhead was equipped with two carbon steel master gate valves, in addition, to the swap valve. The lowermost gate valve is the stuck valve, hence, preventing access to the well. Several attempts to repair and grease the valve body and stems were unsuccessful. Accordingly, the oilfield operator has decided to mill the gate valve, secure the well, and then replace the entire tree. The uncertainty in the well pressure below the master valve posed a significant operational risk. This is due to the impact of well fluid pressure force on the electric line rig-up after the gate valve is milled. Therefore, job planning, design, and execution were guided by a risk based and comprehensive contingency plan that accounted for all probable well control scenarios. The rig-up consisted of coiled tubing flanged risers, annular blowout preventer, Shear/Seal ram, and wireline blowout preventer in order to ensure the presence of adequate well control barriers throughout the operation. Adhering to a ‘safety first’ attitude, the operation was concluded successfully and met its said objectives. The successful massive undertaking of such critical well intervention operation has marked a new milestone in rigless well interventions.