Safe and Successful Restoration of Wellbore Accessibility by Wellhead Gate Valve Milling

Abstract

Well control has been one of the most important items in oil and gas production engineering. The wellhead plays a vital role in well control as it consists of many valves, including the master valve (MV), crown valve (CV), and wing valve (WV). The MV is the lower valve in the wellhead that is directly exposed to well pressure. Therefore, it's very important to ensure the valves holding in terms of functions tests and greasing. Passing the MV that is stuck in a partial closed position is considered a tremendous challenge, not only in well integrity but also for well intervention. The valve cannot be opened to allow for well intervention and cannot be totally closed to withstand well pressure to act as surface barrier in line with API standards. This challenge presents an opportunity to capitalize on milling the MV utilizing a gate valve drilling unit (GVDU). This paper presents a solution that addresses stuck valves across wellhead trees. The conventional practice is to utilize either a workover (WO) rig or coiled tubing (CT) to mill the MV and secure the well to change a defective MV. However, it is more challenging when the well does not meet the minimum barrier requirements and the operation is costly. A new generation of GVDU has been deployed to especially mill such a stuck/defective MV, with no need to utilize (CT) unit nor a wireline (WL) unit -. A 15K pneumatic GVDU has successfully been demonstrated and proven its ability to mill the gate valves to safely restore and gain wellbore accessibility. During the planning phase of this operation, several elements were considered to ensure safe and efficient execution, including conducting a series of peer reviews, comprehensive risk assessments along with well integrity and well intervention peer review team members. During the operation, several challenges have arisen such as rising pressure because of the compressed gas while run in hole (RIH), which was tackled by a modification of the gas bleed-off needle. Moreover, killing the well was challenging due to the fact the MV was in stuck position. Thus, a circulation path was added through pumping water,. Nonetheless, there were three main advantages through utilization of a GVDU; one of which was the easy and light rig-up. Second was safe and quick operation, which was completed in only 2.5 hours. Third was the cost optimization unless idea is to indicate that no cost was involved? This success of this operation has unlocked the well potential after regaining wellbore accessibility. It also resolved the well integrity/control challenge in a safe, an extraordinary expedited intervention, a cost-effective method, and an environmentally safe and minimal environmental footprint.