The proposed solution consisted of the Well Miller® fitted with a customized milling bit and the Well Tractor® to provide the necessary weight on bit (WOB). This solution also provided a catching mechanism to recover the milled coupons and keeping them out of the wellbore. Welltec® developed a two-mill system specifically for this operation in which a smaller, pilot hole would be milled to reestablish communication with the well and equalize pressure, followed by milling the main hole to regain full access downhole. Pressure below the valve was unknown, so contingency scenarios were created to account for high-pressure changes coming from either above or below the valve.
The first several runs were used to adjust to the well conditions and determine the needed WOB and milling speed. The pilot hole was milled using a 1.54” metal matrix compound (MMC) bit. Pressure from the riser was bled, the crown valve was opened, and fluid column communication was verified. A 3.85” MMC bit was then run in hole to mill the main hole. After three hours of effective milling, current observations on the surface indicated that the milling was complete. Upon recovery, the core was discovered in one piece still inside the bit. The full-sized, 3.85” MMC bit with catcher allowed for safety barriers to be installed.
This operation was performed with constant fluid circulation across the tree for the pilot run and injection during the main run.
This operation was the world’s first master gate valve milling operation completed via wireline, proving the lighter intervention was possible and opening the door for similar operations across the industry. Wireline operations are faster, less disruptive, and safer than the CT and workover rig milling solutions. Welltec® milled the Inconel, tungsten carbide-coated valve safely and efficiently. This solution avoided the use of traditional and heavier solutions, which can cause wellhead damage or leaks if not monitored closely.
The client managed to kill the well, install safety barriers, and proceed with the planned wellhead tree replacement. Following the success of this first job, the client awarded Welltec® a similar job in another field, which was also executed successfully.
WELL TYPE: OIL
WELLHEAD TEMPERATURE: 110ºf
WELLHEAD PRESSURE: 1200 PSI
VALVE MATERIAL: INCONEL 718,0.004MM TUNGSTEN CARBIDE COATING
MILLING AT SURFACE: AMBIENT TEMPERATURE