In 2012, for the first time ever in North Africa, a well in a dry environment utilized e-line milling technology to mill out a failed flapper. With this paper the author will describe the actual process from preparation to completion of a world's first operation.
A gas well experienced a malfunctioning 7″×4.56″ 13 Cr. steel downhole flapper valve. Due to several operational challenges including limited well site access and temperatures over 150°C, there was a need for an alternative solution to mill the valve and allow access below it for future well interventions. Furthermore, due to the fact that the well was a gas producer, there was a need to avoid, or minimise introduction of any fluids in the well.
The method of choice was an e-line tractor and milling assembly. Because of the size of the offshore platform this was the only feasible solution. Heavier intervention methods like coiled tubing were not possible to mobilize because of the weather conditions plus the risk of reservoir damage if introducing fluids. The e-line tractor conveyed the toolstring to target depth (2,916 m MD) where the e-line milling tool was activated and milled through the flapper valve in approximately 40 minutes.
After the completion of the milling phase of the operation, another run was performed to set an access sleeve in the milled out flapper valve utilizing an electromechanical setting tool. This access sleeve ensured that entry/re-entry through the milled flapper valve would be easily accomplished each time. The installation of the access sleeve was confirmed by running a 3.25″ gauge through it.
Milling of flapper valves and other well bore obstructions on electric line offers a cost efficient alternative technology to existing methods. Furthermore, it provides HSE benefits and logistical advantages by reducing the amount of required equipment and personnel.