Many subsea completions employ a down hole isolation valve for temporarily closing off production while awaiting first oil or flow line connections. These valves are designed to be opened or closed through surface pressure pulses in the fluid column to activate stored nitrogen in the valve housing. When a valve fails to activate as expected, a reliable contingency plan must be ready or the financial consequences can be large.
With the use of electric wireline tractor technology, a contingency valve opening system allows malfunctioning isolation valves to be mechanically shifted with depth precision and controlled force. This method uses an electrically powered hydraulic stroking tool to shift the valve sleeve open or closed with a selected force of 10K - 30K lbs depending on the type of valve. The stroking tool is either tractor conveyed in high angles or run with only a shifting tool attached in low angles. A new intelligent key tool replaces the spring loaded shifter, to allow the system to be run "slick" and avoid hang ups on down hole profiles that can occur with the conventional spring loaded shifting tools.
An electric line deployed solution is faster to mobilize, more precise in locating shifting sleeves and less expensive than alternative solutions. A review of case histories will prove these points. Also, pre-job planning, integrated team involvement, SIT and operational recommendations will be discussed.
With today's high rig costs, identifying areas where new technology can be used to reduce rig time and improve well construction efficiency is a high priority, especially for operators in deep water regions like the Gulf of Mexico, West Africa or West of Shetlands. One such technology has been the down hole isolation valves used on many deep water, subsea completions for temporarily closing off production from the reservoir. There are several versions of these valves from different suppliers and all have a less than perfect track record. In the event that a valve fails to function on command, (possibly due to loss of the Nitrogen charge) it must then be shifted mechanically. Conventional solutions use either slick line jars to shift the valve in low angle wells or mobilize coiled tubing in high angles. Neither method has the depth precision nor finesse that is often required to engage and positively shift the valve sleeve. It is also difficult to execute these methods in the intelligent completion environment because of the complexity in passing down hole jewelry without damaging or shifting the sleeve devices unintentionally. Finally, coiled tubing mobilizations are slow and costly.
A complimentary new technology to the isolation valves has been the evolution of tractor devices to anchor to the inside of the tubing and apply large hydraulic forces in a controlled and repeatable manner. A hydraulic stroking tool (Figure 1), that is run in the well on electric wireline with a casing collar locator (CCL), can quickly locate the valve (sometimes beyond the reach of slick line or CT). Once located, the shifting tool engages the collets on the shifting sleeve with it's "key" and the stroking tool is then anchored and stroked either up or down with a force that depends on the size and type of valve. This method is found to be less damaging to the shifting sleeve collets as compared to the use of jars and less likely to reclose a valve that was shifted open (down stroke) upon coming out of the hole and exiting the valve sleeve.