Guide arch (gooseneck)
CT string Reel
Stripper Injector
head BOP
Control cabin Power pack
downhole tools and sensors. Real-time pressure and temperature data, along with depth correlations provided by the ACTive in-well live performance system, enable CT crews and operators to measure downhole conditions and monitor events as they unfold.
> Coiled tubing unit. The most distinctive feature of the CTU is its reel, which is manipulated by the CT crew from the control cabin. Some reels can carry more than 20,000 ft [6,100 m] of coiled tubing.
The downhole data provide quantitative feedback on a well’s response to ongoing treat ments. And because these downhole measure ments can be tied to depth, it is possible to correlate them to existing petrophysical measure ments. The CT data can be further correlated to surface indicators and data from offset wells to verify treatment performance. Onsite interpre tation software helps operators evaluate subtle indicators that may alert them to deviations from the job design. They can then respond imme diately to changing downhole conditions by adjusting parameters to optimize treatment while the CT string is still in the wellbore and the treatment is underway. This article briefly reviews CT systems and describes general applications of this technology. Case studies from Malaysia, Canada and Saudi Arabia show how advances in CT measurements and telemetry are helping operators to better implement their downhole treatment programs.
Typical CT Applications
> Inside the CTU control cabin. The cabin, located behind the reel, provides a commanding view of the entire operation. From this vantage point, the CT operator controls all aspects of the coiled tubing operation, including injector rate, pump pressure and downhole tool activation. Satellite communications provide a real-time link to locations around the world.
At the center of any CT surface operation is a coiled tubing unit (CTU) from which a continuous length of flexible steel pipe is spooled. This pipe is kept on a large storage reel during transport to the wellsite. As it is spooled off the storage reel, it passes through a gooseneck and is straightened just before it enters the borehole. At the end of the operation, the flexible pipe is pulled out of the well and spooled back onto the reel (above left). On the hub of the storage reel, a high- pressure swivel joint enables pumping of treatment fluids through the tubing, even while the reel is rotating. An injector head pulls the CT string off the spool and runs it into the wellbore. From the CTU cabin, the CT operator controls the hydraulically driven injector head to regulate the movement and depth of the CT string. A stripper assembly beneath the injector head provides a dynamic seal around the tubing string, which is key for running the CT string in and out of live wells. A blowout preventer (BOP) assembly between the stripper and wellhead supplies secondary and contingency pressure-control functions. The operation is monitored and coordinated from the CTU control cabin (left).
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Oilfield Review
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