CT operational flexibility improved

Coiled tubing (CT) operations are proving to be highly efficient techniques to implement completion or intervention services. Quick to mobilize, rig up and deploy, CT units offer versatility, safety and efficiency to most field operations. Because jointed pipe is not used, trip times are a fraction of those performed using conventional workover rigs. Eliminating pipe connections improves safety because rig floor workers are not required during tripping or pumping operations.

CT is a robust choice for intervention because well servicing tools can be snubbed into wells under pressure. One limiting factor to CT use, however, has been the relative size and weight of the CT reel. Many wells are located on small, single-well satellite offshore platforms with limited crane capacity or deck space. Additionally, many wells in other areas are serviced by elevating boats or offshore workboats that have similar deck space limitations. Some remote locations demand modular equipment that is air-transportable. Until now, the CT reel weight was the limiting factor that made this option impractical.

For some time the industry has sought a solution to deploying CT units to space/weight limited facilities or capacity transportation. Sometimes smaller diameter tubing can be used to reduce reel size and weight, but often this solution jeopardizes operational efficiency because it limits the scope of work that can be performed. Engineers hoped to be able to develop a field applicable splice that could meet all the mechanical and hydraulic requirements of the original coiled tubing, plus be able to pass through the CT injector head and the pressure control stripper.

Limited access wells benefit

Numerous examples exist where the ability to connect CT reels has proven to be the factor that assured the success of the operation. In BP’s Ula Field, offshore Norway, barite and well formation debris opposite the perforated interval prevented production. To return the well back to maximum production a cleanout to total depth was required. Normally, this can be easily and quickly accomplished using a CT unit. However, at Ula, the well was located on a satellite platform whose crane lacked the capacity to lift a conventional CT reel.

With the Schlumberger ReelCONNECT system enabling a safe, high integrity 2 3/8-in. diameter CT splice, two reels were quickly mobilized, transported to the platform and easily lifted into place by the crane. The strings were spliced using the system’s spoolable connector. After testing the connection, the cleanout operation was commenced, debris was successfully removed from the well bore, and the well was put on production at sustained flow rate in excess of 4,500 b/d per day.

Another operator has used the system for sand cleanout, plug retrievals and placement of cement plugs when North Sea winter weather and regulations imposed limitations on simultaneous operation with CT on offshore platforms.

The deployment of CT intervention during winter depended upon finding an acceptable weather window, for transportation, rigging up of equipment and performing the services. Unfortunately, the platform crane had limited capacity to lift the CT reel. With several wells shut-in for up to 12 months, the operator was losing considerable revenue from deferred production. The system enabled the operator to deploy a modular CT unit to resolve the problem of deferred production. Using the platform crane to lift two small CT reels onboard, the job commenced without delay.

Several CT runs were performed in the wells. Following the workover, the nonproducing wells returned to production. The simple implementation of CT connector technology made the difference between immediately resuming production and suffering an indeterminate delay due to adverse winter weather.

A real solution for a reel problem

As its name implies, the system enables efficient splicing of two or more coiled tubing reels. The connector provides a way to quickly and safely splice multiple CT reels together on site (Figure 1).

Smaller platform or workboat cranes can easily lift the smaller reels, which weigh a lot less than conventional reels with a single continuous string of pipe and deploy them on deck. The splicing process is straightforward; the CT operator positions the reels across from each other and both ends of the CT are pulled into the assembly skid and secured. The wireless remote controlled skid allows the operator to stand at a safe distance during the process of pulling and aligning of the CT. The connector assembly skid allows safe handling and preparation of the CT and installation of the spoolable connector. The spliced connection is mechanically as strong as the CT and flexible enough to pass over the gooseneck and through the injector head. Its external profile is the same as the CT in which it is installed, so there is no problem deploying it through the pressure control stripper.

Following the installation of the spoolable connector, the tubing is mechanically and hydraulically tested to assure pipe integrity, then the assembled CT string is spooled unto the work reel. The entire splicing operation takes less than six hours. The connections have been pull-tested to 80% of CT tensile strength. They have been cycle-tested in a built-for-purpose automated test fixture. The fixture simulates bending of the CT on the reel and over the gooseneck with internal pressure, axial tension and injector block clamping force. The connector is rated to a maximum pressure equal to 80% of the CT rating and 300ºF (150ºC).

Once installed, the connector is compatible with standard jar and accelerator combination as well as the friction and drag reduction downhole tools. The connector’s internal profile is large enough to accommodate launching of balls, darts or pigs. Upon completion of operation the downhole end of the CT string is spooled onto the transport reel and the connector is removed to allow the reels to be demobilized. Neither the installation nor the removal of the connector involves welding, so a hot work permit is not required.

Deferred production is the key

Although it may seem that connecting two CT reels onsite involves multiple steps, the total cost of the operation is only a fraction of the cost of the deferred production. And with wells shut-in for protracted periods, it is possible that formation damage could occur preventing the well from ever resuming its full production rate. The system offers a quick and safe solution when weather, regulations or platform crane capacity limitations have prevented a traditional CT intervention.