Safety and efficiency have always been the primary performance measures in the coiled-tubing (CT) industry. This paper describes the feasibility study, development objectives, field test, and launch of a new-generation CT unit in the Norwegian sector of the North Sea. This automated, modular system with its distributed system architecture is designed to improve safety in CT operations, with 15% operational efficiency gain and 30% offshore personnel reduction targeted.
A typical completion on Valhall is a horizontal well completed with 5 to 12 proppant-treated fractures per well in the soft chalk formations. The operations and logistics are complex and involve repeated sequences of perforating with CT, proppant fracture treatment with stimulation vessel, and a combined cleanout/perforating run with CT. On a 24-hour operation offshore, a 13-member crew operate the conventional CT spread comprising the unit, reel, and power stand; well-control equipment; two high-pressure, positivedisplacement pumps; shakers; choke; and a CT tower with the injector head.
The requirements and specifications of the new unit were finalized after a detailed study of operations, platform requirements, and local regulations. Efficiency gains were targeted in the rig-up and rig-down times, and in the overall zone cycle times (operational efficiency). Health, safety, and environmental improvements are achieved by reducing manual handling and lifting operations on board. Distinguishing equipment characteristics are as follows:
Preassembly and integration of components on skids to enable quicker rig-up and reduce manual handling. For example, offshore rig-up typically involves 54 lifts; the new unit cuts this number to 36.
Distributed-control architecture to reduce the number of rig-up connections required. For example, the system design allows a total rig-up with only 36 hydraulic connections instead of the usual 84.
Ability to run larger and heavier pipe (6,000-m length, 2⅞-in. diameter, 90,000-psi yield) at faster rates enables easier completion of difficult wells and reduces the overall zone-cycle time. It also eliminates handling of friction-reducing chemicals while maintaining cleanout efficiency.
Planned reduction in crew through the utilization of automated process control, The benefits of this include the following:
All controls for the choke, shakers, CT unit, and pumps are centralized in the CT unit's control cab. Many equipment controls-related tasks that conventionally were hands-on tasks are performed by the control system to allow the operator to focus on treatment efficiency.
Automated safety features are incorporated into process-control software to reduce safety exposure, particularly in areas prone to human errors.
Cab ergonomics allow the operator to oversee the entire operation and react to any situation quickly and efficiently.