This paper describes the introduction of a new perforating system in Norway, including its development based on operator specifications. Field examples demonstrate the measurable success of the system, showing a three- to sixfold increase in productivity and production rates as high as 8500 m3/D per well.
The Visund field is located in the North Sea, about 150 km off the coast of mid-Norway. High reservoir pressure and insufficient formation strength made it necessary to perforate in relatively heavy completion fluid with the guns oriented for sand prevention. The first wells, perforated in water-based fluid with zinc charges, produced below expectations. Potential causes were identified as insufficient depth of penetration, high overbalance when perforating, and zinc precipitation damaging the formation. There were also indications from other fields that the orienting technology in use was not producing expected results.
The operator started an initiative to improve the perforating system. Design criteria included deep-penetrating, low-debris steel charges that minimize debris and improve performance, increased gun-void volume for a better surge effect, accurate orientation of the perforation tunnel regardless of dogleg severity, and confirmation of the orientation. The operator and the service company collaborated to develop a system that would provide a better solution. The system was tested and qualified before it was introduced in the Visund field. To optimize perforation cleanup during static overbalanced well conditions, a dynamic underbalance method was selected.
Since December 2001, six wells have been completed on Visund using the new system. In one well the dynamic underbalance response was confirmed from downhole pressure gauges run directly above the guns. The combined benefits of the perforating system, the dynamic underbalance, and a special kill pill have resulted in up to sixfold increase in productivity. The gun orientation is verifiably within requirements, and perforating debris have been minimal.