Zonal-Isolation Barriers Meet Valhall Waterflooding, Fracturing Demands

Abstract

Technology Update The Valhall field, operated by BP Norge in the Norwegian North Sea, is undergoing a massive redevelopment that will allow the field to keep producing until approximately 2050. With the field undergoing waterflooding, the operator is investigating strategies to prevent formation damage that could result from a waterflood and to minimize costs as the redevelopment program progresses. The reservoir-management plan relies on multiple-zone water injection, with management of offset water in the producing wells controlled by heavy-duty sliding sleeves. Proppant fracture stimulation of the production wells requires high-differential-pressure isolation between zones. Cementing of the reservoir liner normally provides this isolation between the producing zones, but the presence of cement can render the sliding sleeves inoperable. The use of zonal-isolation-barrier (ZIB) devices that were developed by READ Well Services was identified as a potential solution for meeting the isolation requirements of the producing wells and was implemented, marking the industry's first use of this, specific ZIB technology (Fig. 1). This alternative approach was deemed necessary to limit the risk of damaging the sliding sleeves and reduce other operating risks, when compared with the established practice of running and cementing the reservoir liner. ZIB devices possess the advantages of both cement and mechanical barriers, such as packers, in executing zonal isolations, but without the operational risks associated with these traditional technologies. The basic principle of the ZIB technology is that when pressure is applied to the inside of the liner, the metal outer sleeve will inflate and conform to the profile of the formation. If required, the ZIB can also be expanded in the future—for example, should a washout or water breakthrough occur. The ZIB can be activated by applying pressure from the surface to the entire completion or by deploying a hydraulic-expandable-tubular-system tool by means of wireline, coiled tubing, or drillpipe (Fig. 2). Nine ZIB devices have now been deployed at Valhall with 65/8-in. liners, providing open-hole zonal isolation during fracturing and production operations.