Valhall – Pushing the Limits for Openhole Zonal Isolation ─ Qualification and Field Trial of 10,000-psi Oil-Swelling Packers

Abstract

The paper outlines the full-scale qualification testing of high differential pressure (∆P) swellable element packers (SEPs) for fracture stimulation application in prop fracture stimulation in production wells on the Valhall Field, which is operated by BP Norge AS.The SEPs use solids-laden oil-based mud (OBM) to expand the element installed on the outer surface of the basepipe, which forms part of the reservoir liner. This eliminates the need to spot dedicated swelling fluid.Also discussed is the system used to perform the fracture stimulation in the field. The results of the successful qualification full scale testing up to 10k psi across two 5-meter packers are described. Details are also given for the Valhall Field operation with the deployment and swelling of 20 SEPs, followed by the hydraulic fracturing operation.Reservoir management for the Valhall redevelopment program relies on multi-zone water injection and proactive management of unwanted water production. Produced water isolation is achieved with an arrangement of heavy-duty sliding sleeve circulating devices. A method of annular zonal isolation to prevent flow behind the reservoir liner is essential to success.The oil-swelling SEPs offer a viable alternative and several improvements over the currently used cement barriers. These advantages are described in the paper. At the heart of these is the key requirement that any annular barrier must withstand very high ∆P (10k psi) during stimulation of the individual producing zones.Several unsuccessful attempts had been performed to qualify a SEP to 10k psi for Valhall; therefore, it was decided to try a new design featuring an innovative mechanical end-ring system. This represents a step change in the design methodology of SEPs. It enables reduction of element length and packer OD while retaining high differential pressure (DP) ratings and/or increase the DP rating of long SEPs. The features and benefits of the new SEP design are presented.