The Andrew asset is a strategic hub for BP in the Central North Sea and has been producing from the Palaeocene oil reservoir for the past twenty-two years through a small fixed platform. In addition to the conventional Palaeocene oil reserves, there is an underlying Lower Cretaceous gas-condensate reservoir. The A11z well was drilled as an appraisal well within this low permeability formation and the original completion in 1998 was designed with the intent of performing a future hydraulic fracture. Extended well tests however, identified that gas production facilities were required for production and these were not provided until platform redevelopment in 2015. The stimulation operation has been delayed since due to the highly complex interfaces on an ageing asset and prioritisation of plant reliability work scopes and other simpler intervention work scopes.
Due to the increasing strategic importance of a new black start gas well for the asset hub, the alignment of priorities between the different functions was addressed and the hydraulic fracture operations were executed in June 2018. A multi-disciplinary project team has been established with a remit to manage and simplify the work scopes, enabling an efficient stimulation operation and a safe flowback with minimal impact to the platform reliability. The optimal design for a reliable proppant hydraulic fracture treatment has been crucial to deliver this Regional objective.
The stimulation execution was one of the largest single stage proppant placements for the basin in recent history. The implementation of single mesh proppant for the entire job is a unique deployment for the Region and a novel movement in the global stimulation industry in general, as was the first application of fibres in the North Sea. In addition to the unconventional job design, the Andrew A11z stimulation has become the first proppant fracturing treatment to be executed by BP UK North Sea in twenty-two years.
The successful execution and results of this complex project demonstrates how innovative stimulation design, when combined with effective multi-disciplinary team management and guided by aligned priorities adds significant long-term value but can also extend the life of mature offshore assets and instil confidence to pursue many more similar opportunities in such environments that are all too often discarded due to perceived complexity.