The Clair field is the UK’s largest naturally fractured reservoir. The main development targets are Devonian in age with poor matrix properties. This makes Clair challenging territory for 4D Seismic surveillance, and heavily informs the choice of acquisition for the 4D programme. In 2006, a Permanent Reservoir Monitoring System was installed over Clair Phase 1. The five survey Life of Field Seismic (LoFS) programme has successfully informed Phase 1 depletion planning and well targeting, in addition to demonstrating the value of 4D for Clair Ridge. In 2017 the Clair JV will be acquiring the baseline for a new 4D seismic programme over Clair Ridge. Instead of selecting a permanent reservoir monitoring solution though, the Ridge 4D Programme will be executed using an ultra-high density Ocean Bottom Seismic (OBS) acquisition to suppress the 4D noise. This case study describes the factors that have led to the selection of a Re-deployable OBS solution for the future 4D programme on Clair, marking a departure from Permanent Reservoir Monitoring (PRM) on the field. Consideration is also made to emergent DAS (Distributed Acoustic Sensing) VSP technology, which may help to augment the future 4D programme through the provision of localised, on-demand 4D seismic surveillance.


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