The world's first successful installation of a permanent borehole seismic system in an offshore production well was executed at Valhall. The system is fibre-optic based and has 5 levels of 3C seismic sensors spaced 13m apart. Surveys have been conducted with simultaneous acquisition of permanent seabed and borehole arrays using both active surface sources and passive noise. The active seismic data are of good quality data and processing yields high-resolution images to a distance of 400m from the borehole, complementing the lower-resolution surface seismic data. Time-lapse surveys are expected in 2007, and, in parallel, passive seismic data are being analyzed for potential for reservoir monitoring of fluid fronts using micro-seismic data.
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