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We look at the benefits of placing permanent seismic sensors in a wellbore and recording data over time, either passively or with dedicated surface sources. Implementation involves placing an array of sensors permanently in a well along with the completion string. Challenges include recording data over fluid-flow noise in the well (production or injection) and reliability of the sensors and associated hardware. Applications include 4D imaging and monitoring of reservoir properties, both stand-alone and in conjunction with surface seismic, and mapping of faults and other features using micro-seismic events. Recently, a fibre-optic based system has been created for permanent emplacement in wellbores. This system has been tested with three field trials including a 2006 production well installation. Surveys have been conducted with simultaneous acquisition of permanent seabed and borehole arrays using both active surface sources and passive noise.