Offshore DASVSP Applications and Long-Range Distributed Fiber Optic Sensing

Summary Distributed Fiber Optic Sensing for borehole seismic was introduced ten years ago as a tool to monitor wells regardless of geometry and/or completion. The wide adoption of fiber optic technology has been driven by the need of monitoring using tools that are more cost effective than conventional seismic technology. Applications of DAS offshore include time lapse monitoring of the effects of production and injection, higher resolution seismic in areas of poor illumination, velocity analysis and aiding conventional seismic processing. To date most DAS deployments, several them summarized here, have been conducted with fiber deployed on platforms with fiber not exceeding 12km. Wide availability of subsea wells in various basins requires the need for monitoring longer distances, from tie-ins and umbilicals into the active section of wells. Here we describe a new Interrogator Unit for sensing long fibers with additional attenuation losses as result of subsea connectors. We show how state of the art IUs can overcome optical fading at great lengths without the need of additional subsea devices and or enhanced glass. An example from a test dataset acquired with a 30km optical setup shows long distance seismic monitoring can be effectively conducted with DAS.