Distributed Acoustic Sensing for Permanent Downhole Monitoring

In recent years a new fibre-optic based technology, Distributed Acoustic Sensing (DAS), has emerged which has the potential to revolutionise permanent downhole monitoring. DAS uses a standard single-mode optical fibre deployed along the entire length of the wellbore as the sensor and is able to measure both acoustic and seismic signals along the wellbore. Fibre-optic cable deployed permanently in the well is now being used to monitor the fluid and proppant placement and in-flow along the production zone. Furthermore the fibre can be used to take Vertical Seismic Profile (VSP) measurements in wells where the deployment of conventional geophone is not possible. Once the DAS fibre is permanently deployed no further well intervention is necessary enabling low cost repeat measurements to be made. This technology has the opportunity to transform the ability to make time-lapse VSP measurements. In this paper, we will present further details of the permanent downhole applications for DAS and provide case studies of how DAS is being used in time-lapse VSP and permanent flow measurements.