Acquisition and imaging of ocean-bottom fiber-optic distributed acoustic sensing data using a full-shot carpet from a conventional 3D survey

ABSTRACT Distributed acoustic sensing (DAS) is a novel and fast developing technology that in recent years has been used for turning seabed fiber-optic cables into densely sampled receiver arrays from which the acquired DAS data is used for seismic imaging of the subsurface. The full understanding on how horizontal fiber-optic cables works for these type of applications is still unknown, and more knowledge is therefore needed in data acquisition and imaging. We describe a controlled-source experiment performed offshore Norway, where we interrogated a fiber-optic cable over an area that has it center approximately 100 km from the location on land where the interrogator was installed. The DAS data is compared with towed-streamer data acquired at the same time using a full 3D shot carpet. Data analysis show that the signal-to-noise ratio decreases with increasing distance from the interrogator. We show that the signal amplitude varies with incidence angle. Furthermore, the data quality is considered good at a distance of approximately 130 km from the interrogator, which demonstrates the potential for acquisition of DAS data for subsurface imaging at long distances. For data imaging, we illustrate the importance of using multiple azimuths in the imaging to obtain a subsurface image with sufficient image quality. We find that with the DAS data, we are able to obtain an image quality of the subsurface that is comparable with the towed-streamer data, in particular for areas located directly underneath the fiber-optic cable.