DAS VSP Recorded Simultaneously in Cemented and Tubing Installed Fiber Optic Cables

Summary Distributed Acoustic Sensing in wells is a very successful monitoring technique in Vertical Seismic Profiling surveys. A direct comparison between two types of DAS fiber deployment for VSP is studied. It is found that in the inclined section of the well, where there is enough gravity coupling between the tubing and the casing the response of the two fibers in terms of signal and noise is almost identical. In this situation there is a clear advantage of using DAS fibers on the tubing, given the cost savings and the failure management, the tubing fiber being easily replaceable. However, in the vertical section of the well, where there is very little coupling between the tubing and the casing the tubing fiber records a considerable amount of ringing noise. A phenomenological model for this ringing noise has been proposed. The model explains the noise as the fine rattling of the tubing onto the interior of the casing. Understanding the physical nature of the ringing noise made possible the implementation of a method of attenuating the ringing noise. Nonetheless, the key to future low-cost DAS VSP surveys will be the prevention of such rattling.