Observations from a fiber-pipeline crossing during active and passive seismic acquisition using distributed acoustic...

Distributed acoustic sensing (DAS) with horizontal fibers has recently begun to be utilized for offshore seismic imaging. During a field experiment in the North Sea, using a fiber crossing a gas pipeline, we observed anomalous wave arrivals on a specific range of channels and shot gathers. We analyzed the arrivals and interpret them as shear waves (S-waves) that are generated when the compressional direct waves impinge on the pipeline. The S-waves subsequently propagate through the pipeline and are recorded on the fiber section crossing the pipeline. With an increased usage of the fiber network for seismic acquisition, this P-S converted wave may be observed more often in future acquisitions. Our analysis shows the pipeline acting as a wave guide over several hundred meters for signals generated in the water column. These insights may be useful for DAS-based offshore pipeline monitoring. In addition to the arrivals generated during the active acquisition, we analyzed transient signals occurring at the crossing in the passive data. While their distribution over time correlates with the tides, their generation mechanism remains unclear. No periodic signals that could be attributed to the flow in the pipeline were observed in the vicinity of the crossing.