Evaluating distributed acoustic sensing for crosswell seismic surveys with helical and linear fibers using conventional P-, SH-, and SV-wave sources

Abstract Seismic borehole tomography with standard seismic sources and receivers provides higher-resolution results compared to alternative conventional seismic surveys. The development of distributed acoustic sensing (DAS) for seismic surveys offers practical advantages over conventional sensors, such as higher spatial resolution, repeatable measurements, and time savings. This study details the use of DAS in conjunction with conventional seismic sources at the Svelvik CO2 Field Lab to conduct P-, SH-, and SV-wave crosswell surveys, comparing data obtained from helically wound and linear DAS fibers to evaluate their suitability for crosswell measurements. The use of such controlled active sources allows the generation of controlled, high-energy acoustic signals with defined characteristics that allow noise to be separated, resulting in cleaner and more reliable DAS data for further processing. The P-wave survey provided the best DAS response, and signals were recorded the full length of the borehole (approximately 100 m). The variations in signal-to-noise ratio (S/N) with incidence angle between DAS data sets from different cables indicate that it may be useful to record data on linear and helically wound cable for crosswell surveys to ensure the best P-wave response at source-receiver paths at the same depth. However, for SV-wave surveys, a linear fiber produces higher S/N data. Fluctuations in data quality are observed along the borehole due to differences in cable coupling. SH waves are recorded with low S/N on the DAS, as were the conventional data. Overall, wave arrival times in the DAS data are consistent with conventional data. The comparisons in this study show that good quality crosswell DAS data can be obtained for P- and SV-wave sources, thus providing repeatable, cost-effective SV measurements for time-lapse crosswell tomographic surveys.