oa A Permanent Borehole Seismic Field Trial Comparing Fiber-optic Distributed Acoustic Sensing with Dedicated Geophones and Hydrophones

We show an analysis of data from a permanent borehole fiber-optic Distributed Acoustic Sensing (DAS) and dedicated receiver experiment in Milne Point, Alaska. The test well is 152m in depth and instrumentation consisted of fully instrumenting optical fiber in the well along with reference geophones and hydrophones placed in the well at 16 depth locations at 9.2m spacing, ranging from 15 to 150 m deep. Vibrators generated seismic signals with a 18.2m source point spacing. There are 8 sweeps at each source point. Each sweep time is 12s long and the receiver listening time is 16s. The correlated signal is 4s long and the DAS data have the same recording time as the geophones. The DAS implementation shown here treats each 1m of cable as an individual receiver resulting in a total number of DAS receivers equal to 143. Results detail direct comparison of data from both fiber-optic DAS receivers and the z-component of actual geophones, all permanently cemented in a borehole, with a surface vibroseis source. We examine data amplitude, frequency, phase, noise and other practical issues. We also present quantitative comparisons of signal/noise for both dedicated and virtual DAS receivers as well as some thoughts on the way forward for the DAS technology.