Applications of fiber-optic sensing to borehole seismology

Summary

Distributed Acoustic Sensing (DAS) is an emerging technology that leverages optical fibers to record the seismic wavefield with an unprecedented spatial resolution. In this talk, I will describe various seismic-band applications utilizing optical fibers deployed in boreholes. We first illustrate how records from a vertical DAS array can be simply and effectively processed to construct velocity models, detect microseismic events and earthquakes, locate them, and estimate their magnitude. Then, we show how a horizontal DAS array deployed in an unconventional shale reservoir records guided waves propagating for hundreds of meters with frequencies as high as 700 Hz. Thanks to the high resolution of DAS measurements, guided waves are recorded unaliased despite their very short (< 10 m) wavelength. We compare the field observations with semi-analytical and wave-equation modeling approaches. Guided waves are also strongly affected by open fractures induced by hydraulic stimulation. We use a horizontal cross-well acquisition of perforation shots recorded by a DAS array in a simple, geometrical analysis of horizontal fracture growth. We also analyze guided waves generated by microseismic events and can locate the events despite the unidirectional nature of the DAS measurements.