Distributed acoustic sensing (DAS) for geomechanics characterization: A concise review

Abstract

Microseismic/acoustic emission monitoring is a powerful tool for geomechanics characterization. Recent advances in fiber-optic sensing enable the acquisition of broadband seismic wavefields by exploiting the phenomenon of Rayleigh backscattering that occurs naturally in the fiber-optic. This new, relatively inexpensive technology - distributed acoustic sensing (DAS) - repurposes pre-existing fiber-optic cables (e.g., unused telecom cables or so-called dark fiber) or fit-for-purpose cables as dense seismo-acoustic sensor arrays. Recent studies have shown that DAS can be employed to monitor microseismic activities during hydraulic fracturing, quasi-static geomechanical strains induced by well injection, and acoustic emission signatures during laboratory slope failure. In this review, we first briefly describe the measurement principle of DAS. Then, we present a concise overview of the state-of-the-art progress in DAS-based geomechanics studies, with particular emphasis on geomechanical responses associated with hydrofracturing and shallow geohazard triggering. We further discuss the current challenges of this emerging technology, including low signal-to-noise ratio, single-component sensitivity, large data volume, spatial distance uncertainty, and amplitude response complexity. We conclude by suggesting that DAS coupled to dark fiber networks presents a unique opportunity to detect and monitor microseismic/acoustic emission events and that it offers a new possibility to investigate fine-scale geomechanical processes across multi-kilometer distances.