Curtin/CSIRO Geophysics Group Seminar, 5th August 2021

Distributed Acoustic Sensing for Laboratory Measurements of Elastic Properties at Seismic Frequencies

Date: Thursday, 5^th August, 2021
Time: 10:00 AM – 11:00 AM
Location: CSIRO/ARRC Auditorium, 26 Dick Perry Avenue, Kensington
Presenter: Alexey Yurikov, Research Fellow, Exploration Geophysics, Curtin University

Forced-oscillation stress-strain laboratory measurements are increasingly employed to obtain elastic and viscoelastic properties of rocks at seismic frequencies. Yet these measurements are slow and expensive, due in part, to the use of metal or semiconductor strain gauges, which need to be glued to the sample, are fragile, have relatively low sensitivity, and measure very local strain only, so that the measurements can be affected by a slight misalignment of the system assembly and local heterogeneity of the rock. Emergence of fibre-optic distributed acoustic sensing (DAS) technology provides an alternative means of measuring strain.

Strain measurements with DAS involve wounding an optical fibre around the sample multiple times and connecting it to a DAS recording unit. Pilot experiments performed using this setup on samples of Poly(methyl methacrylate) (PMMA), polyether ether ketone (PEEK), aluminium and dry Bentheimer sandstone samples shows good agreement with strain gauge measurements. Advantages of DAS over strain gauges include much higher strain sensitivity (down to 10-11) and signal-to-noise ratio (and hence, shorter time required for measurements), larger dynamic range, ability to measure average (rather than local) strain in the sample, and robustness at elevated temperatures.

Further research is required to obtain independent estimates of Young’s modulus and Poisson’s ratio, and to port the system into a pressure vessel to obtain rock properties at in situ conditions.