Fracture characterization with GPR: A comparative study
Résumé
Provided that the frequency of the GPR antenna is properly selected, detecting rock fractures is generally an achievable task because most of the investigated rocks are resistive. On the other hand, fractures can be generally envisaged as thin-beds embedded in a homogenous rock formation, thus yielding a complex reflection pattern caused by the reverberation of the GPR signal back and forth within the bed. As a result, dedicated approaches must be developed in order to extract quantitative information about fracture properties, i.e. thickness and permittivity of filling material, encoded in the thin-bed response. This work presents a comparison of two approaches for fracture characterization that we recently tested on synthetic, lab as well as field datasets. Although both approaches rely on amplitude and phase information in the frequency domain, their strategies significantly differ. The first one is based on common-offset data and involves deterministic deconvolution, while the second one processes common-midpoint reflections according to an amplitude-and-phase-variation-with-offset inversion. We test the performance of both approaches on a lab specimen scanned with high frequency antennas. Our aim is to identify shortcomings and advantages of the tested approaches, and to evaluate their outcomes according to the needs of possible field applications, in terms of acquisition time and accuracy.