Rock fracture characterization with GPR by means of deterministic deconvolution

Abstract

In this work I address GPR characterization of rock fracture parameters, namely thickness and filling material. Rock fractures can generally be considered as thin beds, i.e., two interfaces whose separation is smaller than the resolution limit dictated by the Rayleigh's criterion. The analysis of the amplitude of the thin bed response in the time domain might permit to estimate fracture features for arbitrarily thin beds, but it is difficult to achieve and could be applied only to favorable cases (i.e., when all factors affecting amplitude are identified and corrected for). Here I explore the possibility to estimate fracture thickness and filling in the frequency domain by means of GPR. After introducing some theoretical aspects of thin bed response, I simulate GPR data on sandstone blocks with air- and water-filled fractures of known thickness. On the basis of some simplifying assumptions, I propose a 4-step procedure in which deterministic deconvolution is used to retrieve the magnitude and phase of the thin bed response in the selected frequency band. After deconvolved curves are obtained, fracture thickness and filling are estimated by means of a fitting process, which presents higher sensitivity to fracture thickness. Results are encouraging and suggest that GPR could be a fast and effective tool to determine fracture parameters in non-destructive manner. Further GPR experiments in the lab are needed to test the proposed processing sequence and to validate the results obtained so far.