Analysis of Geomaterials using Frequency Modulated Continuous Waves

摘要

In this paper we present the preliminary findings from an investigation into Frequency Modulated Continuous Wave (FMCW) sensing of geomaterial properties. The authors believe that the results from this study represent a world first in the application of FMCW sensing for geomaterial analysis. Accurate modelling of geomechanical dynamics is dependent on understanding in situ rock characteristics and phenomena, such as internal fluid phases and pore geometry. Due to the difficulty in penetrating geomaterial samples, the intrinsic rock parameters and internal processes are typically inferred from post failure analysis. In this research we introduce the theory of FMCW sensing along with seminal results based on analysis of return signal amplitude and phase over a frequency bandwidth of 24-25.5 GHz. Variations in returned signals between different samples are due to radiation backscatter and dispersion. The following geomaterial samples are analysed: Darney, Doddington, Lazonby, Locharbriggs and Red St. Bees Sandstones, Cotswold Cream and Gold Limestones and Ferruginous Ironstone. Ground truth measurements are taken along with samples doped with water and kerosene. Each geomaterial sample can be clearly classified with results indicating that the Darney Sandstone exhibits the clearest response to fluid saturation with an observed phase shift relative to a dry sample of 14.6° and 73.1° for kerosene and water respectively. These results verify the potential of FMCW analysis within the K-band to provide access to critical geomaterial properties.