Analysis of Sandstone Pore Space Fluid Saturation and Mineralogy Variation via Application of Monostatic K-Band Frequency Modulated Continuous Wave Radar

In this paper, we present the preliminary findings from a world-first investigation into monostatic frequency modulated continuous wave (FMCW) radar analysis of porous sandstones and their fluid content. FMCW results, within 24 to 25.5 GHz, provide insights into the rock/pore system as well as into mineral and liquid distributions, both crucial for the quantitative representation of the fluid-rock system for subsequent assessment of the sandstones. Sandstone samples, here characterised using known techniques of energy dispersive x-ray analysis, gaseous secondary electron (GSE) and backscattered electron (BSE) imaging are: Darney, Lazonby, Locharbriggs, and Red St. Bees sandstones, with FMCW results showing that, in the K-Band, the calculated values for relative permittivity, utilising free-space radiation reflection data, give results that are consistent with, and have the potential to predict, the known rock elemental constituents, where each sandstone has different distributions of the dominant quartz and subsidiary other minerals and of grain size and shape distributions. The experimental results support the sensitivity of this sensing modality to variances in rock properties in typical sandstones with complex relative permittivity, ε
_r
* , values for room-dry sandstones ranging from 5.76 to 6.76 and from 12.96 to 48.3 for partially saturated sandstones, with the highest values indicating high relative permittivity mineral inclusion and/or grain angularity. FMCW provides similar results, over slightly larger volumes, to those produced by the current resource-intensive methodologies, but much more easily and cheaply.