Influence of frequency, grade, moisture and temperature on Green River oil shale dielectric properties and electromagnetic heating processes

Development of in situ electromagnetic (EM) retorting technologies and design of specific EM well logging tools requires an understanding of various process parameters (applied frequency, mineral phases present, water content, organic content and temperature) on oil shale dielectric properties. In this literature review on oil shale dielectric properties, we found that at low temperatures (< 200 °C) and constant oil shale grade, both the relative dielectric constant (ε′) and imaginary permittivity (ε″) decrease with increased frequency and remain constant at higher frequencies. At low temperature and constant frequency, ε′ decreases or remains constant with oil shale grade, while ε″ increases or shows no trend with oil shale grade. At higher temperatures (> 200 °C) and constant frequency, ε′ generally increases with temperature regardless of grade while ε″ fluctuates. At these temperatures, maximum values for both ε′ and ε″ differ based upon oil shale grade. Formation fluids, mineral-bound water, and oil shale varve geometry also affect measured dielectric properties. This review presents and synthesizes prior work on the influence of applied frequency, oil shale grade, water, and temperature on the dielectric properties of oil shales that can aid in the future development of frequency- and temperature-specific in situ retorting technologies and oil shale grade assay tools.