Post-Burn Mineralogic and Trace Element Relationships from an In-Situ Oil Shale Experimental Retort: ABSTRACT

Twenty post-burn and two control (unburned) core holes were drilled into a horizontal in-situ oil shale retort at the Geokinetics field site, Uinta basin, Utah. The object of the investigation was to study the mineralogic changes and trace element partitioning resulting from a true in-situ burn of Green River oil shale under field conditions. Minerals were examined by x-ray diffraction and optical microscopy; elemental determinations were performed utilizing x-ray fluorescence, neutron activation analysis, and other analytical chemical techniques. The complex mineral assemblage created was a result of rapid intense heating coupled with fluctuating temperatures, gas and fluid pressure, cooled at a shallow depth, composed primarily of solid solutions of silicates plus cations, primarily Ca²⁺, Mg²⁺, and to a lesser degree Fe²⁺. Distinct zones observed correspond to temperature thresholds, which can be distinguished by increasing degrees of silicification of the carbonate-rich raw oil shale. Trace element partitioning parallels closely the mineral assemblages, with the synthesis of insoluble minerals in the hottest most intensely altered zones, minimizing the extractability of potentially detrimental materials from the residue of in-situ combustion.