| Description |
This work provides a better understanding of radionuclides associated with shale formations and an increase in their concentration accompanying oil and gas production. The mineralogical and inorganic composition of various hydrocarbon rich shales was evaluated with spectroscopic, microscopic, and mass spectrometric techniques. Microstructural analysis by X-ray Diffraction (XRD) determined the quartz, feldspar, dolomite, calcite, and clay composition of the shale. Scanning Electron Microscopy - Energy Dispersive X-ray Spectroscopy (SEM/EDX) revealed the presence of inorganic metals (i.e. U, Th, Pb, etc.) near hydrocarbon rich regions of the shale. Elemental analysis of the bulk mineral phases via multi-collector Inductively Coupled Plasma Mass Spectrometry (ICP-MS) revealed higher concentration of U and Th associated with the organics in shale. A combination of the geochemical and mineralogical data suggests that the anoxic conditions during deposition may have led to the enrichment of the redox-sensitive elements (i.e. U, V, and Mo, etc.) in the Utica and Niobrara formations, while an oxic depositional environment led to a depletion of redox-sensitive elements in the Green River and Mancos formations. Furthermore, our data suggest that rare-earth elements (REE) enrichment is of terrigenous origins, supporting anoxic diagenesis. Knowledge of the inorganic composition, including Naturally Occurring Radioactive Materials (NORM) and Technologically Enhanced Naturally Occurring Radioactive Materials (TENORM) of hydrocarbon rich shales, is essential for the development of advanced environmental techniques that extract the hydrocarbons without polluting the surrounding environment. |
