Synchrotron-Based Transmission X-ray Microscopy for Improved Extraction in Shale During Hydraulic Fracturing

Engineering topics which span a range of length and time scales present a unique challenge to researchers. Hydraulic fracturing (fracking) of oil shales is one of these challenges and provides an opportunity to use multiple research tools to thoroughly investigate a topic. Currently, the extraction efficiency of oil from shale is low but can be improved by carefully studying the processes at the micro-and nano-scale. Fracturing fluid induces chemical changes in the shale which can have significant effects on the microstructure morphology, permeability, and chemical composition. These phenomena occur at different length and time scales which require different instrumentation to properly study. Using synchrotron-based techniques such as fluorescence tomography provide high sensitivity elemental mapping and an in situ micro-tomography system records morphological changes with time. In addition, the transmission X-ray microscope (TXM) at the Stanford Synchrotron Radiation Lightsource (SSRL) beamline 6-2 is utilized to collect a nanoscale three-dimensional representation of the sample morphology with elemental and chemical sensitivity. We present the study of a simplified model system, in which pyrite particles are exposed to oxidizing fluid, and then mixed with quartz particles, to establish the basic understanding of the more complex geology-relevant oxidation reaction. The spatial distribution of the byproduct of the oxidation reaction, ferrihydrite, is retrieved via full-field XANES tomography showing the reaction pathway. Further correlation between the high resolution TXM data and the high sensitivity microprobe data provides insight into potential morphology changes which can decrease permeability and limit hydrocarbon recovery.