Trace Element Geochemistry of Flowback Brines from the Marcellus Shale

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The Ohio State University

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Hydraulic fracturing has become a popular and widely successful method of recovering oil and natural gas from unconventional resources, particularly shales. As hydrocarbons are recovered from black shales, flowback fluid consisting of formation brines and hydraulic fracturing fluids are brought to the surface. The fluids are typically hypersaline and often rich in trace and heavy metals and radionuclides. For this reason, flowback fluids and formational brines are an important area of study as many of these trace elements are toxic environmental pollutants (barium, arsenic, etc.), while others, such as rare earth elements (REE's) and platinum group elements, have potential economic viability. Despite the importance of brines, analysis of their trace metals remain difficult by current analytical methods due to relatively low metal concentrations, high concentrations of dissolved solids and salts, and a lack of matrix matched analytical standards. Therefore, the objective of this project was to develop a robust analytical method for evaluating alkali metals, rare earth elements, lanthanides, and actinides in flowback brines with high total dissolved solids, salt content, and organic contents. To do this, I analyzed flowback samples from wells within the Appalachian Basin, commonly produced from the Marcellus Formation, by inductively coupled plasma mass spectrometer (ICP-MS). Two methods were used to reduce the total dissolved solid and salt concentrations. First, we used a commercial resin to remove salts, which proved unsuccessful. Second, we successfully tried dilution then analysis by ICP-MS of trace element concentrations to a part per trillion level (but still well above ICP-MS detection limits). The results of this project included a sensitivity analysis of the measured elements by concentration. By so doing, these data revealed the viability of this method to get accurate and precise results for the majority of the analytes measured. Additionally, concentrations of rare earth elements and actinides were be compared to their average crustal and oceanic concentrations to provide a geological context for the occurrence of these elements. These plots revealed REE enrichment patterns that are expected by the marine black shale depositional setting of the Marcellus shale, and thus underscored the ability of the dilution method to make geologic interpretations from resultant brine element concentrations.



Trace element, Flowback, Brine, Marcellus Shale, Geochemistry