Flowback and produced waters (FPWs) from hydraulic fracturing (HF) operations contain a complex mixture of organic chemicals including HF additives, their degradation products, and geogenic constituents. Few studies have examined polar HF additives and their degradation products in FPW. This mobile fraction of FPW constituents must be examined to support environmental monitoring and ensure that contaminants of concern are removed from FPW during treatment.<br/><br/>In this study, we applied a complementary target and nontarget screening approach to 33 FPW samples to detect and identify HF additives and their degradation products. The samples were collected from two wells in the Marcellus shale play over 765 days of production. The samples were diluted, filtered, pH adjusted, and concentrated using large-volume injection to remove inorganic matrix. They were then analyzed by means of liquid chromatography and high-resolution mass spectrometry. Thermo Scientific Compound Discoverer software was employed for automated peak picking, blind subtraction, grouping adducts and isotopologues, creating profiles of identified peaks across samples, and assigning neutral molecular formulae. We then used principal component analysis (PCA) to assess differences in the composition of the FPW samples and to prioritize nontarget compounds for structural elucidation.<br/><br/>In the PCA scores plot for each well, one well showed a clear shift from the early stage to the late stage FPWs while the other well showed two samples (FPW from days 1 and 468) as distinct from all other samples. For the latter well, the loadings plot indicated the composition of the FPW sample from the first day was driven by 6,272 features including polyethylene glycols, polypropylene glycols and other alcohol ethoxylates while the unique late stage FPW was driven by 6,140 features including benzalkonium chlorides, cocoamidopropyl dimethylamines, nonylphenol ethoxylates, and 2-butoxyethanol. The high intensities of the surfactants on day 468 indicate that these compounds were directly added to the well during the production phase. This workflow allows for the detection and identification of unknown contaminants regardless of origin.

Nontarget screening of hydraulic fracturing wastewaters identifies undisclosed biocides and surfactants over 765 days of production

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.