Non-Targeted chemical characterization of a Marcellus shale gas well through GC  × GC with scripting algorithms and high-resolution time-of-flight mass spectrometry

A non-targeted study of hydraulic fracturing fluids and corresponding flowback fluids allows for the understanding of the origin of wastewater constituents and provides insight into chemical signatures that may inform wastewater management practices for unconventional gas development. The source water for the hydraulic fracturing fluids, the actual hydraulic fracturing fluids used in four stimulation stages, and four flowback samples were obtained from a single unconventional gas well located in northeastern, PA. The chemical complexity of these fluids required high-resolution non-targeted methodologies. Analyses were therefore performed by GC × GC-TOFMS with the use of mass spectral scripting algorithms to expedite data analysis while maintaining a discovery approach. Our results indicate that during the flowback period hydrocarbon concentrations increase with time. The relative chemical composition remains nearly constant, which is hypothesized to be representative of the hydrocarbons present in the native shale that were extracted during the hydraulic fracturing process. Additionally, a comparison of fracturing fluids and flowback with high-resolution time-of-flight mass spectrometry inferred the fate of three common organic modifiers: ethylene glycol, glutaraldehyde, and cinnamaldehyde. It was determined that ethylene glycol is removed from the well within the first four days of flowback, while polymerization reactions are primary mechanisms of glutaraldehyde and cinnamaldehyde transformation.