Identification of Chlorinated Alkyl Ethoxylate Surfactants in Produced Water from the Marcellus Region and Proposed Subsurface Formation Mechanism

Wastewater produced from hydraulic fracturing of unconventional oil and gas wells is a complex mixture of high levels of salts and variable levels of organics, naturally occurring radioactive material, and microbial life. Due to the increasing amount of produced water generated, wastewater management is a growing challenge. Beneficial reuse of produced water, following fit-for-purpose treatment, can address the need for wastewater management but requires a full understanding of its composition including organic constituents. Here, we identify a new set of chlorinated surfactant transformation products present in water produced from the Marcellus shale region. Produced water samples were analyzed using liquid chromatography-quadrupole-time-of-flight (LC-QTOF) mass spectrometry. Chlorinated surfactants were identified using tandem mass spectrometry (MS/MS), and ethoxylate oligomers were differentiated using Kendrick Mass Defect analysis. Proposed chemical structures of the newly identified chlorinated surfactants were confirmed by comparison with a synthetic reference standard. Mechanistic studies under simulated subsurface conditions were performed. Our results suggest that the chlorination of injected surfactants can occur at 60 °C in the presence of concentrated hydrochloric acid, which is commonly used during well stimulation processes. These findings illustrate the importance of identifying potential transformation products to ensure proper treatment and reuse of produced water.