Impact of oxidizing hydraulic fracturing fluids on kerogen degradation and byproduct release from organic rich marcellus shale

Abstract

The technological advancements have led to improved utilization of organic-rich shales for energy extraction; however, low hydrocarbon (HC) recovery and declining oil and gas prices have pushed industry operators to apply new chemical additives to hydraulic fracturing fluid to increase HC production. Strong oxidizers known as breakers are added to fracturing fluids to increase HC productivity. These oxidizers can potentially degrade shale organic matter, i.e., kerogen, and improve shale permeability. However, there have been very few studies done on the byproducts released from these kerogen degradation reactions. In this study, three synthetic solutions containing oxidative breakers, sodium hypochlorite, sodium bromate, and ammonium persulfate, were reacted with kerogen extracted from Marcellus Shale for 14 days to mimic the shut-in period of a well. The type and amount of volatile organic compounds (VOCs) generated from these reactions were characterized. In addition, molecular structural parameters of kerogen extracts were characterized using ¹³C solid-state NMR analysis before and after the reaction to understand the molecular mechanisms of these degradation reactions. Our results indicate sodium hypochlorite and sodium bromate-based hydraulic fracturing fluid can significantly degrade kerogen by 46% and 60%, respectively; however, they also lead to the release of large amounts of trihalomethanes. This study indicates that oxidative breakers could play a key role in improving the recovery of HCs; however, they also release low molecular weight hydrocarbons into the produced water that may require specialized treatment depending on the produced water end use. Strategies to remove trihalomethanes from produced water may be required when managing fluids produced from reservoirs treated with halogen-containing oxidative breakers.