Hydrolysis of Hydraulic Fracturing Fluid Organic Additives and Their Interaction with Pyrite

The Marcellus Shale is currently one of the largest resources and producers of natural gas in the U.S. Shale gas production is expected to increase in the coming decades and its extraction requires the use of hydraulic fracturing and up to 7 million gallons of water per well. Various chemical compounds are commonly added to the hydraulic fracturing fluid to increase the efficiency of natural gas extraction from the low-permeable shale. Although the reactions of these compounds in surface waters are well documented, their mobility and fate downhole is largely unknown.

The objective of this work was to study the hydrolysis of hydraulic fracturing fluid additives and their interaction with pyrite. Pyrite is a ubiquitous mineral of the Marcellus Shale lithostratigraphy. It is also known to be redox active, and is capable of catalyzing reactions with organic compounds. In this study, the reported solubility, volatility, and hydrophobicity of the most common hydraulic fracturing ingredients was used to assess which compounds are mobile enough to react downhole. The hydrolysis of these selected hydraulic fracturing chemicals was studied, and then each compound was added to an aqueous suspension of pyrite. The transformation products were monitored over time using liquid chromatography triple quadrupole mass spectrometry (LC-QQQ). Preliminary results showed that pyrite catalyzed reactions with the biocide dazomet, producing different products from those observed in the literature for surface waters. This is indicative of pyrite’s reactivity and the need for further understanding of its behavior with hydraulic fracturing fluids. The results of this study will increase the energy sector’s understanding of the fate and efficacy of the chemicals used, and will inform wastewater management schemes of methods to dispose of fracking flowback water.