Substantial reserves of shale oil and gas have been reported in 44 countries across the globe, increasing the world’s known natural gas resources by 47%. Currently, these resources are only recoverable by the use of hydraulic fracturing and horizontal drilling. Of these formations, the Marcellus Shale in Pennsylvania is the largest producing formation, generating on average 14.6 billion cubic feet/day of shale gas. To extract the natural gas, millions of gallons of water are pumped into each well. Various chemical additives are blended into the hydraulic fracturing fluid to control the properties of the well. Of these, biocides form an important class of compounds, as they are used with the intent to eliminate bacterial growth in the well. Although their behavior in surface waters has been widely reported in the literature, their reactions with minerals in the deep near-wellbore environment are not well-known. The Marcellus Shale contains significant deposits of pyrite, a mineral that is both redox active and capable of catalyzing reactions with organic compounds. Our work focused on pyrite interaction with dazomet, one of the most frequently used biocides in the region. The objective of our study was to determine the effect of pyrite on dazomet hydrolysis. Liquid chromatography-triple quadrupole mass spectrometry (LC-QQQ) and gas chromatography-mass spectrometry (GC-MS) were used to monitor reaction rates and products. Our experiments show that dazomet hydrolyzes in water to form various reaction products. On the addition of pyrite, we note a significant increase in the removal rate of dazomet from solution as well as a change in the products of the reaction. The results of this study help us to elucidate the fate of biocides in the Marcellus Shale, and inform stakeholders of the risks of chemical use in the event of a spill or release.

Pyrite-dazomet interactions: Reactivity of a hydraulic fracturing fluid additive

251st National Meeting (2016)

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