ABSTRACT

A dramatic increase in unconventional drilling that utilizes hydraulic fracturing to extract oil/gas over the past decade has led to concern over handling and management of produced/flowback water (PFW; hydraulic-fracturing wastewater) because the potential exists for its accidental release into the environment. This PFW contains high amounts of total dissolved solids acquired from interaction with the reservoir formation. Development and testing of geochemical methods, such as strontium (Sr) isotope ratio (87Sr/86Sr) analysis, to determine the origin of dissolved solids in an environment would be valuable. Samples acquired from different sources in Texas overlying and within the Barnett Shale, such as surface/ground water and PFW, contain unique Sr concentrations and 87Sr/86Sr values, with the potential to be used as a geochemical fingerprint. This study shows that because of the very high concentration of Sr in PFW and its high 87Sr/86Sr value, when as little as 1% of a sample is PFW, the sample experiences a measurable change in 87Sr/86Sr. To determine which phase within the reservoir rock imparts its 87Sr/86Sr to the PFW, sequential extractions were performed on powdered Barnett Shale core samples. Results of the extractions show varying geochemical affinities and distinct 87Sr/86Sr values by leaching solution. However, a direct link to the PFW sample was not conclusive, likely because of the unknown location of the PFW sample and the spatially variable 87Sr/86Sr of the Barnett Shale. Future work requires further cooperation with industry or federal agencies that could provide a more complete set of samples.

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