New Tracers Identify Hydraulic Fracturing Fluids and Accidental Releases from Oil and Gas Operations
Résumé
Identifying the geochemical fingerprints of fluid that return to the surface after high volume hydraulic fracturing of unconventional of oil and gas reservoirs has important application for assessing hydrocarbon resource recovery, environmental impacts, and wastewater treatment and disposal. Here, we report for the first time, novel diagnostic elemental and isotopic signatures (B/Cl, Li/Cl, delta B-11, and delta Li-7) useful for characterizing hydraulic fracturing flowback fluids (HFFF) and distinguishing sources of HFFF in the environments. Data from 39 HFFFs and produced water samples show that B/Cl (>0.001), Li/Cl (>0.002), delta B-11 (25-31 parts per thousand) and delta Li-7 (6-10 parts per thousand) compositions of HFFF from the Marcellus and Fayetteville black shale formations were distinct in most cases from produced waters sampled from conventional oil and gas wells. We posit that boron isotope geochemistry can be used to quantify small fraction (similar to 0.1%) of HFFF in contaminated fresh water and likely be applied universally to trace HFFF in other basins. The novel environmental application of this diagnostic isotopic tool is validated by examining the composition of effluent discharge from an oil and gas brine treatment facility in Pennsylvania and an accidental spill site in West Virginia. We hypothesize that the boron and lithium are mobilized from exchangeable sites on clay minerals in the shale formation during the hydraulic fracturing process resulting in the relative enrichment of boron and lithium HFFF.