New Tracers Identify Hydraulic Fracturing Fluids and Accidental Releases from Oil and Gas Operations

TLDR

Identifying the geochemical fingerprints of fluids that return to the surface after high‑volume hydraulic fracturing of unconventional oil and gas reservoirs has important applications for assessing hydrocarbon resource recovery, environmental impacts, and wastewater treatment and disposal. The study reports novel diagnostic elemental and isotopic signatures (B/Cl, Li/Cl, δ¹¹B, and δ⁷Li) for characterizing hydraulic fracturing flowback fluids and distinguishing their environmental sources. The authors hypothesize that boron and lithium are mobilized from exchangeable sites on clay minerals in shale formations during hydraulic fracturing, enriching flowback fluids with these elements. Data from 39 flowback and produced water samples show distinct B/Cl, Li/Cl, δ¹¹B, and δ⁷Li signatures for Marcellus and Fayetteville formations versus conventional wells, and the boron isotope tool can quantify small fractions (~0.1 %) of flowback fluid in contaminated water, a capability validated by analyses of effluent discharge and an accidental spill site.

Abstract

Identifying the geochemical fingerprints of fluids that return to the surface after high volume hydraulic fracturing of unconventional oil and gas reservoirs has important applications 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, δ11B, and δ7Li) useful for characterizing hydraulic fracturing flowback fluids (HFFF) and distinguishing sources of HFFF in the environment. Data from 39 HFFFs and produced water samples show that B/Cl (>0.001), Li/Cl (>0.002), δ11B (25–31‰) and δ7Li (6–10‰) 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 fractions (∼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 formations during the hydraulic fracturing process, resulting in the relative enrichment of boron and lithium in HFFF.