Determining conventional and unconventional oil and gas well brines in natural samples I: Anion analysis with ion...

Unconventional natural gas extraction by hydraulic fracturing requires millions of gallons of water and generates flowback water, produced water and recycled fluids of varying chemical composition. Ion chromatography (IC) is a relatively low cost and efficient means to determine the anionic composition, however, the wide range in anionic content of these fluids poses a challenge to analytical methods developed for "natural" waters. We report here that the combination of UV and conductivity detectors increased detection sensitivity (e.g., 10-50 ppb) and expanded the number of anions detectable in a single sample run. Samples from four unconventional shale gas wells, two impoundments, nine conventional oil wells, two freshwater streams and mine drainage samples were analyzed in this study. All produced water samples and impoundment samples had high chloride (17,500-103,000 mg L^-1, 93,900 to 134,000 mg L^-1, 27,700 and 30,700 mg L^-1), bromide (178-996 mg L^-1, 183-439 mg L^-1, 230 and 260 mg L^-1) and conductivity (38,500-160,000 μS/cm³, 95,300 to 183,000 μS/cm³, 61,500 and 103,000 μS/cm³), respectively, relative to mine drainage and freshwater stream samples. Molar ratio analysis using Cl^-/Br^- to Cl^- and SO₄^2-/Cl^- to Br^- revealed significant differences between the samples, providing a simple means for distinguishing water impacted by different sources of contamination.