Given interest and concern over rapid development of hydrocarbon production from low permeability reservoirs (e.g., shale gas and tight oil) there is need for tested, reliable methods for the chemical analysis of the associated produced waters. Of particular interest are data for trace elements in produced water, which are important for understanding potential mineral commodity value, environmental and human health impacts, and basic geochemical interpretation. Analytical methods for trace element quantification in aqueous media were largely developed for drinking water and have not been assessed for the complex high salinity matrix of typical produced waters, which can exhibit total dissolved solid concentrations up to 10 times higher than seawater. We will present results for the quantification of 17 trace elements selected for their application to mineral commodities, environmental concern, and/or geologic interpretation (As, Al, Ba, Be, Cd, Cr, Co, Cu, Hg, Mo, Ni, Pb, Rb, Sb, U, V, and Zn) in produced water samples from shale gas and tight oil reservoirs using Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) vs. Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES). Whereas ICP-MS has much greater sensitivity, the exceptionally high salinity of the samples can require dilution up to 1000x or greater or complex pre-concentration prior to detection. Conversely, ICP-OES utilizing an argon humidifier, a high salinity nebulizer, and matrix-matched standards can handle produced waters with little to no dilution but has lower sensitivity. Comparison between the two methods for 15 produced waters samples ranging in salinity from 17 to 370 g/L of total dissolved solids will be presented along with limits of detection, limits of quantitation, recovery from matrix spikes, and sensitivity to variation in major ion composition of the sample matrix. Results from this work will be used to develop a table of suggested analytical approaches for quantitation of each of the specific trace elements. It is hoped that the continuation of these efforts can provide the general public a better assessment of tools available for the chemical analysis of produced waters.

Quantification of trace elements in oil and gas produced waters via ICP-OES versus ICP-MS: Can high tolerance for salinity overcome lower sensitivity?

255th National Meeting (2018)

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