Mineralogical and Geochemical Analysis of Strontium and Barium Sources in the Point Pleasant Formation

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2016-05

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The Ohio State University

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Abstract

Analysis of trace elements in rocks from the Utica-Point Pleasant gas shale play is important because elevated concentrations of trace elements in flowback fluids derived from hydraulic fracturing may be an environmental hazard. Previous reports show high levels of barium and strontium associated with flowback fluids, with no clear explanation as to their origin. The goal of this study is to determine potential sources of Sr and Ba from Utica-Point Pleasant mudrocks that could be released into hydraulic fracturing fluids with which they interact. Polished sections of core were analyzed to determine the concentrations and distribution of trace elements across selected mineralogical/textural regions of the samples. Samples provided by Chesapeake Energy were observed with light and scanning electron microscopy (SEM) to identify areas of interest for analysis by inductively coupled plasma mass spectrometry laser ablation (ICP-MS-LA). SEM backscattered electron images and QEMSCAN mineral mapping helped determine the spatial distribution of the sulfide, sulfate, and carbonate minerals of interest. Energy dispersive spectroscopy was used to obtain semi-quantitative spot chemical analyses of minerals. SEM images show significant quantities of carbonates (CaCO3), barite (BaSO4) and celestite (SrSO4) which may be the sources of high levels of Ba and Sr in flowback fluids previously reported. Analysis from ICP-MS-LA line profiles across a pyrite/carbonate mineral assemblage and surrounding silt and clay-size carbonate/silicate matrix show major elements Mg, Ca, Sr, Ba, Al, Na, Ti, Fe, S, Si and trace elements Mo, Mn, Ni, Zn, La, Ce, U, Th, Rb. Barium concentrations were low in the pyrite and carbonate shells but ranged from 50 to 500 ppm in aluminosilicate clays in the matrix and up to 500,000 ppm in barite. Strontium concentrations ranged from 100 to 500 ppm in the pyrite but range 4000-6000 ppm in the carbonate shells and finer-grained clay-carbonate matrix.

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Barium, Strontium, Geochemistry, Mineralogy, Point Pleasant

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