--> Phosphate Minerals in Utica Shale: A possible Source of Trace Metals in Flowback Water

AAPG Eastern Section Meeting

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Phosphate Minerals in Utica Shale: A possible Source of Trace Metals in Flowback Water

Susan A. Welch1, Julia M. Sheets1, John Olesik1, Anthony Lutton1, Alexander Swift1, Matt Edgin1, Steve Chipera2 and David R. Cole1

1 School of Earth Sciences, The Ohio State University, 125 S Oval mall, Columbus OH 43210
2 Chesapeake Energy Corporation, 6100 N. Western Ave, Oklahoma City, OK, 73118

September 27, 2016 Tuesday 8:00 A.M. AAPG Eastern Section Meeting, Lexington, Kentucky

Abstract

Understanding physical, chemical, and mineralogical properties of the Utica-Point Pleasant formations is important for predicting how the subsurface environment will respond during hydraulic fracturing. This study focuses on characterizing phosphate mineral assemblages and measuring trace element concentrations in Ca-phosphates as compared to other mineral assemblages in the fabric of the mudrock. Although phosphate phases constitute only a few percent of the total rock, they are of general interest geochemically and for hydraulic fracturing in particular because 1) they are commonly porous and thus potentially accessible to input fluids 2) they are relatively soluble and reactive and may represent areas of increased porosity from water-rock interaction 3) they contain elevated concentrations of trace metals (Sr, Ba, REE, U, Th) that can be released to flowback fluids and 4) they represent a nutrient source for subsurface microbes.

A deep core sample (approximately 10,930 feet) of the Utica-Point Pleasant from Washington County, Pennsylvania has been analyzed by SEM (backscattered electron (BSE) imaging, energy dispersive X-ray spectrometry (EDXS), and laser ablation ICP-MS to determine concentrations of trace elements in phosphate phases compared to the surrounding carbonate-clay matrix. Laser ablation results show that the phosphate phases are enriched in La, Ce, U and Th by one to three orders of magnitude compared to the surrounding carbonate-clay matrix and that the concentrations of these elements co-vary. Sr was also enriched in the phosphates, with a maximum measured concentration of ~ 10,000 ppm Sr, however, median Sr concentration in the phosphates was only 2 to 3 folder higher than the surrounding matrix (~ 500 to 2000 ppm). Ba concentrations were substantially lower in the phosphates compared to the surrounding matrix, only a few ppm to a few 10's compared to 50 to 150 in the clays and carbonates.

AAPG Datapages/Search and Discovery Article #90258 © 2016 AAPG Eastern Section Meeting, Lexington, Kentucky, September 25-27, 2016