CHARACTERIZATION OF TRACE METAL CONCENTRATIONS WITHIN THE MARCELLUS SHALE ACROSS THE SOUTHERN TIER OF NEW YORK STATE

The Marcellus Shale is an unconventional shale gas play located in the Appalachian Basin. Due to the size of the Appalachian Basin and the use of hydraulic fracturing in consort with horizontal drilling, the Marcellus Shale is presently the largest producer of shale (natural) gas in the United States. This study focuses on determining the concentrations of trace metals within Marcellus Shale drill cuttings, and how the metals may be released during and after the process of drilling wells for shale gas extraction. The area focused on is across the Southern Tier of New York State, adjacent to ongoing shale gas extraction sites in Pennsylvania. Samples are from twelve drill holes, including cuttings from the basal Union Springs and the overlying Oatka Creek units within the Marcellus Shale. X-ray fluorescence (XRF) analysis was performed to determine total metal concentrations. Cuttings were also analyzed using XRD to determine the effects mineralogy has on metal concentrations. To determine amounts of metals within the Marcellus Shale that can be potentially released post drilling, drill cuttings were leached using 1% HCl under aerobic conditions for 1-day, 14-day, and 90-day periods. The 1-day leaching period mimics drilling activities used to clean well bores prior to hydraulic fracturing, and longer periods mimic cuttings disposal in surface impoundments or landfills. Based on the XRF results, the black, organic-rich portions of the Union Springs contain elevated S, Zn, Cu, Ni, and U. High concentrations of these trace metals were liberated by the 1-day HCl leach. In contrast, the overlying Oatka Creek contained elevated Ba and P as well as more chlorite than the Union Springs. Gradual chlorite decomposition in the HCl solutions slowly releases many elements including Fe, Mg, Mn, Cr, Li, and other trace metals. Pb and Mo concentrations are elevated in both units, and the Mo is quickly released by the HCl solutions. Combined results from the XRF, XRD, and leaching experiments can be used to predict potential metal release sourced from Marcellus Shale drill cuttings. If horizontal drilling to extract shale gas is permitted in the future, differences in metal release from areas of New York State likely to be impacted will better inform drill cutting disposal decisions.