Comparative Laboratory Study of the Geochemical Reactivity of the Marcellus Shale: Rock-Fluid Interaction of Drilled Core Samples vs. Outcrop Specimens

The Marcellus shale is an unconventional reservoir of significant economic potential with Total Organic Carbon (TOC) ranging from 1 to 20%. Hydraulic fracturing is used to extract the shale's resources, which requires large amounts of water and can result in mineral-rich flowback waters containing hazardous contaminants. This study focuses on a geochemical analysis of the flowback waters and an evaluation of the potential environmental impacts on water and soil quality. Drilled core samples from different depths were treated with lab-prepared hydraulic fracturing fluids. Rock samples were analyzed using Energy Dispersive Spectroscopy (EDS), while effluents' chemical compositions were obtained using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). A comparison of results from drilled core samples treated with additives for hydraulic fracturing to those treated with deionized (DI) water confirms that, as expected, the major elements present in the effluent were Ca, Ba, and Cl in concentrations greater than 100 mu g/L. The most concerning elements in the effluent samples include As, Ca, Cd, Pb, Se, S, K, Na, B, Mo, and Mn, with Cd and Cr values averaging 380 and 320 mu g/L, respectively, which are above safe limits. Se concentrations and high levels of Ca pose major safety and scaling concerns, respectively. We also compared Marcellus shale drilled core samples' geochemical reactivity to samples collected from an outcrop.

Automated summary

This study focuses on the geochemical analysis of flowback waters from Marcellus shale and evaluates the potential environmental impacts on water and soil quality. The results show that hydraulic fracturing fluids used to extract the shale's resources result in mineral-rich flowback waters containing hazardous contaminants. The effluent samples contain elevated levels of elements such as Cd, Cr, and Ca, which exceed safe limits and pose risks to safety and scaling.