Geochemical evaluation of flowback brine from Marcellus gas wells in Pennsylvania,USA |
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| Institution: | 1. PetroChina Research Institute of Petroleum Exploration and Development, Beijing 100083, China;2. Nicholas School of the Environment, Duke University, Durham, NC 27708, United States;1. Civil and Environmental Engineering, Colorado School of Mines, Golden, CO 80401, USA;2. Department of Plant and Environmental Sciences, University of Copenhagen, Thorvaldsensvej, 40, 1871 Frederiksberg C, Denmark;3. Department of Civil and Environmental Engineering, Colorado State University, Fort Collins, CO 80523, USA;4. Department of Chemistry, Colorado State University, Fort Collins, CO 80523, USA;5. Department of Soil and Crop Sciences, Colorado State University, Fort Collins, CO 80523, USA |
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| Abstract: | Large quantities of highly saline brine flow from gas wells in the Marcellus Formation after hydraulic stimulation (“fracking”). This study assesses the composition of these flowback waters from the Marcellus shale in Pennsylvania, USA. Concentrations of most inorganic components of flowback water (Cl, Br, Na, K, Ca, Mg, Sr, Ba, Ra, Fe, Mn, total dissolved solids, and others) increase with time from a well after hydraulic stimulation. Based on results in several datasets reported here, the greatest concentration of Cl? in flowback water is 151,000 mg/L. For total Ra (combined 226Ra and 228Ra) in flowback, the highest level reported is 6540 pCi/L. Flowback waters from hydraulic fracturing of Marcellus wells resemble brines produced from conventional gas wells that tap into other Paleozoic formations in the region. The Br/Cl ratio and other parameters indicate that both types of brine formed by the evaporation of seawater followed by dolomitization, sulfate reduction and subsurface mixing with seawater and/or freshwater. Trends and relationships in brine composition indicate that (1) increased salt concentration in flowback is not mainly caused by dissolution of salt or other minerals in rock units, (2) the flowback waters represent a mixture of injection waters with highly concentrated in situ brines similar to those in the other formations, and (3) these waters contain concentrations of Ra and Ba that are commonly hundreds of times the US drinking water standards. |
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