title: Element mobilization from Bakken shales as a function of water chemistry.
abstract: Waters that return to the surface after injection of a hydraulic fracturing fluid for gas and oil production contain elements, including regulated metals and metalloids, which are mobilized through interactions between the fracturing fluid and the shale formation. The rate and extent of mobilization depends on the geochemistry of the formation and the chemical characteristics of the fracturing fluid. In this work, laboratory scale experiments investigated the influence of water chemistry on element mobilization from core samples taken from the Bakken formation, one of the most productive shale oil plays in the US. Fluid properties were systematically varied and evaluated with regard to pH, oxidant level, solid:water ratio, temperature, and chemical additives. Element mobilization strongly depended on solution pH and redox conditions and to a lesser extent on the temperature and solid:water ratio. The presence of oxygen and addition of hydrogen peroxide or ammonium persulfate led to pyrite oxidation, resulting in elevated sulfate concentrations. Further, depending on the mineral carbonates available to buffer the system pH, pyrite oxidation could lower the system pH and enhance the mobility of several metals and metalloids.
authors: Washington University in St. Louis, Department of Energy, Environmental, and Chemical Engineering, Campus Box 1180, One Brookings Drive, St. Louis, MO 631C30, United States.
authors: Lin
authors: L
authors: Wang
authors: Washington University in St. Louis, Department of Energy, Environmental, and Chemical Engineering, Campus Box 1180, One Brookings Drive, St. Louis, MO 631C30, United States.
authors: Scott
authors: S
authors: Burns
authors: Washington University in St. Louis, Department of Energy, Environmental, and Chemical Engineering, Campus Box 1180, One Brookings Drive, St. Louis, MO 631C30, United States. Electronic address: giammar@wustl.edu.
authors: Daniel E
authors: DE
authors: Giammar
authors: Washington University in St. Louis, Department of Energy, Environmental, and Chemical Engineering, Campus Box 1180, One Brookings Drive, St. Louis, MO 631C30, United States. Electronic address: jfortner@wustl.edu.
authors: John D
authors: JD
authors: Fortner
mesh_terms: D002254:Carbonates; D000067071:Hydraulic Fracking; D007501:Iron; D058955:Metalloids; D008670:Metals; D008903:Minerals; D008956:Models, Chemical; D013440:Sulfides; D062065:Wastewater / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000737:chemistry*
chemical_list: D002254:Carbonates; D007501:Iron; D058955:Metalloids; D008670:Metals; D008903:Minerals; D013440:Sulfides; D062065:Wastewater; D014874:Water Pollutants, Chemical; C011342:pyrite
keywords: Bakken formation; Element mobilization; Fluid chemistry; Shale-fluid interactions