CHARACTERIZATION OF MARCELLUS SHALE FLOWBACK/PRODUCED WATER IN PENNSYLVANIA

Recent developments in natural gas extraction from tight shales bring two key water related issues: substantial requirements for water to hydraulically fracture these shales and high salinity wastewater that is generated by this process. Flowback water from the Marcellus Shale in Pennsylvania can be treated by thermal processes to meet the state TDS discharge requirement (i.e., 500 mg/L). However, oil and gas companies are increasingly striving to reuse flowback water for hydraulic fracturing as it reduces water needs and wastewater treatment costs. High concentrations of calcium, barium and strontium may affect its reuse because of their high scaling potential. The objective of this study is to characterize the inorganic composition of flowback/produced water from the Marcellus Shale in the Appalachian basin using the data collected in this study and those that are available in the literature. Quality of flowback/produced water from Marcellus shale was compared with other brines from adjacent formations. The evolution of salinity with time and location across Pennsylvania is also analyzed to provide additional insight into the origin and nature of salinity as it has a major impact on potential management strategies for this wastewater

Chemical analyses performed on 160 flowback and produced water samples collected across Pennsylvania were compared for major characteristics and related trends. Chloride was used as a reference for the comparison as its concentration varies with time of contact with the shale. Major cations (Ca, Mg, Sr, Ba) exhibited variations that cannot always be explained by simple dilution of existing brine with the fracturing fluid. Furthermore, concentrations of these cations and bromide vary greatly from Southwest to Northeast Pennsylvania. Most of these ions are fairly well correlated with chloride concentration except for barium that exhibits strong geographical trends.