PRODUCED WATER GEOCHEMICAL CHARACTERIZATION FROM A MARCELLUS-SHALE NATURAL GAS WELL RESEARCH SITE

We examined the geochemistry of wastewaters that are co-produced with natural gas at the Marcellus Shale Energy and Environment Laboratory (MSEEL) site. MSEEL is a long-term study site operated by the Northeast Natural Energy LLC (NNE) near Morgantown, West Virginia. These wastewaters from extraction of natural gas in shale formation can contain organic and inorganic chemicals from fracturing fluids used during drilling and gas stimulation in host rocks/shale, as well as chemical compounds native to formation water and solid shale. Many of the organic and inorganic substances in wastewater are potentially toxic and pose environmental risks if released due to spills, leaks, or unsafe disposal practices. Samples of flowback and produced waters were collected at a separator and storage tank at the Marcellus Shale Energy and Environmental Laboratory site during November 2015 to April 2019.

Typical of Marcellus shale-gas wells, total dissolved salt concentrations increased steadily after going into production, reaching 115 grams/L after 30 weeks in production. Organics identified in the wastewater include polycyclic aromatic hydrocarbons, glycol ethers, alkanes, and tertiary and quaternary amines, with glycol ether persisting in the transition from flowback to formation water. Major ions included sodium, calcium, and chloride, with maximum concentrations of 1.3, 0.2, and 1.7 moles/L (M). Lithium, potassium, magnesium, strontium, barium, boron, and bromide were present at concentrations > 1 millimole/L (mM); the relative proportions of these solutes varied by no more than a factor of two. Radium activities increased with time in proportion with these solutes, with ²²⁶Ra reaching a maximum of 250 Becquerel/L; ²²⁶Ra/²²⁸Ra ratios were in the range 10-15. Alkalinity, iron, sulfur, and total dissolved ammonium (NH₄T) were present at concentrations exceeding 1 mM, but their proportions were more highly variable.

The composition of wastewater from the storage tank was relatively constant, with compositions near the maximum concentrations observed in water from the separator, although pH was more variable (~3.7 to 7.2). The high dissolved salt and NH₄T concentrations pose the greatest threat to aquatic ecosystems impacted by wastewater spills; Ra likely poses the greatest threat to humans.