Character and Origin of Flowback Brine from Marcellus Gas Wells in Pennsylvania

Rose, Arthur W.; Haluszczak, Lara; Kump, Lee

Large quantities of highly saline brine flow from gas wells in the Marcellus Formation after hydraulic stimulation ("fracing"). 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, and merge with production water. Based on results in several datasets, the greatest concentration of chloride in flowback water is 151,000 mg/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. The highly concentrated parent brine probably represents residual liquid from deposition of the Silurian Salina evaporite salts. This brine was apparently pressed out of the salt and migrated into the younger Paleozoic formations of the region. Trends and relationships in brine composition indicate that 1) increased salt concentration in Marcellus 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 U.S drinking water standards.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013