The Strontium Isotopic and Geochemical Evolution of Produced Waters from the Marcellus Formation
Capo, Rosemary C.; Stewart, Brian W.; Rowan, Elisabeth L.; Wall, Andrew J.; Chapman, Elizabeth C.; Schroder, Karl; Hammack, Richard W.
Production of natural gas and natural gas liquids from shale formations requires hydraulic fracturing and subsequent removal of the injected water and formation waters that are co-produced with gas. The chemistry of the returning waters reflects the original composition of the injection fluid, constituents in the shale formation that were mobilized by the fluid, and the co-mingled formation waters liberated by hydraulic fracturing. Previous work (Chapman et al., 2012, Env. Sci. Technol. 46, 3545-3553) demonstrated that the Sr isotope compositions of Marcellus formation waters collected over a distance of ~375 km fall within a relatively small range (0.7101-0.7121), providing a unique signature for interaction of Marcellus produced water with surface and ground waters. Strontium concentrations and isotope compositions are controlled primarily by mixing with formation waters, which contain very high levels of Sr (up to 5000 ppm), but other chemical species vary depending on the content of the fracturing fluid, shale, and formation water. We will report strontium isotope and geochemical data from several horizontally drilled wells in the Marcellus Formation, with a focus on the changes in chemistry and isotope composition over time as the returned waters shift from mixed injection fluids and formation waters to predominantly formation waters. Returned waters from four wells in southwestern Pennsylvania demonstrate that the Sr isotope composition reaches a constant value within 2-10 days of water return, while the Sr concentration rises more slowly and appears to hit a steady state value within 30 days. As production continues the returned waters primarily reflect the formation water end-member, allowing better understanding of shale water chemistry and evolution.
AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013