Utility of Isotopes to Understand the Effect of Shale Gas Drilling on Water Quality: Examples From the Appalachian Basin

Abstract:

Marcellus Shale of the Appalachian Basin is one of the largest unconventional gas resources in the United States. The main public concern associated with hydraulic fracturing of Marcellus shale is that that the quality of underground sources of drinking water (USDW) and surface waters can be compromised due to well casing or grouting failures, creation of new fracture pathways, and improper disposal of produced water. However, this region has a long history of coal mining and oil /gas development and therefore it becomes very important to be able to distinguish if any incidence of water contamination is associated with legacy mining/drilling activities or the newly drilled shale gas wells. In addition, the complex structural regime of the Appalachian makes it difficult to decouple natural migration of deep brines and stray gas along geological faults/ fractures from new pathways created by hydraulic fracturing activities. In order to effectively assess the effect of shale gas development on water quality of this region there is a need 1) to establish the background geochemical signatures of different water sources and, 2) to develop geochemical fingerprints that can track the sources and fates of brines and stray gas in fresh waters. We will present results from several ongoing research projects which demonstrate applicability of stable isotopes as natural tracers to understand changes in hydrologic connections associated with shale gas drilling in this region.