Distinguishing Natural vs. Anthropogenic Methane in Groundwater in a Shale Gas Basin

Abstract

Abstract The presence of methane in groundwater in areas where shale gas resources are being developed has at times been incorrectly attributed to hydraulic fracturing activities, often due to the difficulty in distinguishing anthropogenic methane from methane naturally present in groundwater. This presentation will summarize the results of a study for development of forensic tools to distinguish natural from anthropogenic methane in the Marcellus Shale area. Analytical data for more than a thousand pre-drill water samples from the Marcellus Shale area has been reviewed and evaluated statistically to investigate potential correlations with observed methane concentrations in groundwater. Results of the study indicated that natural methane concentrations could be correlated to several natural environmental factors, including the ionic composition of the groundwater and the topographic location of the water well. In combination with other lines of evidence, these parameters can be used to distinguish natural from anthropogenic methane. Distinguishing natural from anthropogenic sources of methane in groundwater is particularly important because residential groundwater wells are used for water supply in many areas where hydraulic fracturing is used to stimulate shale gas production. In fact, the preoccupation with impacts to groundwater from hydraulic fracturing activities is not limited to the U.S., as the issue is being frequently raised in other regions with great shale gas potential, such as Mexico, Argentina, Colombia, and the European Union. The findings of the study provide a framework that can be applied at other site to assess the potential impacts of hydraulic fracturing to groundwater resources.