Elucidating hydraulic fracturing impacts on ground water quality using a regional geospatial statistical modeling approach

Hydraulic fracturing operations have been viewed as the cause of certain environmental issues including ground water contamination. The potential for hydraulic fracturing to induce contaminant pathways in ground water is not well understood since gas wells are completed while isolating the water table and the gas-bearing reservoirs lay thousands of feet below the water table. Recent studies have attributed ground water contamination to poor well construction and leaks in the wellbore annulus due to ruptured wellbore casings. In this paper, a geospatial model of the Barnett Shale region was created using ArcGIS. The model was used for spatial analysis of ground water quality data in order to determine if regional variations in ground water quality, as indicated by various ground water constituent concentrations, may be associated with the presence of hydraulically fractured gas wells in the region. The Barnett Shale reservoir pressure, completions data, and fracture treatment data were evaluated as predictors of ground water quality change. Results indicated that elevated concentrations of certain ground water constituents are likely related to natural gas production in the study area and that beryllium, in this formation, could be used as an indicator variable for evaluating fracturing impacts on regional ground water quality. Results also indicated that gas well density and formation pressures correlate to change in regional water quality whereas proximity to gas wells, by itself, does not. The results also provided indirect evidence supporting the possibility that micro annular fissures serve as a pathway transporting fluids and chemicals from the fractured wellbore to the overlying ground water aquifers. (C) 2015 Elsevier B.V. All rights reserved.