Mechanisms leading to potential impacts of shale gas development on groundwater quality

Abstract

The development of shale gas resources was made possible by the combination of horizontal drilling and high‐volume hydraulic fracturing (fracking). Environmental concerns have been raised relative to shale gas production, especially potential impacts on groundwater. Fluids related to unconventional oil and gas (O&G) operations contain chemical compounds that can impact groundwater quality. Such impacts can occur due to (1) the infiltration of surface contaminant releases, (2) failures of the integrity of O&G wells, and (3) upward fluid migration from a shale/tight reservoir along preferential paths that can be natural (faults or fracture zone) or man‐made (O&G wells). Surface releases represent the most probable mechanism leading to groundwater contamination. Improvements in O&G drilling operations under stringent regulations can minimize this risk. Experts identify O&G well integrity as the most challenging issue that may lead to groundwater contamination. Failure of casing and cement can lead to upward fluid flow within or outside O&G wells, especially of methane. Integrity failures leading to fluid migration to shallow fresh water aquifers or to the surface are well understood and can be detected and repaired, but this can be complex and costly. A few regulators now impose groundwater monitoring to detect impacts from integrity failures. Occurrences of communication with existing O&G wells from fracking operations have also led some regulators to impose rules aiming to avoid such potential fluid migration paths. There is an ongoing scientific debate regarding the potential for fluids to migrate upward from exploited shale gas units to aquifers through natural preferential paths. WIREs Water 2017, 4:e1188. doi: 10.1002/wat2.1188 This article is categorized under: Engineering Water > Sustainable Engineering of Water Science of Water > Water Quality

Geochemistry of groundwater in the Saint-Édouard area, Quebec, Canada, and its influence on the distribution of methane in shallow aquifers

“…The most common technique to fracture lowpermeability rocks is hydraulic fracturing, which uses a mixture of water, proppants (generally sand) and chemical additives that are injected at high pressure, generally in horizontal wells in a variable number of individual stages or fracturing events. The advent of fracking technology has M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT 4 caused much debate and concerns among scientists and the public on the environmental risks that these unconventional resources exploration and development activities pose, especially to groundwater quality (Lefebvre, 2017). For this reason, some jurisdictions such as New Brunswick and Nova Scotia (Canada) and New York (U.S.) decided to impose a moratorium on high-volume hydraulic fracturing, at least until the risks for drinking water resources are better defined and understood, and social acceptability is reached.…”

“…Although fracturing has caused much public concern, it is now commonly accepted in the scientific community that the main risks to groundwater quality stem from: 1) the handling and treatment of drilling and fracking fluids as well as flowback water from the well, which can be accidentally spilled or otherwise stored in improperly sealed reservoirs at the surface Lefebvre, 2017), and 2) fluid migration from depths through improperly-cemented gas well casings Jackson et al, 2013b). The incidence of these two contamination pathways can be minimized through the implementation of better industry practices and stricter regulations (Dusseault and Jackson, 2014), and several jurisdictions are starting to implement monitoring programs for drinking water wells located within a certain distance of shale petroleum wells, in order to detect contamination coming from the well or from development-related activities in the immediate vicinity (e.g., Boyer et al, 2012, MDDELCC, 2017.…”

Trace Element Behavior in Methane‐Rich and Methane‐Free Groundwater in North and East Texas

“…Several biological processes consume or produce H + ions. Aerobic oxidation of methane tends to produce H + , decreasing pH, whereas anaerobic oxidation of methane tends to increase alkalinity and increase or maintain pH (e.g., Soetaert et al ; Lefebvre ), as shown in the following equations assuming mildly alkaline conditions. All processes have been described as occurring in groundwater, sometimes with considerable overlap: aerobic oxidation, nitrate reduction, iron reduction, and sulfate reduction (Islas‐Lima et al ; Amos et al , ).…”

Regulations to protect groundwater resources during unconventional oil and gas extraction using fracking

“…UOG extraction and fracking can affect groundwater quality and quantity, and aquifer integrity, in a number of ways (Esterhuyse et al, ; Gorski & Trenorden, ; Lefebvre, ). To limit these adverse effects on groundwater systems, certain aspects must be regulated during UOG extraction (Table ).…”