Groundwater Protection and Unconventional Gas Extraction: The Critical Need for Field‐Based Hydrogeological Research

TLDR

Unconventional natural gas extraction relies on horizontal drilling and hydraulic fracturing, raising concerns that gases, formation waters, and chemicals could contaminate shallow groundwater, yet a lack of field observations and peer‑reviewed studies hampers addressing these risks. The authors aim to discuss case studies that demonstrate how stray or fugitive gas from deep formations can migrate into shallow aquifers and degrade groundwater quality. They illustrate this through examples of uncemented well annuli, poor cement bonding in new and old wells, ineffective cementing practices, and the influence of structural features on natural and induced fracture pathways. They conclude that urgent field‑focused research is needed in two areas: baseline geochemical mapping with time‑series sampling from a sufficient network of monitoring wells, and field testing of mechanisms and pathways by which hydrocarbons and fracturing chemicals may invade and contaminate usable groundwater.

Abstract

Abstract Unconventional natural gas extraction from tight sandstones, shales, and some coal‐beds is typically accomplished by horizontal drilling and hydraulic fracturing that is necessary for economic development of these new hydrocarbon resources. Concerns have been raised regarding the potential for contamination of shallow groundwater by stray gases, formation waters, and fracturing chemicals associated with unconventional gas exploration. A lack of sound scientific hydrogeological field observations and a scarcity of published peer‐reviewed articles on the effects of both conventional and unconventional oil and gas activities on shallow groundwater make it difficult to address these issues. Here, we discuss several case studies related to both conventional and unconventional oil and gas activities illustrating how under some circumstances stray or fugitive gas from deep gas‐rich formations has migrated from the subsurface into shallow aquifers and how it has affected groundwater quality. Examples include impacts of uncemented well annuli in areas of historic drilling operations, effects related to poor cement bonding in both new and old hydrocarbon wells, and ineffective cementing practices. We also summarize studies describing how structural features influence the role of natural and induced fractures as contaminant fluid migration pathways. On the basis of these studies, we identify two areas where field‐focused research is urgently needed to fill current science gaps related to unconventional gas extraction: (1) baseline geochemical mapping (with time series sampling from a sufficient network of groundwater monitoring wells) and (2) field testing of potential mechanisms and pathways by which hydrocarbon gases, reservoir fluids, and fracturing chemicals might potentially invade and contaminate useable groundwater.