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

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.

Salinity of deep groundwater in California: Water quantity, quality, and protection

“…6). The volume of fresh and saline waters that can be classified as USDWs, for which no previous estimate, to our knowledge, exists, is 3,900 km 3 , with 58% in the top 1,000 m (Fig. 6).…”

“…We analyze 938 chemical, geological, and depth data points from 360 oil/gas fields across eight counties in California and depth data from 34,392 oil and gas wells. By expanding previous groundwater volume estimates from depths of 305 m to 3,000 m in California's Central Valley, an important agricultural region with growing groundwater demands, fresh [<3,000 ppm total dissolved solids (TDS)] groundwater volume is almost tripled to 2,700 km 3 , most of it found shallower than 1,000 m. The 3,000-m depth zone also provides 3,900 km 3 of fresh and saline water, not previously estimated, that can be categorized as underground sources of drinking water (USDWs; <10,000 ppm TDS). Up to 19% and 35% of oil/gas activities have occurred directly in freshwater zones and USDWs, respectively, in the eight counties.…”

“…Estimating the quantity of useable groundwater and assessing the risk of groundwater contamination by human activities, such as oil and gas development, require baseline data and an appropriate monitoring framework (2)(3)(4)(5)(6)(7). In this paper, we (i) characterize salinity of deep groundwater aquifers in eight counties across California, (ii) estimate useable groundwater volumes in California's Central Valley, and (iii) evaluate potential saline water migration into freshwater zones and underground sources of drinking water (USDWs) in eight counties in California.…”

Nuclear Waste Disposal: A Cautionary Tale for Shale Gas Development

“…This nuanced statement referring to the process of hydraulic fracturing ignores the known cases of contamination by oil and gas operations [ Jackson et al, 2013 ]. The public does not distinguish between the fracking process and the totality of unconventional oil and gas operations; thus, any reports of contamination seem completely at odds with industry assurances.…”

“…Long-term, field-based hydrogeologic research and monitoring are essential to help resolve the issues [e.g., Jackson et al, 2013 ;Council of Canadian Academies, 2014 ]. However, studies of groundwater impacts have been based largely on sampling water from domestic wells.…”