GEOSCAN Search Results: Fastlink

GEOSCAN Menu


TitleNaphthenic acids in groundwater overlying undeveloped shale gas and tight oil reservoirs
AuthorAhad, J M E; Pakdel, H; Lavoie, D; Lefebvre, R; Peru, K; Headley, J V
SourceChemosphere vol. 191, 2018 p. 664-672, https://doi.org/10.1016/j.chemosphere.2017.10.015
Year2018
Alt SeriesNatural Resources Canada, Contribution Series 20170094
PublisherElsevier
Documentserial
Lang.English
Mediapaper; on-line; digital
File formatpdf
ProvinceQuebec
NTS31H/04; 22A/16
AreaHaldimand; Saint-Edouard
Lat/Long WENS -64.5000 -64.3333 48.8167 48.7500
Lat/Long WENS -73.4167 -73.4167 45.3333 45.1667
Subjectshydrogeology; fossil fuels; carbon isotopes; hydrocarbons; mass spectrometer analysis; groundwater; shales; organic materials; pyrolysis; Principal component analysis (PCA); Orbitrap mass spectrometry; Acid extractable organics; unconventional hydrocarbons; Bicyclic acids; naphtenic acids; microbial alteration; contaminants
Illustrationslocation maps; graphs; tables
ProgramSources, Environmental Geoscience
AbstractThe acid extractable organics (AEOs) containing naphthenic acids (NAs) in groundwater overlying undeveloped shale gas (Saint-Edouard region) and tight oil (Haldimand sector, Gaspé) reservoirs in Québec, Canada, were analysed using high resolution Orbitrap mass spectrometry and thermal conversion/elemental analysis e isotope ratio mass spectrometry. As classically defined by nH2nþZO2, the most abundant NAs detected in the majority of groundwater samples were straight-chain (Z ¼ 0) or monounsaturated (Z ¼ \'032) C16 and C18 fatty acids. Several groundwater samples from both study areas, however, contained significant proportions of presumably alicyclic bicyclic NAs (i.e., Z ¼ \'034) in the C10-C18 range. These compounds may have originated from migrated waters containing a different distribution of NAs, or are the product of in situ microbial alteration of shale organic matter and petroleum. In most groundwater samples, intramolecular carbon isotope values generated by pyrolysis (d13Cpyr) of AEOs were on average around 2 - 3 (permil) heavier than those generated by bulk combustion (d13C) of AEOs, providing further support for microbial reworking of subsurface organic carbon. Although concentrations of AEOs were very low (<2.0 mg/L), the detection of potentially toxic bicyclic acids in groundwater overlying unconventional hydrocarbon reservoirs points to a natural background source of organic contaminants prior to any large-scale commercial hydrocarbon development.
Summary(Plain Language Summary, not published)
Naphthenic acids (NAs) are a complex mixture of carboxylic acids found naturally in crude oil deposits that are potentially toxic to a wide range of aquatic organisms. In this study, NAs were measured in groundwater samples underlying undeveloped shale gas (Saint-Édouard) and tight oil (Haldimand sector, Gaspé) reservoirs in the province of Québec. Although the distribution patterns of NAs in most samples were dominated by several ubiquitous, non-toxic fatty acids, some samples contained relatively greater proportions of potentially toxic alicyclic bicyclic acids. Although concentrations of NAs in most samples were very low, the detection of a group of potentially toxic organic acids in groundwater overlying unconventional hydrocarbon reservoirs points to a natural background source of organic contaminants prior to any large-scale commercial development.
GEOSCAN ID302711