Occurrence and origin of methane in groundwater in Alberta (Canada)

Gas geochemical and isotopic approaches

P. Humez, B. Mayer, J. Ing, M. Nightingale, V. Becker, A. Kingston, Oguz Akbilgic, S. Taylor

Research output: Contribution to journalArticle

32 Citations (Scopus)

Abstract

To assess potential future impacts on shallow aquifers by leakage of natural gas from unconventional energy resource development it is essential to establish a reliable baseline. Occurrence of methane in shallow groundwater in Alberta between 2006 and 2014 was assessed and was ubiquitous in 186 sampled monitoring wells. Free and dissolved gas sampling and measurement approaches yielded comparable results with low methane concentrations in shallow groundwater, but in 28 samples from 21 wells methane exceeded 10mg/L in dissolved gas and 300,000ppmv in free gas. Methane concentrations in free and dissolved gas samples were found to increase with well depth and were especially elevated in groundwater obtained from aquifers containing coal seams and shale units. Carbon isotope ratios of methane averaged -69.7±11.1‰ (n=63) in free gas and -65.6±8.9‰ (n=26) in dissolved gas. δ13C values were not found to vary with well depth or lithology indicating that methane in Alberta groundwater was derived from a similar source. The low δ13C values in concert with average δ2HCH4 values of -289±44‰ (n=45) suggest that most methane was of biogenic origin predominantly generated via CO2 reduction. This interpretation is confirmed by dryness parameters typically >500 due to only small amounts of ethane and a lack of propane in most samples. Comparison with mud gas profile carbon isotope data revealed that methane in the investigated shallow groundwater in Alberta is isotopically similar to hydrocarbon gases found in 100-250meter depths in the WCSB and is currently not sourced from thermogenic hydrocarbon occurrences in deeper portions of the basin. The chemical and isotopic data for methane gas samples obtained from Alberta groundwater provide an excellent baseline against which potential future impact of deeper stray gases on shallow aquifers can be assessed.

Original languageEnglish (US)
Pages (from-to)1253-1268
Number of pages16
JournalScience of the Total Environment
Volume541
DOIs
StatePublished - Jan 15 2016

Fingerprint

Methane
Groundwater
Gases
methane
groundwater
dissolved gas
gas
Aquifers
well
Carbon Isotopes
aquifer
Hydrocarbons
Isotopes
hydrocarbon
carbon isotope ratio
Propane
propane
ethane
Ethane
Carbon

All Science Journal Classification (ASJC) codes

  • Environmental Engineering
  • Environmental Chemistry
  • Waste Management and Disposal
  • Pollution

Cite this

Occurrence and origin of methane in groundwater in Alberta (Canada) : Gas geochemical and isotopic approaches. / Humez, P.; Mayer, B.; Ing, J.; Nightingale, M.; Becker, V.; Kingston, A.; Akbilgic, Oguz; Taylor, S.

In: Science of the Total Environment, Vol. 541, 15.01.2016, p. 1253-1268.

Research output: Contribution to journalArticle

Humez, P. ; Mayer, B. ; Ing, J. ; Nightingale, M. ; Becker, V. ; Kingston, A. ; Akbilgic, Oguz ; Taylor, S. / Occurrence and origin of methane in groundwater in Alberta (Canada) : Gas geochemical and isotopic approaches. In: Science of the Total Environment. 2016 ; Vol. 541. pp. 1253-1268.
@article{e9f5fe94bb9c48cb9268f3d73595cb01,
title = "Occurrence and origin of methane in groundwater in Alberta (Canada): Gas geochemical and isotopic approaches",
abstract = "To assess potential future impacts on shallow aquifers by leakage of natural gas from unconventional energy resource development it is essential to establish a reliable baseline. Occurrence of methane in shallow groundwater in Alberta between 2006 and 2014 was assessed and was ubiquitous in 186 sampled monitoring wells. Free and dissolved gas sampling and measurement approaches yielded comparable results with low methane concentrations in shallow groundwater, but in 28 samples from 21 wells methane exceeded 10mg/L in dissolved gas and 300,000ppmv in free gas. Methane concentrations in free and dissolved gas samples were found to increase with well depth and were especially elevated in groundwater obtained from aquifers containing coal seams and shale units. Carbon isotope ratios of methane averaged -69.7±11.1‰ (n=63) in free gas and -65.6±8.9‰ (n=26) in dissolved gas. δ13C values were not found to vary with well depth or lithology indicating that methane in Alberta groundwater was derived from a similar source. The low δ13C values in concert with average δ2HCH4 values of -289±44‰ (n=45) suggest that most methane was of biogenic origin predominantly generated via CO2 reduction. This interpretation is confirmed by dryness parameters typically >500 due to only small amounts of ethane and a lack of propane in most samples. Comparison with mud gas profile carbon isotope data revealed that methane in the investigated shallow groundwater in Alberta is isotopically similar to hydrocarbon gases found in 100-250meter depths in the WCSB and is currently not sourced from thermogenic hydrocarbon occurrences in deeper portions of the basin. The chemical and isotopic data for methane gas samples obtained from Alberta groundwater provide an excellent baseline against which potential future impact of deeper stray gases on shallow aquifers can be assessed.",
author = "P. Humez and B. Mayer and J. Ing and M. Nightingale and V. Becker and A. Kingston and Oguz Akbilgic and S. Taylor",
year = "2016",
month = "1",
day = "15",
doi = "10.1016/j.scitotenv.2015.09.055",
language = "English (US)",
volume = "541",
pages = "1253--1268",
journal = "Science of the Total Environment",
issn = "0048-9697",
publisher = "Elsevier",

}

TY - JOUR

T1 - Occurrence and origin of methane in groundwater in Alberta (Canada)

T2 - Gas geochemical and isotopic approaches

AU - Humez, P.

AU - Mayer, B.

AU - Ing, J.

AU - Nightingale, M.

AU - Becker, V.

AU - Kingston, A.

AU - Akbilgic, Oguz

AU - Taylor, S.

PY - 2016/1/15

Y1 - 2016/1/15

N2 - To assess potential future impacts on shallow aquifers by leakage of natural gas from unconventional energy resource development it is essential to establish a reliable baseline. Occurrence of methane in shallow groundwater in Alberta between 2006 and 2014 was assessed and was ubiquitous in 186 sampled monitoring wells. Free and dissolved gas sampling and measurement approaches yielded comparable results with low methane concentrations in shallow groundwater, but in 28 samples from 21 wells methane exceeded 10mg/L in dissolved gas and 300,000ppmv in free gas. Methane concentrations in free and dissolved gas samples were found to increase with well depth and were especially elevated in groundwater obtained from aquifers containing coal seams and shale units. Carbon isotope ratios of methane averaged -69.7±11.1‰ (n=63) in free gas and -65.6±8.9‰ (n=26) in dissolved gas. δ13C values were not found to vary with well depth or lithology indicating that methane in Alberta groundwater was derived from a similar source. The low δ13C values in concert with average δ2HCH4 values of -289±44‰ (n=45) suggest that most methane was of biogenic origin predominantly generated via CO2 reduction. This interpretation is confirmed by dryness parameters typically >500 due to only small amounts of ethane and a lack of propane in most samples. Comparison with mud gas profile carbon isotope data revealed that methane in the investigated shallow groundwater in Alberta is isotopically similar to hydrocarbon gases found in 100-250meter depths in the WCSB and is currently not sourced from thermogenic hydrocarbon occurrences in deeper portions of the basin. The chemical and isotopic data for methane gas samples obtained from Alberta groundwater provide an excellent baseline against which potential future impact of deeper stray gases on shallow aquifers can be assessed.

AB - To assess potential future impacts on shallow aquifers by leakage of natural gas from unconventional energy resource development it is essential to establish a reliable baseline. Occurrence of methane in shallow groundwater in Alberta between 2006 and 2014 was assessed and was ubiquitous in 186 sampled monitoring wells. Free and dissolved gas sampling and measurement approaches yielded comparable results with low methane concentrations in shallow groundwater, but in 28 samples from 21 wells methane exceeded 10mg/L in dissolved gas and 300,000ppmv in free gas. Methane concentrations in free and dissolved gas samples were found to increase with well depth and were especially elevated in groundwater obtained from aquifers containing coal seams and shale units. Carbon isotope ratios of methane averaged -69.7±11.1‰ (n=63) in free gas and -65.6±8.9‰ (n=26) in dissolved gas. δ13C values were not found to vary with well depth or lithology indicating that methane in Alberta groundwater was derived from a similar source. The low δ13C values in concert with average δ2HCH4 values of -289±44‰ (n=45) suggest that most methane was of biogenic origin predominantly generated via CO2 reduction. This interpretation is confirmed by dryness parameters typically >500 due to only small amounts of ethane and a lack of propane in most samples. Comparison with mud gas profile carbon isotope data revealed that methane in the investigated shallow groundwater in Alberta is isotopically similar to hydrocarbon gases found in 100-250meter depths in the WCSB and is currently not sourced from thermogenic hydrocarbon occurrences in deeper portions of the basin. The chemical and isotopic data for methane gas samples obtained from Alberta groundwater provide an excellent baseline against which potential future impact of deeper stray gases on shallow aquifers can be assessed.

UR - http://www.scopus.com/inward/record.url?scp=84944088736&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84944088736&partnerID=8YFLogxK

U2 - 10.1016/j.scitotenv.2015.09.055

DO - 10.1016/j.scitotenv.2015.09.055

M3 - Article

VL - 541

SP - 1253

EP - 1268

JO - Science of the Total Environment

JF - Science of the Total Environment

SN - 0048-9697

ER -