Occurrence and origin of methane in groundwater in Alberta (Canada): Gas geochemical and isotopic approaches

Humez, Pauline; Mayer, Bernhard; Ing, Jennifer; Nightingale, Michael; Becker, Veith; Kingston, Andrew; Akbilgiç, Oğuz; Taylor, Stephen

doi:10.1016/j.scitotenv.2015.09.055

Cited by 75 publications

(53 citation statements)

References 47 publications

(42 reference statements)

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“…Hence, there appears to be a correlation between the water type and the number of samples containing elevated methane and ethane concentrations in the shallow groundwaters of Alberta and a consistent relationship between gases in dissolved and free phases as shown in Humez et al (2016a).…”

Section: Major Ion Concentrations and Hydrochemical Water Type Classimentioning

confidence: 64%

“…Since 2006, groundwater samples and dissolved gas and free gas samples from GOWN wells have been routinely obtained where possible for chemical and isotopic analyses. A first assessment of the gas geochemical data set has been reported by Humez et al (2016a, b). This study evaluates both aqueous and gas geochemical and isotopic data of the GOWN monitoring program of shallow groundwater samples.…”

Section: Study Site Gown Networkmentioning

confidence: 99%

“…Pearson correlation analysis was conducted where linear trends between two variables existed. When nonlinear relationship between two variables existed or in presence of outliers, Spearman's ρ and Kendall's τ tests were used instead (Humez et al, 2016a).…”

Section: Isotopic Analysesmentioning

confidence: 99%

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Redox controls on methane formation, migration and fate in shallow aquifers

Humez¹,

Mayer²,

Nightingale³

et al. 2016

Hydrol. Earth Syst. Sci.

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Abstract. Development of unconventional energy resources such as shale gas and coalbed methane has generated some public concern with regard to the protection of groundwater and surface water resources from leakage of stray gas from the deep subsurface. In terms of environmental impact to and risk assessment of shallow groundwater resources, the ultimate challenge is to distinguish (a) natural in situ production of biogenic methane, (b) biogenic or thermogenic methane migration into shallow aquifers due to natural causes, and (c) thermogenic methane migration from deep sources due to human activities associated with the exploitation of conventional or unconventional oil and gas resources. This study combines aqueous and gas (dissolved and free) geochemical and isotope data from 372 groundwater samples obtained from 186 monitoring wells of the provincial Groundwater Observation Well Network (GOWN) in Alberta (Canada), a province with a long record of conventional and unconventional hydrocarbon exploration. We investigated whether methane occurring in shallow groundwater formed in situ, or whether it migrated into the shallow aquifers from elsewhere in the stratigraphic column. It was found that methane is ubiquitous in groundwater in Alberta and is predominantly of biogenic origin. The highest concentrations of biogenic methane ( > 0.01 mM or > 0.2 mg L −1 ), characterized by δ 13 C CH 4 values < −55 ‰, occurred in anoxic Na-Cl, Na-HCO 3 , and Na-HCO 3 -Cl type groundwaters with negligible concentrations of nitrate and sulfate suggesting that methane was formed in situ under methanogenic conditions for 39.1 % of the samples. In only a few cases (3.7 %) was methane of biogenic origin found in more oxidizing shallow aquifer portions suggesting limited upward migration from deeper methanogenic aquifers. Of the samples, 14.1 % contained methane with δ 13 C CH 4 values > −54 ‰, potentially suggesting a thermogenic origin, but aqueous and isotope geochemistry data revealed that the elevated δ 13 C CH 4 values were caused by microbial oxidation of biogenic methane or postsampling degradation of low CH 4 content samples rather than migration of deep thermogenic gas. A significant number of samples (39.2 %) contained methane with predominantly biogenic C isotope ratios (δ 13 C CH 4 < −55 ‰) accompanied by elevated concentrations of ethane and sometimes trace concentrations of propane. These gases, observed in 28.1 % of the samples, bearing both biogenic (δ 13 C) and thermogenic (presence of C 3 ) characteristics, are most likely derived from shallow coal seams that are prevalent in the Cretaceous Horseshoe Canyon and neighboring formations in which some of the groundwater wells are completed. The remaining 3.7 % of samples were not assigned because of conflicting parameters in the data sets or between replicates samples. Hence, despite quite variable gas concentrations and a wide range of δ 13 C CH 4 values in baseline groundwater samples, we found no conclusive evidence for deep thermogenic gas migration into shallow aqu...

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Section: Major Ion Concentrations and Hydrochemical Water Type Classimentioning

confidence: 64%

Section: Study Site Gown Networkmentioning

confidence: 99%

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Redox controls on methane formation, migration and fate in shallow aquifers

Humez¹,

Mayer²,

Nightingale³

et al. 2016

Hydrol. Earth Syst. Sci.

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show abstract

“…Complicating factors include spatial overlap between legacy and newer development and the presence of naturally occurring hydrocarbons in the shallow subsurface. Geochemical data can help resolve these factors and clarify potential impacts to groundwater (1,(7)(8)(9)(10)(11); however, there is a general lack of time series data of sufficient regional extent in most petroleumproducing basins. This problem underlies the rationale behind moratoria on unconventional petroleum development within various municipal and state/provincial jurisdictions (8).…”

mentioning

confidence: 99%

Groundwater methane in relation to oil and gas development and shallow coal seams in the Denver-Julesburg Basin of Colorado

Sherwood

Rogers

Lackey

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

104

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Unconventional oil and gas development has generated intense public concerns about potential impacts to groundwater quality. Specific pathways of contamination have been identified; however, overall rates of contamination remain ambiguous. We used an archive of geochemical data collected from 1988 to 2014 to determine the sources and occurrence of groundwater methane in the Denver-Julesburg Basin of northeastern Colorado. This 60,000-km2 region has a 60-y-long history of hydraulic fracturing, with horizontal drilling and high-volume hydraulic fracturing beginning in 2010. Of 924 sampled water wells in the basin, dissolved methane was detected in 593 wells at depths of 20–190 m. Based on carbon and hydrogen stable isotopes and gas molecular ratios, most of this methane was microbially generated, likely within shallow coal seams. A total of 42 water wells contained thermogenic stray gas originating from underlying oil and gas producing formations. Inadequate surface casing and leaks in production casing and wellhead seals in older, vertical oil and gas wells were identified as stray gas migration pathways. The rate of oil and gas wellbore failure was estimated as 0.06% of the 54,000 oil and gas wells in the basin (lower estimate) to 0.15% of the 20,700 wells in the area where stray gas contamination occurred (upper estimate) and has remained steady at about two cases per year since 2001. These results show that wellbore barrier failure, not high-volume hydraulic fracturing in horizontal wells, is the main cause of thermogenic stray gas migration in this oil- and gas-producing basin.

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“…These results indicate a biogenic origin for the shallow gas (cf. Whiticar et al 1986;Whiticar 1999;Humez et al 2016;Tao et al 2016;Sun et al 2016). The nitrogen-rich biogenic gas may be derived from the degradation of nitrogen-rich organic matter, indicating that the organic matter of the source sediments in the study area is heterogeneous (cf.…”

Section: Foraminiferal Fossils Dominated By Bf ([58 Species;mentioning

confidence: 99%

Characteristics and accumulation model of the late Quaternary shallow biogenic gas in the modern Changjiang delta area, eastern China

Zhang

Lin

2017

Pet. Sci.

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The Changjiang (Yangtze) is one of the largest rivers in the world. It formed a huge incised valley at its mouth during the Last Glacial Maximum; the incised-valley fill, approximately 80-110 m thick, supplies an important foundation for the generation of shallow biogenic-gas reservoirs. Two cores and 13 cone penetration tests were used to elaborate the characteristics, formation mechanism, and distribution of the shallow biogenic-gas reservoirs in the study area. The natural gas is mainly composed of CH 4 (generally[95%) with a d 13 C CH4 and d 13 C CO2 of -75.8 to -67.7% and -34.5 to -6.6%, respectively, and a dD CH4 of -215 to -185%, indicating a biogenic origin by the carbon dioxide reduction pathway. Commercial biogenic gas occurs primarily in the sand bodies of fluvial-channel, floodplain, and paleo-estuary facies with a burial depth of 50-80 m. Gas sources as well as cap beds are gray to yellowish-gray mud of floodplain, paleoestuary, and offshore shallow marine facies. The organic matter in gas sources is dominated by immature type III kerogen (gas prone). The difference in permeability (about 4-6 orders of magnitude) between cap beds and reservoirs makes the cap beds effectively prevent the upward escape of gas in the reservoirs. This formation mechanism is consistent with that for the shallow biogenic gas in the late Quaternary Qiantang River incised valley to the south. Therefore, this study should provide further insight into understanding the formation and distribution of shallow biogenic gas in other similar postglacial incised-valley systems.

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Occurrence and origin of methane in groundwater in Alberta (Canada): Gas geochemical and isotopic approaches

Cited by 75 publications

References 47 publications

Redox controls on methane formation, migration and fate in shallow aquifers

Redox controls on methane formation, migration and fate in shallow aquifers

Groundwater methane in relation to oil and gas development and shallow coal seams in the Denver-Julesburg Basin of Colorado

Characteristics and accumulation model of the late Quaternary shallow biogenic gas in the modern Changjiang delta area, eastern China

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