DOI: 10.5194/hess-20-2759-2016
Scopus记录号: 2-s2.0-84978427397
论文题名: Redox controls on methane formation, migration and fate in shallow aquifers
作者: Humez P ; , Mayer B ; , Nightingale M ; , Becker V ; , Kingston A ; , Taylor S ; , Bayegnak G ; , Millot R ; , Kloppmann W
刊名: Hydrology and Earth System Sciences
ISSN: 10275606
出版年: 2016
卷: 20, 期: 7 起始页码: 2759
结束页码: 2777
语种: 英语
Scopus关键词: Aquifers
; Coal deposits
; Energy resources
; Environmental impact
; Exploratory geochemistry
; Gases
; Geochemistry
; Geological surveys
; Groundwater
; Groundwater geochemistry
; Hydrocarbons
; Hydrochemistry
; Hydrogeology
; Isotopes
; Methane
; Petroleum deposits
; Risk assessment
; Shale
; Sodium
; Stratigraphy
; Surface water resources
; Surface waters
; Water resources
; Elevated concentrations
; Isotope geochemistry
; Isotopic composition
; Methanogenic condition
; Protection of groundwater
; Stratigraphic columns
; Unconventional hydrocarbons
; Unconventional oil and gas
; Groundwater resources
; aquifer
; coalbed methane
; concentration (composition)
; environmental fate
; environmental impact assessment
; environmental monitoring
; exploitation
; geochemistry
; human activity
; hydrocarbon exploration
; microbial activity
; redox conditions
; shale gas
; shallow water
; water management
; water resource
; Alberta
; Canada
英文摘要: 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 > 0.2mg ml-1 characterized by δ13CCH4 values <-55%, occurred in anoxic Na-Cl, Na-HCO3, and Na-HCO3-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, 14.1g% contained methane with δ13CCH4 values >-54%, potentially suggesting a thermogenic origin, but aqueous and isotope geochemistry data revealed that the elevated δ13CCH4 values were caused by microbial oxidation of biogenic methane or post-sampling degradation of low CH4 content samples rather than migration of deep thermogenic gas. A significant number of samples (39.2%) contained methane with predominantly biogenic C isotope ratios (δ13CCH4 <-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 (δ13C) and thermogenic (presence of C3) 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 δ13CCH4 values in baseline groundwater samples, we found no conclusive evidence for deep thermogenic gas migration into shallow aquifers either naturally or via anthropogenically induced pathways in this baseline groundwater survey. This study shows that the combined interpretation of aqueous geochemistry data in concert with chemical and isotopic compositions of dissolved and/or free gas can yield unprecedented insights into formation and potential migration of methane in shallow groundwater. This enables the assessment of cross-formational methane migration and provides an understanding of alkane gas sources and pathways necessary for a stringent baseline definition in the context of current and future unconventional hydrocarbon exploration and exploitation. © 2016 Author(s). Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/78796
Appears in Collections: 气候变化事实与影响
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作者单位: Applied Geochemistry Group, Department of Geoscience, University of Calgary, 2500 University Drive NW, Calgary, AB, Canada; Alberta Environmental Monitoring, Evaluation and Reporting Agency (AEMERA), 9th Floor 9888 Jasper Avenue, Edmonton, AB, Canada; BRGM, French Geological Survey, 3 avenue Claude Guillemin, Orleáns Cedex 2, France
Recommended Citation:
Humez P,, Mayer B,, Nightingale M,et al. Redox controls on methane formation, migration and fate in shallow aquifers[J]. Hydrology and Earth System Sciences,2016-01-01,20(7)