Title
Impact of an historic underground gas well blowout on the current methane chemistry in a shallow groundwater system
Author
Schout, G.
Hartog, N.
Hassanizadeh, S.M.
Griffioen, J.
Contributor
State University, University Park, PA, and approved November 27, 2017 (received for review June 27, 2017) Edited by Susan L. Brantley, Pennsylvania (editor)
Publication year
2017
Abstract
Blowouts present a small but genuine risk when drilling into the deep subsurface and can have an immediate and significant impact on the surrounding environment. Nevertheless, studies that document their long-term impact are scarce. In 1965, a catastrophic underground blowout occurred during the drilling of a gas well in The Netherlands, which led to the uncontrolled release of large amounts of natural gas from the reservoir to the surface. In this study, the remaining impact on methane chemistry in the overlying aquifers was investigated. Methane concentrations higher than 10 mg/L (n = 12) were all found to have δ13C-CH4 values larger than −30‰, typical of a thermogenic origin. Both δ13C-CH4 and δD-CH4 correspond to the isotopic composition of the gas reservoir. Based on analysis of local groundwater flow conditions, this methane is not a remnant but most likely the result of ongoing leakage from the reservoir as a result of the blowout. Progressive enrichment of both δ13C-CH4 and δD-CH4 is observed with increasing distance and decreasing methane concentrations. The calculated isotopic fractionation factors of eC = 3 and eD = 54 suggest anaerobic methane oxidation is partly responsible for the observed decrease in concentrations. Elevated dissolved iron and manganese concentrations at the fringe of the methane plume show that oxidation is primarily mediated by the reduction of iron and manganese oxides. Combined, the data reveal the long-term impact that underground gas well blowouts may have on groundwater chemistry, as well as the important role of anaerobic oxidation in controlling the fate of dissolved methane.
Subject
Groundwater contamination
Well blowouts
Methane
Isotopic fingerprinting
Anaerobic methane oxidation
Geo
GM - Geomodelling
ELSS - Earth, Life and Social Sciences
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DOI
https://doi.org/10.1073/pnas.1711472115
TNO identifier
782680
Source
PNAS
Document type
article