Detection of a CO2 leak in groundwater above a geological storage site: An analogue study using a compromised petroleum exploration well  

Authors / CoAuthors

Feitz, A.J. | Boreham, C.J. | Hortle, A. | Ransley, T.R.

Abstract

A major concern for regulators and the public with geological storage of CO2 is the potential for the migration of CO2 via a leaky fault or well into potable groundwater supplies. Given sufficient CO2, an immediate effect on groundwater would be a decrease in pH which could lead to accelerated weathering, an increase in alkalinity, release of major and minor ions and heavy metals (particularly Pd, Ni and Cr) as well as CO2 mobilisation of trace organic contaminants. These scenarios potentially occur in a high CO2 leakage event, therefore detection of a small leak, although barely perceptible, could provide an important early warning for a subsequent and more substantial impact. Different approaches are required for the detection and quantification of these low level leaks and are the subject of this paper. A 3 year groundwater survey was recently completed in the Surat Basin, which provided comprehensive water and isotopic analysis of groundwaters together with their exsolved gases. The gases were analysed for composition, -13CCO2, -13CCH4 and -2HCH4. Methane is prevalent in the major Surat Basin aquifers (e.g. Mooga, Gubberamunda and Hutton sandstones) and is invariably associated with a bacterial (methanogenic) carbonate reduction source, evident from its isotopic signature ('13CCH4 ~ -70', '2HCH4 ~ -220'). In addition to methane and low levels of CO2, trace ethane is common. Two neighbouring wells, however, were quite different to the other 85 wells surveyed. Their exsolved gases contained comparatively high ethane, but also C1-C6 hydrocarbons in addition to methane. Methane isotope systematics were significantly different from other groundwater wells completed in the same formation. The -13C of the CO2 was similar to the surrounding groundwater wells, but the relative proportion of CO2 in the gas was significantly higher. Combined, these characteristics are consistent with hydrocarbon biodegradation. There was little difference in the groundwater chemistry for these wells compared to the regional baseline. The study provides a useful analogue study for detection, at various scales, of a leaky well associated with a geological storage site. Compositional and isotopic analysis of exsolved gases from groundwater samples could be used to demonstrate non-equilibrium conditions and intrusion of exogenic CO2. Abstract for the 2013 International Association of Hydrologist Congress, Perth

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nonGeographicDataset

eCat Id

75406

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Keywords

• External PublicationAbstract

( Theme )

• isotopes

( Theme )

• carbon dioxide

( Theme )

• environmental

( Theme )

• geological storage of CO2

( Theme )

• groundwater

• AU-QLD

Australian and New Zealand Standard Research Classification (ANZSRC)

• Isotope Geochemistry

• Published_Internal

Publication Date

2013-01-01T00:00:00

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Australian Government Security ClassificationSystem    

Classification - unclassified

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Creative Commons Attribution 4.0 International Licence    

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asNeeded

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environment

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Product arose out of "The Greenhouse Gas Storage Groundwater Project", a collaborative project between GA and State of Queensland Department of Employment Economic Development and Innovation, GSQ (2009-2011).

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[-27.5, -27.0, 149.0, 149.5]

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Abstract builds on groundwater data survey data collected inthe Surat and Bowen basins under the collaborative "The Greenhouse Gas Storage Groundwater Project" between GA and GSQ (2009-2011). 149.0 149.5 -27.5 -27.0