Scaling the Geochemical Effects of Potential Gas Leakages from Deep Underground Storage Systems into Shallow Aquifers

Marton Berta1, Frank Dethlefsen1, Markus Ebert1, Andreas Dahmke1
1 Christian Albrechts Universität zu Kiel, Institut für Geowissenschaften, Abteilung Angewandte Geologie

O 15.1 in Forum Junge Hydrogeologen (H 36, NW III)

28.05.2014, 12:00-12:20, H36, NWIII

The storage of compressed gases (air, methane, or hydrogen) in the subsurface is important for the new energy concept in Germany (“Energiewende”), because renewable energy is not available at all times. Storage of surplus energy in form of compressed air may bridges an energy shortfall over several hours to few days, while seasonal energy storage can be achieved by using compressed methane or hydrogen, either by a later combustion with subsequent electrification or by feeding the gases into the gas grid. Numerous underground gas storage plants are required to support this concept and the following impacts of potential gas leakages on shallow aquifers are considered in this study: Air leaking from a high pressure reservoir potentially oxidizes pyrite in reduced overlying aquifers like lignite sand. The increase of sulfate concentration, the decrease of pH, and the release of toxic trace elements might be a risk for drinking water. Methane leakages may cause reduction of sulfate in the pore water to sulfide or iron(III) reduction from the solid phase, generating dissolved iron(II), what may also damage the quality of the produced water. Similar reductive processes, possibly completed by the reduction of carbonates, are expected in case of hydrogen leakages as well.

Potential environmental effects have to be predicted for storage sites by risk assessment, probably using site specific sediments and groundwater in laboratory experiments. Column experiments at in situ aquifer conditions applying high gas pressures of up to 50 bars are very elaborate. However, it is unclear if such high pressure experiments have to be conducted for each site. Transfer functions extrapolating data gained in normal pressure laboratory experiments to high pressure conditions are therefore highly desirable. The presented study focuses on these transfer functions.

So far, we tested an artificial pyritic sand and a natural lignite sand in flow-through column experiments at oxygen partial pressures of up to 1 bar with a flow speed of 0.6 m/day simulating an environment formed by a gas leakage in a shallow aquifer. As expected, pyrite oxidation was observed, but the reaction order regarding dissolved oxygen show higher values (0.75-0.91) than known from commonly used kinetic rate laws. The results are compared to results from high pressure column experiments (pO2 = 10 bar) using the same materials to develop a transfer function for estimating the environmental effects for in-situ conditions in shallow aquifers (depth ~500m) from laboratory experiments at normal P/T conditions. A similar experimental method is going to be used to evaluate the effects of the mentioned reductive gases.

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Letzte Änderung 01.11.2013