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Berta Márton a német Szövetségi Környezetügyi, Természetvédelmi és Nukleáris Biztonsági Minisztérium referensének előadására:
Experimental investigation of hydrogeochemical consequences of gas leakages into shallow aquifers
Helyszín: Zoom, regisztráció: https://forms.gle/d15LD9cWodvSKgQ29
Időpont: 2020. november 16. 17.00 óra

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További információ: cszabo@elte.hu; aradi.laszloelod@ttk.elte.hu

Experimental investigation of hydrogeochemical consequences of gas leakages into shallow aquifers

Márton Berta
(Bundesministerium für Umwelt, Naturschutz und nukleare Sicherheit)

The fluctuating energy production of renewable sources, most importantly wind turbines and photovoltaic panels, implies the necessity of energy storage.  Already operating possibilities for large scale geological energy storage include storage of compressed air (CAES), methane, and hydrogen.  For the safe and sustainable implementation of subsurface energy storage, assessment studies and monitoring strategies are needed, based on proper process understanding and supported by evaluating numerically modeled scenarios of subsurface use.  In case of gas storage, this process understanding included knowledge gaps regarding gas-specific reactions to be expected in shallow aquifers following a leakage of compressed air, methane, or hydrogen.  Here it will be shown how such reactions can change the composition of the groundwater, potentially leading to conflicts between uses of the subsurface.
Experiments representing hydrogeological reactive conditions characteristic to a shallow aquifer influenced by a gas plume were carried out and evaluated.  The applied experimental approach most importantly included flow-through column experiments using a sediment from a shallow Pleistocene aquifer percolated by the groundwater from the same aquifer as well as auxiliary batch and column experiments with further materials.  The water used to percolate the experimental sediment columns was saturated by the respective gas to represent partial pressure conditions taking place within a dissolved gas plume in a shallow aquifer after a leakage of compressed air, methane, or hydrogen.
Experiments on leakage of compressed air showed pyrite oxidation.  At oxygen partial pressures between 0 and 11 bars pyrite oxidation caused an increase in sulfate concentration and a decrease in pH.  A PHREEQC model on reaction kinetics was developed to include a surface passivation term describing the inhibition of more than 90% of the pyrite reactivity.  Methane was not oxidized within one year in the presented flow-through column experiments.  This finding acknowledges earlier studies describing no methane oxidation if methane or its electron acceptors are newly introduced into an aquifer.  In contrast to methane, elevated concentration of hydrogen immediately triggers a series of redox reactions.  Changes in groundwater composition were found in experiments with hydrogen partial pressures between 1 and 25 bars.  The resulting reduction of ferric iron, nitrate, sulfate, and carbonate have major effects on groundwater, including the increase of acetate, nitrite, and sulfide concentrations and pH; along with decreasing electric conductivity.  Based on these observations, a descriptive reaction model was developed.
The conclusions have direct applications beyond the description of hydrogeochemical conditions not explicitly studied before. The observed behavior of gas-saturated subsurface environments improved process understanding for gas leakage scenarios and serves as base for characterization of gas storage sites as well as leakage monitoring strategies.