EGU2020-13889, updated on 12 Jun 2020
https://doi.org/10.5194/egusphere-egu2020-13889
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Aquifer-CO2 Leak project: Physicochemical characterization of the CO2 leakage impact on a carbonate shallow freshwater aquifer

Anélia Petit1, Adrian Cerepi1, Corinne Loisy1, Olivier Le Roux1, Léna Rossi1, Pierre Chiquet2, Audrey Estublier3, Julien Gance4, Bruno Garcia3, Lisa Gauchet3, Benoit Hautefeuille5, Bernard Lavielle6, Laura Luu Van Lang2, Sonia Noirez3, Benoit Texier4, Pierre Bachaud3, and Sarah Bouquet3
Anélia Petit et al.
  • 1EA 4592 Georessources et Environnement, ENSEGID-Bordeaux INP, avenue des Facultés, Talence 33400, France
  • 2Terega, 40 avenue de l’Europe, CS 20522, Pau Cedex 64010, France
  • 3IFP Energies nouvelles, 1 & 4 avenue du Bois Preau, Rueil-Malmaison 92852, France
  • 4IRIS Instruments, 1 avenue Buffon, Orléans 45100, France
  • 5AXINT, 181 route de l’Azergues, Lucenay 69480, France
  • 6CENBG-IN2P3,19 rue du Solarium, Gradignan 33170, France

This work is part of the Aquifer CO2-Leak project, started in 2018 for a 4-years duration and that aims at evaluating the impact of CO2 leakages from a geological storage site and developing new monitoring tools and methodologies. The present study aims to understand, quantify and model the environmental impact of a CO2 leak on water quality in the carbonate freshwater aquifer and understanding CO2-water-carbonate interactions.

This research has been performed on an experimental site located in Saint-Emilion (Gironde, France), in an underground quarry within a 30-meter-thick carbonate formation dated to the Upper Oligocene. The facies vary from wackestone to grainstone, and are associated with high values of porosity (from 25 to 45%) and permeability (between 5 and 20 D). A gas mixture, composed of CO2 (90%), He (9%) and Kr (1%), was injected in the aquifer through a borehole located upstream hydraulic gradient. The total injected volume was 200 liters for 1h30.

The seven other boreholes downstream in the injection well were fitted with in-situ probes which automatically measured pH, electrical conductivity, and CO2 fraction. Periodic water samplings have been undertaken, to determine the elementary concentrations by ionic chromatography. The spread of dissolved CO2 in the freshwater aquifer has influenced the physicochemical parameters at the various measurement points and thus has been followed in the time.

The interaction between the CO2 and the limestones causes the dissolution of the calcite, releasing Ca2+ and CO32- in the solution, which are distributed between H2CO3, HCO3- and CO32-. The comparison of the results before and after the passage of the plume highlights a dissolved CO2 concentration increase, combined with an increase of electrical conductivity and temperature, as well as a decrease in pH values.

The evolution of the physicogeochemical signature in the aquifer allow to understand the reactive and transport processes during a migration of a CO2 plume in a leakage context. The acquisition of these results will make possible to model a leakage in a complex natural reservoir.  Electrical conductivity and pH measurements seem to be excellent indicators for monitoring a gas plume during CO2 geological storage. The laboratory analyzes lead to better understand the CO2-water-carbonate interactions produced at the field scale and the relationships with petrophysical properties.

Batch measurements study the evolution of the electrical conductivity, monitored as a function of the COconcentrations. Comparison of experiments using only water, water and sand or water and limestone, have shown that only the presence of carbonate ions allows an increase in this geophysical parameter.

 

By means of these different tools and measures, the propagation of a CO2 leak will be followed through the modification of physicochemical parameters in the aquifer. This should also change the electrical resistivity values across the unsaturated zone. The electrical resistivity tomography should be a complementary tool in order to support these results, and to represent a 3D image plus time of the CO2 plume.

How to cite: Petit, A., Cerepi, A., Loisy, C., Le Roux, O., Rossi, L., Chiquet, P., Estublier, A., Gance, J., Garcia, B., Gauchet, L., Hautefeuille, B., Lavielle, B., Luu Van Lang, L., Noirez, S., Texier, B., Bachaud, P., and Bouquet, S.: Aquifer-CO2 Leak project: Physicochemical characterization of the CO2 leakage impact on a carbonate shallow freshwater aquifer, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13889, https://doi.org/10.5194/egusphere-egu2020-13889, 2020

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