Geological storage

Schematic representation of geological CO2 storage Source: BGR

Targets of this subject area:

• Determination of interfacial properties for the system rock – CO₂-rich fluid – formation water.
• Measurement of reaction kinetics and thermodynamic stability of different minerals as a function of fluid compositions.
• Simulation of geochemical reactions to optimize experimental design and to predict geochemical reactions with very low rates.
• Studying the influence of geochemical rock alteration on mechanical properties of rock material by combined geochemical and geomechanical investigations.

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Rock alteration by carbon dioxide Source: BGR

The permeability of a geological structure controls its suitability as a storage site for fluids such as CO₂. Its permeability depends on the volume and connectivity of the pores. If there is more than one fluid present in the rock, interfacial properties are also important. Therefore, interfacial tensions between CO₂-rich fluids and formation water as well as contact angles between fluids and rocks will be measured experimentally.

Reaction cell for geochemical experiments made of gold/titanium Source: BGR

For an assessment of geochemical reactions of CO₂-rich fluids with formation water and reservoir or barrier rocks under in situ conditions, data on reaction kinetics and thermodynamic stability of various minerals will be determined experimentally. In the experiments, mineral separates and “typical” reservoir rocks will be allowed to react with synthetic formation water and process fluids under reservoir temperature and pressure conditions. Experiments will be performed in inert batch or flow-through reactors. The composition of minerals/rocks and fluids will be analysed before and after the experiment to observe the geochemical reactions.

To optimize experimental design (e.g., time scales), simulation of experiments will be performed. Experimentally determined data, in turn, will be used to improve the data base for modelling. This way, it will be possible to also predict geochemical reactions with very low reaction rates.

Schematic representation of triaxial cell for geomechanical investigations Source: MLU

Furthermore, it will be investigated in combined geochemical/geomechanical experiments if observed mineralogical/geochemical changes influence mechanical properties of the rock material.

For this, as a first step, CO₂-rich fluids will be pumped through selected rock samples in coupled autoclaves under reservoir pressures and temperatures. As a second step, mechanical properties of the geochemically altered rock samples will be investigated to deduce information about the likeliness of fracturing and, hence, the long-term stability of the storage complex.