Numerical Modelling

Numerical models serve as a theoretical framework to quantitatively understand natural geological and engineered systems involving rock-water interaction. Models integrate data and concepts acquired from experimental and field observations and allow one to simulate the complex interplay of processes that have redistributed matter and heat in the geological past (e.g. hydrothermal ore deposits, alteration of oceanic crust) or that control the feasibility, sustainability and safety of subsurface utilization (e.g. geothermal energy, storage of radioactive waste or CO2 sequestration). 

We use state-of-the-art numerical tools ranging from geochemical equilibrium codes such as PHREEQC or GWB to sophisticated reactive transport codes such as ToughReact, FLOTRAN, PFLOTRAN or CrunchFlow. Two multi-core servers in the IfG provide sufficient computational performance for complex 3D or high resolution THC simulations.

Education: Because numerical modelling has become an integral part of geological research and consulting, we offer courses in which students are introduced to the use of geochemical models. For Master students specializing in Environmental & Resource Geochemistry we offer a course which takes a more in-depth look at the fundamentals of reactive transport modelling.

Equilibrium modelling refers to the use of geochemical speciation codes such as PHREEQC or Geochemist’s Workbench. PHREEQC in particular is an essential tool for any geochemist who is interested in a theoretical description of the equilibrium state of water-rock-gas mixtures at given PTX conditions.

Transport modelling refers to the simulation of transport of non-reactive species. These could be natural tracers such as the anions I-, Br- and Cl-, water isotopes δ18O and δ2H and noble gases (mainly He). Measured concentration profiles of non-reactive tracers in combination with measured transport parameters and the palaeo-hydrogeological evolution at a particular site allows one to use transport simulations to test the consistency of these constraints on a formation scale. 

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Reactive transport modelling evolved some 25 years ago by coupling geochemical reaction modelling (equilibrium or kinetic) and groundwater flow/solute transport modelling. Other processes such as heat transport or mechanical deformation can also be incorporated into these models. Coupled models were developed by realizing that chemical reactions in geological systems are driven by solute fluxes across gradients or interfaces (e.g. rock composition, temperature) and that quite often the feedback mechanisms between different physico-chemical processes cannot be ignored to explain certain observations or to make predictions about processes and patterns in the subsurface. 

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Many clay rocks swell during water uptake and develop a swelling pressure if their volume is confined. The chemistry of the saturation water influences this swelling behaviour: forces between mineral grains and between the sheets of clay minerals, as well as the pore structure, depend on the pore water composition. We work on the implementation of this coupling between pore water Chemistry and Mechanical aspects in reactive transport codes.

Swelling pressures of confined montmorillonite
Swelling pressures of confined montmorillonite, equilibrated with different NaCl or CaCl2 solutions of different ionic strengths (data from Karnland et al., 2006, SKB TR-06-30)