Three-dimensional analysis of coupled thermohaline flow and reactive transport in fractured geothermal reservoirs
Final Report Abstract
Groundwater flow and the transport of contaminants in groundwater can be heavily influenced by spatial and temporal variations in water density. Water density increases with water salinity, and it increases with water temperature. Situations where variable-density flow occurs are fractured rock (where salinity and temperature of deep water affects water density), and coastal regions (where seawater salinity increases water density). This project aimed at understanding variable-density flow in fractured rock, and in coastal regions. These aims were realized in two PhD dissertations accompanied by two other PhD dissertations not paid by this grant, approximately 15 Master projects, and one Bachelor project. An important outcome of this project was the generation of a three-dimensional mathematical model of a coastal aquifer. That model was used and will be used in the near future to investigate different human and natural impacts on groundwater resources, in particular in the context of climatic change (sealevel rise, change of tidal activity, change of river discharge, change of evaporation and rainfall patterns, etc.). Importantly, not only can this model be applied to simulate reality at that particular site, but knowledge about how to efficiently simulate scenarios can be transferred to other coastal areas around the globe. Another important outcome of this project was the development of an efficient time-stepping method to noniteratively simulate variable-density flow and transport problems. This new method make future computer simulations much faster so that a larger number of possible scenarios can be simulated in a timely manner. From a more academic standpoint, contributing a new time-stepping method to the community is an excellent achievement. What was surprising during the course of this Emmy Noether project were the simulations results of the thermohaline (double-diffusive) convection in fractured rock. It was expected that due to the different diffusivities and in the presence of an extremely highly anisotropic medium, well-distinct horizontal layers of mixed fluid would be generated. This has previously been demonstrated in heterogeneous porous media in laboratory experiments. One reason for this unexpected outcome could be the numerical setting of thermohaline flow where front and back boundaries of the two-dimensional model were assumed to be perfectly isolating (@T=@n = 0). In future studies, this assumption could be relaxed and replaced by conducting front and back boundary layers.
Publications
- Grid convergence of variable-density flow simulations in discretely-fractured porous media. Advances in Water Resources, Vol. 34. 2011, Issue 6, pp. 760-769.
Graf T., Degener L.
(See online at https://doi.org/10.1016/j.advwatres.2011.04.002) - Non-iterative adaptive time stepping with truncation error control for simulating variable-density flow. Advances in Water Resources, Vol. 49. 2012, pp. 46-55.
Hirthe E.M., Graf T.
(See online at https://doi.org/10.1016/j.advwatres.2012.07.021) - Heat and solute tracers: How do they compare in heterogeneous aquifers? Groundwater, Vol. 53. 2015, Issue S1: Tracers in the Subsurface, pp. 10-20.
Irvine D.J., Simmons C.T., Werner A.D., Graf T.
(See online at https://doi.org/10.1111/gwat.12146) - Modelling the effects of tides and storm surges on coastal aquifers using a coupled surface–subsurface approach. Journal of Contaminant Hydrology, Vol. 149. 2013, pp. 61-75.
Yang J, Graf T, Herold M, Ptak T.
(See online at https://doi.org/10.1016/j.jconhyd.2013.03.002) - Assessing the saltwater remediation potential of a three-dimensional, heterogeneous, coastal aquifer system. Model
verification, application and visualization for transient density-driven seawater intrusion. Environmental Earth Sciences, Vol. 72. 2014, Issue 10, pp 3827–3837.
Walther M., Bilke L., Delfs J.-O., Graf T., Grundmann J., Kolditz O., Liedl R.
(See online at https://doi.org/10.1007/s12665-014-3253-2) - Impact of fracture network geometry on free convective flow patterns. Advances in Water Resources, Vol. 71. 2014, pp. 65-80.
Vujevic´ K., Graf T., Simmons C.T., Werner A.D.
(See online at https://doi.org/10.1016/j.advwatres.2014.06.001) - Generation of dense plume fingers in saturated-unsaturated homogeneous porous media. Journal of Contaminant Hydrology, Vol. 173. 2015, pp. 69-82.
Cremer C., Graf T.
(See online at https://doi.org/10.1016/j.jconhyd.2014.11.008) - Seawater intrusion in fractured coastal aquifers: A preliminary
numerical investigation using a fractured Henry problem.
Advances in Water Resources, Vol. 85. 2015, pp. 93-108.
Sebben M.L., Werner A.D., Graf T.
(See online at https://doi.org/10.1016/j.advwatres.2015.09.013) - How appropriate is the Thiem equation for describing groundwater
flow to actual wells? Hydrogeology Journal, Vol. 24. 2016, Issue 8, pp. 2093–2101.
Tügel F., Houben G.J., Graf T.
(See online at https://dx.doi.org/10.1007/s10040-016-1457-0) - Impact of topography on groundwater salinization due to ocean surge inundation. Water Resources Research, Vol. 52. 2016, Issue 8, pp. 5794-5812.
Yu X., Yang J., Graf T., Koneshloo M., O’Neal M.A., Michael H.A.
(See online at https://doi.org/10.1002/2016WR018814) - Improving control of contamination from waste rock piles. Environmental Geotechnics, Vol. 4. 2017, Issue 4, pp. 274-283.
Broda S., Aubertin M., Blessent D., Hirthe E.M., Graf T.
(See online at https://doi.org/10.1680/envgeo.14.00023)
