Process-specific relations describing the change of hydraulic porous-medium properties due to biogeochemical reactions

• Applicant: Dr.-Ing. Johannes Hommel
• Subject Area: Hydrogeology, Hydrology, Limnology, Urban Water Management, Water Chemistry, Integrated Water Resources Management
• Term: since 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 380443677

Subsurface fluid storage helps to reduce climate change (sequestration of CO2) or for energy storage (CH4, H2) to cope with unpredictable production of renewable energy. Fluids have the potential to leak through damaged cap rocks or wellbores. Engineered precipitation of calcium carbonate has been demonstrated to seal such leakage pathways. Successful field demonstrations of this technology have been completed by our collaborators at Montana State University (MSU). More and more researchers are investigating induced calcium carbonate precipitation (ICP), such as e.g. the new collaboration partners at the Heriot-Watt University and the University of Bergen. ICP can be achieved: microbially (MICP), enzymatically (EICP), or thermally (TICP). Fundamentally, those methods rely on the in-situ hydrolysis of urea altering the geochemistry resulting in calcium carbonate precipitation in the presence of calcium.The transport of reactants is a central process for ICP and its numerical modeling. The reactants include, urea, calcium, and for MICP and EICP the ureolytically active microbes or the enzyme urease, respectively. ICP leads to a change in the hydraulic properties of the surrounding porous medium, creating a fully coupled system of reactive transport in which the reactions determined by the transport of reactants feed back on it by affecting transport-relevant properties. The effects of ICP on the porous medium's hydraulic properties, e.g. its permeability or capillary-pressure-saturation relation, are in current numerical models only accounted for by simplified or generalized approaches. However, the advances in imaging technology, and the increase in microfluidic investigations provide a host of rich data sets enabling to improve the parameterization of the effects of ICP on porous-media hydraulic properties. In many applications of ICP the reduction in permeability is the main goal of the application and should thus be predicted as accurately as possible by the numerical models.This project aims at developing detailed process-specific parameterizations for the effects of ICP on porous-media hydraulic properties. Comparing the effect of the same process for various experimental setups or the effect of different processes, e.g. MICP and EICP in an initially identical setup, will enable to separate process-specific effects from setup-specific effects due to e.g. the experimental initial and boundary conditions or the investigated porous medium. This separation increases the confidence when transferring the developed process-specific relations from laboratory to application-relevant scenarios. These scenarios serve to investigate the increase in predictive capabilities of models for ICP due to the process-specific parameterizations of the effects of ICP on porous-medium properties developed in this project. Possible scenarios for this are the field-tests and large-scale experiments on ICP performed by the collaborators at MSU.

• DFG Programme: Research Grants
• Co-Investigators: Professor Dr.-Ing. Rainer Helmig; Professor Dr.-Ing. Holger Steeb