Research Project C04

Porosity and permeability are two major hydraulic properties that govern flow through porous media, while there are different processes in many different fields of applications that can cause pore space to evolve due to fluid-solid phase change. For the time being, this project puts a focus on induced calcite precipitation as an engineering option for targeted sealing of flow pathways in porous media or for targeted improvement of soil strength. Noteworthy, hydraulic alterations due to calcite precipitation are inseparable from mechanical alterations. While our primary focus is first of all on the experimental observation of the hydraulic alterations in terms of porosity-permeability relations due to growth of carbonates in the pore space, we plan to address later on also the topic of mechanical alterations.

In the first funding period, the project has focused on experimental EICP (enzyme-induced calcite precipitation) in microfluidic cells. Setups and imaging techniques (microscopy, XRCT) were developed to analyze pore-space changes as seen in Figure 1 and to link calcite precipitation to permeability alterations via pressure monitoring as seen in Figure 2. Analyzing precipitation patterns in pore throats and bodies is crucial for deriving porosity-permeability relationships from morphological changes. This requires a reliable workflow to produce and observe reproducible patterns. Quasi-1D setups differ from 2D ones, where flow can bypass obstructions more easily. Experimental work was done in close cooperation with the external partner at the Center for Biofilm Engineering, Montana State University, Bozeman. Modelling-supported interpretation of microfluidic precipitation experiments was done in collaboration with research project C02.

During FP 2, the project investigated how enzyme-induced (EICP) and microbially induced (MICP) calcium carbonate precipitation compare in microfluidic cells with respect to precipitation patterns and  porosity-permeability relations. Furthermore,  biofilm formation was studied under shear as seen in Figure 3 and in the Video 2 in a collaboration with research project C01, affect pore structure and hydraulic behavior. Porosity-permeability relationships were mainly analyzed in microfluidic systems through imaging and numerical simulations. The comparison of EICP and MICP, along with different cementation strategies, showed that boundary conditions—such as forced flow versus constant pressure—are particularly critical near injection zones. Additionally, the evolution of mechanical properties in porous media was studied numerically to support future research directions. Also in FP2, we have strongly involved the external partner from MSU Bozeman in the experimental work and interpretation of results.

We have developed with research project B05 and the project INF (M. Schneider) computationally efficient pore-scale Stokes model, which can be used to analyze the microfluidic results with respect to permeability and its anisotropy. Furthermore, we work with research project C05 on the comparison between our microfluidic calcite precipitation and their experimental approaches on the REV scale with small cylindrical cores.

The project has also contributed to the FP2 vision topic ‘’calcite dissolution’’ by investigating CO₂-dependent driving forces for calcite dissolution in karstic systems.

All research activities within this project are closely aligned with the CRC-wide vision topic “salt.” A central objective is to enhance conceptual modelling approaches at the REV scale for bio-concrete production using microbially induced calcium carbonate precipitation (MICP). In doing so, we aim to benefit from the mechanistic, less phenomenological modelling strategies developed in related sub-projects such as C01 and B01.

The project will focus on the strong coupling between hydraulic and mechanical property changes in porous media during MICP-based bio-concrete formation by using the experimental setup as seen in Figure 4. Particular emphasis will be placed on validating and parameterizing a constant-cement model that links porosity changes to stiffness. This effort will rely on experimental data obtained from C04, B05, and Z02. Another major goal is to establish numerical simulation as a key tool in optimizing bio-concrete production processes, by developing reliable workflows and refining experimental setups in line with principles of experimental design. Furthermore, an open question from earlier project phases—concerning the differing behaviour of MICP in glass versus PDMS microfluidic cells—will be addressed in close collaboration with research project Z02.

There has been a long-standing collaboration between the work groups of Holger Class and Rainer Helmig in Stuttgart and the group of Robin Gerlach and Al Cunningham at Montana State University. The intensive scientific exchange resulted in a number of high-ranked joint publications.

In the Biofilm Center at MSU Bozeman, there is an outstanding experimental facility which will be of great use for research project C04. Altogether, within SFB 1313 the successful joint research is expected to be continued.