Jens-Oliver Schwarz

Real-time 3D imaging of Haines jumps in porous media flow

Newly developed high-speed, synchrotron-based X-ray computed microtomography enabled us to directly image pore-scale displacement events in porous rock in real time. Common approaches to modeling macroscopic fluid behavior are phenomenological, have many shortcomings, and lack consistent links to elementary pore-scale displacement processes, such as Haines jumps and snap-off. Unlike the common singular pore jump paradigm based on observations of restricted artificial capillaries, we found that Haines jumps typically cascade through 10–20 geometrically defined pores per event, accounting for 64% of the energy dissipation. Real-time imaging provided a more detailed fundamental understanding of the elementary processes in porous media, such as hysteresis, snap-off, and nonwetting phase entrapment, and it opens the way for a rigorous process for upscaling based on thermodynamic models.

Simulation of Fluid Flow on Fractures and Implications for Reactive Transport Simulations

The diverse numerical simulation techniques employed to predict fluid flow properties of fractures yield differing results which limits their applicability for reactive transport simulations. Basically the fluid flow simulation techniques can be divided in two groups: (i) techniques that yield average fluid flow characteristics and (ii) techniques that produce space-resolved properties. These differences may have substantial impact on the reactive transport simulations but may also depend on the fracture characteristics. For this reason, a sensitivity analysis of the geometrical properties of fractures on the fluid flow properties is conducted and evaluated with respect to their impact on reactive transport modeling. Although employing space-resolved simulation techniques, the results of the tests show average values for permeability and fluid velocity that are comparable to previous studies that used other simulation techniques. Observed fluid flow channeling appears to be related to fracture surfaces matching and anisotropy. However, average flow velocities at potential sites for reactive transport differ up to a factor of five from the average ones for the entire fracture. Furthermore, extreme values at reactive transport sites may differ even more and the flow may be directed against the applied pressure gradient. For studies concerned with simulation of reactive transport, these deviations are crucial and should be explicitly considered in the calculations. Hence space-resolved fluid flow simulations should be employed for the simulation of reactive transport.

Microstructure of the Shaly Facies of Opalinus Clay on the Mm-nm Scale

Opalinus Clay is one of the fine-grained sedimentary formations investigated as a possible geological repository for the long-term storage of radioactive waste. Porosity, pore size, pore shape and connectivity of pores will help to define sealing capacities of a host rock. Here a combination of FIB-SEM, BIB-SEM and µ-CT has been used in order to investigate the nm-mm scale microstructure of the Shaly facies of Opalinus Clay in 2D and 3D. The µ-CT measurements gave a 3D overview of the microstructure of a 2 mm core down to a 2.6 µm voxel size. Which showed cracks, larger bivalve fragments and pyrite nodules embedded in a matrix, which was investigated down to the nm scale (enabling to image the pores) in 2D using the BIB-SEM method. FIB-SEM measurements were afterwards performed on selected areas to investigate the pore shape and connectivity in 3D down to the nm scale.