Research Spotlight: University of Illinois at Urbana-Champaign

The University of Illinois at Urbana-Champaign (UIUC) is home to a variety of porous-media-related scientific studies in several academic departments and campus units. A few examples of our ongoing activities follow.

Department of Civil and Environmental Engineering

The research group of Professor Al Valocchi has been active over many years in the area of groundwater hydrology, solute transport, and aquifer remediation. Valocchi’s research focus is computational modeling of pollutant fate and transport in porous media, in particular the development and application of models that couple physical, geochemical, and microbiological processes over a wide range of spatial and temporal scales. Recent work has focused on pore-scale processes, including comparison of simulations with micro-fluidics experiments performed by research collaborators. Figure 1 shows the case of biofilm growth along a transverse mixing line between an electron donor and acceptor; this has practical application to assessing intrinsic biodegradation of contaminant plumes at legacy hazardous waste sites. The results indicate that clogging due to biomass growth affects the important feedbacks among flow, mixing, and reaction. See Tang et al (2013) for more information.

Figure 1. Comparison of micro-fluidics experiments and pore-scale simulation for biofilm growth along a transverse mixing line. Electron donor and acceptor are injection along left boundary and biodegradation results in biofilm development. Top row shows results from microfluidics experiment in a 2D micromodel; circles indicate solid grains and biofilms are dark zones in the pore space. Bottom row shows results from pore-scale simulation that includes lattice Boltzmann method for flow and transport with a cellular automata model for biofilm spreading; biofilms are indicated in dark red.

Through the Illinois Center for Geological Sequestration of CO¬2 (see below), Valocchi’s group is also collaborating with a group at University of Notre Dame who are conducting micromodel experiments of liquid CO2¬ drainage at reservoir pressure. Comparison of experiments with direct numerical simulations using a new lattice Boltzmann code is shown in Figure 2 (Chen et al., 2017). The overall primary and secondary flow paths observed in the experiments are reproduced in the simulations, albeit at a higher Capillary number. The Capillary number and viscosity ratio for the experiment is matched for the simulations, however the Reynolds number in the experiment is larger than the simulations due to the low viscosity of CO2. Inertial effects are important and need to be considered for multiphase flow of supercritical CO2.

Figure 2. Top row shows experimental results of final liquid CO2 distribution for drainage in a 2D micromodel with a heterogeneous pore structure based on a thin section of a real reservoir rock. CO2 is dyed green; water is dark and the solid grains are not visible. Flow is from left to right. Bottom row shows results from 3D lattice Boltzmann simulations. CO2 is red, water is blue, and solid grains are black. Each panel corresponds to different flow rate (Capillary Number).

A new rock mechanics laboratory is led by Assistant Professor Roman Makhnenko, who is working on coupling poromechanical response of geomaterials with multi-phase fluid flow. The research is devoted to development of experimental methods for proper assessment of fluid-saturated rock behavior under representative in-situ conditions. High-pressure/high-temperature triaxial compression cells and core flooding apparatus are used for measuring poroelastic, inelastic, creep, strength, and flow characteristics of rock cores. Sandstones, limestones, shales, and granites are tested for geo-energy applications that include deep CO2 and nuclear waste storage, as well as enhanced geothermal systems. Injection-induced microseismicity in reservoir and crystalline rock is recorded with acoustic emission sensors and found to be dependent on a number of factors including the acidity of the pore fluid. Specific attention is paid to characterization of time-dependent poromechanical and flow properties of shales, which appear to be anisotropic, and strongly influenced by temperature, effective stress, degree of saturation and chemistry of pore fluid. Thermo-hydro-mechanical coupled processes induced by fluid injection deep underground are studied experimentally and allow for development of more realistic constitutive models. More details are given in Makhnenko and Labuz (2016) and Makhnenko et al. (2017).

Department of Geology

The research group of Assistant Professor Jennifer Druhan emphasizes the ability to predict the chemical and physical behavior of water in the near surface environment in order to understand natural and anthropogenic cycles and support resource sustainability. A key underpinning is the recognition that water-rock interactions take place at interfaces; therefore, the structure of porous media and the aqueous geochemistry that takes place within it must be treated as coevolving phenomena. To study this behavior, Dr. Druhan’s group have developed a diverse array of field and laboratory scale reactive transport experiments in conjunction with numerical simulations focusing on (bio)geochemical reactions in groundwater. Particular emphasis is placed on leveraging the coupled behavior of reactivity and stable isotope fractionation to probe subsurface chemical and physical heterogeneity (Figure 4). These studies involve experiments that guide theoretical treatment of isotope-specific kinetic rate laws within reactive transport models. Members of the Druhan research group work with the US National Science Foundation Critical Zone Observatories (CZOs) to develop new models for weathering and solute fluxes in a changing climate, and with the US Department of Energy Subsurface Biogeochemical Research Program and Energy Frontier Research Program to model subsurface carbon dynamics ranging from soils to CO2 storage reservoirs. Though diverse in application, the Druhan team leverages common principles of reactivity and transport to explore the coupling of physical structure and chemical transformation in near-surface environments.

More details about Druhan’s research are published in Druhan et al. (2014, 2015) and Druhan and Maher (2017).

Figure 4: Reactive transport simulation of steady state CrO42- and δ53Cr across a randomly generated heterogeneous flow field with correlation length of 5 cm and variance of 1cm2 .

Department of Mechanical Science and Engineering

Professor Kyle Smith’s research group investigates transport phenomena in electrochemical devices for energy storage and water desalination. In such devices heterogeneous, porous electrodes are used to facilitate the simultaneous transport of ions and electrons to interfaces between solid material and electrolyte filling its pores. Figure 5 shows a Li-ion battery used to store energy electrochemically. Here, Smith develops computational models to predict electrode microstructure as a function of fabrication conditions used, including the shape of constituent particles used. The microstructure shown in Fig. 5 possesses platelet-shaped “active particles” that absorb lithium ions upon electrochemical reduction and sphere-like carbon particles that facilitate electron conduction to these particles (Smith et al., 2012).

Continuum modeling of local potential and concentration fields in the electrolyte and in the solid phase are used to determine effective conductivity and diffusivity parameters for up-scaling to a homogenized description of coupled ionic/electronic transport in porous electrodes (Nemani et al., 2015; Smith and Dmello, 2016). Using this approach Smith develops novel microstructures to tune transport rates and thereby decrease cost, increase lifetime, and increase efficiency.

Department of Food Science and Human Nutrition

Foods pose interesting porous media problems, which are of importance to both food industry and consumers. With consumer’s demand for healthy, wholesome and nutritious food products, without compromising with taste and texture, it becomes challenging to optimize food processes. Foods exhibit multiscales (e.g. micropores in cell walls, mesopores in cell cytoplasm and macropores at tissue scale); are composed of multispecies (salts, biochemicals, chemical compounds); multiphases (water, oil, vapor, etc.); are heterogeneous; undergo phase and state transitions; and are often subjected to high temperatures during processes such as frying, cooking and extrusion. It is tedious to obtain desired texture, taste and nutritional attributes of foods during processing using purely experimental approaches due to the complexity of involved mechanisms.

Prof. Pawan Takhar’s research group is using continuum thermodynamics based porous media theories to solve the food-processing problems. Some examples of porous media applications studied in his lab include—optimizing quality and nutritional attributes of selected fruits and vegetables during drying using two-scale non-Fickian transport relations; reducing stress-cracking in foods by solving non-Fickian transport and stress equations; solving unsaturated transport relations during expansion of starch for food, feed and biomedical applications; studying recrystallization in frozen-foods during freeze-thaw cycles; modeling unsaturated transport processes during frying to reduce oil uptake in poroviscoelastic food matrices.

Takhar used Hybrid Mixture Theory to develop unsaturated transport relations for a poroviscoelastic food matrix interacting with hydrophilic and hydrophobic fluids. The developed generalized Darcy’s law relations for the water and oil phases included cross-effects resulting from presence of multiphases (oil, water, gas) in the unsaturated pores. The Darcy’s law relations included novel integral terms incorporating the effect of viscoelastic relaxation on fluid transport. These equations can be used for predicting both Darcian and non-Darcian fluid transport during processing of biopolymeric materials in a wide range of temperatures and fluid contents. The developed temporally non-local generalized Darcy’s law was coupled with two-scale mass balance, energy transport and phase-change equations to study transport mechanisms involved in frying of foods. The developed equations were used to calculate water, vapor and oil distribution in pores of foods during frying, the thermomechanical changes in the poroviscoelastic matrix, and pore and capillary pressure profiles. The solution of equations predicted experimental data on moisture content and temperature profile during high temperature frying of rice crackers, potatoes and chicken nuggets.

Professor Youngsoo Lee’s research focus has been controlled release of a target compound which is an important topic in the food and nutrition fields. His research group studied the release of sodium in the oral cavity during mastication. Understanding the factors affecting the release of sodium from food matrices in the mouth and the relationship of these factors to saltiness perception will aid in the worldwide effort to decrease sodium content in foods. The structure of food is a significant factor to understand how sodium is released in an oral cavity. The structural properties (porosity, tortuosity, and sizes of protein aggregates or fat particles) and the secondary properties (texture, serum release, and rheological properties) of the food matrix were identified as critical factors affecting the release of sodium from food matrices during mastication (Kuo and Lee, 2014; Kuo et al., 2016). Professor Youngsoo Lee’s group is continuing the research on structure – release relationship in foods.

Center for Geologic Storage of CO2: Advancing knowledge of injection-induced seismicity

A 2013 National Academy of Sciences report, Induced Seismicity in Energy Technologies, stated that “Given that the potential magnitude of an induced seismic event correlates strongly with the fault rupture area, which in turn relates to the magnitude of pore pressure change and the rock volume in which it exists, large-scale CCS may have the potential for causing significant induced seismicity.” The Center for Geologic Storage of CO2 (GSCO2) aims to advance the world’s knowledge of carbon dioxide (CO2) injection-induced seismicity so that energy-related activities can be controlled at unprecedented scales for a safe and secure future. To do this, the GSCO2 focuses research on an overarching research question:

What are the mechanisms of injection-induced microseismicity, and can we control and predict its occurrence?

Five research themes have been designed to address this question: Reservoir-scale Geology, Microseismicity, Geomechanical Measurements, Geochemical Reactions, and Pore-scale Pressure Transmission.

Center research is based on the collective experience and varied expertise of the research team including work at the Illinois Basin–Decatur Project, among the world’s few saline injection sites and the GSCO2’s deep subsurface observatory. The thematic-driven research uses data gathered by this observatory to test hypotheses and validate models. Most of the Center’s research is focused on the strata (sandstones) of the injection reservoir and underlying crystalline basement in which the observed microseismic events occur.

The GSCO2 is an Energy Frontier Research Center sponsored by the Office of Basic Energy Sciences, which is a division of the Office Science within the US Department of Energy. The Center consists of eleven institutions: the Illinois State Geological Survey, University of Illinois at Urbana-Champaign, Texas Tech University, University of Notre Dame, University of Texas at Austin, University of Southern California, NORSAR, SINTEF, Los Alamos National Laboratory, National Energy Technology Laboratory, and Schlumberger.

References available through download here (15 KB).