Christopher Zahasky

University of Wisconsin–Madison | UW · Department of Geoscience

Migration of variably sized fines or geogenic colloids is a significant concern for the long-term efficiency of aquifer management and reservoir injection and extraction operations. Characterizing the migration of colloids in porous media has been widely studied; however, few studies have quantified sub-core colloidal transport behavior and related...

Knowledge of the spatial distribution of fracture apertures is essential for reliable characterization of flow and transport processes in fractured systems and for better understanding of physicochemical matrix–fracture interactions. Here, we propose and test two image-based methods, thereby extending the current experimental capabilities to charac...

Understanding flow, transport, chemical reactions, and hydro-mechanical processes in fractured geologic materials is key for optimizing a range of subsurface processes including carbon dioxide and hydrogen storage, unconventional energy resource extraction, and geothermal energy recovery. Flow and transport processes in naturally fractured shale ro...

Perfluoroalkyl acids (PFAAs) are persistent environmental contaminants that sorb to air-water and solid interfaces throughout the vadose zone. These sorption processes lead to decadal leaching of PFAS from the source zones to groundwater systems. While these processes are increasingly well understood, critical gaps exist in describing the verticall...

Quantification of heterogeneous multiscale permeability in geologic porous media is key for understanding and predicting flow and transport processes in the subsurface. Recent utilization of in situ imaging, specifically positron emission tomography (PET), enables the measurement of three‐dimensional (3‐D) time‐lapse radiotracer solute transport in...

As a part of climate change mitigation plans in Europe, CO2 storage scenarios have been reported for the United Kingdom and the European Union with injection rates reaching 75 – 330 MtCO2 yr⁻¹ by 2050. However, these plans are not constrained by geological properties or growth rates with precedent in the hydrocarbon industry. We use logistic models...

Plain Language Summary Solutes and contaminants dissolved in a fluid, such as water, are carried along with the fluid as it migrates in the subsurface. In some subsurface settings, there are multiple fluids present. For example, above the water table a zone of soil and rock has pores filled with different fractions of water and air; in geologic car...

As a part of climate change mitigation plans in Europe, CO2 storage scenarios have been reported for the United Kingdom and the European Union with injection rates reaching 75 – 330 MtCO2 yr-1 by 2050. However, these plans are not constrained by geological properties or growth rates with precedent in the hydrocarbon industry. We use logistic models...

As a part of climate change mitigation plans in Europe, CO2 storage scenarios have been reported for the United Kingdom and the European Union with injection rates reaching 75 – 330 MtCO2 yr-1 by 2050. However, these plans are not constrained by geological properties or growth rates with precedent in the hydrocarbon industry. We use logistic models...

We investigate chemical transport in laboratory rock cores using unidirectional pulse tracer experiments. Breakthrough curves (BTCs) measured at various flow rates in one sandstone and two carbonate samples are interpreted using the one‐dimensional Continuous Time Random Walk (CTRW) formulation with a truncated power law (TPL) model. Within the sam...

Small‐scale heterogeneities in multiphase flow properties fundamentally control the flow of fluids from very small to very large scales in geologic systems. Inability to characterize these heterogeneities often limits numerical model descriptions and predictions of multiphase flow across scales. In this study, we evaluate the ability of pore networ...

Integrated assessment models have identified carbon capture and storage (CCS) as an important technology for limiting climate change. To achieve 2 °C climate targets, many scenarios require tens of gigatons of CO2 stored per year by mid-century. These scenarios are often unconstrained by growth rates, and uncertainty in global geologic storage asse...

Accurate determination of petrophysical and multiphase flow properties in sandstones is necessary for reservoir characterization, for instance for carbon dioxide and hydrogen storage in geological formations or for enhanced oil recovery. Several studies have examined the effect of heterogeneities, such as fractures, bedding planes and laminae, on c...

Small-scale heterogeneities in multiphase flow properties fundamentally control the flow of fluids from very small to very large scales in geologic systems. Inability to characterize these heterogeneities often limits numerical model descriptions and predictions of multiphase flow across scales. In this study, we evaluate the ability of pore networ...

Spontaneous imbibition—the process of a wetting fluid displacing a nonwetting fluid purely by capillary forces—is a ubiquitous phenomenon in porous and fibrous materials. Here we present a new experimental method for quantification of spontaneous imbibition in geologic materials. This method makes it possible to perform spontaneous imbibition under...

Recent studies have demonstrated that positron emission tomography (PET) is a valuable tool for in-situ characterization of fluid transport in porous and fractured geologic media at the laboratory scale. While PET imaging is routinely used for clinical cancer diagnosis and preclinical medical research—and therefore imaging facilities are available...

The analysis of dispersive flows in heterogeneous porous media is complicated by the appearance of anomalous transport. Novel laboratory protocols are needed to probe the mixing process by measuring the spatial structure of the concentration field in the medium. Here, we report on a systematic investigation of miscible displacements in a microporou...

We present a trajectory-based technique for calculating solute transport in a porous medium that has several advantages over existing methods. Unlike streamlines, the extended trajectories are influenced by each of the important parameters governing transport, including molecular diffusion and transverse dispersion. The approach is complete and doe...

Improved methods for predicting fluid transport and vesicle connectivity in heterogeneous basalts are critical for determining the long-term reaction and trapping behavior of sequestered carbon dioxide and maximizing the efficiency of geothermal energy production. In this study we measured vesicle geometry, pore connectivity, and vesicle surface ar...

Accurate descriptions of heterogeneity in porous media are important for understanding and modeling single phase (e.g. contaminant transport, saltwater intrusion) and multiphase (e.g. geologic carbon storage, enhanced oil recovery) transport problems. Application of medical imaging to experimentally quantify these processes has led to significant p...

Understanding and quantifying the role of reservoir heterogeneity on multiphase flow and the immobilization of CO2 is essential for predicting and validating models of long-term CCS reservoir performance. In this study a novel imaging technique known as Positron Emission Tomography (PET) is used to image pulse tracer transport through a heterogeneo...

Assuring the storage security of geologically sequestered CO2 is essential for proper project management and long-term emissions reductions. Storage security relies not only on comprehensive site characterization prior to injection and careful reservoir management, but also on having a suite of intervention and remediation strategies available to i...

Assuring CO2 storage security is essential for the widespread implementation of carbon capture and sequestration. Appraising the potential for leakage through faults in seals is an important component of site screening, assessment, and selection. The focus of this study is to understand and quantify the potential rates of CO2 leakage via faults and...

One of the greatest concerns that the public has with large-scale adoption of CCS technology is the potential risk of carbon dioxide leakage from sequestration reservoirs. Among other things, addressing these concerns will require developing intervention and remediation strategies that can be quickly and effectively implemented should leakage occur...

We examine the influence of initial fabric on the development of fractures in experiments in which clay cakes are sheared over two horizontal base plates that move past each other in wrench-fault motion. An anisotropic fabric in the kaolinite was produced during the preparation of the clay cakes for these experiments. To produce the fabric, the cla...

Constraints available at the Earth's surface on the geometry of geologic folds often are discontinuous, consisting of scattered bedding surface outcrops representing the position and orientation of different stratigraphic surfaces. For this reason, characterization of fold geometry from surface data, by methods such as sequential balanced cross sec...

Folded sedimentary rocks often exhibit complex, non-cylindrical geometries. Improved methods for constraining complex fold geometry from surface data such as measurements of strike, dip and geographic coordinates of bedding contacts are necessary to advance our understanding of the complex relationship between fold geometry and geologic fracture pa...