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Underground fractures serve as flow conduits, and they may produce unwanted migration of water and other fluids in the subsurface. An example is the migration and leakage of greenhouse gases in the context of geologic carbon sequestration. This study has generated new understanding about how acids erode carbonate fracture surfaces and the positive feedback between reaction and flow. A two-dimensional reactive transport model was developed and used to investigate the extent to which geochemical factors influence fracture permeability and transmissivity evolution in carbonate rocks. The only mineral modeled as reactive is calcite, a fast-reacting mineral that is abundant in subsurface formations. The X-ray computed tomography dataset from a previous experimental study of fractured cores exposed to carbonic acid served as a testbed to benchmark the model simulation results. The model was able to capture not only erosion of fracture surfaces but also the specific phenomenon of channelization, which produces accelerating transmissivity increase. Results corroborated experimental findings that higher reactivity of the influent solution leads to strong channelization without substantial mineral dissolution. Simulations using mineral maps of calcite in a specimen of Amherstburg limestone demonstrated that mineral heterogeneity can either facilitate or suppress the development of flow channels depending on the spatial patterns of reactive mineral. In these cases, fracture transmissivity may increase rapidly, increase slowly, or stay constant, and for all these possibilities, the calcite mineral continues to dissolve. Collectively, these results illustrate that fluid chemistry and mineral spatial patterns need to be considered in predictions of reaction-induced fracture alteration and risks of fluid migration.

This study investigated how subsurface and atmospheric leakage from geologic CO2 storage reservoirs could impact the deployment of Carbon Capture and Storage (CCS) in the global energy system. The Leakage Risk Monetization Model was used to estimate the costs of leakage for representative CO2 injection scenarios, and these costs were incorporated into the Global Change Assessment Model. Worst-case scenarios of CO2 leakage risk, which assume that all leakage pathway permeabilities are extremely high, were simulated. Even with this extreme assumption, the associated costs of monitoring, treatment, containment, and remediation resulted in minor shifts in the global energy system. For example, the reduction in CCS deployment in the electricity sector was 3% for the “high” leakage scenario, with replacement coming from fossil fuel and biomass without CCS, nuclear power, and renewable energy. In other words, the impact on CCS deployment under a realistic leakage scenario is likely to be negligible. We also quantified how the resulting shifts will impact atmospheric CO2 concentrations. Under a carbon tax that achieves an atmospheric CO2 concentration of 480 ppm in 2100, technology shifts due to leakage costs would increase this concentration by less than 5 ppm. It is important to emphasize that this increase does not result from leaked CO2 that reaches the land surface, which is minimal due to secondary trapping in geologic strata above the storage reservoir. The overall conclusion is that leakage risks and associated costs will likely not interfere with the effectiveness of policies for climate change mitigation.

We developed the Leakage Risk Monetization Model (LRiMM) which integrates simulation of CO2 leakage from geologic CO2 storage reservoirs with estimation of monetized leakage risk (MLR). Using geospatial data, LRiMM quantifies financial responsibility if leaked CO2 or brine interferes with subsurface resources, and estimates the MLR reduction achievable by remediating leaks. We demonstrate LRiMM with simulations of 30 years of injection into the Mt. Simon sandstone at two locations that differ primarily in their proximity to existing wells that could be leakage pathways. The peak MLR for the site nearest the leakage pathways ($7.5/tCO2) was 190x larger than for the farther injection site, illustrating how careful siting would minimize MLR in heavily used sedimentary basins. Our MLR projections are at least an order of magnitude below overall CO2 storage costs at well-sited locations, but some stakeholders may incur substantial costs. Reliable methods to detect and remediate leaks could further minimize MLR. For both sites, the risk of CO2 migrating to potable aquifers or reaching the atmosphere was negligible due to secondary trapping, whereby multiple impervious sedimentary layers trap CO2 that has leaked through the primary seal of the storage formation.

This paper presents a new method—the Technique of Iterative Local Thresholding (TILT)—for processing 3D X-ray computed tomography (xCT) images for visualization and quantification of rock fractures. The TILT method includes the following advancements. First, custom masks are generated by a fracture-dilation procedure, which significantly amplifies the fracture signal on the intensity histogram used for local thresholding. Second, TILT is particularly well suited for fracture characterization in granular rocks because the multi-scale Hessian fracture (MHF) filter has been incorporated to distinguish fractures from pores in the rock matrix. Third, TILT wraps the thresholding and fracture isolation steps in an optimized iterative routine for binary segmentation, minimizing human intervention and enabling automated processing of large 3D datasets. As an illustrative example, we applied TILT to 3D xCT images of reacted and unreacted fractured limestone cores. Other segmentation methods were also applied to provide insights regarding variability in image processing. The results show that TILT significantly enhanced separability of grayscale intensities, outperformed the other methods in automation, and was successful in isolating fractures from the porous rock matrix. Because the other methods are more likely to misclassify fracture edges as void and/or have limited capacity in distinguishing fractures from pores, those methods estimated larger fracture volumes (up to 80 %), surface areas (up to 60 %), and roughness (up to a factor of 2). These differences in fracture geometry would lead to significant disparities in hydraulic permeability predictions, as determined by 2D flow simulations.

This paper addresses a particular domain within the sphere of activity that is coming to be known as personal digital papers or personal digital archives. We are concerned with contemporary writers of belles-lettres (fiction, poetry, and drama), and the implications of the shift toward word processing and other forms of electronic text production for the future of the cultural record, in particular literary scholarship. The urgency of this topic is evidenced by the recent deaths of several high-profile authors, including David Foster Wallace and John Updike, both of whom are known to have left behind electronic records containing unpublished and incomplete work alongside of their more traditional manuscript materials. We argue that literary and other creatively-oriented originators offer unique challenges for the preservation enterprise, since the complete digital context for individual records is often of paramount importance—what Richard Ovenden, in a helpful phrase (in conversation) has termed “the digital materiality of digital culture.” We will therefore discuss preservation and access scenarios that account for the computer as a complete artifact and digital environment, drawing on examples from the born-digital materials in literary collections at Emory University, the Harry Ransom Center at The University of Texas at Austin, and the University of Maryland.

The definition of environmental engineering has been updated to be: develop solutions for problems of "planetary health," a phrase that concisely and inclusively captures the breadth of public health, global health, and one health. This new definition is consistent with the missions of the American Academy of Environmental Engineers and Scientists and Association of Environmental and Science Professors (AEESP), and it encompasses the environmental engineering grand challenges of the National Academies of Science, Engineering, and Medicine. The updated job description of environmental engineers is both an opportunity and a challenge. To solve problems of planetary health, environmental engineers will apply foundational principles of engineering science and engineering design, including sustainability and life-cycle assessment, all of which is well established in the ABET program criteria for educational programs in environmental engineering. It is also essential to improve social contracts to promote justice, equity, diversity, and inclusion across individuals, communities, and countries. The skills and practices to solve this second challenge, for example, environmental justice, are still emerging in the field. There are strong parallels between the field of environmental engineering and the profession of nursing, for which the 150-year-old mandate of Florence Nightingale is still relevant: promote wellness, prevent illness, and cure disease, which are best supported by a healthy environment, including fresh air, pure water, sanitation, hygiene, and sunlight. Environmental engineering, nursing, and other professions of caregiving can partner and share strategies to achieve planetary health. [ABSTRACT FROM AUTHOR]