EMSL Pore Scale Modeling Challenge/Workshop

Report covers the background for the workshop, objectives, important research directions, necessary capabilities and overall recommendations

FATE AND TRANSPORT OF RADIONUCLIDES [U(VI), Sr, Cs] IN VADOSE ZONE SEDIMENTS AT THE HANFORD SITE

Physical and chemical heterogeneities are inherent in subsurface environments due to varying: mineralogy, pore geometry, solution saturation, and solute concentration. The goals of this research were to study the heterogeneities that influence radionuclide fate and transport in the Hanford vadose zone. Hanford was established for nuclear weapons development and has significant subsurface contamination. Specific objectives were:1. Investigate the influence of secondary precipitate formation on strontium and cesium fate and transport in sand under unsaturated conditions.2. To evaluate pore scale processes of uranium release from sediment to pore water.3. To investigate uranium release rates from contaminated Hanford sediments reacted with Columbia River water.4. To quantify diffusion limited mass transfer of soluble U into micro-fractures.Waste storage tanks have leaked into the subsurface causing a change in saturation and a solute gradient of leachate into pore water. Simulations displayed non-ideal transport of strontium and cesium in solution unsaturated flow. The incorporation of strontium into secondary precipitates can be fast, leading to retarded transport of strontium. Cesium incorporation into neoformed feldspathoids will occur slowly and depends on mineral transformation and ripening.Legacy contamination of the Hanford 300 Area resulted in persistent uranium release from capillary fringe sediments. Rising river stages flood these sediments perturbing the chemical state of the system. Simulations showed uranium release after contact with river water was dependent on contact time. Uranium concentrations in micro-pores were higher than in larger pores, causing a diffusion gradient. When solution-to-solid ratio was narrow, the water became supersaturated with respect to uranium, and it precipitated. Initial release of uranium was 6 to 9% of the total. As solution-to-solid ratio widened, portion of uranium released increased steadily, suggesting a diffusion rate limited release of uranium. These results imply that uranium can remain trapped in the sediments for extended periods of time.Diffusion rate limited release of contaminants due to complex geometry contributes to control of Hanford subsurface contamination. We investigated diffusion of colloids into micro-channels. Colloids (0.2 ìm) diffusion into larger factures (10 to 30 ìm) could be modeled using the calculated infinite linear coefficient but diffusion into smaller fractures (3 to 5 ìm) was reduced by as much as 2.68 times

'Me For You': Lessons About Everyday Video Messaging From Skype Qik Position paper for CHI 2015 Workshop Everyday Telepresence: Emerging Practices and Future Research Directions

Abstract In this position paper we outline the opportunities and challenges of pure asynchronous video messaging as an everyday utility. We recruited 53 users to try Skype Qik 'in the wild' for two weeks from its launch in October 2014. We found users orienting to an organizational principle that we term 'Me For You', a self-conscious yet creative orientation that allowed users to transform features of their everyday affairs into show-about-ables that can be subject to and warrant the interrogative gaze of a Qik recipient. We found that such acts implied a reciprocity that was valuable in some special contexts, while at other times proving dissonant with assumptions about mundane communicative practices between particular parties. To warrant another's gaze requires artfulness, but in some relationships one might not want to demand that artfulness in return. We argue that richness is not a matter of mode but of perceived control, within which the morality of gaze represents an ongoing challenge for designing everyday telepresence

Geochemical Narrowing Of Cement Fracture Aperture During Multiphase Flow Of Supercritical CO2 And Brine

For carbon capture and storage operations, wells are used as a necessary conduit for injecting CO2 at depth, but they can also act as leakage conduits if the cement seals are compromised. The specific objective of this research was to experimentally investigate the nature of self-healing of a fracture within cement under multiphase flow of CO2 and brine, and to compare the findings with the predictions of a recently developed model. This was accomplished by flowing a multiphase mixture of supercritical CO2 and brine through a cement fracture. The influent end of the fracture was degraded as evidenced by the formation of cracks across the surface. At the effluent end of the fracture, the initial aperture of 137 μm was reduced to 50 μm. This reduction by 87 μm compared well with an aperture reduction of 80 μm predicted by a recently developed model tested in this study. Self-healing of the fracture contributes to permeability reduction through the potential leakage pathway

Relative permeability for water and gas through fractures in cement.

Relative permeability is an important attribute influencing subsurface multiphase flow. Characterization of relative permeability is necessary to support activities such as carbon sequestration, geothermal energy production, and oil and gas exploration. Previous research efforts have largely neglected the relative permeability of wellbore cement used to seal well bores where risks of leak are significant. Therefore this study was performed to evaluate fracturing on permeability and relative permeability of wellbore cement. Studies of relative permeability of water and air were conducted using ordinary Portland cement paste cylinders having fracture networks that exhibited a range of permeability values. The measured relative permeability was compared with three models, 1) Corey-curve, often used for modeling relative permeability in porous media, 2) X-curve, commonly used to represent relative permeability of fractures, and 3) Burdine model based on fitting the Brooks-Corey function to fracture saturation-pressure data inferred from x-ray computed tomography (XCT) derived aperture distribution results. Experimentally-determined aqueous relative permeability was best described by the Burdine model. Though water phase tended to follow the Corey-curve for the simple fracture system while air relative permeability was best described by the X-curve

Nano-Minerals Plus Higher Temperatures Accelerate the Release and Transport of Carbon from Sediment

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Atomic Origins of the Self-Healing Function in Cement–Polymer Composites

Motivated by recent advances in self-healing cement and epoxy polymer composites, we present a combined ab initio molecular dynamics and sum frequency generation (SFG) vibrational spectroscopy study of a calcium–silicate–hydrate/polymer interface. On stable, low-defect surfaces, the polymer only weakly adheres through coordination and hydrogen bonding interactions and can be easily mobilized toward defected surfaces. Conversely, on fractured surfaces, the polymer strongly anchors through ionic Ca–O bonds resulting from the deprotonation of polymer hydroxyl groups. In addition, polymer S–S groups are turned away from the cement–polymer interface, allowing for the self-healing function within the polymer. The overall elasticity and healing properties of these composites stem from a flexible hydrogen bonding network that can readily adapt to surface morphology. The theoretical vibrational signals associated with the proposed cement–polymer interfacial chemistry were confirmed experimentally by SFG vibrational spectroscopy

Polymer-Cement Composites with Self-Healing Ability for Geothermal and Fossil Energy Applications

Sealing of wellbores in geothermal and tight oil/gas reservoirs by filling the annulus with cement is a well-established practice. Failure of the cement as a result of physical and/or chemical stress is a common problem with serious environmental and financial consequences. Numerous alternative cement blends have been proposed for the oil and gas industry. Most of these possess poor mechanical properties, or are not designed to work in high temperature environments. This work reports on a novel polymer-cement composite with remarkable self-healing ability that maintains the required properties of typical wellbore cements and may be stable at most geothermal temperatures. We combine for the first time experimental analysis of physical and chemical properties with density functional theory simulations to evaluate cement performance. The thermal stability and mechanical strength are attributed to the formation of a number of chemical interactions between the polymer and cement matrix including covalent bonds, hydrogen bonding, and van der Waals interactions. Self-healing was demonstrated by sealing fractures with 0.3–0.5 mm apertures, 2 orders of magnitude larger than typical wellbore fractures. This polymer-cement composite represents a major advance in wellbore cementing that could improve the environmental safety and economics of enhanced geothermal energy and tight oil/gas production