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FRINATEK-Fri prosj.st. mat.,naturv.,tek

Cross-scale modeling of CO2/hydrocarbon conversion in hydrofractured shale

Awarded: NOK 7.8 mill.

Our team has performed analysis of structural and electronic properties of shale materials. We have developed and explored the formalism needed to study crystal structure, molecular storage, formation and breakage of surfaces and in nanoporous structures. Using the ab initio Born-Oppenheimer molecular dynamics (MD) within the density functional theory (DFT), we developed a model for analysis of formation energy, surface reconstruction and CO2-surface interaction. We found that CO2 interaction on SiO2 surface has physisorption nature, and it can be improved in the presence of dangling bonds or surface defects. The model was further used for the analysis of CO2 interaction with the shale using both first principles simulations and MD simulations. From on computed results, we showed that the interaction has the physisorption nature and only surface defects can contribute to the chemical interaction with CO2 molecules. Because of this and since CO2 and H2O injection in shale systems can induce significant changes for the porosity and formation of supercritical CO2 phase, we developed the model for amorphous SiO2 shale and supercritical CO2 and performed the detailed analysis of their optical properties. The results from DFT dielectric response were directly used in the analysis of Casimir-Polder interaction discussed. Here, the effects of background salt and pH on surface charge, finite molecular size corrections, and van der Waals forces have been considered. Modifications to both intermolecular forces and membrane permeability due to presence of background charges have been considered. Casimir forces can induce quantum levitation of thin films on a substrate. These quantum forces and the related quantum levitation effects are not simply a theoretical curiosity but can in fact influence how a CO2 gas bubble in water interacts with porous shale surfaces. Recent investigations indicate that the formation of CO2 bubbles in water plays the key role in the CO2 storage in shale systems. Moreover, CO2 bubbles are found to be highly stable and could provide CO2 trapping for a number of years. Taking the matter further we studied the effect of background salt on the thickness of wetting films on melting ice and on the dynamics of supercritical CO2 bubbles within such films. We have found that CO2 bubbles within a water film on ice are attracted towards the ice-water interface and repelled from the vapor-water interface. We have focus our efforts on including the finite molecular size in the expression for the Casimir-Polder energy which has provided us with estimates of the dispersion contribution to the binding energies between methane and CO2 molecules and between one molecule and a planar surface. We have investigated the accuracy of Lennard-Jones potentials based on interactions in bulk fluids, the approach used in standard simulations for methane transport, near surfaces. We have found surface catalytic effects that alter the interaction when two methane molecules are near interfaces or in pores. Moreover, investigations of air-water interfaces reveal that the Lifshitz interaction by itself does not promote ice growth. On the contrary, we find that the Lifshitz force promotes the growth of an ice film, up to 1-8 nm thickness, near silica-water interfaces at the triple point of water. Our results provide a model for how water freezes on glass and other surfaces, and we also suggest that it should be possible to measure these effect with the use of already available experimental techniques. We have developed a model to describe the dielectric properties of amorphous SiO2 and SiO2 polymorphs. We found that the properties are directly dependent of the volume of the material, and the dependence is mainly caused by the change of nanoporosity and nano cavities at the atomic scale. Furthermore, we have demonstrated that liquid water can exist in ice-filled pores and cavities. For thick vapor layers between ice and pore surfaces, a nanosized water sheet can be formed due to repulsive Lifshitz forces. In the absence of vapor layers, ice is inhibited from melting near pore surfaces. In between these limits, we find an enhancement of the water film thickness in silica and alumina pores. In the presence of metallic surface patches in the pore, the Lifshitz forces can dramatically widen the water film thickness, with potential complete melting of the ice surface. We have also investigated how the presence of salt ions influences the equilibrium thickness of the Casimir-induced water layer on ice surface. We predict an equilibrium water film thickness for the ice-water-vapor system that increases with the increase in concentration of salt in the water phase. The results are directly applicable to the melting of ice under the equilibrium conditions. We have found that the predictions strongly depend on the model employed for the effective polarizability of the ion in water.

In shale gas systems, natural gas is produced directly from organic-rich shales through drilling and hydrofracturing. The methane is adsorbed at interfaces, absorbed by the kerogen shale, and contained as free gas and/or gas dissolved in water in pore vol umes and fracture apertures. Interestingly, the affinity for carbon dioxide is stronger than the affinity for methane, and carbon dioxide may therefore be used to enhance gas production. This project involves fundamental research on the molecular physisor ption/chemisorption and the meso-scale gas transport processes in nanostructured shales. The project strategy is to combine our knowledge from condensed matter physics, forces theories for molecules, and continuous transport models to explore details in the physical properties and processes of carbon dioxide and methane in water-rich shale nanostructures. This will be realized by four scientifically intertwined work plans. WP1: Analyses of crystal structure and surface reconstruction by means of density functionals. WP2: Atomistic simulation of surface of adsorption and desorption. WP3: Green functions modeling of physisorption and chemisorption to analyze surface-gas-water interactions, molecule formation, and stiction. WP4: Explore the surface-near tr ansport and deformation in shale systems with a direct simulation Monte Carlo approach. The project will be carried out and completed at the Department of Physics at University of Oslo by the research teams at Geophysics, linked to Center for the Physi cs of Geological Processes, and at Structure Physics, linked to the Centre for Materials Science and Nanotechnology. Strong international collaboration will serve for networking, exchange of knowledge, and scientific visibility. Long-term international re search visits by the PhD student and the postdoctors will strengthen these contacts.

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FRINATEK-Fri prosj.st. mat.,naturv.,tek