Yunfeng Liang de l’Université de Kyoto, présentera un séminaire le 27 février 2014 à 14h00 dans la bibliothèque du laboratoire PHENIX (7e étage, bâtiment F, porte 754) intitulé :
Gas behaviour in nanopores for unconventional shale
Résumé
At first, I will give an overview of the research activities in our group, mainly, application of molecular simulations (a major part of nanogeosciences) in oil and gas industry. Then, I’ll focuse on an ongoing research on molecular dynamics (MD) simulations of water in silica nano-pores. The task is to understand the NMR relaxation behavior better. To do so, we traced the translational and reorientational motion of water molecules, and obtained diffusion coefficient and the correlation function, respectively. Then, we estimated the correlation time by curve fitting to exponentially decay components with the damped least squares method. Finally, we applied Bloembergen-Purcell-Pound theory and deduced the distribution of NMR calculated relaxation time. It was found that the calculated NMR relaxation time decreases with pore size, and varies with the shape, and moreover, the decrement of the hydrophilic surface is larger than that of the hydrophobic one. This finding is in good correspondence with experimental observations. It enables a direct link between the molecular dynamics and NMR relaxation behaviors.
Regarding to gas flow dynamics, we calculated the mean free path and slip velocity in silica nanopores, and evaluated the slip velocity as a function of Knudsen number using MD simulations. Then, we implemented the slip velocity obtained from MD simulations in Lattice Boltzmann Method simulations. As for the fluid-solid boundary, we adopted counter slip boundary condition, which enables us to configure the slip velocity at the wall so as to satisfy that obtained from MD simulations. Finally, we simulated the gas flow in nanopores with different pore geometries. For a simple slit geometry, it was found that the slip flow induced high permeability, which is about 1.0-1.8 times of that for non-slip flow. For systems with complicated geometries, we demonstrated that permeability of slip flow can be estimated from the pore profile.
*In collaboration with Prof. Toshifumi Matsuoka, Nobuhito Yoshitani, Rongjuan Li, Kazuki Umeda, Hirotatsu Yamabe, and Kazuya Kobayashi.
