I am a postdoctoral fellow in Juanes Research Group. I obtained my PhD degree in hydrology from Uppsala University, Sweden in December 2012. My research interests include coupled hydro-geomechanical processes, and multiphase flow and transport in porous and fractured media, with applications to contaminant remediation in the subsurface, geological storage of CO2, oil/gas recovery, etc.
1. Poromechanics modeling
I develop a 3D micromechanical model of solid-fluid interactions based on the discrete element method (DEM). The key ingredients of this model are the granular assembly representing the solid phase, the pore-network allowing fluid flow, and the momentum exchange between the solid and fluid. The figure below shows schematics of granular assemblies together with their incident pore-networks: (left) a five-grain system and (right) a cylindrical pack.
Currently, I apply this model to study of physical mechanisms of earthquake triggering due to fluid pressure perturbations. A schematic for the scenario of an impermeable fault is shown below.
2. Two-phase flow and transport in fractures
Two-phase flow in fractures occurs as a “competition” between the fluids for the pore or void space under the combined influence of capillary, gravitational, viscous, and inertial forces. The interplay of these forces is in turn influenced by the fluid and fracture properties. The figure below shows a comparison of experimental and simulated fluid-fluid displacement patterns (from left to right) in a rough fracture. The flow (drainage) is in the capillary-dominated regime, and the model (described here) I developed for the simulation is based on invasion percolation with trapping, including the effect of in-plane curvature which contributes to the capillary pressure. The gray scale in the simulated pattern indicates invading time.
Fracture apertures strongly control fluid-fluid displacement. The figure below shows drastically different drainage patterns for various combinations of the geostatistical parameters of the aperture field (more details can be found here).
Yang, Z., I. Neuweiler, Y. Meheust, F. Fagerlund, and A. Niemi (2016), Fluid trapping during capillary displacement in fractures. Advances in Water Resources, 95, 264-275. http://dx.doi.org/10.1016/j.advwatres.2015.07.015.
Yang Z., L. Tian, B. Jung, S. Joodaki, F. Fagerlund, R. Pasquali, R. Vernon, N. O’Neill, and A. Niemi (2015), Assessing CO2 storage capacity in the Dalders Monocline of the Baltic Sea Basin using dynamic models of varying complexity. International Journal of Greenhouse Gas Control. 43, 149-160. http://dx.doi.org/10.1016/j.ijggc.2015.10.024.
L. Tian, Z. Yang, B. Jung, S. Joodaki, M. Erlström, Q. Zhou, and A. Niemi (2015). Integrated simulations of CO2 spreading and pressure response in the multilayer saline aquifer of South Scania Site, Sweden. Greenhouse Gases: Science and Technology, In Press. http://dx.doi.org/10.1002/ghg.1583.
Yang, Z., A. Niemi, L. Tian, S. Joodaki, and M. Erlström (2015), Modeling of pressure buildup and estimation of maximum injection rate for geological CO2 storage at the South Scania site, Sweden, Greenhouse Gases: Science and Technology,5(3) 277-290. http://dx.doi.org/10.1002/ghg.1466.
L. Tian, Z. Yang, F. Fagerlund and A. Niemi (2015), Effects of permeability heterogeneity on CO2 injectivity and CO2 storage efficiency coefficient. Greenhouse Gases: Science and Technology, In Press. http://dx.doi.org/10.1002/ghg.1540.
Yang, Z., A. Niemi, F. Fagerlund, T. Illangasekare and R. Detwiler (2013), Dissolution of dense non-aqueous phase liquids in vertical fractures: effect of finger residuals and dead-end pools, Journal of Contaminant Hydrology, 149, 88-99, http://dx.doi.org/10.1016/j.jconhyd.2013.03.006.
Yang, Z., L. Tian, A. Niemi and F. Fagerlund (2013), Upscaling of the constitutive relationships for CO2 migration in multimodal heterogeneous formations. International Journal of Greenhouse Gas Control, 19, 743- 755. http://dx.doi.org/10.1016/j.ijggc.2012.11.015.
Yang, Z., A. Niemi, F. Fagerlund and T. Illangasekare (2013), Two-phase flow in rough-walled fractures: comparison of continuum and invasion-percolation models. Water Resources Research, 49(2), 993–1002, http://dx.doi.org/10.1002/wrcr.20111.
Tong F., A. Niemi, Z. Yang, F. Fagerlund, T. Licha and M. Sauter (2013), A numerical model of tracer transport in a non-isothermal two-phase flow system for CO2 geological storage characterization. Transport in Porous Media, 98(1), 173-192, http://dx.doi.org/10.1007/s11242-013-0138-x.
Yang, Z., A. Niemi, L. Tian and M. Erlström (2013), Modelling of far-field pressure plumes for carbon dioxide sequestration. Energy Procedia, 40, 472-480, http://dx.doi.org/10.1016/j.egypro.2013.08.054.
Yang, Z., H. Zandin, A. Niemi, and F. Fagerlund (2013), The role of geological heterogeneity and variability in water infiltration on non-aqueous phase liquid migration, Environmental Earth Sciences, 68(7), 2085-2097, http://dx.doi.org/10.1007/s12665-012-1894-6.
Yang, Z., A. Niemi, F. Fagerlund, and T.H. Illangasekare (2012), Effect of single-fracture aperture statistics on entrapment, dissolution and source depletion behavior of dense non-aqueous phase liquids, Journal of Contaminant Hydrology, 133, 1-16, http://dx.doi.org/10.1016/j.jconhyd.2012.03.002.
Yang, Z., A. Niemi, F. Fagerlund, and T. Illangasekare (2012), A generalized approach for estimation of in- plane curvature in invasion percolation models for drainage in fractures, Water Resources Research, 48(9), W09507, http://dx.doi.org/10.1029/2012WR011829.
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Cambridge, MA 02141, USA
email: zbyang 'at' mit 'dot' edu