Akademik Veri Yönetim Sistemi
Tez Türü: Yüksek Lisans
Tezin Yürütüldüğü Kurum: Universitaet Stuttgart, Civil and Environmental Engineering, Department of Hydromechanics and Modelling of Hydrosystems, Almanya
Tez Danışmanı: Rainer Helmig
Tezin Onay Tarihi: 2004
Tezin Dili: İngilizce
Desteklendiği Program: Diğer
Özet:
In regions with abandoned coal mines considerable amount of methane migrates to
the surface. This methane can cause restricted use of land and is a potential risk for
the residents. This fact resulted in the installation of extraction wells in many mining
areas to be able to control the methane migration to the surface. If the amount and
concentration of the extracted methane-air mixture is high enough, it can be utilized
as an energy source. For the development of mine gas repositories no reliable tests
exist to evaluate the productiveness or the optimal operation of the extraction wells.
Due to usual complex geology and physical behavior of mine gas repositories numerical simulations can help to get better understanding of these systems and to identify
the important processes influencing the productiveness.
In this work the model of Kobayashi [2004], a 2-phase (water,gas) 3-component
(methane, air, water) model, was extended by introducing the mixture viscosity of
the gas phase as a function of temperature, the effect of tortuosity on the diffusion of the components, the diffusion of methane in the water phase as a function
of temperature and the solubility of methane in the water phase as a function of
temperature and pressure.
The comparison of the advective and diffusive transports showed that diffusive transport was dominant for the test cases (Pe << 1). Several cases were successfully tested
in the unsaturated homogeneous domain. In purely advective transport fingering
effect was observed, if less viscous and less dense fluid (methane) displaces more
viscous and more dense fluid (air), flow may show instabilities called fingering. In
purely diffusive transport density and viscosity differences between air and methane
did not affect the transport process.
Subsequent to the homogenous case, the methane migration in a heterogeneous and
unsaturated domain was tested. For purely advective transport the heterogeneous case showed instabilities too. However, the low velocities reduced the fingering effect
in the low permeable aquitards. Unlike the homogeneous case, the heterogeneous
case could reach the steady state, because with time the density effect got smaller.
For the heterogenous case pressure distribution correlated very well with previous
1-phase simulations and measurements.
Finally, methane migration in partially saturated heterogeneous domain was tested.
Within the water body relative permeability of the water phase was set to zero for
the sake of keeping the water level constant over time, which prevented advective
transport in the saturated water body. It was observed that for a constant methane
source pressure in the gas phase is increasing below the water body. This results
in higher pressure differences in partially saturated heterogeneous domain than in
unsaturated heterogeneous domain.