Browsing by Author "Kobayashi, Kenichiro"

Filter results by typing the first few letters
Now showing 1 - 1 of 1
  • Thumbnail Image
    ItemOpen Access
    Optimization methods for multiphase systems in the subsurface : application to methane migration in coal mining areas
    (2005) Kobayashi, Kenichiro; Helmig, Rainer (Professor)
    This thesis has two foci. The first focus is the development of a so-called simulation-optimization model. An optimization algorithm, Simulated Annealing (SA), is coupled with a Multiphase/ Multicomponent simulator, MUFTE-UG, to solve a real-world simulation-optimization problem (henceforth MUFTE-SA). In this thesis, the simulation-optimization model is tailored to the study of better (optimal) methane-extraction strategies from an abandoned coal mine in the Ruhrgebiet, Germany. The question of how to deal with the methane from abandoned coal mines is always of great concern for the administrators. Thus, I try to provide one numerical tool to support this decision making in the context of extraction-well operations. The skills required for modelling, for example using computational fluid dynamic theories, have been making progress for the past couple of decades. So nowadays, additionally, the importance of developing a so-called decision-support system integrating these skills is starting to be noticed. This simlation-optimization model is designed to answer these new requirements.Although, the use of the simulation-optimization model in this thesis is limited to the investigation of better methane-extraction strategies, the model itself can be utilized anologously for many processes whose abstracted aspects can be modelled by the multiphase/ multicomponent model. In the past, this sort of simulation-optimization model could only be applied to an artificially designed example since the computational time needed to make real-world simulations is generally enormous, although optimization procedures require dozens, hundreds, thousands of iterations. Thus, a pseudo parallelization design of the optimization procedure is proposed in order to use a parallel computer, having succeeded in reducing the total computational time by a factor of 23. The second focus is to make comparative studies using different model concepts (i.e. a two-phase and a two-phase/ three-component model) for the simulation of methane-migration and methane-water interaction processes in saturated coal mines. This work includes the new development of a two-phase (liquid, gas) / three-component (water, air and methane) model in order to incorporate mass-transfer processes between the phases. Considering the mass transfer processes between the phases sometimes becomes very important, especially when the coal mine is modelled after groundwater rebound. This is because the dissolution of the methane in the liquid phase is relatively high under some conditions.