SIMULATION OF COMPLEX MULTIPHASE, MULTI-COMPONENT, REACTING FLOWS IN POROUS MEDIA

Abstract

In this study we are concerned with the modelling of multi-component, multiphase chemically reacting flows in porous media, with particular application to the spontaneous combustion of coal and the extraction of coalbed methane. These two related problems involve complex multiphase, multi-component flow in a porous medium. Chemical reactions, adsorption, gaseous diffusion and changes in porosity and permeability are important in one or both of these problems. These matters are discussed in general in the first few chapters of the thesis. Several models for the spontaneous combustion of coal that include the effect of a diminishing reaction rate are investigated and a new formulation in the form of a generic power law model is introduced. A numerical module for modelling the spontaneous combustion of coal is described, based on the TOUGH2 code. A new equation of state (EOS) module is developed including realistic physical properties for all gases involved. The modified version of TOUGH2 is used for modelling the adiabatic method for testing the reactivity of coal samples. The results agree very well with experimental measurements for coal samples from different mines in New Zealand and Australia. Moisture effect on the reaction rate was then introduced to TOUGH2 using a new twophase EOS module with water and air broken into its main components (Nitrogen, Oxygen, Carbon dioxide and Argon). Finally the production of methane from low rank coalbeds is investigated. A new EOS for mixture of water and methane is developed and incorporated into the TOUGH2 code to produce a new and versatile coalbed methane simulator. It is validated by running some simple test problems and comparing results with those obtained with the commercial COMET simulator.