Increasing global demand for energy and declining fossil fuel resources continue to make coal deposits a primary source of energy. However, the process of converting coal into valuable syngas through surface gasification requires conventional mining, extraction, transportation, storage, surface processing, ash and environmental handling. Moreover, most coal deposits are located at great depth and have thin coal seams, making them either un-mineable or uneconomical using current technologies. Underground coal gasification (UCG) is an exciting alternative technique for producing syngas from coal conversion in-situ. This will eliminate the need for conventional mining and some surface facilities, increase safety, and lower capital expenditures. It is imperative that we develop accurate UCG models and simulations capable of incorporating the impacts of multi-disciplinary phenomena, in particular in the UCG process where there is no direct access to the developed underground reactors.

Small-scale models can be used to investigate the mechanisms and details of the various phenomena taking place during UCG. Most of the models in the literature apply the CFD (computational fluid dynamics) approach to predict the experimental results or explore the effects of the operational parameters on the process at lower pressures. However, the CFD models include more details, such as multi-component diffusion of the gas components and turbulent flow. Applying these models to field scale simulations can be very expensive.

The similarities between UCG and heavy oil in-situ combustion make it possible to use a thermal compositional hydrocarbon simulator to simulate the UCG process. Complex geology, various well configurations, and multi-phase flow can be efficiently simulated using models developed in the oil and gas industry. This study focuses on the adaptation of a commercial hydrocarbon simulator to model UCG processes at great depth by using applied techniques to convert the coal per gasification module. It presents assumptions and procedures to evaluate the required properties and kinetics of chemical reactions. Small-scale models are used to validate the proposed methods both quantitatively and qualitatively. In addition, large-scale numerical simulation models are used to compare the performance of different technologies. The Thulin test is modeled using a cross-sectional domain. We also explore issues and possible solutions associated with UCG modeling in tight coal seams.