An Efficient Modeling Approach to Simulate Heat Transfer Rate between Fracture and Matrix Regions for Oil Shale Retorting

The conversion of hydrocarbons in oil shale into liquid fuels has gained interest due to decreasing conventional oil reserves. Thermal conversion involves heating fractured rock and recovering gas and liquid phase products. The efficiency of this process is markedly dependent on heat transfer limitations between fracture porosity and rock matrix. Computer models are useful tools for process optimization. Explicit modeling of heat transfer processes within rock fragments would require great computational effort, making inverse modeling and forward process optimization very difficult if not impracticable. In this article, we evaluate the feasibility of using first-order heat transfer formulations to approximate these processes by comparing first-order model results with a rigorous explicit formulation and by comparison with laboratory retorting experiments published in the literature. Comparison of the two modeling approaches indicates that the first-order heat transfer approximation can be used without significant loss of accuracy if the block size and/or heating rate are not too large, as quantified by a proposed dimensionless heating rate. However, computational effort can be decreased by an order of magnitude compared with explicitly simulating diffusive heat transfer.