Numerical simulation of thermal and reaction fronts for oil shale upgrading

This paper analyses reaction and thermal front development in porous reservoirs with reacting flows, such as those encountered in oil shale upgrading. A set of dimensionless groups and a 1D code are developed in order to investigate the important physical and chemical variables of such reservoirs when heated by in situ methods. Theory necessary for this study is presented, namely shale decomposition chemical mechanisms, governing equations for multiphase flow in porous media and necessary closure models. Plotting the ratio of the thermal front speed to the fluid speed allows one to infer that the reaction front ends where this ratio is at a minimum. The reaction front follows the thermal front closely, thus allowing assumptions to be made about the extent of decomposition solely by looking at thermal front progression. Furthermore, this sensitivity analysis showed that a certain minimum permeability is required in order to ensure the formation of a traveling thermal front. Compared to varying deposit porosities and kerogen activations energies, varying temperature, pressure and permeability are more important.

► We model shale oil extraction by in situ thermal upgrading using an in house code.
► Hot gas injection and conduction heating are found to be viable methods.
► Reaction wave progression can be tracked solely by monitoring the thermal wave.
► Dimensionless flow rate governs oil recovery by hot gas injection.
► Dimensionless depletion region length governs oil recovery by conduction heating.