Comparison of flow nonuniformities in oil shale pilot retorts with those predicted by numerical flow simulations

The primary obstacle to commercial recovery of shale oil is the presence of flow nonuniformities in in situ oil shale retorts. In an effort to evaluate the causes of these nonuniformities, we have compared flow data from an experimental retort with computer flow simulations. We found that in areas where the large-scale sweep efficiency was adequate, local nonuniform flow was caused by (a) channeling in regions of high permeability (i.e., along the retort wall and around larger blocks), (b) accelerations in flow around cross-section blockages, and (c) exothermic chemical reactions that change the gas viscosity.