Abstract: A modified in-situ retort for the retorting of oil shale is constructed by mining an open space having a volume of twenty-five to thirty-five percent of the volume of the retort in the bottom of the retort and thereafter blasting the oil shale that is to remain in the retort as rubble in a manner to cause random free fall of the shale particles onto the rubblized bed. Blasting occurs sequentially from the bottom of the unfragmented shale immediately above the open space to the top of the retort. At each blast, there is an open space below the shale to be broken in the blast having a volume at least one-third the volume of that shale, and the timing of the blasts is such that movement of the broken shale is not interfered with by shale broken in the preceding blast. There is no withdrawal of oil shale that would cause downward movement of the rubble that is to be retorted in-situ. The resultant in-situ retort is characterized by a high and uniform permeability.

Abstract: An in-situ retort is formed in an oil shale deposit by a sublevel caving method in which the starting slot for the sublevel caving is at opposite ends of the retort on adjacent sublevels. Any zones of high permeability that are formed adjacent to the starting slots are limited in vertical extent to the vertical spacing of the sublevels and are spaced from the zones of high permeability in adjacent sublevels by the length of the retort. A source of channeling through the retort that is caused by the usual sublevel caving mining method is thereby eliminated.