| 摘要 |
A subterranean formation containing oil shale is prepared for in situ retorting by initially excavating a void in a lower portion of a retort site. A primary sub-round of explosive is placed in a portion of formation within the retort site above the void, and a secondary sub-round of explosive is also placed in unfragmented formation above the void. In one embodiment, the primary sub-round comprises explosive placed in separate pairs of longitudinally spaced apart upwardly converging blasting holes. Explosive in the primary sub-round is detonated for fracturing unfragmented formation along a boundary defined by the upwardly converging blasting holes to separate a portion of formation from adjacent unfragmented formation for forming at least one new face above the separated portion of formation. The separated formation contains the secondary sub-round which is detonated after the separated formation commences moving under gravity toward the void, and before the separated formation reaches the bottom of the void, for explosively expanding the separated formation toward the new face and toward the void for forming at least a portion of a fragmented permeable mass of formation particles in an in situ oil shale retort.
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