In situ recovery of shale oil

Abstract

An in situ oil shale retort is formed in a subterranean oil shale deposit by excavating a columnar void having a vertically extending free face, drilling blasting holes adjacent to the columnar void, loading the blasting holes with explosive, and detonating the explosive in a single round to expand the shale adjacent to the columnar void toward the free face to fill with fragmented oil shale the columnar void and the space in the in situ retort originally occupied by the expanded shale prior to the expansion. A room having a horizontal floor plan that coincides approximately with the horizontal cross section of the retort to be formed is excavated so as to intersect the columnar void. The room can lie above the columnar void, below the columnar void, or intermediate the ends of the columnar void. The expanded or fragmented shale has a low average void volume. The void volume of the fragmented shale increases at the bottom of the in situ retort. In one embodiment the higher void volume is obtained since the ratio of the cross-sectional area of the columnar void to the horizontal cross-sectional area of the retort is decreased near the bottom. Backfilling part of a void with fragmented shale prior to explosive expansion provides a high void volume in another embodiment. In an embodiment with a room at the bottom of the columnar void, shale in one region can expand downwardly toward the room as well as toward the columnar void and hence has a higher void volume than a region where shale expands only toward the columnar void.