Method of rubbling a pillar

摘要

Shale oil is recovered from a subterranean formation containing oil shale by excavating formation to form at least one void, leaving zones of unfragmented formation above and below each void and leaving at least one support pillar of unfragmented formation in the void. Explosive is placed in at least one of the zones of unfragmented formation for explosively expanding the zone of unfragmented formation toward the void. The pillar is prepared for explosive expansion by drilling substantially horizontal blastholes in the pillar and by loading explosive charges into the blastholes. Thereafter, the explosive charges are detonated in a single round of explosions for explosively expanding the pillar toward the void. At least one of the zones of unfragmented formation is then expanded toward the void to form a fragmented permeable mass of formation particles containing oil shale in an in situ oil shale retort. Gas is introduced into the fragmented permeable mass for establishing a retorting zone in the fragmented mass wherein oil shale is retorted to produce gaseous and liquid products and for advancing a retorting zone through the fragmented mass. Gaseous and liquid products are withdrawn from the retort.