Two-stage oil shale retorting process and disposal of spent oil shale

Abstract

Formation is excavated from an in situ oil shale retort site for forming at least one void within the retort site, leaving at least one remaining zone of unfragmented formation within the retort site adjacent such a void. The remaining zone is explosively expanded toward such a void for forming a fragmented permeable mass of formation particles containing oil shale in an in situ oil shale retort. Oil shale in the in situ retort is retorted to produce liquid and gaseous products, leaving a mass of spent oil shale particles in the in situ retort. Oil shale particles excavated from the in situ retort site are separately retorted, such as in a surface retorting operation, producing liquid and gaseous products and spent surface retorted oil shale particles. The spent surface retorted particles are disposed of by forming an aqueous slurry of the particles, and pumping the slurry into a spent in situ retort. In one embodiment, the aqueous slurry is introduced into a hot lower portion of the spent retort where contact with hot spent oil shale particles generates steam which, in turn, is withdrawn from the spent retort in usable form. In another embodiment, water from the aqueous slurry introduced into a spent in situ retort collects at a level within the retort. The water can be recovered by drilling a drainage hole upwardly from a lower level drift into the level within the spent retort where the water collects and draining the water through the drainage hole to the lower level drift for recovery.