Method for controlling void fraction distribution in an in situ oil shale retort

摘要

A method for forming an in situ oil shale retort in a retort site in a subterranean formation is provided. The in situ oil shale retort contains a fragmented permeable mass of oil shale particles formed within top, bottom, and side boundaries of the retort site. At least one void is excavated in the subterranean formation within the boundaries of the retort site, while a zone of unfragmented formation is left within the boundaries of the retort site adjacent such a void. An inlet is formed in a zone of the retort adjacent the intersection of a first side boundary of the retort site and the top boundary of the retort site and an outlet is formed in a zone of the retort adjacent the intersection of a second side boundary of the retort site and the bottom boundary of the retort site. The second side boundary is on the opposite side of the retort site from the first side boundary. An array of explosive charges is formed in the zone of unfragmented formation and the charges are detonated for explosively expanding the zone of formation toward the void for forming the fragmented mass within the boundaries of the retort site. The explosive charge pattern and detonation sequence are provided so that the fragmented mass formed has a lower void fraction in a center region of the retort and a higher void fraction in regions of the retort adjacent the side boundaries.