Cratering in the deep cratering region to form an in situ oil shale retort

摘要

An in situ oil shale retort in a subterranean formation contains a fragmented permeable mass of formation particles. Such a fragmented mass is formed by excavating a horizontally extending void within the boundaries of the retort, leaving a zone of unfragmented formation above and/or below such a void. A plurality of vertical blasting holes are drilled in such a zone and loaded with explosive charges for forming an array of explosive charges sufficiently close together to interact and fragment formation substantially to a plane at the ends of the charges remote from the void. The scaled depth of burial of such an array is in the range of from about 6 to 12 mm/cal.sup.1/3. The explosive charges are detonated in a single round for expanding such a zone towards the void for forming the fragmented mass of particles in the retort.