Explosive expansion of formation in lifts for forming an in situ oil shale retort

摘要: An in situ oil shale retort is formed by excavating a lower level void adjacent the bottom boundary of site subterranean formation, leaving zone unfragmented formation within side boundaries overlying void. At least portion explosively expanded downwardly towards plurality lifts. Vertical columnar explosive charges are placed each lift and detonated single round with time delay between successive lifts sufficient for first to move out way not interfere initial expansion next lift. Preferably, second after detonation range from about five thirty milliseconds per foot burden distance When plural above expanded, it preferred that delays progressively increase up.