Process for use in blasting in situ retorts and the like

A process for use in forming an upright, modified in situ, oil shale retort, comprising the steps of:

• (a) excavating a generally horizontal mine in a subterranean formation of oil shale at a depth which is to generally coincide with the bottom of the retort;
• (b) drilling a substantially vertical blast hole in said subterranean formation of oil shale at a sufficient depth to communicate with said mine;
• (c) providing an open-ended tubular canister having a diameter slightly smaller than said blast hole;
• (d) casting a concrete disc about a drainpipe so that said drainpipe extends through said disc and upwardly above said disc, said concrete disc being cast with a diameter slightly smaller than said canister;
• (e) placing an expandable bag in said canister upon said disc, pouring a cementatious slurry into said bag, and substantially supporting said bag of cementatious slurry with said disc;
• (f) lowering said canister containing said bag of cementatious slurry on said disc, to a desired depth in said blast hole;
• (g) expanding said bag of cementatious slurry against the walls of said blast hole by dropping said disc and said bag to a preselected distance below said canister, so that the level of cementatious slurry in said bag falls below the top of said drainpipe;
• (h) allowing said cementatious slurry in said bag to generally conform to and set against said walls of said blast hole in said subterranean formation of oil shale to form a concrete plug substantially across said blast hole, with said drainpipe extending upwardly through said plug for permitting drainage of water through said plug;
• (i) setting an explosive charge on said concrete plug;
• (j) detonating said explosive charge to blast and explosively rubblize said oil shale into said mine to form at least part of a generally upright, modified in situ retort;
• and
• (k) repeating steps (d) through (j) at progressively higher levels in said blast hole until the entire retort is explosively formed and the said oil shale in said retort is rubblized.