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Abstract

A method is provided for operating an in situ oil shale retort in a subterranean formation containing oil shale. The retort contains a fragmented permeable mass of formation particles containing oil shale, within top, bottom and side boundaries of unfragmented formation. A drift is in communication with a lower region of the fragmented mass for withdrawal of liquid products of retorting and an off-gas comprising gaseous products of retorting. A gas-sealing bulkhead is placed across the product withdrawal drift and a water spray is installed in the drift through the bulkhead. An upper region of the fragmented mass is ignited for establishing a combustion zone therein. A retort inlet mixture comprising an oxygen-supplying gas is introduced into the top of the fragmented mass for advancing the combustion zone downwardly through it to thereby establish a retorting zone on the advancing side of the combustion zone for producing the liquid and gaseous products. A retort off-gas comprising such gaseous products is withdrawn from the retort through the product withdrawal drift. The temperature of the off-gas is monitored in the vicinity of the gas-sealing bulkhead. When the off-gas temperature reaches a selected value below the design temperature of the bulkhead, sufficient water is sprayed into the off-gas stream in the drift to maintain the temperature of the off-gas in the vicinity of the bulkhead below its design temperature.

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First Claim