Situ retort with high grade fragmented oil shale zone adjacent the lower boundary

摘要

An in situ oil shale retort is formed in a subterranean formation containing oil shale. Such an in situ oil shale retort contains a fragmented permeable mass of formation particles containing oil shale including a lower moiety and an upper moiety of said fragmented mass. The fragmented permeable mass of formation particles has top, bottom and side boundaries. A first portion of the formation is excavated from within the boundaries of the fragmented mass being formed to form a void. A second portion of the formation is excavated from within the boundaries of the fragmented mass being formed to form at least one additional void in communication with the first void and leaving a third portion to be expanded toward such an additional void. Fragmented particles from the excavation of such an additional void are deposited in the first void to provide a lower moiety of the fragmented permeable mass of formation particles. The third portion of the formation is explosively expanded toward such an additional void to provide an upper moiety of the fragmented permeable mass of formation particles. A retorting zone is passed through the upper and lower moieties of the fragmented mass for recovering liquid and gaseous products including shale oil.