Occidental Oil Shale, Inc.

Rex T Ellington

An in situ oil shale retort containing a fragmented permeable mass of formation particles having a generally uniform permeability across horizontal cross-sections of the retort is provided. To form the retort, underground formation is explosively expanded by explosive charges placed in a selected pattern. The combination of spacing distance and powder factor of central explosive charges is selected to produce a center portion of the fragmented permeable mass having a first average particle size (d.sub.1) and a first average void fraction (e.sub.1). The powder factor for perimeter explosive charges and the spacing distance between central charges and adjacent perimeter charges are selected to produce a perimeter portion of the fragmented permeable mass having a second particle size (d.sub.2) and a second void fraction (e.sub.2). The second average particle size (d.sub.2) and the second average void fraction (e.sub.2) are related to the first average particle size (d.sub.1) and the first average void fraction (e.sub.1) so that the relation ##EQU1## is in the range of from about 0.33 to 3.0.

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Norman, OK, United States of America

Rex T Ellington