Pfa an and Hafnian identities in shu e algebras

A retorting zone advances through a fragmented permeable mass of particles containing oil shale in an in situ oil shale retort in a subterranean formation containing oil shale. The fragmented mass comprises layers of formation particles of differing kerogen content corresponding to strata of differing kerogen content in the subterranean formation. The retorting zone advances in a direction substantially perpendicular to such layers in the fragmented mass. Kerogen in oil shale in the retorting zone is decomposed to produce gaseous and liquid products including shale oil, and shale oil is withdrawn from the fragmented mass. The rate of shale oil production in the retort depends upon th kerogen content of such a layer in such a fragmented mass through which the retorting zone advances. To determine the locus of the retorting zone with respect to such layers in the fragmented mass, formation is assayed for kerogen content for defining the locus of at least one such layer in the fragmented mass before retorting, and the rate of shale oil production from the retort is monitored. The locus of the combustion zone can be estimated from the locus of the retorting zone so determined.