| abstract |
The locus of a processing zone advancing through a fragmented permeable mass of particles in an in situ oil shale retort in a subterranean formation containing oil shale is determined by withdrawing a sample of gas passing through the retort through a channel through unfragmented formation and in fluid communication with the retort, and analyzing the composition of withdrawn gas. The channel can be artificially formed such as by hydraulic fracturing of unfragmented formation, or can be a naturally occurring permeable layer such as a tuff bed in the formation containing oil shale. |