"The hot-film sensor technique of fluid flow measurement has been developed and is being applied to well logging for evaluating in situ fracturing and retorting experiments in the Green River Formation oil shale of Wyoming. Natural, hydraulic, and/or explosive fractures in oil shale have been evaluated by air injection and production flow logging techniques. Fracture depths, types (horizontal or vertical), and flow characteristics within a system of wells designed for an in situ combustion test have been determined before and after fracturing. Gas flow profiles were also determined before ignition, during combustion, and after combustion termination."