"A feasibility study on the use of tracer pulses to assess the degree of fracturing in an undenground formation is presented. The study consisted of the following three phases: (1) a laboratory study on sand packs and open tubes, which developed a correlation between dispersion of the pulse and size of the flow channels; (2) a test on a retort, 11 ft in dia and 45 ft high, packed with shale rubble. Void volume was measured, but evaluation of channel size was not possible because of interference from the space unoccupied by the matrix; (3) a field test on an explosively fractured shale formation. Pressure, flow, and transit time led to qualitative estimates of fracture pattern, but quantitative detection of dispersion in the formation was overwhelmed by dispersion effects in the well. (auth)"