Unfocused gamma ray density logging - PetroWiki

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Unfocused gamma-ray density logging is also sometimes called gravel-pack density logging. While focused density logs assess wellbore fluids, the unfocused density logs look at the fluid below the screen or in the gravel pack. The unfocused gamma ray density logger incorporates a compacted slug of Cesium-137 near the bottom of the device. A counter determines the counts/min (intensity) of the gamma rays; this information is transmitted through the logging cable to the surface, where the count rate is plotted against depth. From the Cesium-137 source, some of the gamma rays are transmitted to the detector through the tool body ("direct" transmission), some by the wellbore fluid between the tool and the casing ("indirect" transmission), and some through the material outside the casing (also "indirect" transmission).