The accuracy of density measurements obtained with gamma-gamma logging tools is of utmost importance information evaluation. Quantification of this accuracy allows the density measurement to be used with increased confidence and enhanced interpretive sophistication. For this reason, the accuracy of the gamma-gamma Z-Densilog instrument is examined based on test pit measurements and field data. The test pit data base contains in excess of 1000 different entries. It includes measurements carried out with 15different Z-Densilog instruments in various lithologies, in boreholes of different sizes filled with either air, water or mud, and in a wide array of mud cake types and thicknesses. The mud cake array is comprised of 1/4-, 1/2-, and 3/4-inch thick mud cakes of light mud, light barite, heavy barite, and hematite muds. In addition to these test pit measurements, field data are presented for wells where both complete logging and full-core information are available. In this manner, the accuracy of the Z-Densilog instrument is assayed under realistic, routine-type field conditions, as well as in the more ideal environment prevailing in test pits.

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