Abstract: The strata in Tuha basin are rich in minerals with high radioactivity, and their CR values are close to or higher than that of surrounding shale, thus resulting in that the shale content computation, lithologic identfication and interpretation can not be made by the traditional logging interpretation method for quartz sandstone. This paper presents some methods for computing the shale content and lithological analysis of shale-sand strata, which include the CNLflective porosity diferential method and the CNLCDL crossplot. The study also proposed the mechanism of efect of shale on sand conductivity and its shale-correction methods for sandstone reservoir with different sand-shale resistivity propertics. These methods have been well applied in the logging and geologic evaluation of high radioactity sand shale strata in Tuha basin and could be as a guide for simi lar strata evaluation study of other areas.

Key words: Tuha basin, radioactivity, sandstone, lithologic intepretation, shale content, correction