Gamma ray spectral data assists in complex formation evaluation

Recent experiences with gamma ray spectral logging in open hole and cased boreholes illustrate its broad scope of problem-solving capability in formation evaluation. Application of such gamma ray spectral data may be made either qualitatively, such as in detailed stratigraphic correlation, recognition of rock types of different facies, high permeability and fracture identification, location of watered-out intervals, etc., or on a quantitative basis to determine reservoir shaliness, source rock potential of argillaceous formations, potash concentration, etc. The present discussion focuses on the basic measuring principles and illustrates interpretive experiences in open and cased wellbores penetrating clastic and carbonate reservoir rocks, argillaceous formations, evaporite zones, igneous rocks, and mineral deposits such as coal, uranium, and potash