Gamma-gamma logging in the lithology identification of Cretaceous at the southwestern margin of Ordos basin
In recent years,breakthroughs have been made in searching for Cretaceous sandstone type uranium deposit in the southwestern margin of Ordos basin.Due to the special depositional environment of Cretaceous in the study area,non-conducting gypsum-type minerals have been widely developed in the mudstones and siltstones of Huanhe formation,which makes it difficult to accurately interprete the lithology by the conventional logging curves.In order to accurately distinguish the difference between non-permeable(mudstone and siltstone)and permeable rocks,the physical parameters of the rocks in the study area were measured,it was found that the density of mudstone and siltstone is greater than that of sandstone.Gamma-gamma logging is widely used in sandstone-type uranium geophysical logging to calculate the density of strata,and the parameters of the long and short source distance logging are the parameters of its intermediate measurements.In order to better play its role,the principle of gamma-gamma logging was clarified,combined with the fitting relationship between the natural gamma and the long and short source distances,the short source distance logging curves with strong anti-interference were preferred,and the correction method of eliminating the influence of the radioactive layer by eliminating the natural gamma curves from the long and short source distances was proposed.The short source distance curve of gamma-gamma logging can better explain the Cretaceous lithology of the study area,which is of reference significance for the geophysical logging of Cretaceous sandstone uranium mines in the southwestern margin of the Ordos basin.
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