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Gamma logs of measured surface sections provide an excellent correlation tool in wildcat areas where well control is sparse and outcrops are abundant. Gamma logs of measured surface sections can be correlated with gamma logs of any nearby wells that have penetrated the same strata. Subtle changes in lithology that may have been missed during routine section measuring are detected by surface gamma measurements. Furthermore, gamma measurements over covered intervals may give clues to the nature of the buried lithology.
A portable scintillation counter is used to take gamma measurements. These measurements are recorded along with lithologic descriptions. Five-foot-intervals provide the best results.
Surface gamma logs are successfully used in correlating members of the Jurassic Twin Creek Limestone from wells in the northern Utah Overthrust to outcrops in north-central Utah. They are also useful in correlating upper Paleozoic rocks in the Basin and Range province.
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