Carbon/oxygen logging is used to determine oil saturation in cased holes without knowing formation water salinity.

When the carbon/oxygen tool is used alone, in non-extreme conditions, the accuracy of the interpreted So is calculated to be ±23 saturation units at 20% porosity. The uncertainty increases rapidly as porosity decreases.

Field examples illustrate its potential value and practical problems created by the measurement statistics, borehole fluid changes and remaining mud filtrate.

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