Comparison of Core and Log Carbon/Oxygen Ratios in South Belridge Diatomite


Richard M. Ostermeier,
Shell Development Company

SPWLA 34th Annual Logging Symposium, June 13-16, 1993



Core derived carbon/oxygen ratios (COR) are compared to log measurements made both open and cased hole in the Diatomite Formation of South Belridge Field, California. The log measurements were made with Schlumberger’s Gamma Spectroscopy Tool (GST) operated in inelastic mode and logged continuously at 60 feet per hour. At a 2.5 foot vertical resolution this provides a COR precision of 0.016 which translates roughly into an oil saturation precision of about 5 percent, all at the 68 percent confidence level. Core porosities and fluid saturations, corrected for in situ conditions, were used in the comparisons, along with formation matrix and fluid compositions.