An Improved Residual Oil Evaluating Method Using Carbon/Oxygen Spectroscopy Logging in Lime-Bearing Shaly Sand Formation

Summary By measuring the carbon-characteristic gamma-ray counts and oxygen-characteristic gamma-ray counts in the inelastic spectrum, the carbon-oxygen log can accurately reflect the formation’s oil saturation. Because the content of carbon and oxygen in the formation has a direct impact on the carbon-oxygen log, in mixed lithology formation, the carbon-oxygen (C/O) is different due to the change in the proportion of carbon and oxygen elements. The correction method considers that the influence of different formation lithology on it is single. Through practical application, the interpretation model will have large errors in different lithological strata. In this paper, the carbon-oxygen (C/O) of sandstone formations containing chlorite and calcium carbonate is simulated, and the variation law of the carbon-oxygen (C/O) under different lithology and pore conditions is obtained. Through analysis, an improved interpretation model of carbon-oxygen (C/O) has been built. By comparing the results of the conventional interpretation model and the improved interpretation model under different gray matter and different shale content formation conditions, it is proved that the improved interpretation model can more accurately reflect the oil saturation of the sandstone formation which content chlorite and calcium carbonate. The improved interpretation model also improves the interpretation of low porosity oil saturation.