Abstract: Total organic content(TOC)of organic rich shale is an important parameter in resource assessment.In order to predict the TOC of shales in the non-cored wells in the study area,this paper established a mathematical model of TOC for the target layer through logging interpretation.Based on an analysis of the relationship between the measured TOC of cores sampled from the Yanchang Fm in 20 wells and the corresponding logging parameters,we found that the measured TOC values are positively correlated with the logarithm of Rt and GR,but not insignificantly correlated with AC.Multivariate analysis method was used to establishe a mathematical model for predicting TOC of the Yanchang organic-rich shale with the logarithm of Rt and GR.Its application in the cored Liuping-177 well gave a mean error of 5.35% between the logging interpreted TOC and the measured TOC.The mathematical model was used in calculation of TOC of the Yanchang organic-rich shale in 46 non-cored wells.The spatial distribution of TOC of the Yanchang organic-rich shale in the study area was mapped based on these calculation results and the measured TOC of additional 20 cored wells.The TOC distribution is consistent with the distribution of sedimentary microfacies,verifying the reliability and effectiveness of this method.

Key words: resistivity, gamma ray, logging interpretation model, total organic carbon, shale gas, Ordos Basin