Estimation on organic carbon content of source rocks by logging evaluation method as exemplified by those of the 4th and 3rd members of the Shahejie Formation in western sag of the Liaohe Oilfield

One of the most important tasks of evaluating natural resources of petroliferous basins is to determine the organic matter abundance of source rocks in the basin. The usual method for assessing the organic carbon content of source rocks is based on laboratory analyses. There is a deviation in calculating organic carbon content due to the heterogeneous distribution of organic matter and the artificial factors when sampling. According to the continuous characteristics of information logging, the conventional logging curves (mainly acoustics and resistivity, etc.) were calibrated with the organic carbon experimental data of cores, cuttings or sidewall cores. The organic carbon content of source rocks of the 4^th (Es₄) and 3^rd (Es₃) members of the Shahejie Formation in western sag in the Liaohe depression was estimated directly by a great amount of continuous data including resistivity and acoustic logging, etc. Comparison between the results from computer processing and lab analysis of logging data shows that the organic carbon contents derived from the computer processing of logging data have the same reliability and accuracy as the lab analysis results. The present data show that this method is suitable to evaluate the source rocks of western sag in the Liaohe depression and has great potential in evaluating natural resources of sedimentary basins in the future. On the basis of logging data of source rocks, experimental data and existing geochemical analyses of the Liaohe Oilfield, the corresponding total organic carbon (TOC) isograms of source rocks were plotted. The source rocks of Es₄ and Es₃ of the Shahejie Formation are thought to be beneficial to hydrocarbon accumulation due to the high TOC.