Quantification of Total Organic Carbon (TOC) content in a source rock is essential to assess the development potential of an unconventional reservoir. Although TOC value greater than 1.0–1.5 wt. % is considered as an indicator of a good quality source rock, this information alone is not sufficient. Adequate convertible in-situ organic carbon content is required to generate hydrocarbons that would be commercially producible. The generation index of hydrocarbon is obtained by additional screening processes to determine the level of maturity (LOM) and organic matter type. Together, these processes give further assessment of the potentiality of an unconventional reservoir.
Utilization of high resolution log derived data of the reservoir can contribute to overcome most of the constraints of core sampling and provide real time in-situ reservoir characterization. TOC in potential source rocks significantly influences the response of the well-logs collected for the characterization and monitoring purposes. Over the last two decades, several methods/models have been developed to quantify TOC from logs. They are based on measurements of gamma ray, resistivity, density, sonic, neutron, as well as nuclear magnetic resonance (NMR) tools. Several of the well-log derived TOC quantification methods are indirect measurements and require empirical correlations of the log data and geochemical characteristics of the cores while other methods are based on direct measurements from the logs. The accuracy of empirical correlations and quantification methods depends on several factors including the specific characteristics of the organic-rich shale source rock. In this paper, various TOC quantification methods utilizing well-log data are introduced using Eagle Ford shale source rock data. An evaluation and comparison of these methods have been made.
