Dynamic assessment of organic carbon content and hydrocarbon generation and expulsion efficiency in source rocks

The relationship of the yields and efficiencies of oil generation and expulsion with total organic carbon content (TOC) was analyzed based on thermal simulations of typical natural marine source rocks and artificial source rocks. (1) The simulation results show a positive linear correlation between the yields of oil generation and expulsion and TOC, and a nonlinear correlation between the efficiencies of oil generation and expulsion and TOC. The correlation coefficients are related to kerogen type, lithology and thermal maturity. (2) Source rocks with high TOC contents (generally over 2.0%) always have higher yields and efficiencies of oil generation and expulsion throughout the simulation experiments, when compared to source rocks with middle (0.5%-2.0%) and low (less than 0.5%) TOC contents, which indicates that only source rocks with high TOC contents have the capacity to form large oil fields. Source rocks with low TOC content do not generate large hydrocarbon accumulations even if they are very thick. (3) In the process of geological evolution, the TOC content and the capability of hydrocarbon generation and expulsion for source rocks are changing continuously. Correspondingly, the evaluations of source rock and resources should be dynamic.