TOC changes in the process of thermal evolution of source rock and its controls

查看全文 作　　者：ZHONG Ningning1, LU Shuangfang2, HUANG Zhilong1, ZHANG Yousheng1, XUE Haitao2 & PAN Changchun3 1. The Key Lab of Petroleum Accumulation Mechanism of State Educational Ministry at University of Petroleum, Beijing 102249, China;2. Exploration Geoscience Department of Daqing Petroleum Institute, Daqing 163000, China;3. Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China 出　　处：《Science China Earth Sciences》索引2004年第47卷第z2期,共9页 摘　　要：Through geological observation, simulation in laboratory and numerical modeling, the factors that control the changes in total organic content (TOC) of source rock have been studied. When the formula DTOC=(TOC0-TOC)/TOC0 (original organic carbon content in the rock) is used to measure the TOC (total organic carbon content) changes in the source rock through geological time, the degrees and directions of such changes are determined by losses and relative amounts both of organic and inorganic matter in the source rock. The DTOC equa-tion, which is used to calculate the loss rate in the process of maturation for the source rock, is therefore obtained by analyzing the mass balance relations. For a certain type of source rock with a certain maturation history, the changes of its TOC respond only to the rates of hydrocarbon generation and expulsion. In actual cases of geological entities, DTOC generally ranges from -0.05 to 0.2, while the calculated reconversion coefficient (k) for organic carbon content remains between 0.90 and 1.25. Only in an ideal situation where there are extremely high rates of hydrocarbon generation and expulsion can the DTOC value experience significant changes, with k reaching up to 2.5. It is concluded, therefore, that the cri-terion for carbonates source rock assessment, based on reconverting the TOC to the value of its original state, may have overestimated the course of the carbon-reduction, which is likely in many cases to make a poor source rock sound better. 关 键 词：source rock appraisal, carbonates, low limit of organic matter abundance, rate of HYDROCARBON generation and expulsion, TOC value.