Standard Related to TOC Classification Evaluation of Carbonate Oil Source Rocks

Key words: 
• carbonate rocks /
• oil source rock /
• organic matter abundance /
• material balance principle /
• grading evaluation

Abstract: The study of evaluation criterion of carbonate oil source rocks is a basic research subject which has significant influences on exploratory decision and has important theoretical and practical value. In this paper, calculations have been performed about amount of oil generation, remained oil of unit area carbonate rocks at different geologic conditions by the parameters (strata, geohistory, and thermal history) in Tarim basin, Bohai Bay basin, and Ordos basin. According to the material balance principle, oilexpulsion amount has been worked out (oilexpulsion amount = amount of oilgeneration － amount of remained oil). We regard it as an index to present the classification evaluation of oil source rocks, figure out the corresponding organic enrichment, and establish the classification evaluation tables of carbonate oil source rocks in Tarim basin, Bohai Bay basin, and Ordos basin. Based on the simulating calculation, find that TOC industrial threshold value (TOCgy ) decreases with the increasing source rocks thickness; decreases at first and then increases with the increasing maturity and decreases with the better type of organic matter. Investigations indicate that the evaluation Standard of carbonate oil source rocks have great variance with the differences of geologic conditions. Based on the analysis, we induce the threshold values, TOC are "0.25, 0.5, 0.8, 1.5", which correspond with the classes, "non, ineffective, poor, moderate and good source rocks" of mature carbonate oil source rocks whose organic matter type is Ⅱ.