应用岩石热解数据S2-TOC相关图进行烃源岩评价

应用岩石热解数据评价烃源岩的传统方法具有一定的局限性。由于矿物基质的吸附或“死碳”的影响，有机质类型的“范氏图解”往往夸大烃源岩有机质类型的非均质性。对松辽盆地上白垩统不同有机质丰度和有机质类型的烃源岩生烃动力学研究表明，它们具有相似的生烃动力学特征，说明尽管有机质丰度存在较强的非均质性，但其有效源岩类型（区别于应用范氏图划分的有机质类型）是一致的。这些烃源岩的岩石裂解烃（S2）与有机质丰度（TOC）的相关系数很高，与生烃动力学的分析结果一致，表明应用S2-TOC相关图划分烃源岩的有机质类型可以更真实地反映烃源岩的有效源岩类型，S2-TOC相关图是评价烃源岩有效源岩类型的有效手段。过去岩石热解数据用于反映烃源岩成熟度的主要指标是tmax，tmax对于偏Ⅱ／Ⅲ型的烃源岩比较适用，而对于Ⅰ型烃源岩，由于生油窗内变化不明显，tmax不能完全反映有机质的成熟过程；而且tmax也受运移油等其他因素影响。不同成熟度的烃源岩的S2-TOC图分析结果显示，随着成熟度的增加，S2-TOC的回归斜率和TOC逐渐减小；利用不同成熟度的烃源岩建立的S2-TOC图可用于评价烃源岩的成熟度。松辽盆地不同沉积相中烃源岩的S2-TOC相关图的特征表明。只要有有利的有机质保存条件，各沉积相下均可发育优质的烃源岩；S2-TOC相关图可以反映烃源岩形成的沉积环境和有机质保存条件。

Source rock evaluation using the S2-TOC plot from Rock-Eval pyrolysis

The application of Rock-Eval data into source rock evaluation has some limitations. For example, the modified Van Krevelen diagram for the identification of organic matter type is used to overestimate the heterogeneity of organic matter type in a source rock due to adsorption of mineral matrix or/and influence of ＂dead carbon＂ Hydrocarbon generation kinetic analysis of the Upper Cretaceous source rocks with different types and abundance of organic matter in the Songliao Basin shows the presence of a similar kinetics, indicating that the effective organic matter types are similar for these source rocks although their concentrations of organic matter are distinct. Good correlation between pyrolytic hydrocarbon yield （S2） and total organic carbon （TOC） of these source rocks is in accordance with the result of hydrocarbon generation kinetics, suggesting that the plot of S2 vs. TOC can be used to determine the effective organic matter type of source rocks, tin.,, as a main maturity parameter from Rock-Eval pyrolysis, is preferred by type Ⅱ/Ⅲ organic matter. For type I organic matter, however, its variation is little within the ＂oil window＂ and can not completely reflect the maturity process of this type of organic matter. In addition, tmax is probably affected by other factors, such as migrated oil. The S2-TOC plots of different maturity source rocks show that the slope of linear regression of Rock-Eval S2 vs. TOC decreases with maturity increasing, indicating that the S2-TOC plot can be used to evaluate the deposition environments in the Songliao maturity of source rock. S2 vs. TOC plots of the source rocks with different Basin present that excellent source rocks can develop in various deposition environments if a good organic preservation condition is provided. Therefore, plots of S2 vs. TOC can also reflect depositional environments of source rocks and preservation conditions of organic matter.