风化作用对高演化黑色岩系有机质影响因素分析——以塔里木盆地柯坪地区玉尔吐斯组为例

Weathering effects on high-maturity organic matter in a black rock series:A case study of the Yuertusi Formation in Kalpin area,Tarim Basin

通过对塔里木盆地柯坪地区东二沟剖面下寒武统玉尔吐斯组不同风化程度岩石样品的有机地球化学、扫描电镜和能谱分析,探讨了风化作用对岩石有机质特征的影响。结果表明:风化作用越强,有机碳丰度越低、生烃潜力越差,黑色页岩样品中的有机碳和氯仿沥青"A"含量的最大风化丢失量在95%以上,硅质岩风化丢失量小于50%。气候、暴露地表时间等因素是岩石发生风化作用的主要外部因素;矿物组成和有机质赋存方式是影响风化程度的重要内部因素,有机质以游离态形式赋存在高演化页岩中更易发生化学风化而丢失。因此,不能仅根据野外剖面烃源岩样品现今地化特征来进行烃源岩评价和油气资源量评价,而应考虑风化作用的影响。

The effects of weathering on organic matter of black shales has been studied using organic geochemistry,scanning electron microscopy and X-ray fluorescence energy spectrum. The black shales were collected from the Lower Cambrian Yuertusi Formation along Dong＇ergou section in Kalpin area,Tarim Basin. As weathering increased,organic abundance became much smaller,and hydrocarbon generation potential became poorer. The maximum weathering losses of organic matter and chloroform bitumen ＂A＂were more than 95% in black shales and less than 50% in siliceous rocks,indicating that siliceous rocks were more resistant to weathering. Climate and surface exposure time were the main causes for rock weathering. Mineral composition and organic matter occurrence determined weathering degree. Free organic matter occurring in over-mature shales was easily lost through weathering. In petroleum evaluation,it is important to not only study the present geochemical features of source rocks,but also to considerweathering effects.