东营凹陷烃源岩排烃的地质地球化学特征

Geological and geochemical characteristics of hydrocarbon-expulsion from source rocks in Dongying Depression

利用地质地球化学信息研究烃源岩的排烃行为是一种重要而有效的手段,东营凹陷较为丰富的地质地球化学信息对研究烃源岩的排烃行为具有重要的意义。东营凹陷烃源岩排烃的地质地球化学特征显示其排烃行为存在较强的非均质性:单层泥岩边缘地区排烃效率高,内部排烃效率相对较低,这种现象在厚层泥岩中(大于30m)表现更为明显,其中通常存在一定的相对“滞排区”;不同的压实阶段,排烃效率也不相同,快速压实带较缓慢压实带及稳定压实带排烃效率稍高。东营凹陷存在两类超压体系:一类是相对开放性质的,幕式排烃是其重要的排烃方式之一,其排烃效率较常压系统高,排烃效率平均在50%左右(常压体系排烃效率一般在40%左右);另一类是相对封闭性的,为良好的超压“封存箱”,其排烃效率较常压系统低,排烃效率平均在20%左右,其地质地球化学行为显示一定的滞排特征,排烃行为不明显。研究结果认为压实不均衡是东营凹陷形成沙三中异常高压的主要原因,生烃作用是其形成沙四上超压的主要机制,而沙三下同时具备压实不均衡及生烃作用的双向增压效应。

Using geochemical information to study hydrocarbon-expulsion beha vi or is an important and effective measure. The abundance of the geochemical infor mation in Dongying Depression has great significance in studying hydrocarbon-ex pulsion behavior. The geochemical characteristics indicate that the hydrocarbon-expulsion in Dongying Depression had strong heterogeneity: the efficiency of h ydrocarbon-expulsion in the edge of mud is much higher than that in the inner, which is more obvious in the thick mud (thicker than 30 m), and there are stagna nt-expulsion zones in the thick mud commonly; in different compaction phases th e efficiency of hydrocarbon-expulsion has discrepancies: the efficiency in the rapid-compaction phase is higher than that in the slow-compaction phase and th e stabilized-compaction phase. There are two types of overpressured systems: th e open and the relatively closed. The episodic hydrocarbon-expulsion is an impo rtant hydrocarbon-expulsion behavior in the open system, and its efficiency (50 %in average) is 40%higher than that in normal pressure system. The closed syst em is overpressure compartment and its efficiency of hydrocarbon-expulsion is l ow (20%in average), and the characteristics of geochemistry demonstrate the sta gnant-expulsion. The disequilibrium compaction is considered to be the primary reason for the overpressure formation in the middle part of the Third Member of Shahejie Formation, hydrocarbon- generation is the key factor for the overpressure in the upper part of the Fou rth Member of Shahejie Formation, and the overpressure in the lower part of the Third Member of Shahejie Formation is a result of the both factors.