开放、封闭两种体系对比模拟确定深层烃源岩成烃机制——以东营凹陷沙四段烃源岩为例

为研究济阳坳陷南部东营凹陷不同演化阶段的成烃特征,选取古近系沙河街组四段(Es4)烃源岩,进行开放、封闭两种体系程序升温条件下的生排烃热模拟实验,对比了组分的产率及相互转化关系。模拟样品来自该区南部斜坡带的官107井Es4上段,其有机碳含量位于该套烃源岩频率分布统计的主峰,具有广泛的代表性。实验结果表明:①干酪根直接降解以生成重质油和气态烃为主,轻质油大多来源于重质油的二次裂解;②烃源岩在形成轻质油时即可以大规模排出,现有的动力学条件下难以造成油的裂解生气;③烃源岩形成大分子重质油是生烃开始的标志,而进一步降解形成轻质油则是烃源岩排烃开始的标志。实验结果从成烃机制上解释了东营凹陷凝析油和天然气主要来源。

A study of hydrocarbon generation mechanism of deep source rocks based on the comparison of experimental simulations in open and closed systems: A case study from the Es4 member in the Dongying Sag

In order to study the characteristics of hydrocarbon generation at different maturity stages of source rocks in the Dongying Sag, southern Jiyang Depression, we performed experimental simulations of hydrocarbon generation and expulsion in a closed and an open system at rising temperatures by using source rock samples from the 4th member of the Paleogene Shahejie Formation (Es4).  Their yields and reciprocal transformation of compositions were compared. The samples were acquired from the upper Es4 in the well Guan 107 in the southern slope of the Dongying Sag. Their TOC content occurs at the main peak of the frequency distribution from the TOC statistics of this set of source rocks, and thus is representative. The following conclusions were obtained. ①The products of direct kerogen degradation are mainly heavy oil and gaseous hydrocarbons, while light hydrocarbons mainly comes from the secondary cracking of heavy oil; ②Light oil can be largely expelled immediately after they are generated by source rocks, and thus it is difficult to crack the light oil into gas under existing kinetic conditions; ③The appearance of macromolecular heavy oil from source rocks marks the beginning of hydrocarbon generation, while the appearance of light oil from further degradation of the heavy oil marks the initiation of hydrocarbon expulsion. The experimental results can be used to explain the origins of condensate oil and gas in the Dongying Sag.