东营凹陷牛38井沙河街组烃源岩生排烃评价

AN INVESTIGATION ON GENERATION AND EXPULSION OF HYDROCARBON FROM SOURCE ROCKS OF THE SHAHEJIE FORMATION IN THE WELL NIU-38, DONGYING DEPRESSION

东营凹陷牛 38井沙河街组三段烃源岩从沙三下亚段向沙三中 上亚段为一从高水位深湖相向低水位前三角洲相发展的沉积旋回 ,该沉积环境控制从下向上发育不同类型的有机质。相应地 ,该段烃源岩品质从下向上变差 ,其中沙三中亚段上部及沙三中亚段中部烃源岩产烃能力小 ,沙三下亚段烃源岩整体品质好 ,局部存在优质烃源岩。其优劣性体现了在该段烃源岩中 ,Ⅰ型干酪根具有高的生产力 ,而Ⅲ型、Ⅱ2 型干酪根生烃潜力很低 ,基本为无效有机质。计算结果显示不同数据点的烃源岩单位质量原始生烃潜量可相差 3个数量级 ,体现了烃源岩存在强烈的非均质性。有机碳的非均质性分布为其提供了物质基础 ,而湖盆的旋回式沉积及湖平面的波动性变化是其内在原因。同时 ,本文也提供一种计算生排烃量的新方法 ,结果表明该方法较为有效可行。

The source rocks of the lower part of Member 3, Shahejie Formation from the Well Niu 38 in the Dongying Depression, with a deep water lake facies, was deposited in a highstand system tract. Up to the middle part of Member 3 of the Shahejie Formation, the sedimentary facies changed to be a prodelta facies in a lowstand system tract. In such a sedimentary environment, different kerogen types in the source rocks were formed from the lower part to the middle part of the member. The source rocks in the lower part were rich in high contents of organic matter and type Ⅰ of kerogen, which were believed as effective source rocks (high generation and expulsion of hydrocarbons) in the depression. The source rocks in the middle part were in low contents of organic matter and type Ⅱ 2 or type Ⅲ kerogen, regarded as ineffective ones. Although the source rocks in the lower part were highly heterogeneous in their organic matter contents and kerogen types, their capacities of hydrocarbon generation and expulsion might be quite different: the higher TOC and the better type of kerogen, the more quantity of hydrocarbons generated and expulted from the source rocks. A new method for predicting the quantities of the hydrocarbon generation and expulsion was presented in this paper. The prediction results showed that the quantities of hydrocarbon generation were differentiated in three decimal scales, which were corresponding to strong heterogeneity in the source rocks. The heterogeneity was believed as a result of the lacustrine cyclothemic sedimentation and the lake level fluctuation.