东营凹陷富有机质烃源岩顺层微裂隙的发育与油气运移

根据岩心观察，在东营凹陷沙河街组三段下亚段和沙河街组四段上亚段烃源岩中，发现大量顺层面分布的微裂隙，且大部分为亮晶方解石所充填。裂隙发育段在平面上的展布较广，在纵向上始于2900～3000m左右，与烃源岩成熟阶段对应。岩石学和有机地化研究表明，裂隙一般限于高有机质丰度、纹层理发育的页岩中，而有机质丰度较低、具块状层理的泥岩一般不发育，表现出较强的非均质性。裂隙发育与有机质丰度以及成熟度的关系表明，烃类生成是水平裂隙产生的主要原因。进入成熟阶段的富有机质烃源岩大量生烃，造成孔隙流体压力迅速上升，并最终导致顺层裂隙的产生。由于沙河街组三段下亚段和沙河街组四段上亚段以泥、页岩互层为特征，因而裂隙发育的非均质性造成裂隙发育段与裂隙不发育段的纵向叠置，并决定了其排烃过程以近似于三角洲前缘砂泥岩互层的排烃方式，从而一定程度提高了烃源岩的排烃速率和排烃效率。

Microfracture Occurrence and Its Significance to the Hydrocarbons Expulsion in Source Rocks with High Organic Matter Abundance, Dongying Depression

In the Dongying Depression, high abundance of parallel microfractures are found in the hydrocarbon source rocks of the upper unit of E 2-3 s 4 Member and the lower unit of E 2-3 s 3 Member. Most of the microfractures are filled with secondary calcite. The layers with microfractures are extensive in the basin and appear at about 2900~3000 m, which are consistent with the top depth of the maturation stage of hydrocarbon source rocks. Lithological and geochemical studies show that the occurrence of microfractures in the rocks is heterogeneous. Most of microfractures are found in the paper laminated shales with high organic matter abundance, while still none is found in the massive mudstones with lower organic matter abundance. The relations between organic matter abundance, organic matter maturation and the occurrence of microfractures indicate that hydrocarbons generation is the key reason for the parallel microfractures to produce. When maturated the source rocks with high organic matter abundance begin to generate a great deal of hydrocarbons, which quickly raise the pore pressure and lead the rocks to fracture at last. As the upper unit of E 2-3 s 4 Member and the lower unit of E 2-3 s 3 Member are interbedded with shales and mudstone, and the occurrence of microfractures is heterogeneous and only limited to shales, the layers with microfractures and layers lack of microfractures are intercalated. So, we propose that the expulsion of hydrocarbons in this section will be similar to source rocks of intercalated sands and muds in front of the delta, and can improve hydrocarbons expulsion efficiency.