二连盆地优质烃源岩发育特征及成藏贡献

二连盆地由众多小凹陷组成,物源多、相变快且热演化程度较低,是否发育优质烃源岩决定了油气藏的勘探方向。通过建立残余有机碳含量与氢指数相关关系,以及不同沉积环境下有机碳含量的变化,发现浅湖与较深湖等稳定沉积区优质烃源岩发育,河流与滨浅湖等不稳定沉积区主要发育中—差烃源岩;利用残余有机碳对不同沉积相带烃源岩级别进行划分,稳定沉积区可划分出优质[w(TOC)>2%]、中等[1%<w(TOC)<2%]与差[w(TOC)<1%]烃源岩,不稳定沉积区可划分为中等[w(TOC)>1%]与差[w(TOC)<1%]烃源岩。同时,依据测井计算残余有机碳的方法划分出了各凹陷不同级别烃源岩的厚度及分布。优质烃源岩与油气藏有较好的亲缘关系,且资源贡献率大,占烃源岩总体积20%以上的优质烃源岩资源贡献率超过了70%,其分布区是寻找规模储量的有利区域。

Characteristics of high-quality hydrocarbon source rocks and their contributions to reservoirs in the Erlian Basin

The Erlian Basin consists of many sags characterized by multiple provenances, changeable phases and a low degree of thermal evolution.The identification of high-quality source rocks determines the direction of exploration efforts.By building correlations between TOC and HI, and analyzing the changes of organic carbon contents under various sedimentary circumstances, we have shown that stable sedimentary areas such as shallow lakes and relatively deep lakes commonly develop high-quality source rocks, and unstable sedimentary areas like rivers and shallow shore lakes commonly develop poor- or medium-quality source rocks.We can use TOC to classify source rock levels.The source rocks from stable sedimentary areas are divided into high (TOC > 2%), medium (1% < TOC < 2%) and poor (TOC < 1%) quality source rocks.The source rocks from the unstable sedimentary areas are divided into medium (1% < TOC < 2%) and poor (TOC < 1%) quality source rocks.Furthermore, based on TOC values calculated from well logging data, the thickness and distribution of different levels of source rocks can be ascertained.High-quality source rocks have a close relationship with oil and gas reservoirs, and are the main sources of oil to these reservoirs.The source contribution from high quality source rocks is > 70% even though they constitute only 20% of total source rock volume.Consequently, the distribution zones of high-quality source rocks are commonly favorable areas for large scale reserves.