由下扬子区海陆对比分析南黄海盆地下志留统烃源岩特征及其主控因素

Characteristics of Lower Silurian Hydrocarbon Source Rocks and Their Main Controlling Factors in the South Yellow Sea Basin Based on Land-Ocean Comparison in the Lower Yangtze Region

针对南黄海盆地海相油气勘探的重大需求,在收集、整理下扬子苏、浙、皖地区地质和地化资料的基础上,依托科学钻探CSDP-2井岩心,系统对比了南黄海盆地与下扬子陆区早志留世古地理背景和沉积充填特征,进而利用一系列地化测试数据总结了南黄海盆地下志留统烃源岩特征并探讨其主控因素。研究结果表明:南黄海盆地大陆架科学钻探CSDP-2井目前已钻遇了坟头组和高家边组上部两套丰度很低的厚层、暗色(粉砂质)泥岩,其有机质类型主要为Ⅱ2型,热演化程度已整体进入过成熟阶段;受控于全球海侵事件和扬子板块构造活动的发展阶段,早志留世初期深水陆棚环境逐渐向后期的浅水陆棚环境演变,加之早期较高的初级生产力和良好的保存条件,使得下扬子区高家边组下部烃源岩的品质明显高于上部,并以底部黑色笔石页岩段有机质丰度最高。因此,南黄海盆地高家边组底部理应存在一套优质烃源岩层,可作为下一步页岩气勘探的重点层位。

To meet the demand of marine origin oil-gas exploration in the South Yellow Sea basin,the authors systematically analyzed and compared the palaeo-geographic setting and sedimentary filling characteristics of Early Silurian between the South Yellow Sea basin and the land area in the Lower Yangtze plate based on the geological data of Jiangsu,Zhejiang,Anhui regions and the cores of well-2,then summarized the characteristics of the Lower Silurian hydrocarbon source rocks,and further discussed their main controlling factors in the South Yellow Sea basin.The results showed that two sets of source rocks of the Fentou Formation and the upper part of the Gaojiabian Formation were drilled in the well CSDP-2,which are thick,dark and silty mudstone with low abundance typeⅡ2organic matter,and all of them are at over-maturity stage.Controlled by the development stage of global transgression and the tectonic activity of the Yangtze plate,the Early Silurian sedimentary environment in the lower Yangtze region gradually changed from initial deep water shelf to shallow water shelf.In addition,under the influence of the early high primary productivity and good preservation condition,the source rock quality in the lower part of the Gaojiabian Formation is obviously better than that in its upper part,and the abundance of organic matter in the black graptolite shale in the bottom section is the highest.Therefore,we believe that there should be a set of high quality hydrocarbon source rocks at the bottom of the Gaojiabian Formation in the South Yellow Sea basin,which can serve as the next key layer for shale gas exploration.