苏北盆地溱潼凹陷阜二段烃源岩生烃潜力及形成环境

Hydrocarbon Generation Potential and Genetic Environments of Second Member of Funing Formation in Qintong Sag,Subei Basin

在阜二段层序划分基础上,通过大量有机地球化学分析系统评价阜二段烃源岩,揭示优质烃源岩的发育层段和形成环境。结果表明,溱潼凹陷阜二段中、下部烃源岩生烃条件较好,优质烃源岩主要分布于七尖峰亚段、四尖峰亚段和龟背亚段,形成于半咸水的还原环境中,TOC大于2%,有机质类型以Ⅰ型、Ⅱ_1型为主,有机质生源构成为低等水生生物和陆源高等植物,有机质成熟度普遍达到成熟阶段。阜二段顶部和底部的烃源岩品质相对较差。建立了阜二段泥页岩层序—沉积发育模式,认为烃源岩发育受控于区域气候变化、降水强度、水介质条件和陆源物质供给等因素,阜二段沉积早期到晚期,水体盐度逐渐降低,沉积环境由强还原到弱还原变化,蒸发作用减弱,古气候由干旱变为潮湿,阜二段沉积中期最有利于形成优质烃源岩。

Based on sequence division of the second member of Funing Formation,we assessed the source rocks through a lot of organic geochemical analytic system. Results showed that the source rocks at middle and lower parts of the second member of Funing Formation in Qintong Sag had better hydrocarbon generation conditions,high-quality source rocks concentrated in Qijianfeng,Sijianfeng and the submember of Guibei and were formed in brackish oxygen-free environment with TOC higher than 2%,organic matter types being dominated by Type I and Ⅱ_1,biological origin of organic matter being lower hydrobiontes and terrestrial higher plants,and organic matter being high-maturity. Source rocks at top and bottom of the second member of Funing Formation were relatively poorer. We also established the sequence-sedimentary development mode for mudstone in the second member of Funing Formation,and believed that the development of source rocks were controlled by regional climate change,precipitation intensity,aqueous medium conditions,terrestrial material offering and other factors. From early sedimentary stage to late stage,the water salinity of the second member of Funing Formation gradually decreased,sedimentary environment turned from strong reduction to weak reduction,evaporation got weakened,and paleoclimate changed from drought to humid. The middle stage of sedimentation in the second member of Funing Formation was most favorable for forming high-quality source rocks.