松辽盆地南部长岭断陷青一段陆相页岩地球化学和沉积环境特征

Characteristics of Geochemistry and Depositional Environment of Terrestrial Shales in theFirst Member of Qingshankou Formation of Changling Fault Depression in the Southern Songliao Basin

针对松辽盆地南部长岭断陷青一段陆相页岩地球化学和沉积环境特征认识不清的问题,系统开展有机地球化学、分子地球化学和元素地球化学实验,明确研究区陆相页岩生烃潜力,探讨沉积环境特征对有机质富集的控制作用。研究结果表明:青一段陆相页岩富含有机质,TOC平均为1.71%,氯仿沥青“A”平均为0.52%,具有良好的生烃潜力。干酪根类型主要为Ⅰ型和Ⅱ1型,有机质热演化处于成熟阶段,热解参数T_(max)平均为447℃,R_(o)平均为1.06%;C 27-C 29规则甾烷指示页岩有机质主要来源于藻类等低等水生生物,兼具部分高等植物输入,微量元素比值和生物标志化合物参数指示古生产力水平较高,页岩来源于咸水-微咸水还原环境,有利于有机质保存;氯仿沥青“A”与P/Ti、Sr/Ba之比具有正相关关系,表明古生产力和保存条件共同控制页岩有机质富集。按照TOC>2.00%、S 1>1 mg/g的页岩油“甜点”评价标准,确定有利区面积为5000 km^(2),体积法计算页岩油地质储量为54.7×10^(8)t。研究结果对松辽盆地南部页岩油资源潜力评价具有战略指导意义。

In response to the problem of unclear understanding of geochemistry and depositional environment characteristics of terrestrial shale in the first member of Qingshankou Formation of Changling fault depression in the southern Songliao Basin,the experiments on organic geochemistry,molecular geochemistry and elemental geochemistry were systematically carried out to clarify the hydrocarbon generation potential of terrestrial shale in the study area,and to explore the controlling effect of depositional environment characteristics on the enrichment of organic matters.The study results show that the terrestrial shale in the first member of Qingshankou Formation is rich in organic matters,with an average TOC of 1.71%and an average chloroform asphalt"A"of 0.52%,which has good hydrocarbon generation potential.The types of kerogen are mainlyⅠandⅡ1,and the thermal evolution of organic matter is at a mature stage,with the average pyrolysis parameter T_(max)of 447℃and average R_(o)of 1.06%;the C 27-C 29 regular sterane indicates that the organic matter of the shale is mainly originated from lower-order aquatic organisms,such as algae,and partly imported from higher-order plants,the ratio of trace elements and biomarker compound parameters indicate that the paleoproductivity level is high,and the shale is originated from saline-water and brackish-water reducing environment,which is favorable for organic matter preservation;the chloroform asphalt"A"has a positive correlation with P/Ti and Sr/Ba,which suggests that the paleoproductivity and the preservation conditions jointly control the organic matter enrichment of shale.According to the evaluation criteria of shale oil"sweet spot"of TOC>2.00%and S 1>1 mg/g,the favorable area is determined to be 5000 km^(2),and the geological reserves calculated by volumetric method is 54.7×10^(8)t.The study is of strategic significance for the evaluation of shale oil resource potential in the southern Songliao Basin.