饶阳凹陷蠡县斜坡北部沙一下亚段细粒沉积岩岩相类型及地质意义

Lithofacies types and geological significance of fine-grained sedimentary rocks in lower sub-member of Shahejie formation in northern Lixian slope of Raoyang sag

为进一步探究饶阳凹陷蠡县斜坡北部非常规油气勘探潜力,以西柳地区沙河街组一段下亚段为研究对象,通过岩心观察、薄片鉴定、扫描电子显微镜、全岩X射线衍射、全元素测定及有机地球化学实验分析的综合应用,对目的层段岩相类型及控制因素进行分析。结果表明:西柳地区沙一下亚段湖泊沉积岩主要发育中有机质粉砂质混合细粒沉积岩、中有机质块状黏土岩、高有机质页状灰质混合细粒沉积岩、高有机质页状灰质黏土岩和高有机质页状灰岩5种岩相类型;特征元素比值参数垂向上的变化反映了沙一下亚段沉积时期具有一定阶段性,即沙一下亚段底部形成于低物源影响、高水体盐度及强还原环境,而上部细粒沉积岩形成于较高物源影响、低水体盐度及较弱还原条件的沉积环境,沉积环境的变化控制了岩相的发育及有机质的赋存状态。研究结论有利于深化断陷湖盆细粒沉积岩基础研究,同时为后续非常规油气勘探提供参考。

In order to further explore the potential of unconventional oil and gas in the northern Lixian slope of Raoyang sag, the lithofacies types and their controlling factors of the lower sub-member of the first member of Shahejie formation(Es1) in the Xiliu area were analyzed through the comprehensive application of core observation, thin sections identification, scanning electron microscope, analysis of whole rock X-ray diffraction, determination of all elements and organic geochemical experiments. The results show that the lacustrine sedimentary rocks of the lower Es1in Xiliu area are mainly developed with medium organic silty mixed fine-grained rock, medium organic massive claystone, high organic shale calcareous mixed fine-grained rock, high organic shale calcareous claystone and high organic shale limestone. The vertical change of the elemental parameters reflects that the sedimentary period of the lower Es1has stages. The bottom of the lower Es1is formed in a low provenance, high water salinity and strong reducing environment, while the upper fine-grained rock is formed in the environment of relatively high provenance, low water salinity and weak reduction. The change of depositional environment controls the development of lithofacies and occurrence state of organic matter. This conclusion is conducive to deepen the basic research on fine-grained sedimentary rocks in the rifted lake basin, and provides a reference for subsequent unconventional oil and gas exploration.