渤海湾盆地东营凹陷古近系细粒沉积岩特征及沉积环境

随着泥页岩油气勘探的深入,详细解剖细粒沉积岩的岩石类型和组成,对后续储集层研究中优势岩石组合的确立有重要意义。通过岩心观察、全岩X射线衍射等分析手段,以矿物含量和沉积构造作为主要依据,将渤海湾盆地东营凹陷古近系沙三下沙四上亚段细粒沉积岩划分为9种岩石类型,其以纹层状混合细粒沉积岩、块状混合细粒沉积岩、纹层状灰岩、纹层状粉砂质灰岩、纹层状黏土质粉砂岩为主。由特征元素比值Ca/Mg、Na/Al、Fe/Mn、Sr/Ba、V/(V+Ni)值及Ti、Al含量的垂向变化,可知东营凹陷细粒沉积岩在古气候、古水深、古盐度及水体氧化还原性、陆源输入程度等方面的演化具有明显阶段性,其气候在沙四上亚段沉积时期表现为由干冷变暖湿,在沙三下亚段沉积时期呈现暖湿相对湿冷暖湿相对湿热的演化;且在不同的演化阶段,岩石组合及特征均有差异。因此,温暖湿润的气候和陆源输入量的增加有助于纹层状混合细粒沉积岩大量沉积,而较为寒冷干燥的气候和相对低的陆源输入易于沉积纹层状粉砂质灰岩。这一结论有利于深化断陷湖盆细粒沉积岩岩石学的基础研究,可为后续油气勘探开发奠定坚实的基础。

Lithologic characteristics and sedimentary environment of fine-grained sedimentary rocks of the Paleogene in Dongying sag,Bohai Bay Basin

With the development of shale oil and gas exploration,it is necessary to dissect the type and composition of fine-grained sedimentary rocks in detail,which is of great significance for the establishment of dominant rock assemblage in subsequent reservoir studies. Fine-grained sedimentary rocks are well developed in Dongying sag,Bohai Bay Basin. By means of core observation,X-ray diffraction of whole rock and analysis methods,the carbonate minerals,clay minerals and silty minerals are considered to be the main mineral components of fine-grained sedimentary rocks in Donying sag. According to mineral content and sedimentary structure,the fine-grained sedimentary rocks of the lower submember of Es3 member and the upper submember of Es4 member can be divided into 9 kinds of rock types,in which the laminar mixed fine-grained sedimentary rocks,the massive mixed fine-grained sedimentary rocks,the laminar limestone,the laminar silty limestone and the laminar argillaceous siltstone are relatively well developed. Based on the vertical variation of the characteristic element ratio of Ca/Mg,Na/Al,Fe/Mn,Sr/Ba,V/(V+Ni),and the element content of Ti and Al,it is deduced that there are some obvious evolution stages of fine-grained sedimentary rocks in palaeoclimate,palaeowater depth,palaeosalinity,oxidative or reductive properties of the water,and the content of terrigenous clastics input. The palaeoclimate changed from dry and cold to warm and humid in the depositional period of upper submember of Es4,and developed from warm and humid to relatively cold and humid to warm and humid to relatively hot and humid in the depositional period of the lower submember of Es3. In conclusion,warm and humid climate together with the increase of terrigenous clastics contributed to deposit large amounts of laminar mixed fine-grained sedimentary rocks,whereas the laminar silty limestone tended to deposit in relatively cold and dry climate as well as less terrigenous clastics input. This conclusion is conducive to deepen the basic research of fine-grained sedimentary rocks in the faulted lacustrine basin,and can lay a solid foundation for future exploration and development of oil and gas.