Research On Petrological Characteristics And Heterogeneity Of Shale Formation Of Ek₂ In Cangdong Sag,Huanghua Depression

The shale formation of Ek₂ in Cangdong sag is thick and has a huge hydrocarbon potential which is bright in oil exploration prospects.But research on petrological characteristics and heterogeneity of shale formation of Ek₂ is relatively deficient.Using the theory of sedimentary petrology,sequence stratigraphy and reservoir geology and others,a comprehensive study on petrological,organic geochemical and pore characteristics of shale formation is conducted in this paper,through core observation,thin section identification,quantitative evaluation of minerals by scanning electron microscopy,X-ray diffraction,Rock-Eval,Ar-field emission scanning electron microscopy,N2 adsorption and desorption experiment and a variety of laboratory data.Firstly,lithofacies classification is made and lithofacies of shale formation of Ek₂ is recognized in research area.Then study on organic geochemical and pore characteristics against different lithofacies is conducted.Lastly,influence factors on heterogeneity of shale formation of Ek₂ are discussed.Lithofacies of shale formation in research area includes clay shale,sandy shale,sandstone,dolomitic shale,dolomite and mixed sedimentary rock,it is complex and heterogeneous.Different lithofacies have different organic geochemical characteristics and pore characteristics.Dolomitic shale,mixed sedimentary rock,sandy shale and clay shale are middle-high organic carbon content abundant,as well as high of hydrocarbon potential and mainly typeⅠorganic matter.Sandy shale,mixed sedimentary rock and clay shale are rich in pores,and the first two lithofacies have better pore structure.The second member of Kongdian formation in Cangdong sag is a set of intact three-order sequences,which can be further divided into 11 forth-order sequences(Ek₂⁴（1）—Ek₂¹（11）.In lowstand system tract（Ek₂⁴（1）—Ek₂⁴（2））,sandstone is the main lithofacies,and is low in organic carbon content.In transgressive system tract（Ek₂³（3）—Ek₂²（8））,sandy shale and mixed sedimentary rock are two main lithofacies,and organic carbon content is middle to high.In highstand system tract（Ek₂¹（9）—Ek₂¹○11）,lithofacies is complex and organic carbon content is high to low.After comprehensive analysis,it is concluded that Ek₂³（5）—Ek₂²（7）and Ek₂¹（9）is favorable sequence where pore is developed.