Study On Diagenesis Of Sandstones From The Lower Cretaceous In The Qingdao Area,Riqingwei Basin

The Riqingwei Basin is located in the middle section of the Sulu Orogenic Belt,which represents the junction of the North China Craton and the Yangtze Craton.The geographic area of the basin covers the offshore areas of Rizhao,Qingdao and Yantai.A set of deep-water gravity flow sedimentary system was developed in the basin,and some typical sections can be found in the Lingshan Island,Zhougezhuang,Dingzi Bay,Yakou of Laoshan Mountain,Wulian of Rizhao.At present,the studies about the origin,depositional background,controlling factors and diagenesis of the strata is limited.This thesis takes the typical sections of Zhougezhuang and Lingshan Island areas in Qingdao as main object of study,and studies diagnesis of the Lower Cretaceous sandstones of Qingdao area in the Riqingwei Basin.It has great theoretical and realistic significance to solve the above mentioned academic problems and estimate the prospects of oil and gas resources.Base on the achievement of the previous,diagenesis types,evolution of diagenetic environment,and diagenetic sequence of sandstones in the study area were discussed,on the basis of field observation and description,observation of casting and conventional thin sections,cathodoluminescence and fluid inclusion analysis.The following several understandings were drawn:?The rock types mainly consist of feldspathic litharenite and lithic arkose.The debris is mainly composed of magmatic rocks and metamorphic rocks.The matrix maily consists of kaolinite and illite.The cement types mainly are siliceous cementation,clay mineral cementation and carbonate cementation.?According to the observation under the microscope,pore types mainly consist of primary pore,secondary pore and micro fracture.? The diagenesis types mainly consist of compaction,cementation,metasomatism,dissolution and fracturing.The diagenetic evolution sequence is as follows:Early compaction?Clay miscellaneous base?A small amount of kaolinite?Plastic debris and mica deformation?Early micrite calcite and aicrocrystalline calcite?Dissolution of detritus and feldspar?Kaolinite precipitation?Transition from montmorillonite to Illite?Quartz secondary enlargement and authigenic quartz microcrystals?Formation of bright and intergranular calcite?Quartz dissolution?Cementation or replacement of ferruginous calcite and ferruginous calcite?Diagenetic fracture formation.?According to geochemical indexes such as fluid inclusions and characteristics of rock structure,it is determined that the diagenetic stage of this area is in the middle late diagenetic stage;Based on the comparative analysis of sedimentary structural evolution history of the basin and Jiaolai Basin,the evolution process of diagenetic environment in this area is clarified.Sandstone in the study area is strongly influenced by magmatic activity in the process of diagenesis.Although there are many organic matters in the study area,magmatic activity accelerates the evolution of organic matter maturity,the release of acid matter is very small,and the whole process of diagenesis is dominated by alkaline environment,resulting in poor physical properties of sandstone reservoir in the study area.