Reservoir Characteristics And Secondary Pore Genesis Of Chang 8-10 In The Wuqi-Zhidan Area

Triassic Yanchang formation in Ordos basin is the focus of current exploration and development in Changqing Oilfield.But the existing research on Yanchang formation is mainly focused on the combination of the upper Yanchang group,Wuqi-Zhidan area located in the central part of Ordos Basin,Northern Shaanxi.The reservoir has strong heterogeneity and complex hydrocarbon distribution the synthetic analysis of the combination of the under Yanchang group is less.Therefore,this paper,based on the understanding of regional tectonic setting and provenance,reservoir characteristics,development regularity and genesis of secondary pores of the combination of the under Yanchang group are analyzed,provides a theoretical basis for oil and gas exploration.Through the detailed observation of the core,according to the lithology,physical property,electrical property and oily characteristics of coring wells,single well facies analysis is carried out.This paper holds that Chang 8,Chang 9 develop Sub-facies of shallow-water delta front,and Chang 10 develop sub-facies of shallow water delta plain.On the premise of single well analysis,combined with the working method of reservoir configuration,several sections are selected to draw the sand body connecting well diagram,under the control of the object source direction,on the basis of establishing the sand body profile,the sand body layout of the research area is drawn,and it is found that Chang 8,Chang 9 single channel sand body is thin,the interlayer thickness is big,the sand body connectivity is poor,the plane thickness is small.Chang 10 single sand body thickness is big,the connectivity is good,and the plane thickness is bigger.Through the observation and particle size analysis of thin sections,casting sheet,SEM.In this paper,the types of rock,the types of gaps and the structure characteristics of sandstone size,separation and grinding circle in the composite reservoir under the extension group are studied,and it is considered that there is no significant difference in the rock types of the Chang 8-Chang10 reservoir.The structural characteristics of sandstone are basically similar.The research area developed 6 types of diagenetic facies,and the diagenetic sequence is further summarized.The main pore types and pore structure of the research area are clarified through pore infiltration analysis,mercury analysis and the pore image analysis of the casting sheet.The pores in the study area are mainly formed in the type of the secondary pores by the dissolution of the diagenesis period,and the pore structure can be subdivided into 5 types.The reservoir in the study area is typical low ~ extra low pore,low ~ ultra-low permeability reservoir,in which from the Long 81 to Long 101 the reservoir physical property is gradually better,and on the plane,from the east to the middle and then to the west porosity and permeability of the value is decreasing,where the reservoir physical property becomes worse.The formation of reservoir pores in the study area is influenced by many factors,the main factors are the distance between reservoir and source rock,the way of oil and gas migration,the period of oil and gas accumulation,the sedimentation and diagenesis of reservoir,and diagenesis is the key factor affecting the formation of secondary pores and the development of high quality reservoirs.The difference of diagenesis in different strata leads to the formation of porosity.