Research On Characteristics And Grading Evaluation Of Tight Reservoir In Es4-Ek1 Section Of South-central Jinxian Sag,Jizhong Depression

This issue derives from the cooperative project between China University of Petroleum?East China?and Huabei Oilfield of China National Petroleum Corporation.South-central Jinxian sag is rich in oil and gas resources,but now the characteristics and the main controlling factors of tight reservoir are not clear,which restrict the development in research area.To solve these problems,we carry out the research about reservoir prediction.On the basis of extensive literature research,this paper summarized predecessors'research results of the work area and the exploration status of tight reservoirs,and then the paper evaluated and analyzed the characteristics of tight reservoirs from three aspects,which are sedimentary characteristics,tight reservoirs'characterization and reservoir classification and evaluation.The study used core observation,casting lamella,logging data and other data comprehensively to determine the types of sedimentary facies and the types of pore throat of Es4-Ek1 in the study area.The main sedimentary facies which are developed in the study area are braided river delta facies,alluvial fan facies,fan delta facies,lacustrine facies.The main type of pore is dissolved pore,and then is primary pore.This studyfound some intracrystalline pores in the rocks and microcracks can also be seen occasionally.Moreover,dissolving pores in the lithic fragment can hardly be seen in the rocks.The necking throat is locally developed,the laminated throat or the curved lamellar throat is mainly developed and the control shape throat is relatively developed.Through a variety of experimental analysis,this paper analyzed the pore structure characteristics of reservoirs.In the meantime,the study combined the results of a variety of experimental analyses and this paper used different kinds of methods to calculate the upper limit and lower limit of the tight reservoir in the study area.The study found out that the lower limit of porosity is 3.54%and the lower limit of permeability is 0.065×10^-3?m²;the upper limit of porosity is 11%and the upper limit of permeability is 1×10^-3?m².This paper formulate a comprehensive grading evaluation criterion for reservoir according to physical parameters,saturation of mobile fluid,and some parameters of pore throat,such as pore structure types,reservoir quality index,pore throat radius,mainstream throat radius.And then this paper divide the tight sand-conglomerate reservoir of Es4-Ek1 in the south and central areas of Jinxian sag into five levels,which are conventional reservoir,type?tight reservoir,type?tight reservoir,type?tight reservoir and not reservoir.