Keywords: 
• Reservoir /
• Diagenesis /
• Hydrocarbon accumulatian

Abstract: Raoyang Sag is located in central part of Jizhong Depression, Bohaiwan basin. Since the discovery of "buried hill" carbonate hydrocarbon reservoir in 1975,overall regional petroleum exploration activities have been carried out. Eogene sandstone reservoirs followed the Yre-Mesozoic carbonates have become the new petroleum exploration targets.This paper has discussed the origin,type,vertical distribution of sandstone reservoir porosity in Eogene in Raoyang Sag. The evolution and vertical distribution of sandstone porosi-ty have been classified into 5 phase through mechanical and chemical diagenesis study:1)Shal-low buried(<2000 m) primary porosity phase,2)Mixed primary and dissoived secondary porosity phass(2000--2800 m),3)Pure dissolved secondary porosity phase ( 2800-4000m),4) Inter crystal residual and dissolved secondary porosity phase (4000-4599 m),and 5)Micro-fissure storage phase (>4500 m). Meanwhile the authors have quantitatively described and predicted the reservoir storage capacity in different porosity evolution stages.Now the discovered hydrocarbon accumulations in Eogene in Raoyang sag are concentrat-ed between 2000-3500 m interval. This study has discussed the existence possibilities of deep buried sandstone hydrocarbon reservoirs:1)Sufficient and abundant hydrocarbon sources.Depth of the maximum hydrocarbon expulsion of Eogene petroleum source rocks in Raoyan ranges from 3800 m to 5300 m,2 ) Deep buried sandstone reservoirs show 'the tendency of ab-normal pressure,which is favorable for the preservation of various origin porosity,3)Corelaboratory analysis data indicate that in deep burial domain,the sandstone reservoirs still pos-sess the storage capability of porosity value 5%15%and permeability value <0. O1一50X10^-3.μm². 4)In deep burial domain(>3800 m ) the content of illite and montmorillonite mixed一layer clay mineral in sandstone bodies has been extinct,but the shale in same burial do- main still posses illite and montmorillonte mixed-layer that has 12%montmorillonite layer,which may bring about the forming of subtle entrapment.