Abstract
Sedimentary characteristics and diagenetic evolution of reservoir rocks in the northern part of Songliao Basin are discussed here,taking the sandstone of Da-qing Oilfield as an example.They are represented mainly by terrigeneous coarse siltstone and fine-grained sandstone,mostly belong to detrital feldsparthic sand-stone and greywacke.The physical properties containing oil constrained essen-tially by sedimentary and diagenetic conditions vary greatly,they are getting worse mainly with the buried depth of reservoir,having little affects by its lithologic character.The most favourable reservoir rocks are the upper and middle oil-bearing assemblages buried above the depth of 1,500 m,including Heidimiao,Saertu,utaohua and Gaotaizi pay zones,the lower pay zones,buried within the depth of 1,500-2,000m or 1,500-2,500m such as Fuyu and Yangdachengzi zones,arefairly favorable;the still deeper strata below 2,000m or 2,500m depth,e.i.sandstones beneath the second member of the Quantou Formation,are considered as posble gas-bearing zones.The primary porosity and permeability of sandstones were constrained by sedimentation,while those of secondary origin were largely constrianed by diagenetic conditions.Common authigenic minerals in this area consist mainly of quartz,feldspar,montmorillonite,kaolinite,illite,chlorite and other tran-sitional phases of clay,with small amount of calcite,siderite and glauconite.They were formed during diagenesis from chemical consolidation.Special attention have been attached to attributes of authigenic assemblages and their mode of occurrence in this study in order to estimate their influence on physical properties of reservoir,and therefore,to predict the possible damage which might occur during oil production.
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