| Zhongshachuan area of Wayaobao oil field is a typical extra-low permeable oil field that it is in early development stage at present,and Chang 2,Chang 4+5 and Chang6 are main oil bearing series in Late Triassic.Chang 4+5 oil-bearing bed is regarded as mian research object of this paper,according to its drilling,logging,outcrop observation and kinds of assayed data,and through these experimental methods such as the X-ray diffraction,physical property test,scanning electron microscope,intrusive mercury experiment etc.,the paper analyzed lithology,pore structure,diagenesis,physical property, non-homogeneous property of Chang4+5 reservoirs,which provides geological basis for development adjustment of the area.Thesis of the study made as follows:Chang 4+5 reservoir of Yanchang formation is divided into two oil sub-groups: Chang4+51 and Chang 4+52.Chang 4+52 oil-bearing bed is one of the major oil producing formations in the study area,Chang 4+52 formation is divided into the three beds:Chang 4+521,Chang 4+522 and Chang 4+523;The Chang 4+5 member belongs to a sedimentation facies of Zichang-Ansai delta.Micro-facies are mainly occurred in the submerge distributary channel and distributary bay,the channel is a distribution of NE-SW tending and a stable channel development,morever,its sandbodies are fundamentally together; Chang4+5 reservoirs is mainly fine arkose and grayish feldspar sandstone.Compositional maturity is low and textural maturity is medium to preferably.Grain size sorting is better and the grain shape is most subangular;The research of the clastic reservoir indicates that dominant diagenesis types are compaction,cementation,replacement and dissolution,furthermore,diagenesis has experienced from late diagenesis A stage to late d,iagenesis early of B stage;We draw the conclusion that the reservoir space of the Chang 6 oil-bearing is dominated by intergranular pore,and secondary dissolution pore,main minimal-fine throat and fine throats are caused by low permeability,average permeability is 0.77×10-3μm2 and porosity is10.18%,which formed the extra-low permeable and ultra-low permeable reservoir;Pore throat types are medium fine pore and throat, small-fine pore-fine throat and fine pore-fine throat-mierothroat,and a little macroporous-medium pore and coarse throat;Reservoir sensibility of Yanchang formation is weak in zhangshanchuan area,five sensibilities show the degree of below average and even it will not exercise a great influence.Reservoir interlaminar heterogeneity of Chang 4+5 shows medium to strong,innerlayer and plane heterogeneity is weak and a strong microcosmic heterogeneity.According to the division scheme of ultra-low permeable reservoir of Yanchang formation,Chang4+5 reservoir will be divided five categories through multi-parameters and kinds of analysis methods,author thinks Chang4+5 reservoir is mainlyⅢa type (54.97%),andⅡa,Ⅱb,Ⅲb,Ⅳtype reservoir of(4.15%,8.55%,21.01%,7.39%),there lacks good reservoir;Ⅱtype(medium reservoir) shows a higher porosity and permeability, and it emerges only in local;Distribution ofⅢtype bad reservoir is common in the area, porosity and permeability is relatively lower;On the whole,Chang 4+5 reservoir sandstone of Yanchang formation are mainlyⅢa type.Therefore,there are mainly medium low pore reservoir and ultra-low permeability-ultra-low permeability type in the study area.
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