Abstract: The sandstones of Chang 101 of G52 well area in Ansai oilfield are mainly fine-medium grained,mediumcoarse-grained arkose,lithic arkose,with low compositional maturity and high structure maturity.The interstitial materials mainly include clay minerals,laumontite,carbonate and secondary quartz.Reservoirs are low porosity,medium-low permeability and low permeability reservoirs,which their physical property distribution is relevant to the development degree of sand body,sedimentary facies and diagenetic effects.According to thin section,cast thin section and scanning electron microscopy analysis,pore types of Chang101 are mainly primary pore(intergranular pores,micro-pores within the matrix) and secondary pore(intergranular dissolved pores,intragranular dissolved pores,cast film hole,cement dissolved pores,intercrystal pores and micro-cracks) two categories.The reservoir throats mainly consist of necking throat,contracted throat,sheet or curved sheet-throat,bundle throat and other throats.Finally,the reservoirs are divided into four categories through comprehensive evaluation of parameters,and the reservoir Chang101 mainly belongs to class Ⅰ and class Ⅱ.