Abstract：
Tuffaceous sandstone is the main hydrocarbon reservoir rocks in the HailarTamtsag Basin，tuffaceous content increased with strata to be older，and the reservoir has higher heterogeneity.By microanalysis of many thin sections，the study shows that the reservoirs compositional maturity and texture maturity is lower，and the main reservoir space is secondary vugularsolution porosity.The proportion of secondary porosity increased with strata to be older.In this paper，the method of porosity genesis is proposed and the lower limit of highquality reservoir is identified，porosity of tuffaceous sandstone is 10％，permeability is 0.1×10-3μm2，the proportion of secondary porosity is 30％.Delta front subfacies is the formation foundation of tuffaceous sandstone.Disslution of organic acids and leaching of meteoric water are the formation of the main factors of highquality reservoir.
2011, Vol. 46 
