Abstract: Volcanic detritus are dominant in those composing the reservoir greywacke in the Songliao Basin，and their content can be up to 60%. Matrix of the lithic sandstones, with volume percent Ca. 11% to 19% of matrix, is dominantly tuffaceous, with minor siliceous and calcite cement. They formed in continental faulting basins and their sedimentary facies mainly include river, delta and fan delta. Both compositional and textural maturities of the sandstone are low,whereas such reservoir features as porosity and permeability are generally high. Data from thinsection, skeletal cast and electron microscope indicate that clastic components, matrix and diagenetic fluid are three main factors governing reservoir features of the sandstone rich in volcanic fragments. Alteration of volcanic grains during deeply buried stage can cause secondary inter-and/or intra-grain spores resulting in improvement of the reservoir features. Post-diagenetic variations related to the reservoir features include：(1) Primary porosity of greywacke is sharply reduced during burial-diagenesis；(2) Solution, devitrification as well as forming and recrystallization of secondary mineral can increase primary porosity as a whole；(3) Reaction between diagenetic fluid and volcanic materials can result in abundant secondary pore, which improved physical characteristics of the reservoir sandstone.

Key words: deeply buried strata in Songliao Basin, greywacke reservoir, volcanic fragments, diagenesis, porosity and connectivity, evolution of pore-space