Abstract: Through the tuff core description, well logging, seismic data, X-ray diffraction, scanning electron microscopy, physical properties, and other test data of Yingcheng Formation in Dehui fault depression of Songliao basin, combined with the structural background analysis, the authorsstudied the geological characteristics of tuff reservoirs. The results show that the mineral components of the tuff in Yingcheng formation are mainly quartz, feldspar, and clay minerals. Tuff is widely distributed in the region, and composed of several superimposed units in vertical direction that underwent weathering and alteration. The logging curve has three peaks and two valleys. According to the tuff scale and gas-bearing characteristics, the volcanic edifice can be classified into three categories: small tuff volcanic edifice, large tuff volcanic edifice, and super large tuff volcanic edifice. The tuff reservoir has middle porosity and low permeability. There are two factors of low yield: the first one is higher content of clay minerals(especially the imam mixed layer), and the second one is compaction. The porosity of tuff reservoir layer accounts for more than 80%.The main reservoir space types are dissolved pores and dissolved fractures, andthe dissolved pores are mainly feldspar dissolved pores and matrix dissolved pores. The fracture development is a key factor in the formation of  tuff reservoir, and there is a  high possibility to find high-yield gas reservoirs in the shallow and middle areas(especially in the high part of the structure). Using logging curve(neutron and density) can predict tuff reservoir effectively. 

Key words: reservoircharacteristics, volcanicedifices, tuff, YingchengFormation, Dehuifault depression