Abstract: The Mesozoic volcanic rocks are the most important gas reservoir in the northern Songliao Basin. 5 lithofacies and 15 subfacies have been recognized in the volcanics. The best reservoirs were generally found in three of the fifteen subfacies including pyroclastic bearing lava flow（Ⅱ₃）, upper effusive（Ⅲ₃） and inner extrusive（Ⅳ₁）subfacies. The corresponding logging characteristics are as follows: the Ⅱ₃ is characterized by high value of Gama Ray (GR) with low amplitude dentiform outline, and by mediahigh value of Dual Lateral Logging of Resistivity (DLL) with low frequency and low amplitude dentiform outline; the Ⅲ₃ is high in GR with low amplitude dentiform shape, DLL value of the Ⅲ₃ is mediamedia high and with shapes of finger or hill figure; the Ⅳ₁ shows high value of GR with media amplitude dentiform shape, its DLL is media highhigh value with media amplitude dentiform shape. Besides, undergroundexplosive breccia facies（Ⅰ₃）and outer extrusive facies（Ⅳ₃）can also be good reservoirs. Gas can cause DLL of the reservoir volcanics increasing markedly but water does the contrary. The DLL of dry volcanic rocks indicates facies and rock type dependent, in the sequence of volcanogenitic sedimentary facies＜extrusive facies＜explosive facies＜volcanic vent facies＜effusive facies; tuff＜lava.

Key words: Songliao Basin, volcanic lithofacies, volcanic reservoir, deep basin gas, well logging facies