1�� College of Earth Sciences��Jilin University��Changchun 130026��China; 2�� Exploration and Development ��esearch Institute of Jilin Oilfield��Songyuan 138000��Jilin��China; 3�� ��esearch Center of Palaeontology �� Stratigraphy of Jilin University��Changchun 130061��China

Petroleum geologists have paid great attentions to the volcanic reservoirs of Songliao Basin in NE Chi- na�� There are plenty of subvolcanic rocks in the Songliao Basin accompanying the Early Cretaceous Yingcheng Formation�� The logging data show the good reservoir potential of these intrusive rocks but the distribution char- acteristics and formation mechanisms of these reservoirs are not clearly understood�� Based on the previous stud- ies by using coring��cuts and logging data of Yingtai rift depression�� the reservoirs' characteristics of intrusive rocks are presented�� There are two types of intrusive rocks namely the syenodiorite- porphyrite and diabase which occur as laccolith and/or sill��both having the characteristics of low gamma and high density with little primary porosity and permeability�� The prevalent reservoir porosity is the secondary porosity��such as spongy/cavernous pore��tectonic fracture�� The laboratory data of porosity of diabase can reach 6.7%��but the permeability is less than 0�� 6 ×10^-3 μm ² ��median pressure is high��indicating that the pore throat of this kind reservoir is small�� The maximum logging porosity is about 12%�� The change of porosity does not correlate to the buried depth�� It is the major significant differences in the distributive characteristics compared to the normal sedimentary rock reservoirs�� Most of intrusive rocks underwent alteration diagenesis whilst some were subjected to precipitation diagenesis�� The spongy and cavernous pore can be formed during the alteration processes of plagioclase to illite and pyroxene to chlorite�� The secondary porosity is greatly correlated with the alteration intensity of matrix�� plagioclase and pyroxene�� There are pyroxenes and more plagioclases in diabase��which cause the higher alteration intensity than the syenodiorite- porphyrites in the same acid fluid�� So the porosity of diabase is higher than that of syenodiorite- porphyrites�� The top or/and bottom part of intrusive rocks develop the higher porosity�� Because those parts are easy to contact formation fluid��and the shrink fractures give the more surface for reaction be- tween fluid and rock�� The porosity of intrusive rocks is same to the volcanic rocks in Yingtai rift depression and Xujiaweizi rift depression which bear the prolific gas�� It suggests good reservoir potential�� Intrusive rocks are hosted by the dark mudstone which indicates semi- deep and deep lake facies belt��