Research Institute of Exploration and Development, Daqing Oilfield Limited Company, Daqing 163712, Heilongjiang, China

The fractures in volcanic reservoirs are widely developed in Yingcheng Formation of Songliao Basin, but there are much different in fracture scale in various facies. Based on the study of measured data and microscopic characteristic observation of fractures in volcanic reservoirs of peripheral outcrop and combined with drilling core research, the author considers that the fractures in volcanic reservoirs can be divided into 3 genetic types, including primary fractures, secondary fractures and human-induced fractures, and the structural fractures from the secondary fractures play a decisive role to hydrocarbon migration and accumulation. Effusive facies, extrusive facies and volcanic conduct facies are most developed in the structural fractures, the linear densities are 22 /m, 18 /m and 14 /m respectively, while the explosive facies are not developed, with only 4 /m in line density. The period for the structural fractures forming are the early and late stages of Yingcheng Formation in Early Cretaceous, and of the Nenjiang Formation in Late Cretaceous, in which the two formers are main stages. The fracture strikesmost developed in north-east trending, accounted for 50%; while the north-west, south-north and app roximate east-west trendings take the second place. Generally, the fractures is low in filling degree, but the opening situation and effectiveness are relative good. The research results can compared with the developing regularity of the fractures in the Xujiaweizi depression.