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

Through the study of logging response, seismic reflection and pore microstructure of basalt in Xujiaweizi fault depression of Songliao Basin, the reservoirs' characteristics in relation to lithology and facies are analyzed. The main controlling factors on basalt reservoirs are revealed. Distribution of reservoirs is studied by inversion and the reservoirs are grouped into three types based on the inversion results to predict favorable exploration zones. It is revealed that pores in basalt reservoirs comprise primary pore, secondary pore and structure-eroding fissure, with porosity of 6%~12% and permeability of 0.01~1 mD. Basalt shows low gamma ray on well log and is represented by high amplitude continuous reflectors on seismic. The most effective reservoir types are basaltic volcanic breccia and basaltic breccia tuff, followed by basalt. The best reservoirs are usually found in crater facies, followed by near crater facies. Type �� is the favorable zone for exploration in the northern Xujiaweizi fault depression, with extensive basalt distribution, better physical properties and more potential resources.