Lithologic and Lithofacies Characteristics of Volcanic Rock and Their Controlling Effects on Reservoirs of Changling Fault Depression in the South of Songliao Basin

The Changling fault depression is the largest fault depression in the south of Songliao Basin. The deep formation in the depression with a low exploration degree contains abundant hydrocarbon resources, where volcanic rocks are distributed extensively, as a good reservoir of oil and gasses. According to core observation, thin section identification and integration of well log and 2D/3D seismic data, the Yingcheng formation and Huoshiling formation are rich in volcanic rocks, mainly consisting of lava and pyroclastic rocks. 5 types of volcanic lithofacies and 11 types of volcanic subfacies such as explosive facies, overflow facies, volcanic conduit facies, extrusive facies and eruptive-sedimentary facies can be identified, which are mainly overflow facies and explosive facies. The volcanic rocks in the depression are distributed along big deep faults and superimposed by many times of volcanic eruption in the vertical direction in models of eruption of both central type and fissure type. And three volcanic eruption cycles can be identified in the Yingcheng formation. Statistics show that the rhyolite in the lower part and the upper part subfacies of overflow as well as the tuff in pyroclastic flow subfacies of explosive have many gas pores, solution pores and fractures, which may serve as a good reservoir.