Mafic-intermediate volcanic rocks are widely developed in the Cretaceous Yixian Formation (K

1y

) in the periphery of Liaohe oilfield in southern Songliao Basin

and commercial oil flow has been tested in these volcanic rocks in Zhangqiang depression.Based on core observation and slice analysis

14 different rock types have been recognized in the Yixian Fm vocanic rocks.Among them

andesitic lava and andesitic volcanoclastic rocks have the greatest thickness and most extensive distribution.The volcanic lithofacies can be divided into 3 lithofacies and 7 subfacies

of which effusive lithofacies accounts for about 84%.The volcanic reservoirs have 6 main types of primary and secondary reservoir spaces and 4 kinds of pore associations.The plane and vertical distribution of reservoirs are jointly controlled by lithology

lithofacies and faults.The reservoir space types

reservoir capacity

permeability and connectivity are determined by diagenesis and tectonism.According to analyses of physical property and reservoir data

the most favorable reservoir facies belts include the pyroclastic lava

vesicular mandelstone lava

volcanic conduit facies (volcanic neck lithofacies or concealed explosion breccia lithofacies) and the upper effusive lithofacies.It is highly possible for the hydrocarbons to accumulate in the vent and proximal vent lithofacies

as well as the upper and top of volcanic eruption cycle/stage in areas adjacent to hydrocarbon kitchen and/or the structural high of deep large faults.