Abstract: 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.

Key words: hydrocarbon accumulation pattern, reservoir characteristics, lithology and lithofacies, volcanic rock, Yixian Formation, periphery of Liaohe oilfield