Gas pooling conditions and exploration direction in deep Songliao Basin

Gas exploration has not been very successful in deep Songliao Basin,except for the Xujiaweizi,Changling and Yingtai fault depressions.Seismic data,outcrop data,core observation and laboratory test results were integrated to study the gas pooling conditions in the basin,including the architectures of the deep fault depressions,source rocks and volcanic reservoirs.The following results were obtained:The distribution of deep gas reservoirs are controlled by fault depressions,volcanic rocks,faults and unconformities.The main stage of deep fault depressions was during the deposition of the Shahezi Formation,with 34 mutually-independent clustering fault depressions of different sizes.Each depression has its own independent petroleum system and gas is mainly distributed in the inherited fault depressions.The source rocks are completely distributed in each fault depression,in the central part of which there are best source rocks featured by sheet-like parallel reflection configuration,good stratification and continuity from the seismic reflection.The development of volcanic reservoirs is controlled by lithofacies,lithology,top structures and eruption cycles.The depressions were evaluated with sub-depressions as appraisal unit.The medium-to-small fault depressions with good pooling conditions have relatively large exploration potential,and Shuangcheng(Yingshan)and Lindian depressions are believed to be favorable for future exploration.