Abstract:

Intermediate and mafic volcanic rocks of Songliao basin mainly are developed in Anda subsag,which gas productivity takes about 60% of total productivity in the deep layers of the study area.The source rocks of intermediate and mafic volcanic gas reservoir are dark mudstone and coal developed in Shahezi Formation.Reservoirs are dominated by trachyte,basalt and volcanic breccia of the Third Member of Yingcheng Formation.Regional cap is mudstone of the Second Member of Denglouku Formation,besides these,there are many kinds of lithologic and structural traps,which benefit to reservoir-forming.The characteristics of effective reservoir are analysised by property and permeability data.Then combining comprehensive log interpretation and gas testing results, the distribution of gas reservoir both on longitudinal and horizontal sections is analysised.The main factors of intermediate and mafic volcanic gas reservoir-forming of Yingcheng Formation in Anda subsag are studied. Lithology and lithofacies influence the development of effective reservoir,and trachyte and basalt of effusive facies are mainly effective reservoir type.Intermediate and mafic volcanic breccia of explosive facies have best property and permeability which should be paid special attention. Volcanic cycles control the longitudinal distribution of gas reservoir,that is gas reservoirs mainly locate in the top and upper of each volcanic cycles/stages. Volcanic edifice facies belts control the horizontal distribution of gas reservoirs.The gas reservoirs distribute mainly in cracter-near cracter facies belts.

Key words: Songliao basin, Yingcheng Formation, intermediate and mafic volcanic gas reservoir, reservoir-forming main factors, volcanic rocks