Petroleum Geological Characteristic Of Huoshiling-Yingcheng Formation In Yushu Fault Depression,Songliao Basin

In recent years,with thebreakthrough of deeppetroleum exploration in easternFault Subsidence Zone,Songliao Basin,the faulted depression shows a broad prospect of exploration.The Yushu fault depression isa composite semi-graben basin in the eastern fault zone,which located in the southeastern uplift area of Songliao Basin.It consists of two secondary depressionincluding Yudong and YuxiFault depressions.The exploration area is 2741km2.The fault layer is mainly composed of Huoshiling Formation,Shahezi Formation and Yingcheng Formation.Based on the seismicinterpretation data,the stratigraphic-structure framework of the study area is established.The results show that the two sub-fault depressions are both semi-graben systems controlled by the echelon fault combination,and mirroring secondary fault depression assemblage separated by the middle of Yushu uplift.Huoshiling Formation is widely distributed in study area and less affected by the basin-controlling fault,Shahezi Formation and Yingcheng Formation are strictly controlled by the basin-controlling fault and distributed in the depression.Based on the core analysis and the single well face analysisof the six wellsin the study area,the lithofacies model of Huoshiling Formation,Shahezi Formation and Yingcheng Formation were established.Six types of lithofacies are identified in the study area,which are lacustrine face,delta face,fan delta face,sublacustrine fan face,nearshore subaqueous fan face and volcanic face,and can be divided into 12 sedimentary subfacies,21 sedimentary microfacies.By using the seismic facies identification method,the relationship between the lithofacies and the seismic facies is established,and the lithofacies distribution of Huoshiling Formation,Shahezi Formation and Yingcheng Formation is restored.Huoshiling Formation develops the lacustrine-fan delta sedimentary system with largescale volcanic eruption facies and the overflow facies.Shahezi Formation mainly develops the lacustrine-fan delta-nearshore subaqueous fan sedimentary system.Yingcheng Formation develops the lacustrine-fan delta-nearshore subaqueous fan sedimentary system,with scattered volcanic overflow face.The analysis of the drilling core test data shows that the dark mudstone of Huoshiling Formation and Shahezi Formation are the main source rocks of Yushu fault depression.The geochemical test data shows that the maturesource rocks havehigh abundance of organic matter,and its kerogentype is mainly II2.Clastic rocksare the important reservoirs in the area,Its physical properties are characterized by special low porosity and extra-low permeability.Volcanic rocks that widely distributed in Huoshiling Formation and Yingcheng Formation can provide extra reservoir space.Self-generating and self-reservoiring,lower-generating and upper-reservoiring,upper-generating and lower-reservoiring are main 3 types of source-reserve-cap assemblages.The petroleum geological conditions shows that the volcanic domes belt of central uplift near two sides source rock in secondary depression of Yudong Fault depression is the favorable exploration play in this study area.