| The southeastern part of Songliao Basin mainly includes 8 fault depressions of Wangfu,Yudong,Yuxi,Dehui,Lishu,Shuangliao,Sanchahe and Zengsheng.The potential of oil and gas resources is huge,but no systematic research has been carried out on the petroleum accumulation rules of the Huoshiling-Yingcheng Formations in the southeast of Songliao Basin.Therefore,there is still no unified understanding of the regional fault depression combination and evolution,the sedimentary system and favorable reservoir distribution,the reservoir controlling factors and the accumulation rules of the Huoshiling-Yingcheng Formations in the study area.This article takes the Huoshiling-Yingcheng Formations of 8 fault depressions in the southeast of Songliao Basin as the research object.Based on the previous research results of a large number of single fault depressions,applying new theory and new methods in the fields of sedimentary geology,petroleum geology and geophysics,using seismic interpretation,drilling well analysis and core observation,combing with rich oil and gas test results,we systematically studied the structure,combination and evolution mechanism of fault depressions in the southeastern part of the Songliao Basin,summarized the tectonic,filling evolution and reservoir differentiation of different fault depression types,revealed the controlling factors and the rules of hydrocarbon accumulation in different structural styles.On the basis of stratigraphic correlation,through the joint interpretation of 2D,3D seismic sections and structural analysis of faulted basins,the axial directions of 8 faultedbasins in the study area are mainly NE,NNE and near SN,mainly controlled by NNE,NE,near SN and NW faults.According to the plane connection pattern of the control faults,the study area fault depressions can be divided into three half graben types: single-fault type,phase-composite type and multi-lateral composite type.On the basis of the fine seismic interpretation and the study of tectonic framework,combined with the regional tectonic evolution background,the balanced section method is applied to divide the tectonic evolution of the study area into the initial fault depression stage,the strong fault depression stage and the fault decay stage.The total stratum stretch of the fault depression of different structural styles in the study area is about 0.68~5.73 km.In the near SN-controlled single-fault fault depression,the total stratum stretch during the faulted period is the largest,about 5.73 km,and the corresponding formation stretch rate is17.54%;The total stratum stretch of the phase-composite fault depression controlled by NNE-NE faults is the second,about 5.20 km,and the corresponding formation stretch rate is 16.46%;In the multi-lateral composite fault depression,the total stratum stretch is the smallest,about 0.68 km,and the corresponding formation stretch rate is 1.95%.Through the comprehensive analysis of the core,logging data and key-seismic-profiles,the distribution characteristics of the sedimentary facies belt of the Huoshiling-Yingcheng Formations in the study area were restored.During the Huoshiling period,the volcanic facies is dominated the north and south of the study area,and the semi-deep lake facies deposits developed in the middle.In the sedimentary period of the Shahezi Formation,the basin of the faulted depression expanded,formed a lake-fan delta-sublacustrine fan sedimentary system in which widely distributed the fan delta sand body;Compared with the Shahezi period,the edge-controlled basin fault activity in the Yingcheng period was relatively weakened,and the lake water body became shallower,but the lake basin range was enlarged,formed a lake-fan delta-sublacustrine fan sedimentary system.Through the homogenization temperature measurement of reservoir hydrocarbon fluid inclusions,combined with the representative single well burial thermal evolution history of Dehui and Wangfu fault depressions,it is determined that the single-fault fault depressions of the study area have experienced at least two oil and gas filling events in the reservoirs of the Huoshiling-Yingcheng Formations.They are the Quantou-Qingshankou period and the end of the Qingshankou-Nenjiang period,and their corresponding hydrocarbon accumulation time are 98.3~91.0Ma and 88.9~81.0Ma respectively;The reservoirs of the Huoshiling-Yingcheng Formations of the phase-composite fault depressions have experienced at least three hydrocarbon filling events,namely the end of the Yingcheng period,the Quantou period and the end of the Qingshankou-Nenjiang period,and the corresponding accumulation time are 100.0 Ma,97.9 to 94.6 Ma and 87 to83 Ma respectively.According to the correlation analysis of the deep petroleum distribution and accumulation characteristics and main controlling factors in the key fault depressions,it reveals four key controlling factors of the oil and gas accumulation of the Huoshiling-Yingcheng Formations in the southeast of Songliao Basin: development of semi-deep lacustrine high-quality source rocks,development of volcanic domes,or the presence of the tongue up-dip sandstone pinchout of fan delta front or lens-shaped sublacustrine fan sand body,volcanic domes near the hydrocarbon generation sag in the volcanic rock area,faults.Based on the comprehensive analysis of the geological conditions of oil and gas accumulation in the fault depression,combined with the petroleum accumulation rules and controlling factors,two favorable hydrocarbon accumulation model s are established.Single-fault fault-depression hydrocarbon accumulation model:(1)The source rocks and the laterally interacting reservoir sand body constitute the updip-tip lithologic accumulation belts on the slope zone,(2)In the central secondary bulge forms the volcanic dome accumulation belts dominated by vertical migration and the lens-type lithologic accumulation belts or the tectonic-lithologic composite accumulation belts dominated by lateral migration,(3)On the edge of gentle slope forms the volcanic dome accumulation belts dominated by vertical migration.The phase-composite fault-depression hydrocarbon accumulation model:(1)In the central secondary bulge west-wing slope,the source rocks and the laterally interacting reservoir sand body constitute the updip-tip lithologic accumulation belts intercalated with the lithologic-fault composite accumulation belts,(2)In the central secondary bulge forms the volcanic dome accumulation belts dominated by vertical migration and the updip-tip lithologic accumulation belts or faulted anticline accumulation belts dominated by lateral migration,(3)In the central secondary bulge east-wing slope,the source rocks and the laterally interacting reservoir sand body constitute the updip-tip intercalated with the lens-type lithologic accumulation belts,(4)On the edge of the steep slope of the basin-controlling faults on both sides of the fault depression,forms the volcanic dome accumulation belts dominated by vertical migration. |
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