| Songliao basin is a large Mesozoic-Cenozoic composite sedimentary basin with fault subsidence and depression dual structure. It consists of six first-order structural units, which are the western slope, the southwestern uplifted area, the southeastern uplifted are, the central fallen area, the northeastern uplifted area and the northern plunged area. In the basin, the south of Nenjiang River, second- Songhua River and Lalin River is called southern Songliao basin. The earth's crust of Songliao basin can be divided into three parts, the upper crust, the middle crust and the lower crust. Moho surface at the bottom of the lower crust becomes shallow from margin to center, and the depth of depocenter is symmetrical with Moho surface by a mirror plane. While in faulted basin, the depth of depocenter is somewhat off-lying to Moho surface, which coincides with Lster's complex-shear model.The base of southern Songliao basin, which is made up of mesometamorphic rock and metamorphic vulcanite, is composed of the base of North China platform and the southern extension of Caledonian and Hercynian folded belt which is located in northern edge. The basement faults developed too much, and were comprised of four fault systems, which were NE and NNE direction fault system, NW direction fault system, EW direction fault system and SW direction fault system. Among them, NE and NNE direction faule system plays an important role in the formation and development of Songliao basin. The sedimentary cover of southern Songliao basin is made up of Mesozoic-Cenozoic stratigraphy. From bottom to top, they are: Huoshi- ling formation, Shahezi formation, Yingcheng formation, Denglouku formation and Quantou formation which developed in lower Cretaceous; Qingshankou formation, Yaojia formation, Nenjiang formation, Sifangtai formation and Mingshui formation which developed in upper Cretaceous; Yi'an formation, Da'an formation and Taikang formation which developed in Tertiary. In the basin, volcanic rock is widely distribut- ed with whole rock types, which is generated by magmatic activity in the middle and late periods of Yanshan movement.In southern Songliao basin, three associations of structural style are distinguished, which are fault phase, depression phase and inversion phase. The structural style of fault phase is characterized by half garben formed by the extention of listric faults and is absence of typical double faulted graben. The inversion phase is first formed in the later Nenjiang period, and is reformed to a pattern by structural movement in the later Mingshui period. According to the study of balanced section, before Denlouku period, a intensive extention existed in Songliao basin, and the extension became weak in the later Yingcheng period, which caused basal long-range integral uplift. Intensive extention occurred in Denglouku period, while in Quantou-Nenjiang period, weak extention occurred, the earth's crust subsided slowly, and was filled persistently. Triple compression happened after Nenjiang, Mingshui and Yi'an Formation were deposited. Based on above mentioned research, the structural evolution of Songliao basin can be divided into four stages: extensional rifting stage, depression stage, structural inversion stage and Cenozoic fault sag stage.According to the comprehensive research to outcrop, core, well logs and seismic data, Mesozoic-Cenozoic deposition in southern Songliao basin is divided into three megasequences, that is intermontane megasequence in Jurassic and rifted basin mega-sequences in Cretaceous and Paleogene-Neogene. Three supersequence sets, seven sup- ersequences and nineteen sequences are distinguished in rifted basin megasequences in Cretaceous. The sedimentary system in fault subsidence Period is characterized by near source, multiple source and multiple sedimentary systems. While in the depression Period, the sedimentary system is controlled by three main provenance, and developed alluvial fan-fan delta-lacustrine sedimentary systems which come from Zhenlai-Baicheng.Alluvial fan- braided river- delta- lacustrine sedimentary systems which come from Tongyu-Baokang and alluvial fan-fluvial-delta-lacustrine sedimentary systems which come from Changchun- Huaide. The feature of sedimentary systems are variant in different depositional period.Basing on the research of tectono-sedimentary evolution, current geothermal field, organic thermal evolution and modeling buried history and thermal history were studied. The high-geotemperature zone in southern Songliao basin covers Honggang- Da'an-Heidimiao area, and geo-temperature decreases successively with the approach of surrounding uplift. While geothermal gradient is high in the central uplifted area, and decreases outward in proper order. The depth of hydrocarbon source rocks entry into oil generation threshold is usually about 1500-1600 meters, however, the depths are different in different areas, and in shallow buried areas, the depths are low. The result of modeling buried history and thermal history demonstrates that: the deposition rate and subsidence rate are the highest in the Shahezi and Yingcheng periods, the rates are higher in the Quantou and Mingshui periods, and the rates are low in the Denglouku, Qingshankou, Yaojia and Sifangtai periods. In the Huoshiling period, the geotemperature are higher. A apparent cooling occurred in the Shahezi period. Afterward, the geotemperature ascended sullenly in the later Yingcheng period until the Denglouku period, and a wellmarked ascending happened in the Qingshankou period. However, after the Yaojia period, the geotemperature began to drop, and the rate of falling temperature attained to the maximum in the Mingshui period.There are two series of excellent source rocks: Qing 1 member and Nen 1-2 members in southern Songliao basin, which are formed in semi-deep and deep lacustrine with distributing widely, high abundance of organic matter and good kerogen type. In the later Nenjiang period, the source rocks of Qing 1 member had been begun to largely expel oil and gas, and the source rocks of Nen 1-2 member began to enter the threshold of hydrocarbon expulsion. Reservoir rocks were mainly formed in fan delta facies with seldom in fluvial, alluvial fan and offshore lake facies. In longitudinal section, Fuyang, Gaotaizi, Putaohua, Saertu and Heidimiao oil reservoirs are all belong to the middle oil-bearing assemblage. Through oil-source correlation, the hydrocarben of Fuyang, Gaotaizi and Putaohua oil reservoirs comes from the source rocks of Qing 1 member, the hydrocarben of Sa'ertu oil reservoir is mainly from Qing 1 member with a little from Nen 1-2 member, and the hydrocarben of Heidimiao oil reservoir is mainly from Nen 1-2 member.Computational solution of fluid potential in Songliao Basin indicate that present fluid potential of oil layers is always a belt of high fluid potential at Da'an Depression-Changling Depression. The fluid potential gradually decline from westward to eastward. Belt of high fluid potential constitute the first order of fluid separation trough. The composition of fluid potential in the west of the center fluid separation trough is simple,but that in the east is more complex. According to fluid potential at the center separation trough,which can be divided into 1-2 allogenetic(authigenic)open reservoir-forming dynamic system in the west,another 2-3 allogenetic(authigenic)open( semi-closed)reservoir-forming dynamic system in the east .Each constitute is a relatively independent concourse unit. Basing on the result above and through the multidisciplinary analysis of thermal alteration history, tectono-sedimentary evolution history and oil gas reservoir- forming dynamic system of hydrocarbon mother rock, combinating the research of reservoir fluid inclusion, analyzing oil gas filling course, and finally we establish the oil gas reservoir- forming pattern of Songliao Basin.Suming up: reservoir- forming dynamics,core is dynamic system and course of oil gas migratory concentration , researching the generating,migratory,concentration and distribution pattern of oil gas in basins. Basin,s tectono-sedimentary evolution and thermal evolution control the formation and evolution of reservoir- forming dynamic system, hence the research of tectono-sedimentary evolution and thermal evolution history is the basis. This paper establishes the pattern of oil and gas reservoir-forming of Songliao Basin. By researching oil gas reservoir-forming geologic setting,tectono-sedimentary evolution and thermal evolution history,utilizing computational solution of fluid potential,dividing different time,s reservoir-forming, dynamic system, discussing the course of oil and gas reservoir-forming in reservoir-forming dynamic system. |
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