| By using research idea of petroleum accumulation dynamic system,this article had taken Maichen sag of Beibuwan basin as an example to analyze the dynamic factors of petroleum accumulation system and improve the research workflow and techniques on the basis of several sigle factor dynamic evoluation research including basin forming and sedimentary filling,hydrocarbon generation and migration range,energy field and accumulation drive power,oil&gas migration network,etc.By testing and mesurement,a lot of testing data,such as source rock geochemical data,fluid inclusion data,sandstone reservoir property data,layer temperature and formation pressure,rock physical parameter,had been provided to study on this topic.Focusing on the petroleum volume with commercial scale as the object of study,a view had been presented in this article that there are 3 key parameters,petroleum quantity,petroleum drive power and migration pathway,could be used to describe the process of petroleum generation-migration-accumulation,and a MEP method,which include the mass,energy,and pathway of petroleum,had been established to study the dynamic variation of these three parameters during different geological phases and to provide more quantitative parameters for the evaluation of different petroleum accumulation systems and to point out those advantageous exploration targets at last.The oil-source analysis indicated that the dark mudstone of Liushagang formation in Maichen sag is the major source rock.At the end of early Oligocene,there were local area generating hydrocarbon and the hydrocarbon generating range gradually increased.Up to now,the accumulative oil generating quantity is 1206 × 106t and the accumulative gas generating quantity is 225.64 × 109m3 depening on the calculated result of improved Monte Carlo method.On the basis of fluid potential field study,Maichen sag had been divided into 5 small generation units according to the potential trend and the unit I has the bigget hydrocarbon generation intensity.The fluid inclusion analysis illustrated that there were 3 accumulation stages,corresponding to early Miocene,Middle Miocene and the end of Miocene,of petroleum accumulation at least in Maichen sag in accordance with the major hydrocarbon generation stage.Based on the analysis of geotemperature field,formation pressure field and fluid potential field,oil&gas accumulation dynamic patterns had been established and accumulation dynamic conditions during the major accumulation stages had been discussed.Paleogeothermal gradient had been restored by using fluid inclusion method and paleo-heat-flow method that indicated geothermal gradient gradually increased after 6Ma.The calculated results of formation pressure indicated that there existed over-pressure features in the top of Liushagang formation which distributed over the deep depression and the inner slope zone of Maichen sag and had the relationship with hydrocarbon generation increasing over-pressure.The analysis of fluid potential indicated that the southern faulted zone and the northern slope zone were the advantageous zones of oil&gas migration.For quantificationally describing oil&gas accumulation drive power during different stages,this article had established 4 dynamic patterns of petroleum accumulation including the dynamic pattern of overpressure driving,the dynamic pattern of lateral communication,the dynamic pattern of lateral sealing,the dynamic pattern of buoyancy drive and given out the calculation methods to calculate the oil&gas migration drive power conditions during 3 major accumulation stages to guide the boundary division of accumulation dynamic systems at last.By using techniques including stress analysis,seismic predication,sedimentary facies,reservoir property evaluation and sandstone lateral distribution analysis,the petroleum migration pathway framework had been researched.A viewpoint had been pointed out that the major fracture forming mechanism is stress fracture.The large-scale fracture zone formed during major tectonic movement stages distributed over the middle part of slope and the southern faulted zone.With the faults penetrated into the matured source rock during tectonic movement stages,the fracture developed zones with faults became the highway of petroleum primary migration together,so called"migration corridor" and "migration fault" which was high efficient primary pathway of episodic petroleum migration.Based on the analysis of migration fault and sandstone connectivity,this article had established 2 petroleum migratin pathway frameworks:the one was the southern boundary fault-fan petroleum migration system;another was the slope delta-fault petroleum migration system.This article had described and analyzed the features of different petroleum migration pathway framework.This article had established the dynamic division idea and basis of petroleum accumulation dynamic system and divided the petroleum accumulation dynamic system of major accumulation stages in Maichen sag to point out the exploration direction.To distinguish with the traditional petroleum accumulation group,petroleum accumulation system and petroleum system,this article had divided Maichen sag into 5 petroleum accumulation dynamic systems on the basis of dynamic evolution of petroleum accumulation dynamic elements with the parameters of "mass,energy,pathway",which included hydrocarbon generation unit division,petroleum migration pathway framework,the relationship of drive power and resistance power of petroleum migration,sedimentary system and sandstone reservoir distribution,trap distribution,etc.This article had described and summarized the hydrocarbon generation unit,generation quantities,migration pathway framework,reservoir system,accumulation drive power and accumulation pattern to point out the petroleum accumulation dynamic system I,II,IV were the advantageous accumulation area. |
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