| The research area is located in Maichen sag of Beibuwan Basin have experienced multiphase tectonic movements.A large number of faults make the different tectonic units of static structure and dynamic evolution process in the basin complexity and diversity,further affect the depositional system,reservoir forming conditions and process.Although the predecessors have done a lot of research of the Beibuwan Basin,the lack of the data of the basin and its complexity,resulted in the limitation of the understanding.The research area is lack of the analysis of the reservoir forming control,based on the diversity of the structure.At the same time,the oil and gas reservoir were found generally in Liushagang formation of Beibuwan basin,just rarely be found in Weizhou formation.But the commercial oil deposit were found in Weizhou formation of Maichen sag,and main controlling factors of hydrocarbon accumulation of Weizhou formation are unclear.So,this research analyze the electrofacies,individual-well facies,well-tie facies and in-plane facies,based on the regional sedimentary characteristics,core observation,well logging data and so on to determine the major sedimentary facies and plane distribution characteristics of the study area.Evaluate the reservoir and capping formation combined with the previous research results.Determine the space development characteristics and favorable distribution area of the source-reservoir-cap assemblage.Analyze the fault formation stage,the geometric characteristics and fault sealing characteristics of different layer and segment.Forecast the fault sealing based on the methods of Shale Gouge Ratio,and the ratio of sand and mud.Analysis of what faults have translocation and what have sealing function in different fault combination.According to the profile of faults,structure the oil and gas migration pattern under the controlling of the faults.Compare and analyze the differentconditions and characteristics of hydrocarbon accumulation between the structure of found petroleum reservoir and loss well,discuss the main controlling factors of hydrocarbon accumulation and hydrocarbon accumulation mode.Through the above describe,obtained following conclusions:?1?The third section of Weizhou formation in the northern slope zone of the research area is a set of fan delta deposition.The second section of Weizhou formation is a set of fluvial-delta deposition.Both of the third and second section of Weizhou formation in the southern fault zone of the research area is nearshore subaqueous fan deposition.?2?The main source rock is the dark mudstone of lake facies in the second and third section of Liushagang formation.Totally,the thickness of source rock became thin from south and west to north and east.The secondary source rock is from Weizhou formation.The average of TOC of the second section of Liushagang formation is 1.92%,the measured value of potential of generating hydrocarbon is between 1.33mg/g and 7.82mg/g,the measured value of chloroform bitumen?A?is between 0.038%and 0.4592%,total hydrocarbon content is between 311ppm and3069ppm.Totally,the source rock's quality from Liushagang formation is very well.The value of Ro is between 0.60%and 0.90%.Most of the value of Tmax is over 435?and some of it beyond 440?.The source rock has already matured and has reached the stage of hydrocarbon generation.The organic matter type of the source rock of Liushagang formation is?1 and?2??3?The thickness of reservoir became thin from northern and southern provenance to deep sag belt.The thinnest area is the center of the basin.The main rock of reservoir of the northern slope zone is feldspathic litharenite,and the secondary is lithic arkosic.The main reservoir pore is inter-grain pore.The average of porosity is between 9.46%and 17.63%.The average of permeability is between 2.72×10-3?m2and 45.12×10-3?m2.So the reservoir of northern slope zoneis low-medium porosity and ultralow-low permeability.Sandstone and conglomerate reservoirs are mainly exist in the southern fault zone of the research area.The pore types include intergranular pore,solution pore and fracture.The average of porosity is between 0.8%and 1.7%.The average of permeability is between 2.72×10-3?m2 and45.12×10-3?m2.So thereservoir of southern fault zone is ultralow porosity and permeability.The main cap in the research area is the regional cap of the second section of Weizhou formation,and the local mudstone cap of third section of Weizhou formation,and the tight sandy gravel cap of the southern fault zone of the research area.Near the sandstone development region of deep sag belt of the northern slope zone and nearshore subaqueous fan deposition of the southern fault zone are the best area of reservoir-cap association of Weizhou formation.?4?Evaluate the fault sealing based on the methods of the ratio of sand and mud,Shale Gouge Ratio,fault plane normal pressure,an angle between tectonic stress and fault strikes.?5?The main controlling factors of hydrocarbon accumulation are:The main controlling factors of the northern slope zone are the ability of local cap sealing,and itsdistribution range and fault sealing;the main controlling factors of the southern fault zone are high quality reservoirs'distribution range,the faults'distribution range which ditches the source rock,and the fan root lateral sealing.?6?The main hydrocarbon accumulation mode of the research area is?lower product and upside reservoir?,the secondary is?auto-product and auto-reservoir?.One mode of the northern slope zone is the oil and gas came from source rock of Liushagang formation,transported vertical to Weizhou formation and accumulated.Another is oil and gas came from source rock of Weizhou formation,transported lateral to Weizhou formation and accumulated.Fault-nose and fault-block pattern trap of the rising side of fault are the main type of traps,probability have some fault–litho composite trap.The southern fault zone of the research area developed the vertical overlap nearshore subaqueous fan deposition.Because of the deeply buried,forming the subtle trap what is sealed by fan root physical character different.The oil and gas came from source rock of Liushagang formation and Weizhou formation transported lateral to the fan trap in contact with it and accumulated.Or transported vertical along the boundary fault and associated fault to the fan trap of Weizhou formation and accumulated. |
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