Geological Characteristics And Distributions Of The Hydrocarbon Reservoirs Of Volcanic Rocks In 3rd Member Of Kongdian Formation In Weibei Sag

Located on the east side of Changwei depression,Weibei sag is a typical strike-slip pull-apart basin in Tanlu fault zone,covering an area of 880km~2,is the mainly exploration target area in Shengli Oilfield,Volcanic reservoirs were developed during the deposition period of the third member of Kongdian Formation.Due to lack of in-depth study of its genesis,which have affected the reservoir-type oil and gas exploration processGenetic mechanism,reservoir development and reservoir-forming characteristics of these volcanic reservoirs has not been in-depth study,thus influenced exploration process of the oil and gas.In order to solve this problem,based on comprehensive theory and technology of volcanic rocks petrology,geochemistry,reservoir geology and petroleum geology,genetic mechanism,diagenetic evolution,reservoir characteristics of volcanic reservoirs and its relationship with reservoir forming were studied systematically.The results show that:The volcanic rocks of the third memberof Kongdian Formation are mainly made of overflow basalts.the early Cenozoic extensional activities of the Tan-Lu fault zone controlled the development of the Weibei strike-slip pull-apart basin which had a close relation with petrogenesis of Paleocene basalt.Indian-Asian continental collision and Pacific plate subduction in Paleocene caused intense left-lateral pull-apart of the Shandong segment of the Tan-lu fault zone.Intense activity of slip faults and lithosphere thinning caused Paleocene basalt eruption in Weibei sag.The volcanic rocks of the third memberof Kongdian Formation are divided into two volcanic eruption cycles,seven volcanic eruption stages.A complete volcanic effusive phase can be vertically divided into three subfaciess:the upper subfacies,the middle subfacies and the lower subfacies,Stomatal almond structure is developed in the upper subfacies,which is the main type of volcanic reservoirs.the primary pores and fractures generated by weathering-leaching and fault activities are the most abundant types.Subaqueous volcanic rocks had low physical property in the northern sag,Subaerial volcanic rocks had high physical property in the Southern slope zone and Zaohu fault-nose zone.The diagenetic evolution of the volcanic reservoir can be divided into four stages,syngenetic diagenesis stage,exodiagenesis diagenesis stage,burial diagenesis stage and Subsidence after tectonic inversion diagenesis stage.The reservoir capacity is closely related to weathering-leaching of exodiagenesis diagenesis stage and Faulting and dissolution of late burial diagenesis stage.Combined with volcanic facies distribution determined that the Zaohu fault-nose zone and the east Southern slope zone are the most favorable reservoir development area.High-quality dark mudstone of middlelower submember of the second member of Kongdian Formation Provided the oil and gas for northern subsags belt and northern part of Zaohu fault zone.Oil shale and lime mudstone of middleupper submember of the second member of Kongdian Formation were considered to be the chief source rocks to southern slope zone and southern part of Zaohu fault zone and The upper overflow subfacies subjected intense weathering were the main reservoir,Fractured-pore was the main reservoir space.reverse fault blocks with greater displacement exposed directly to Two groups of source rocks and formed a favorable trap-source configuration.Grooming network formed by fault and weathering crust provided favorable migration conditions.Dark mudstone of middlelower submember of the second member of Kongdian Formation provided a favorable cap rock condition.Three kinds of accumulation modes were summarized which are near-source lithofacies controlled accumulation model in northern subsag belt,middle-source fault-lithofacies controlled accumulation model in Zaohu fault zone and far-source faults controlled accumulation model in southern slope zone.Zaohu fault zone and southern slope zone were favorable area of hydrocarbon accumulation.The exploration method effectively guide the exploration deployment.