Study On Petroleum Geology And Accumulation Conditions In Yuncheng Basin

Yuncheng Basin is an important part of Cenozoic Fen-Wei graben in southeastern margin of Ordos Basin,which has similar tectonic background and sedimentary filling evolution history with Weihe Basin.The Weihe Basin is characterized by relatively thick lacustrine source rocks and favorable reservoir-cap conditions,showing good hydrocarbon resource potential.At the same time,the Fen-Wei graben separated from the Ordos Basin and evolved independently in the late Cretaceous,which has the same pre-Mesozoic stratigraphic system as the Ordos Basin.Therefore,the potential of oil and gas resources in Yuncheng Basin has been concerned for a long time.However,compared with the Ordos basin and Weihe Basin,the exploration degree of Yuncheng Basin is very low,and there is a lack of systematic research on the formation development,the development characteristics and hydrocarbon generation conditions of source rocks,and the combination of source rock,reservoir and cap rock.It is an important problem for oil and gas exploration in Yuncheng Basin to confirm the development of Mesozoic and Paleozoic strata and determine the hydrocarbon formation,reservoir-reservoir-cap conditions and the basic characteristics of hydrocarbon accumulation.In this paper,based on the drilling data of Jitan 1 well in Yongji Depression,which developed well in the Cenozoic of Yuncheng Basin,and combined with the regional geological data of Yuncheng Basin periphery,the formation development is deeply studied,the hydrocarbon source rock and its hydrocarbon generation characteristics are determined,and the geological conditions of oil and gas accumulation in Yuncheng Basin are comprehensively evaluated.This paper is of great significance to the oil and gas exploration of new areas,new strata and new fields in Ordos Basin.The drilling of Jitan 1 well in Yuncheng Basin encountered Cenozoic,Lower Paleozoic and Middle-Late Proterozoic strata,and the drilling revealed that the Yuncheng Basin lacked paleogene,Mesozoic and Upper Paleozoic strata.Jitan 1 well has a good correlation with the lower Paleozoic strata in the adjacent area,and the lateral variation is small.The characteristics of Cenozoic strata in Weihe Basin are similar.Combined with the data of logging,logging,core and outcrops,yuncheng basin maily experienced the neoproterozoic Marine facies clastic rock,early Paleozoic Marine carbonate rocks and late Paleozoic Marine deposition,Mesozoic and Cenozoic lacustrine facies sedimentary environments evolution.The comprehensive analysis shows that the fault of paleogene in Yuncheng Basin is elision of cycle stage,while the fault of Upper Paleozoic and Mesozoic strata is structural deficiency,not sedimentary gap.By means of organic petrology,organic geochemistry and sedimentary geochemistry,It is revealed that three sets of potential source rocks of Proterozoic,Paleozoic and Cenozoic developed in Yuncheng Basin.The petrology,geochemistry and formation environment of source rocks are studied and evaluated.The 32 meters’ black mudstone in the lower part of cuizhuang formation is medium to good source rock,and the Cambrian mudstone and carbonate rock in the lower Paleozoic,the Zhangjiapo formation and Lantian-Bahe formation in Cenozoic are poor to non-source rock.Cambrian carbonate basin development in lower palaeozoic era-clastic rocks and Cenozoic neogene clastic rock 2 sets of reservoir and corresponding cover layer,can be totally divided into 2 sets of reservoir and caprock.The main trap types are stratigraphic trap,lithologic trap,structural trap and composite trap.Oil and gas migration conducting system mainly include fault,unconformity and fault,sand body conducting system.There are two oil and gas reservoir systems in Yuncheng Basin,which are respectively proterozoic lower generation,upper reservoir and upper cap accumulation system and Cenozoic self-generation,self-storage and self-cap accumulation system.The lower part of the reservoir system is in good condition,which is not conducive to the formation and preservation of oil and gas due to the tectonic movement since Mesozoic.The comparison of hydrocarbon accumulation conditions between Yuncheng Basin and the Cenozoic Weihe Basin shows that the Cenozoic in Weihe Basin is better than that in Yuncheng Basin,and both of them are self-generation,self-storage and self-cover type.The comprehensive analysis shows that the mudstone source rocks of The Middle-Late Proterozoic Cuizhuang Formation in Yuncheng Basin have good hydrocarbon generation potential,and the Neoproterozoic reservoir forming system of the lower generation,upper reservoir and upper cap has good exploration prospects.