Research On Genetic Relationship And Enrichment Patterns Of Hydrocarbon Resources Of Ordos Basin

Unconventional and conventional hydrocarbon resources coexist in in Ordos Basin.According to drilling data,geochemical data and seimic data,by use of oil and gas geochemistry,structural geology,sedimentology and petroleum geology theory,based on the distribution characteristics of oil and gas,this paper analysized the relationship of oil and gas resources,clearified the type of oil and gas coexist system in Ordos Basin,identified the combinaiton type,established oil and gas migration and accumulation pattern.On that basis,the controlling factors were revealled,and exploration target was selected,which lay the foundation for efficient exploration and development.The main achievements and findings are as follows:1.According to the analysis of component features,carbon isotope characteristics and biomarkers characteristics between hydrocarbon and source rocks,it was concluded that coalbed methane and shale gas are genetic related to conventional gas and tight gas,while shale oil is genetic related to conventional oil,tight oil and oil sand.2.There are two coexist systems including oil and gas coexist system and gas coexist system.Paleozoic gas,coalbed methane,shale gas and tight gas belong to the gas coexist system,which is divided into coalbed methane-shale gas-gas,coalbed methane-shale gas-tight gas and shale gas-tight gas subsystem.Mesozoic conventional oil and gas,shale oil and gas,tight oil and gas and oil sand belong to oil and gas coexist system,which is divided into shale gas-tight gas-conventional gas,shale oil-tight oil-conventional oil and coalbed methane subsystem.3.Fault,reservoir and unconformity compose the migration pathway of oil and gas.Among these,fault is the most important migration path due to link the reservoir and source rocks.Unconformity is the main migration pathway of Lower Paleozoic conventional natural gas and conventional oil in Mesozoic,fault is the main migration pathway of Sulige gas field,fault and sand body are the main migration pathway of Ansai and Xifeng oil field in the lower part of Yanchang Formation.4.There are 4 northeast direction,4 northwest direction and 4 east-west direction fracture trend zone in the Ordos basin,the dominant small faults and the hidden fractures in the fracture trend have improved the reservoir physical properties,and the oil and gas resources have the characteristics of complex zonal distribution along the fault trend.5.Majiagou Formation and overlying coal measure source rock directly contact due to the Caledonian movement,formed at the lower part of the conventional natural gas,the upper part of the coal seam gas in vertical to the combination?Yanshan movement in the basin tectonic inversion occurs,resulting in Upper Paleozoic coal measure hydrocarbon source rock and the Mawu5-Mawu10 dolomite reservoir layer lateral contact,forming a combination of coal seam gas-conventional gas lateral.The unconformity controlled Mesozoic oil-bearing horizons formation in the Indosinian movement is also important influence factor of shale oil and gas tight oil and gas combination.6.The lagoon peat flat and tidal flat peat flat in carboniferous-Permian benxi stage and taiyuan stage,the River flood peat bogs and the peat bogs in the lake delta plains in shanxi period controlled the distributions of Coal seam.Lagoon,delta plain,flood plain and shallow lake sedimentary environments controlled the distribution of the dark mud shale.Braided river,delta depositional system controlled the sand body distribution of shanxi and xiashihezi period.The delta-lacustrine depositional system in Yanchang Formation and river-delta depositional system in Yan'an Formation lay the foundation of shale oil and gas-tight oil and gas-conventional oil and gas combination.7.On the basis of comprehensive analysis of coal-bed methane,shale gas and tight gas of Ordos Basin,this paper selected four CBM-shale gas-tight gas joint-rich region,there are two blocks in the northern part of Western thrust belt and one block in Yimeng uplift and one block in North Shanxi slope,which is the biggest one.The target exploration intervals are Taiyuan Formation and Shanxi Formation.There are six shale oil-tight oil joint-rich blocks in Ordos Basin,concentrated in the southwest of North Shanxi slope.Among these blocks,Block Xifeng and Huachi are with relatively favorable geological conidtions,which are the prime exploration target.And the shale oil exploration interval is Chang 7 group,while the tight oil exploration interval is Chang 6 group at Fuxian and Huachi area.