The Researching Of The Characteristic Of Yan9 And Chang2's Oil Reservoir In Jiyuan Of Dingbian Area In Ordos Basin.

Ordos Basin is a polycyclic superposition basin which possesses abundant oil & gas resources and has bright prospects in oil & gas exploration. Jiyuan oilfield is one important generative area of oil of Dingbian area in Ordos basin. Yanan formation's Yan9 and Yanchang formation's Chang2 oil beds are two primary oil beds in it .For the sake of deeply researching and the rules of hydrocarbon accumulation and distribution, it is necessary to study characteristic of oil storage in the Yan9 and Chang2 oil beds.The theories of sedimentology and petroleum geology and borehole geophysics as direction, on the basis of collecting the data of geology, drilling, logging, oil testing, combining with geology, geophysics, geochemistry, combining with geology investigations in the field and research indoors, using many testing methods and analytical techniques, Yan9 and Chang2 oil beds of Jiyuan oilfield were deeply studied in strata, structure,sediment,reservoir characteristics and characteristic of oil storage.On the basis of these methods, the paper researched the rules of accumulation and the distribution of oil and gas and controlling factors of it.West monocline as background, nosing structures were developed in Jiyuan oil field. Sedimentary microfacies of Yan9 and Chang2 oil beds were river channel sand bar,crevasse splay,natural levee,flood plain, distributary channel, low-lying land between river channel and so on. Yan9 reservoir developed meandering river sediment and sand bodies' configuration presented a band shape of north-east and nearly south-north trend. Chang2 reservoir developed distributary channel deposit of delta plain and sand bodies' configuration presented a band shape of north-east, north-north- east, north- north- west and nearly south-north trend.The paper synthesized a lot of the data of core analysis and result of log interpretation . Yan9 reservoir was moderate porosity-low permeability in the majority, low porosity-ultra low permeability individually. The kind of Yan9 reservoir was II type . Chang2 was worse than Yan9 in physical property of reservoir, Main porosity and permeability types of which were ultra low porosity-ultra low permeability, low porosity-ultra low permeability, moderate porosity- ultra low permeability .some was moderate porosity-low permeability. The reservoir types were mainly as III type, some was II type of Chang2.The physical property of reservoir was determined by sedimentary microfacies in researching field. Because the hydrodynamic pressure of Fluvial channel and distributary channel were very strong and the size of grain was large, well gradation, as well as less cementing material, the physical property was well. The main part of sand body which was vantage ground for the hydrocarbon accumulation often had higher porosity and permeability. But the characteristic of the boundary of sand body was opposite to it. The lithology of interchannel and interdistributary area were mainly silty mudstone and mudstone, it was the good lateral barrier and oil usually didn't accumulate in there. The diagenesis had both constructive and destructive effect to the physical property of reservoir.. The destructive effect was mechanical compaction or pressolution and cemented fill in the early period. The constructive effect was denudation in late diagenesis in the environment of burial and developed a lot of emposieu which improved the physical property of reservoir.The researching of the condition of oil accumulation indicated Chang7 was the main oil source rock in the Jiyuan oilfield. Permeable sandstone was the main petroleum migration pathway of Yangchang Formation, and oil reservoir distributed chiefly at hydrocarbon generation center or regions around it. Surface of Triassic unconform ity and ancient stream channel sandbody of Jurassic constituted the major migration pathway of Yanan Formation, the oil reservoir accumulated primarily in the ancient stream channel and places near the surface of unconform ity.Yan9 oil reservoir was dominated by Jurassic palaeogeomorphology. The traps were mainly compacted structure and stratigraphy barrier. Fluvial facies accumulated oil.Chang2 oil reservoir usually developed compacted structure because of differential compaction and had nosing structure and arched structure in well developeing sand body, where would developed structural-lithologic reservoir if having stratigraphy barrier in the updip direction. Distributary channel facies was in favor of accumulating oil.