Study On Sedimentary, Sequence Evolution And Lithologic Oil Pool Of Yanchang Formation In Triassic, Ordos Basin

Ordos basin is one of the large inland basin of abundant energy andmineral source of Mesozoic in the east of our country. And it was preservedintegrally. The Yanchang Formation of Triassic is not only researchedearly, but also the first obtain oil gas strata of the basin. For a numberof years, it is the primary target of oil and gas exploration. On the basisof substantive field and indoor practice development work, the boundaryof sediment, the source, the sedimentary system, the basin developmentmode, the sequence stratigraphy, the bottom shape of lake and thelithology reservoir were researched.By the analysis of tectonic, the character of stratigraphy and borderfacies of both sides and the seismic analysis, the boundary of sedimentof Yanchang Formation was researched. The fracture zone of the westHelanshan and the west Liupanshan constitute the northwest and southwestboundary. The west of the Basin can extend to the south of Gansu alongthe Hexi corridor. The east of the Basin can extend to the west of Helan,the north of Helan and the middle-west of Shanxi. By using paleocurrentdirection, clastic particles style and characteristic, heavy mineralcombination, quartz cathode luminescence and rare earth elementallocation model, we researched the source condition of basin. Thenortheast source came from the hypometamorphic rock of the south Yingshan.The southwest source came from fracture zone of the Qingling andQilianshan and Longxi block mass 'metamorphic rock and Eopaleozoicsedimentary rock. The northwestward source came from west Helanshan'metamorphic rock and sedimentary rock. The south source came from thenorth Qingling' metamorphic rock and carbonatite.The primary facies are alluvial fan facies, fluvial facies, delta facies and lake facies. The northeast of basin upgrowth flat gradient typelake delta sedimentary system, the southwest upgrowth scarp braided streamdeltaic deposit system. The author found sedimentary facies model andanalysed the depositional pattern and ore mass unfold law in differentphases.The Yanchang Formation is divided into one tectonic sequence and fourthird-order sequences by use of theory and method of continental sequencestratigraphy. The framework of sequence stratigraphy of YanchangFormation was built. At the same time, the sediment and evolution of everysequence were discussed.By using the stratigraphy thickness method, the sediment microfaciescombined method as well as high resolution sequence stratigraphy meanssynthetically, the lake basin knickline was ascertained. On the bases ofthe emendation of fossil water deep and stratigraphy thickness, theancient landform of lake basin in Yanehang period was restored,homologous digital elevation model was erected, and triaxialityvisualization analyses was made.The characteristic, enrichment law and the element of lithologicreservoir accumulation was summarized. The impact that the bottomconfiguration of lake basin on lithologic trapas and the control of thesequence stratigraphy on lithologic reservoir were analysed.