Study On Sedimentary System And Oil-gas Enrichment Regularities Of Early-Middle Jurassic In Mid-Eastern ShanBei Slope

The Ordos Basin is one of those where oilfields are discovered at the earliest time, also is the second largest hydrocarbon-bearing basin which contains abundant oil and gas resource in china, the main oil-bearing are Triassic Yan'chang formation and Jurassic Yan'an formation.As one of the most important oil-bearing in the Mid-Eastern of Shanbei slope, Jurassic Yan'an formation has been one of the important successor of oil-bearing formation in this area. Jurassic oil distribution could be not only restricted by Sedimentary facies of Yan'an formation and distribution of the sandbodies,but also the paleogeomorphology on the end of Triassic. Therefore ,on the basis of reseaching of the sedimentary facies,it is very important to intensively characterize the paleogeomorphology of pro-Jurassic that to choise the proper theory of discussion.This article takes the south Ansai oilfield in the Mid-Eastern of the Shanbei slope for example,on the basis of High Resolution Sequence Stratigraphy,combined with the outcrop of field section,cores,logging and other geological materials,further to set up sequence stratum system.By restricted of this system,we divided the main oil-bearing of Yan'an formation Yan9 and Y8 into Yan9₃,Yan9₂,Yan9₁ and Yan8₃,Yan8₂,Yan8₁.Through outcrop observation,combined with previous research results,we hold that Early Jurassic source of Fuxian group is mainly from the western, northwestern and northern, and the provenance of the Middle Jurassic Yan'an Formation is mainly from the northern and north-eastern Department.At the same time ,through the systematic study of early Jurassic sedimentary system in studied area based on the analysis of provenance,we hold that The sedimentary systems were River-delta depositional systems during the Early and Middle Jurassic in this area ,in which Fuxian Group was the filled deposit of alluvial fan-braided or fluvial rifer depositional systems,Yan10 was braided fluvial river-meandering river depositional system,Yan9～Yan7 was delta front depositional system.Using the comprehensive measures of the strata thicknesses chart of Fuxian period and Fuxian+Yan10 period,the sand bodies distribution chart,sedimentary facies and palaeo-eroded landform in the top of Yanchang formation to recoverage of the pre-Jurassic Palaeogeomorphology in detail,we can divid palaeogeomorphology of studied area into incised-valley,valley Slope,overbank platform and Valley-downbend uplife ect, analyze the various Characteristics of paleogeomorphology units.Finally, characteristics for the Jurassic reservoir, we mainly from the source of oils, palaeogeomorphology, hydrocrabon migration pathway, reservoir types, hydrocarbon accumulation patterns and characteristics of reservoir and so on to discuss the hydrocarbon enrichment of Jurassic reservoir, combination of production,production test, and Old Well review and other information to select a number of favorable target areas, and make the next step of oil and gas exploration.