Study On The Sedimentary Facies Of The Member 4+5 And 3 Of Triassic Yanchang Formation In Huachi Area

Huachi area is located in the southeast of the Shanbei Slope, one of the secondary tectonic units of Ordos Basin, its main oil-bearing bed is the Triassic Yanchang Formation. With exploration extent promoted and exploration step speeded, Chang3 and Chang4+5 oil beds take on a good exploration prospect. Based on Lithology, Sedimentology, Basin Dynamics and so on, using many kinds of analysis and testing methods, the sedimentary facies of Chang3 and Chang4+5 oil beds which belong to Triassic Yanchang Formation in Huachi area are studied well.According to the stratigraphic division scheme of Triassic Yanchang Formation of Ordos Basin, considering company's practice, the aim of the dissertation, widely ranging mark beds, well logging data, thickness gauge,and sedimentary cycle, we did delicate strata division on Chang3 and Chang4+5 oil beds.From top to bottom, it can be divided into 10 small beds.This is a good base for later work.Combining heavy and light minerals, paleocurrents,rare earth elements and quartz cathodeluminescence,provenance of the aim beds are analyzed and it is known that there are two kinds of provenances of different orientation about Chang3 and Chang4+5 oil beds. One is the northeast provenanace, the other is the southwest provenance. Of the two, northeast provenanace is of great importance.In view of the marks of identifying and divising sedimentary facies, it is thought thar Chang3 and Chang4+5 oil beds contain meandering river delta facie, braided river delta facie and lake facie. Of these facies, there exit meandering river delta front subfacie, meandering river predelta facie, braided river delta front subfacie, braided river predelta facies, shllow lake facie and deep lake facie. Apart from these, there are also many microfacies. Deep lake microfacie don't exist in Chang3 oil bed. Sandbody of different microfacie exist in both Chang3 and Chang4+5 oil beds. Distribution of facies affects the distribution of sandbody. Underwater distributary channel sandbody is the main component in Chang3 oil bed, meanwile, besides underwater disrtibutary channel sandbody, turbidite is another chief sandbody in Chang4+5 oil bed. Underwater disrtibutary channel sandbodies mainly present bands and turbidites mainly appear flower-like or sector. Delicate study on sedimentary environment of the aim beds provides some theory for the futher exploration and development.