The Sedimentary Microfacies And Paleogeography Of Xinghe-Zhangqu Area In Ansai Oilfield

Xinghe - Zhangqu area of Ansai oilfield is located in Yishan slop of Ordos basin, whose main producing bed is Chang 6 oil-bearing formation. According to the characters of lithology, electricity and oiliness, Chang 6 oil-bearing formation is subdivided into Chang 6₁, Chang 6₂ and Chang 6₃, and Chang 6₁ is further subdivided into Chang 6₁¹ and Chang 6₁². Chang 6₁¹ could be subdivided into Chang 6₁^1-1, Chang 6₁^1-2. Chang 6₁^1-3. Based on the temporal rock mark and application of the stratigraphic cycle and high-resolution sequence theory, the stratigraphic correlation is maken, and the two theoretical methods are taken to compare to each other either.According to analysis of facies mark, such as rock type, sedimentary texture and structure, paleontology and logging facies, facies analysis indicated that Chang 6 oil-bearing beds is a front-delta sedimentary system, which could be subdivided into 6 microfacies: underwater distributary channel, underwater interdistributary bay, underwater natural levee, mouth bar, diatal bar and sheet sand, in which underwater distributary channel and underwater interdistributary bay are the main microfacies, and mouth bar, distal bar and sheet sand are hard to be preserved in the study area, so they hardly developed. On the basis of regional geological background, with geological character and logging facies analysis, the distribution of the microfacies in the plane is distinguished, and the lithofaies paleogeography of Chang 6 is studied either.The lithology of the reservoir of Chang 6 oil-bearing formation are main arkose and lithic arkose sandstone, secondly feldspthic lithic sandstone and a little feldspthic lithic quartz sandstone. Reservoir physical property is characteristic by low porosity and low permeability. Intergranular pore and dissolved pores in grains are the main pore type. Fine throat-small pore and micro-fine throat-small pore are the main pore structure type. The heterogeneity of the reservoir is marked, and the physical property in the centre of the sandbody is much better. Because of the development of the secondary pore, parts of the wells are with fine porosity, permeability and oil saturation. By the control elements analysis of reservoir, it is showing that sedimentary microfacies and diagenesis are the main elements that controlled and influenced the development and distribution of the reservoir in the study area.Sedimentary character controls the sandbody type, and the distribution of the sedimentary microfacies in the plane controls the distribution of the reservoir, and the distribution of the reservoir controls the distribution of the hydrocarbon. The distribution of Chang 6 oil bearing formation is controlled by underwater distributary channel of the delta front, where is the main enrichment area of the hydrocarbon. Lithology occlusion has certain influence for the distribution of the hydrocarbon.