Research On Sedimentary System, Reservior Characteristics For Yanchang Formation In Zhenyuan-Jingchuan Field, Ordos Basin

There has been good exploration prospects in Mesozoic of the south of Ordos basin, after many years of exploration, with the increase of the drilling numbers and the gradual improvement of geological understanding, the industrial oilgas wells were got in the Yanchang Formation of Upper Triassic in Zhenyuan-Jingchuan area, a number of oil and gas reserves were submitted. But it is generally the low level of exploration, reservoir sand belongs in a low prosity and supper-low permeability reservoir, the physical characteristics of reservoir is poor, These objective factors directly restricted the oil and gas exploration in the area, therefore strengthening the studies of sedimentary microfacies and reservoir characteristics, and then carrying out comprehensive evaluation of reservoir of target bed, all those will be an important foundation and prerequisite for guiding the next oil and gas exploration.In this paper, the author synthetieally applied sedimentation, well logging, Petroleumgeology, ect, on the basis of studying on the core of well drilling in the district, fully utilize logging well, well drilling core and testing and analyzing materials to study the types and characteristics of depositional systems profoundly, further explored the characteristics and laws of the evolution of lithofacies paleogeography of the Yanchang Formation. At the same time, detailly discussed genetic types and distribution characteristics of reservoir sand, and the main results and understanding are as follows:According to lithological characteristics, sedimentary structures, profile structure, logging markers, Braided River Delta and lacustrine depositional system were recognized in Yanchang Formation, carrying out a detailed study of sedimentary micro-facies in the depositional system, setting up a deposition model for it. On this basis, lithofacies paleogeography characteristics of different times of Yanchang Formation from chang 9 to chang 4+5 were studied, which revealed evolution laws.Systemly studied petrologic characteristics, physical properties, pore types, pore textures of reservoir sand, and diagenesis which affect reservior, according to physical parameters and pore textures characteristics, reservoir sand of Yanchang Formation in the studied area is divided into four categories, the types ofⅠandⅡ.reservoir have good reservoir flow capacity, others are poor, summarize that the types ofⅡandⅢreservoir are the main reservoir of Yanchang Formation in the studied area, and the type ofⅢis the largest percentage.The reservoir physical property of underwater distributary channel and mouth bar sands in delta front is better in all kinds of sedimentary micro-facies, that of distal bar and shallow lake sand bars is poor, in all kinds of lithology, The reservoir physical property of fine sandstone is better, that of siltstones is poor, and fine sandstone is the main reservoir lithologic types in the studied area.The genetic types of reservoir sand in the studied area is deeply studied, underwater distributary channel, superimposed distributary channel, mouth bar, superimposed mouth bar, and complex causes types composed of underwater distributary channel and mouth bar or distal bar, etc, and reservoir characteristics of reservoir sand body of different genetic types are detailly studied, on this basis, make a detail study for reservoir sand′s distribution law of reservoir group in Yanchang Formation, all those provides an important basis for further oil exploration of Yanchang Formation in the studied area.