Sequence Stratigraphy And Sedimentary Systems Research Of Yanchang Group In Fuxian Block, South Ordos Basin

Ordos basin is a folding large scale basin, and it is a uncontrolled flowing basin in Triassic system. Fuxian block located in Yishan slop, south Ordos basin, it is one of six petroleum prospecting blocks which belong to China PetroChemical Corporation. In order to systematically analyze the sequence stratigraphy characteristics and depositional system and distribution of the favorable reservoir, the thesis applied the analytical method of high-definition sequence stratigraphy, sedimentology, seismic sedimentology, the sequence stratigraphic characteristics, the deposition systems characteristics in sequence framework and the distribution of the favorable reservoir are synthetic studied.Based on the study of the drilling core, bore log and seismic data, the framework of the high-definition sequence stratum in Yanchang group of upper Triassic of south Ordos basin is established, 4 triple sequence cycle(SQ1—SQ4) and 11 quadruple sequence cycle(Sq1—Sq11) are identified and correlated in the region, and the vertical superposing pattern and the horizontal evolving law of the sequence stratum in the Yanchang group were summarized, and the pattern of the highlight sequence filling are set up. The research demonstrated that tectonic descent, the sea level changing and sediments supplying are the main controlling factors of the sequence stratigraphy .Thesis generally analyses the heavy mineral, grain size, the crop of thin slice and palaeoflow of Ordos basin, and judges that Fuxian block is controlled by northeast and south east supply in Yanchang group which is in upper Triassic.Three sedimentary systems have been recognized, including delta facies, lacustrine facies, deep water density current facies etc, and it is pointed out that the delta facies especially the delta front valley subfacies widely developed in this area, while deep water density current facies can be merely found in Beidaode, Zhangcunyi, and Yangquan etc. The vertical sedimentary system evolution of Yangchang group stands for a cycle of sedimentation: the early stage of lakes and delta(SQ1), the prosperous stage of lakes and delta(SQ2), the abortional stage of delta (SQ3)and the dying stage of delta(SQ4).It is concluded that there are several sandbody types, including the under branch-river sandbody and mouth bar of the delta subfacies , clast flow and muddy flow sandbody of deep water density current . The the distribution law and main controlling factors of different reservoir sandbody in the sequence stratum framework are indicated and the time-space distribution law of the favorable sandbody in the main sequence is summarized.