THE ANALYSIS OF HYDROCARBON ACCUMULATION CONDITION OF UPPER PALAEOZOIC OF THE SOUTHWEST ORDOS BASIN

The source rocks in the Southwest Ordos Basin are mainly the coalbed and melanomudstone of Taiyuan Fm and Shanxi Fm,and the content of organic carbon is 0.2%～7.95%,its kerogen is Ⅱ-Ⅲ type and the mean value of R_o is 2.34%,and the rocks are generally of hige-or-super maturation.The reservoir are mostly the distributary channel sand of delta plain and subaquatic distributary channel sand,belonging to the Ⅱ-Ⅲ type.The caprocks are primarily the mud of littoral and shallow lake facies with good continuity and is well Closed.The gas continuously migrates to Qingyang area by means of diffusion through crevice and collects in litho-stratigraphic traps formed in Permian.The Hydrocarbon migration is generally controled by reservoir bed and regional tectonic.To the east of Huianbao-Shajingzi Fault is the Tianhuan SynCline in whose east slope there is comparatively developed regional tectonic of synCline and antiCline,and with the fairly good reservoir condition,it has the primary enrichment of gas.The main preffered exploration areas are the Jingchuan-Ningxian's mild slope and the top point of the tectonic of the good reservoir in the Huanxian-Zhenyuan synCline.