Relationship of SlopeBreak, Slope Type with Hydrocarbon PoolForming of the Upper Triassic from Jiyuan Area, the Northwestern Ordos Basin

Key words: 
• slopebreak zone (line) /
• slopeshaped delta front and platformshaped delta front /
• slope types and hydrocarbon pool /
• the Yanchang Formation of the Upper Triassic /
• Jiyuan area /
• the Ordos Basin

Abstract: The northwestern, western, southern and southeastern depositional margin of the Ordos basin is tectonic slopebreak controlled by tectonic movement occurred at the end of the Triassic, where alluvial, fandeltaic and braideddeltaic sedimentary suite developed. While the eastern and northeastern margin belong to depositional slopebreak because of its gently uplifting during the late Triassic, which resulted in the meanderingdeltaic sedimentary system. Two types of slopes including slopeshapedfront and platformfront can be recognized in the Jiyuan area, northwestern Ordos Basin, based upon analysis on feature of the basin margin, types of depositional facies and sediments, thickness of the strata, spatial assemblage and distribution of the sandstone bodies, and changes of the sandstone grain size, combined with seismic interpretation for topographic form of the Chang 4+5Chang 7 lake basin. Research result shows that sandstones at the slopeshapedfront are of greater thickness with relatively developed secondary dissolution pores and higher permeability values in delta front setting where sandstones tend to be of low porosity and very low permeability. Thus, sandstones at the slopeshapedfront with the better reservoir potential in Jiyuan area are optimistic regions for hydrocarbon accumulation. This study will provide a new idea and a fresh approach to explore and search for hidden oil pools at a delta depositional system in depression basins.