Abstract:

By meas of sequence stratigraphy and analysis method based on base level cycle，the data of well drilling，logging，2D and 3D seismic survey are comprehensively

analyzed，three boundaries in Huoshaogou Formation and Baiyanghe Formation of Tertiary，Shida Sag，Jiuquan Basin are identified，which are classified as one suppper long

term base level cycle(the 2ndlevel sequence) SLSC1 and two longterm base level cycle(the 3ndlevel sequence) LSC1 and LSC2.It is pointed out that in Tertiary

SLSC1 of Shida Sag，there are well developed alluvial fan sedimentary system，braided river sedimentary system and shallow lacustrine sedimentary system.Constrained by

isotime stratigraphic framework，the internal relationship between base level cycle and the development law and distribution feature of reservoir rocks，cap rocks and

reservoircap association is analyzed in detail，it is also pointed out that there is huge exploration potential in Tertiary in the area，the favorable reservoir area

are the ones located in middle alluvial fan and the fan margin braided channels in LSC1 base level semirising cycle，as well as in braided channels in LSC2 base level

semirising cycle，laterally，the structural and lithological association reservoirs in middle alluvial fan and alluvial fan margin in the north of Bainan well 5，south

of Dan well 7 and the west of Bainan well 2，as well as the lithological reservoirs developed in the setting of structure are favorable area for hydrocarbon exploration.

Key words: Shida Sag, Tertiary, base level cycle, reservoircap association, exploration potential