Study On The Sequence Stratigraphy Of Permian And Triassic Strata In The Taibei Depression Of Turpan-hami Basin

Turpan and Hami Basin lie in the east of Xinjiang province,Taibei depression is the biggest depression in the basin,and aslo the most important hydrocarbon habitat.With the developing of exploration in Jurassic,Permian-Trassic become a new field for oil exploration.However,the Permian-Trassic in Taibei depression burial deeply,and has the complex structure and low quality seismic cross-section,which limit the further exploration in Permian-Trassic.By the high accuracy analysis of outcrop,the equitime compare frame in north of Taibei depression was constructed,and combinating the seismic cross-section and well log research,the equitime compare frame of internal depression was constructed too, which has the very important significance for oil and gas exploration in Taibei depressionThe Permian-Triassic of Taibei depression could be divided into two second-order sequences and four third-order sequences.The two second-order sequences indicate that Taibei depression experienced two evolutionary stages:the phase of intracontinental rift basin during C-P_1-2 and the mountain front phase during P₃-T.And the four third-order sequences are Yiexitu formation-Daheyan formation of middle-lower Permian,Tarlong formation of middle Permian,Cangfanggou group of upper Permian and lower Triassic,and Xiaoquangou group of middle-upper Triassic respectively.The distinction of their systems tract are:①LST develop well in the fringe of the lake basin.The precipitation facie of LST are mainly composed by fluvial and shoreland facies,and the stacking patterns of parasequence sets are progradation and aggradation.②The precipitation facie of LTST are mainly composed by demi-deep water facies.The stacking patterns of parasequence sets are retrogradation.③The precipitation facie of HST are mainly composed by shoreland and meare facies.The stacking patterns of parasequence sets are aggradation- progradation.Integrating the research of seismic cross-section,well log and outcrop,it can be concluded that the Taibei depression has developed a good hydrocarbon source-reservoir-cap systems. The 1st source rock in the research area formed in the LTST of S_Ⅱ,which remain partly because of it's depositional pattern and weathering in later;The 2st source rock in the research area formed in the LTST of S_Ⅳ,and distribute widely,but the best dark peat and sapropelic coal part are maldistribution in the area.At the same time,several reservoirs formed in different LST of different sequence.