Tectonic Evolution Characteristics Of The Lower Middle Ordovician Yingshan Formation In Bachu Area Of The Tarim Basin

By using geological, drilling, logging and seismic data, the process ofpalaeostructure recovery experiences from one-dimensional single well burial historyanalysis to two-dimensional tectonic evolution history research, eventuallythree-dimensional Petromod software application. The top of Yingshan Formation’spalaeostructure can be recovered by the point-line-plane comprehensive consideration,combined with a variety of recovery methods. By choosing the best method and theoptimal data, the ancient fracture system and compaction correctionshould beconsideredduring the process of palaeostructure recovery. The recovery result has aguiding significance to oil and gas exploration and evaluation of Bachu area.Bachu area experienced strong extruding deformation such as lateHercynian-Himalayan movements, combined with weak tectonic movementsuch asearly Caledonian movement. its strata superimposed the multi-phase deformation,forming a plurality of unconformity, such as the First-order tectonic unconformitywhich is the top surface of the Ordovician (T70), the top surface of the lowerDevonian Keziertage Formation (T60), pre-Mesozoic erosion surface (T50), the topsurface of the Palaeogene (T22) etc. By comparing with different strata denudationcalculating method and alladvantages and disadvantages, finally choose depositionrate method to restore the top surface of Yingshan formation（T74），choose thestrataseismic construction extrapolating method combined with well strata contrastingmethod to restore the top surface of the Ordovician (T70), the top surface of the lowerDevonian Keziertage Formation (T60), pre-Mesozoic erosion surface (T50) and thetop surface of the Palaeogene (T22). The characteristics of the Yingshan Formation’stop surface in different period are got through restoring the ancient tectonic. After thefirst act of mid-Caledonian, Bachu is characterized by integral uplifting with thesouth part of the Bashituo Fault locating at the southwest of Bachu uplifted relativelystronger. In the third act of mid-Caledonian, the west of the Yingshan Formation ishigher than the east, and in the east, the north region of Bachu is a little higher thanthe south. The burial depth ranges from400m to1600m. In the early Hercynian, thesouth region of Yingshan Formation is higher than the north in general. The burieddepth is commonly600m to2400m. In the late Hercynian, Both north region andsouth region of Yingshan Formation is relatively higher than the central region. Theburial range is3000m to5000m. In the early Himalayan, the north region of Yingshan Formation is higher than the south and the west is higher than the east. The burialdepth ranges from1600m to4400m.