Analasis Of Relationship Between Tectonic Evolution And Oil-gas In Bachu Uplift In Tarim Basin

Bachu uplift is located in the western part of the central uplift in Tarim basin andthere has nearly no Mesozoic deposit so as to be disputed over all the times. Now thatseveral scholars refer to the point that Bachu uplift formed in Himalayan tectonicmovements, this paper reinforce that Bachu uplift and faults in the uplift were mainlyraised in the Hereynian period by the analysis of the faults and local structural traps.By making the evolution figures of tectonic we assume that the development of Bachuuplift has the feature of cyclicity. There are some normal fault formed in Sinian. Andthe site raise and uplift in Caledonian. It then subducted in the early Permian andappear to have no pull apart structure. Later it raised in the late Permian and subsidedin the early Tertiary soon. Finally it turned to a uplift with fracture after stronglyuplifting in Himalayan period.Based on the studies of former scholars this paper raises the model that howbachu uplift raise in Mesozoic. We believe that shearing is the ultimate function inthis section. The fault system in Bachu uplift can be divided into three sect which arethe west, the middle and the east. The east and west part have the figures of arc onplanar surface while the middle one is straight. Sectionally, the tectonic styles of westand east systems of fault are both strike-sliding, however, faults in the middle almostappear along the axial plane of fault-propagation folds and have nearly strike-slidingstructure. From that we can see the uplifting in Bachu area was not united anduniform, which is connected with the time schedule of tectonic evolution. And it isthat the ununiform press formed Bachu uplift.Oil fields in Bachu uplift has been controlled greatly by the degree of tectonicevolution. First of all, this region used to be uplift in a long geologic term and was notgood for oil concentration.Secondly, however, the conbonate reservoir in Cambrianand Ordovician was formed by erosion, which happened when this site was exposedup the water level. Thirdly, there are no Msozoic deposite thanks to the uplifting sinceHercynian movement. Carboniferous and Permian reservoir had been greatlymeliorated in one hand and in the other hand it is not good for the prevservation ofpreexistent oil and gas reservoirs. Fourthly, this site uplifted strongly in lateHimalayan period and former faults acted strongly, which destroyed the former oil and gas pools.According to the analysis of Bachu's oil and gas fields we believe that gas is themain hydrocarbon form in this region. The southern tectonic section and the westernfault control tectonic section are good places. Besides, the karst gap reservoirs inCambrian and Ordovician are important in the future and the degree of thesereservoirs lies on whether there have some faults that connected the source rocks andthe reservoirs.