Influence Of Tectonic Compression On The Fluid Pressure In Kuqa Depression

Kuqa Depression has been involved in the tectonic setting of strong compression since Cenozoic. It thrusts from foreland of the orogen to the depression with complex structures such as faults, thrusts and fault—related folds. It is distinct from the other basins by hydrodynamic occurrence and its development. In terms of overpressure, there is not only deposition overpressure, but also tectonic overpressure, which is very important in forland basin. Thus, the characteristic study of fluid pressure in Kuqa Depression and evaluation of the contribution from over pressure of the tectonic compression are significant in understanding the relationship between tectonic stress field and fluid dynamic field in foreland basins, meanwhile, they play important roles in guiding the study of hydrocarbon accumulation in foreland basins.Based on previous research results, applyed by structrual analysis (fault, folds, joints), test of anisotropy of magnetic susceptibility(AMS), the test of AE in this thesis to study the orientation and magnitude of the tectonic compression since Cenozoic. Characteristics of fluid pressure are analysed beteen the excess pressure measured and that calculated by the time of largest buried depth period though compaction curve of mudstone. On the basis of distribution of mud and gypsum and salt rock of Kumugeliemu Formation and Suweiyi Formation,and quantitative evaluation is obtained of the contribution of overpressure of the tectonic compression in different tectonic units.The most significant fruits and major recognition of this thesis can be summarized as follows.Fluid pressure measurement indicates that the distribution of abnormal pressure in Kuqa Depression is various. Both of the pressure of Bashenjiqike Formation and Kumugeliemu Formation shows the same regulation:pressure gradient reduces from the foreland thrust belt to the depression, and the north Tarim uplift is just drops to hydrostatic pressure.Compaction curves of mudstone show that undercompaction was common in the entire Kuqa Depression from the foreland thrust belt to the north Tarim uplift. The excess pressure during the largest buried depth period was mostly over 1 OMpa.Kuqa Depression has experienced multi—periods of tectonic compression since Cenozoic. Field observation, seismic profiles, as well as magnetic fabric analysis show strong compression in the study area. The structural framework of the Kuqa Depression also was formed during this stage. The studies above indicate that the direction of the tectonic compression is mainly N—S direction with the deviation which is less than 30°to the west and east, and the maximum compressive stress range from 50Mpa to 100Mpa.Horizontal distribution of Paleogene mud, gypsum, and salt rocks is various. It reaches the peak in the Dabei area of east Kelasu and in middle of the Baicheng Sag. The thickness of mud, gypsum, and salt rocks reduce from the to north and south,and in the area of Yingmai of the north Tarim uplift it almost pinches.The contribution of over pressure of the tectonic compression is closely related to tectonic unit in the Kuqa Depression. The evaluation results show that the contribution rate of internal depression ranges from 20%—50% in the Kuqa Depression, while no tectonic compression exists in the north Tarim uplift.