Abstract：
The thrust and fold belt of south Junggar Basin,north Tianshan,is still activity since Cenozoic time,and the development of an activity fault and fault-related folds.Well data show that overpressures are developed in the Paleocene Anjihai Formation mudstones and Ziniquanzi Formation mudstones,which are the main detachment surfaces of thrust faults.Based on the surface survey and interpretations of 2D/3D seismic data as well as well data for many years,dip distribution of thrust fault in the thrust and fold belt of south Junggar Basin has a selection of statistically preference,with mainly concentrated peaks at 30±5°and 50±5°.Under continuing compressional stress,analysis of the stress show that the optimal orientation for fault reactivation,at which the ratio of effective principal stresses attains a positive minimum(i.e.maximum fluid pressure),when thrusts dipping at 30±5° to maximum principal compressive horizontal stress,σ1.Frictional lockup is expected when a reactivation angle of thrusts to σ1 equals 50±5°,steep reverse faults require more supra-lithostatic fluid pressures for continued reactivation. The stress analysis and actual measurement of strata pressure data by wells show that overpressures mechanism is resulted from tectonic stress, i.e. tectonic overpressures. These researches indicate that a continuously activity faults in the thrust and fold belt of south Junggar basin has resulted in the reactivation of the earlier formed faults by the later compressive forces, and tectonic overpressure along the surface of the faults of accumulating petroleum, in which hydrocarbon migration has a dynamic balance with hydrocarbon accumulation over a long period of time.
2012, Vol. 47 
