IS TECTONIC UPLIFTING THE GENESIS OF ABNORMAL HIGHPRESSURE?

In many articles and works in China,tectonic uplifting was regarded as the genesis of abnormal highpressure.This opinion omitted the effects on fluid pressure by the decrease of fluid temperature and the rebound of pore volume in the process of uplifting.Calculations show that neither of the two factors can be neglected completely.Tectonic uplifting inclines to forming abnormal lowpressure rather than abnormal highpressure.Since the decrease of load and temperature in the process of uplifting makes unisostatic compaction and other factors tend to stopping,tectonic compression often becomes the most principal genesis of overpressure in uplifted areas.Therefore,caution is needed when using the seismic method to predict the distribution of abnormal pressure in the areas where tectonic uplifting happened in later and recent periods.Tectonic uplifting resulted in the disappearance of paleooverpressure in the gas bearing measures of some basins(for example,the Ordos Basin).This is mainly because of the fluid state changes caused by uplifting,not only because the gas suppling amount of hydrocarbon source rock was less than the dispersed amount of natural gas.