Based on locations of source rock and key factors controlling genesis of overpressure systems

overpressure systems in sedimentary basins can be classified into deep overpressure system and shallow overpressure system.The former have mature to overmature source rocks

and overpressure is widely distributed

especially in Meso-Cenozoic basins;while the later lack of mature source rock

and the distribution of overpressure zone is generally limited in foreland basins

i.e.dual overpressure system occurs in foreland basins.Based on the analyses of generation and sealing of hydrocarbons in deep overpressure system

it is believed that hydrocarbon generation would be the primary factor controlling overpressure systems

while others are only secondary factors that further increase formation pressure.The upper overpressure system has been formed as the result of late tectonic compression on the basis of early normal pressure reservoirs.Correct discrimination of the two types of overpressure systems is essential to the study of hydrocarbon generation

migration and accumulation.Deep overpressure system is especially important to petroleum exploration

as it is the"chemical reaction furnace"of hydrocarbon generation

provides the original power for hydrocarbon migration

and determines the phase state and mode of migration and characteristics of accumulation.Generally

hydrocarbons would be difficult to accumulate in deep overpressure system.However

hydrocarbon accumulations can be formed in overpressure system when the original balance of temperature and pressure is broken due to structural uplifting or faulting.