ABNORMAL PRESSURE AND HYDROCARBON ACCUMULATION
Du Xu;Zheng Hongyin;Jiao Xiuqiong(China Offshore Oil Exploration and Development Research Center,Hebei,074010)
Many abnormal overpressure fields have been found both at home and abroadwith more intensified petroleum exploration. According to statistic results,there are morethan 180 overpressure basins in the world,of which 160 basins are rich in hydrocarbon,abnormal high pressure fields account for 30 percent of the total fields of the world.Thisissue introduces the basic conception,features and classification of formation pressure,discusses in detail the contributing factors of abnormal pressure,such as hydrocarbon gen-eration,under-compaction, cracking of liquid hydrocarbon,epigenesis of clay mineral,tectonism,change of temperature,etc.;systematically explaines the mechanism of over-pressure in typical oil bearing basins worldwide and primary migration of hydrocarbon inoverpressure strata,as well as the relationship between overpressure and hydrocarbon ac-cumulation. On this basis,five kinds of overpressure reservoir models can be concluded:(1)overpressure reservoirs with lower permeability in the overpressure system:(2)reef(or turbidite)reservoirs within overpressure formations;(3)normal and/or overpressurereservoirs in transition zone with the lithology of regressive deltaic plain and branchingchannel sandstone above the overpressure zone,(4)reservoirs above or below the over-pressure zone,(5)reservoirs with normal pressure in drainage zone far away from over-pressure system,This paper can be the guide for further exploration in new or old oil andgas provinces.