Formation Mechanism of Underpressure Strata and Its Effect on Oil-Gas Accumulation
负压地层形成机制及其对油气藏的影响

Basins with abnormal pressure characteristics are numerous in China; nevertheless, up till now, studies have been mainly focussed on the overpressure system, and insufficient attention has been paid to the abnormal underpressure system. Extensive deposition within the basin results in strata of great thickness, and the uplifting procedure of sedimentation leads to serious erosion and the erosional unloading phenomenon, finally forming the underpressure area. There are of course many other factors such as temperature of the strata which can produce underpressure. It is therefore very important to consider all the factors in an integrated way in the exploration of the underpressure basin. This paper deals with the underpressure of Baise basin and analyses its formation and its effects on oil-gas accumulation. Underpressure causes regional back flow of fluids, forms underpressure seal windows, stimulates the second oil gas transition, thus affecting the distribution of oil gas reservoirs and forming some oil gas accumulations associated with underpressure.