Pressure evolution and formation mechanism of overpressure in Dongpu depression,Bohaiwan Basin

Key words:  Dongpu depression  overpressure  salt-gypsum rock  pressure evolution  formation mechanism

Abstract:

The pressure evolution and present pressure characteristics in north part of Dongpu depression were analyzed based on the measured pressure, mudstone sonic log interval, the pressure recovery by fluid inclusions and basin modeling. The overpressure formation mechanism was analyzed combined with core observation, and the contribution rate of hydrocarbon generation on the overpressure caused by different mechanisms was discussed. The conclusions are as follows. Firstly, that residual pressure evolution experienced three stages:primitive accumulation-release-reform, and two overpressure formation periods are corresponded with the oil and gas accumulation period. Secondly, the distribution of paleo-pressure and present pressure are controlled by tectonic framework, fault activity and plaster salt-gypsum rock distribution. Moreover, the formation in subsag belt or below/between the salt-gypsum rock developed larger residual pressure. Lastly, overpressure formation is mainly caused by compaction disequilibrium, hydrocarbon generation and salt-gypsum rock effect. In addition, the contribution rate of hydrocarbon generation on the overpressure is related to the thermal evolution of source rocks.