Calculation and application of plane pressure decrease gradient

As a driving force for oil and gas migration, the overpressure change rate has a relationship with oil and gas migration mode. In order to quantitatively identify the hydrocarbon migration modes in overpressure basins, some calculation ideas and methods of the application of formation pressure decrease gradient were established, and were applied in the Bonan Subsag, Zhanhua Sag, Bohai Bay Basin. Based on measured pressure and single well predicted pressure, the pressure distribution characteristics of the main hydrocarbon migration layer were analyzed. According to the characteristics of overpressure genesis, sedimentary facies and faults, different pressure drop gradient calculation methods were applied to the uniform pressure attenuation zone, the inhomogeneous pressure decrease zone of sedimentary facies transformation and the inhomogeneous pressure decrease zone of the faulted zone. The results show that the pressure decrease gradient is the highest in the deep sag of Bonan Subsag, followed by the fault step, steep slope and gentle slope zones, and the pressure decrease gradient near the vertically connected faults is higher. The variation characteristics of oil and gas migration mode under overpressure control were quantitatively explained so that the location of hydrocarbon enrichment can be effectively judged.