Pressure Evolution and Its Effect on Petroleum Accumulation in Nanpu Sag, Bohai Bay Basin

This article aims to discuss the evolution of genetic mechanisms of overpressure, based on the numerical situation technique to recover the paleopressure formation and evolution, and combined with the evolution of sedimentation rate, hydrocarbon generation and porosity. And further study the accumulation significance of pressure evolution. The forward modeling indicates that the overpressure evolution in the sag is divided into three stages: original forming (before the erosion of Dongying Formation), release (during the erosion of Dongying Formation) and reform (since the end of Dongying Formation). Compaction disequilibrium is the main cause of overpressure before the erosion of Dongying Formation, which is beneficial to hydrocarbon emission. Overpressure release occurred during the erosion of Dongying Formation, which leads to the early reservoir adjustment to a certain extent. Hydrocarbon generation is the main cause of overpressure since the end of Dongying Formation, and coupling of the hydrocarbon generation, two hydrocarbon accumulation periods and fault activities played an active role in hydrocarbon accumulation. On one hand, a large quantity of hydrocarbon migrated along with fracture and sandstone to form inner-source plays. On the other hand, hydrocarbon migrated along with oil-source faults to form above-source plays under the high residual pressure difference between source rock and reservoir providing. The beneficial hydrocarbon accumulation regions are closely related to the stress distribution. Generally, the depth of oil reservoir and pressure coefficient is positive correlation under different plays of pressure coefficient distribution. The present study suggests that the future exploration would focus on higher value of pressure coefficient under different plays of pressure coefficient distribution.