Characteristics and genetic mechanism of formation pressure in sags of Raoyang Depression

Key words:  formation pressure  pressure structure  overpressure mechanism  hydrocarbon generating pressurization  Raoyang Depression

Abstract:

Using pressure data and simulation results of fluid pressure, this study analyzed the distribution of abnormal pressure and the contribution of disequilibrium compaction and hydrocarbon generation to overpressure in Raoyang Depression. The results show that overpressure is widely developed in Raoyang Depression, but the scale of overpressure varies significantly in different sags. Vertically, overpressure exists in Paleogene, including E_d, Es_1and Es₃. There are four types of overpressure structures in Paleogene, including the single pressure structure and three double overpressure structures:the upper pressure stronger than lower, lower pressure stronger than upper, and upper pressure equally close to the lower pressure. In plane, overpressure center is corresponding to the depositional center in four sags, of which Hejian and Liuxi sags developed the strongest overpressure. Overpressure centers migrate through time from Es₃ Formation to Es₁ Formation, and the overpressure scale is significantly reduced in the southern sags, while slightly increased in the northern sags. For Dongying Formation, disequilibrium compaction is the main mechanism generating overpressure, whereas for Es₁ and Es₃ Formations, both disequilibrium compaction and hydrocarbon generation are the main mechanisms. The different contribution ratio of the disequilibrium compaction and hydrocarbon generation to overpressure leads to various structures of overpressure that coexist and affect the distribution of hydrocarbons.