Petroleum generation and preservation within an overpressured system in sedimentary basins

Overpressured system is a relative sealed or semi-sealed system in a sedimentary basin. Previous studies showed that overpressured system has an important influence on petroleum generation and preservation in petroliferous basins, and abnormally high pressure can make distinctive effects on the thermal evolution of organic matter as revealed by the lab work on mechanisms of organic-inorganic interactions under different stresses. It demonstrated as following: (1) the influence of overpressure is a function of organic matter maturation; (2) a threshold of overpressure is necessary for obvious effects on vitrinite reflectance under geological condition; (3) overpressures, occurring at the different stages of organic matter transformation, play different roles on hydrocarbon generation; and (4) the responses of overpressure on the hydrocarbon generation will vary with organic matter types. Until now, mathematic models, including chemical kinetics and thermodynamic models, have been applied to assess the influence of overpressure on organic matter maturation. However, improvements should be made to confirm the threshold of overpressure with respect to the different thermal stages of organic matter and predict the trends of pre-exponential factors and activation energies. Compared with chemical kinetic models, the thermodynamic model is much more easy and convenient to field application, but its reliability and practice are still unclear and being under the investigation. Because overpressure retards the thermal cracking of crude oils, it has been a sweet spot to explore the petroleum resources in deeper overpressured compartment of petroliferous basins.