沉积盆地超压系统内油气的生成与保存

Petroleum generation and preservation within an overpressured system in sedimentary basins

沉积盆地内的超压系统是一个相对独立的封闭-半封闭体系,与油气生成、保存关系密切。超压系统内矿物介质、有机质、水相互作用过程以及有效应力对有机质演化的作用机理研究揭示了超压对有机质演化具有显著的阶段性和差异性,具体表现在:(1)压力的影响程度是有机质演化程度的函数;(2)超压/压力效应对有机质演化发生显著影响需要达到某一最小值,即门限值;(3)在有机质演化不同阶段发育的超压对生烃的影响不同;(4)同一超压系统内,不同类型有机质对超压的响应具有差异性。迄今,已经建立了超压/压力对有机质演化影响程度的定量化模型,包括化学动力学模型和热力学模型两类。化学动力学模型仍有许多需要改进的地方,如压力影响的阀值、指前因子和活化能随反应时间的变化规律等,相对而言,热力学模型似乎更简单、易用,但其可靠性和普适性还有待时间的检验。由于异常高压对超压系统储层内原油的热裂解反应具有抑制效应,有利于深部高温高压储层内液态烃的保存,因此,含油气盆地深部高温高压地层已成为一个较为有利的石油勘探领域。

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： （!） 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.