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超压可由以下过程产生:(1)压应力的增加;(2)孔隙流体或岩石基质的体积变化;(3)流体运移或浮力作用。由于不均衡压实作用,在埋藏过程中上覆沉积物负荷可产生相当大的超压,尤其是在低渗透性沉积物的快速沉降过程中更易产生超压。在构造活动区,水平应力的变化可以快速形成并释放大量的超压。由体积变化引起的超压机制必须具备完好的封闭才是有效的。由水热膨胀和黏土脱水造成的流体体积增加量很小,它不能形成较大的超压,除非具备“完美”的封闭条件。烃类的生成和裂解成气可能形成超压,这取决于干酪根的类型、有机物质的丰度、地热史以及岩石的渗透性。然而,这些过程在一个封闭的系统内又是互相制约的,因为压力的增加可能会阻止有机质的进一步变质。必须认识到现在还不能证实烃类生成和裂解产生超压的潜力。由于水头使流体流动,可在浅埋藏的“很好地铅封”的盆地中形成相当大的超压。通过计算表明,烃类产生的浮力和渗透作用仅能产生局部的很小的超压。在不可压缩流体中气体的向上运动也可产生很大的超压,但需要进一步调查。在许多沉积盆地中,与应力有关的机制最有可能引起超压。
Overpressure can be caused by: (1) an increase in compressive stress; (2) a change in volume of a pore fluid or a rock matrix; and (3) a fluid migration or buoyancy effect. Due to the unbalanced compaction, overburden loading can cause considerable overpressure during burial, especially overpressure during rapid settling of low permeability sediments. In the tectonic activity zone, changes in horizontal stress can quickly form and release large amounts of overpressure. The overpressure mechanism caused by the volume change must be well sealed to be effective. The fluid volume increase due to thermal expansion of water and the dehydration of clay is small and it can not create large overpressures unless it has a “perfect” closure. Hydrocarbon generation and cracking can form overpressures depending on the type of kerogen, the abundance of organic matter, the geothermal history, and the permeability of the rock. However, these processes are again mutually constrained in a closed system because the increased pressure may prevent further deterioration of the organic matter. It must be recognized that the potential for overpressure in the generation and cracking of hydrocarbons has not yet been demonstrated. Due to the fluid head flowing through the head, considerable overpressure can form in the shallow buried “well sealed” basin. The calculation shows that the buoyancy and infiltration caused by hydrocarbons can only produce local small overpressure. Upward movement of gas in an incompressible fluid can also produce large overpressures, but further investigation is needed. In many sedimentary basins, stress-related mechanisms are most likely to cause overpressure.