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覆盖在油气储层之上的欠压实页岩起着有效的压力封闭层作用。主要原因是它的异常流体压力、高可塑性和高毛细管压力。这些特征可阻止储集层中流体的垂向流动。虽然压力封闭层对任何圈闭都是有益的,但对构造带附近地区的深部致密气藏特别有效。在这些地区,如果没有压力封闭层适当地封闭储集层,聚集的天然气就有可能从构造裂缝和断裂中漏失到地面,封闭层的可塑性几乎可以立即封闭张开的裂缝(从地质上讲)。这种自身封闭机理可阻止天然气的向上逸散。压力封闭层还能阻止构造事件后地表水向下渗滤。这种渗滤过程有可能通过冲洗和生物降解,使已聚集的油气质量变坏。当页岩渗透率降低到不再能发生正常压实和流体排放的水平以下时,在压实的中间阶段便形成压力封闭层。压力封闭层形成的地质时期和埋藏深度可以结合烃类的生成、热成熟度和运移以及圈闭形成的时期来解释,这样便可更好地估价石油勘探的前景。众所周知,在许多地区,例如路易斯安那—得克萨斯海湾海岸盆地、美国落矶山和加利福尼亚海岸山脉地区、加拿大的众多盆地以及北海、尼日尔三角洲、委内瑞拉和阿根廷等,压力封闭层具有重要作用。
Unconsolidated shales overlying the reservoir act as an effective pressure seal. The main reason is its abnormal fluid pressure, high plasticity and high capillary pressure. These features prevent the fluid in the reservoir from flowing vertically. Although the pressure seal is beneficial for any trap, it is particularly effective for deep tight gas reservoirs in the vicinity of the structural belt. In these areas, the accumulation of natural gas could leak from structural fractures and fractures to the ground without the closure of the pressure envelope properly closing the reservoir. The plasticity of the closure layer closes the open fracture almost immediately (geologically) . This self-sealing mechanism prevents the natural gas from escaping upward. Pressure seals also prevent surface water from leaking down after structural events. This diafiltration process has the potential to degrade the quality of the accumulated oil and gas by washing and biodegrading. When the shale permeability drops below the level at which normal compaction and fluid discharge no longer occur, the pressure-seal layer is formed at an intermediate stage of compaction. The geologic period and burial depth of the pressure seal formation can be explained in combination with the hydrocarbon generation, thermal maturity and migration, and the period of trap formation, so that the prospect of oil exploration can be better assessed. It is well-known that in many areas, such as the Louisiana-Gulf Coast Basin in the United States, the United States Rocky Mountains and the California Coast Mountains, numerous basins in Canada and the pressure sea closures play an important role in the North Sea, the Niger Delta, Venezuela and Argentina.