Mechanisms for Abnormal Pressure Seal in Pressure Compartments:A Review

Mechanism for pressure seal is still a baffling problem in pressure compartment research,and attracts much attention from researchers.Knowledge of the time scales over which these abnormal pressures are maintained is essential for understanding the processes of oil and gas generation,migration and conservation.Generally there are two directly different conceptions of abnormal pressure seal mechanisms : the static and the dynamic.The static school deems that rocks,which are nearly impermeable(permeability10-11 μm2),can prevent almost all movements of fluids,such as evaporites and intensively mineralized rocks can act as pressure seals.While the gas coming out of solution form gas-saturated water in layered sequences of fine and coarse-grained rocks can bring enormous capillary pressure to seal the abnormal pressures and the capillary pressure is additive.In contrast,the dynamic school claims that both compartment and seals in a water face continued environment the abnormal pressures will be balanced at low rate diffusion even with the existence of low permeability seals(permeability10-8—10-10 μm2),which have excellent seal ability to prevent water movements.However,the low permeability rocks can reduce the dissipation rates of anomalous pressures to an extremely low level.In other words the pressures are maintained in a long period.The static and dynamic overpressure seal mechanisms have their own factual basis,but gas-water of two phase capillary pressure and low rate diffusion seal mechanisms may have more universal meaning.