Summary

Fault zones are usually considered to influence hydrocarbon migration in two ways. Either they are assumed to be open pathways of high permeability or they are considered as barriers to the flow. A third important possibility is introduced here. In this case, inactive faults can allow hydrocarbons to migrate across them when activity on an adjacent fault induces a pressure pulse that can promote migration of hydrocarbons across the inactive fault. In other words, the seal is viewed as a temporary barrier (or retardation feature), which leaks when a fault related fluid pressure event allows the entry pressure to be exceeded. This is in contrast to the normal model where a seal leaks because of an increase in hydrocarbon column, so that the buoyancy force exceeds the entry pressure of the fault rock. Under the new model hydrocarbons may migrate across the inactive fault zone for the time period that the fluid pressure difference is above the critical entry pressure during the earthquake cycle. Numerical models of this process are presented to demonstrate the impact of this mechanism and its role in filling traps with bounding sealed faults.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah