The fault-seal problem is of particular importance in California because of the many significant regional and local fault systems affecting more than half of the known oil pools.

Fault seals are not only barriers to the migration of oil and gas in fault-trap fields, but are also important as secondary traps on anticlinal closures. The sealing effect of faults has complicated the field development, reservoir studies, pressure maintenance, and secondary-recovery programs, particularly in multi-block, multi-zone fields. Several factors which influence the effectiveness of fault seals include (1) lithologic type of sedimentation, (2) type of faulting, (3) depth of burial during faulting, (4) magnitude of fault displacement, (5) secondary cementation in fault zone, (6) differential fluid pressure across faults, and (7) time of faulting versus accumulation.

The lithologic type of the sediments appears to be one of the most important factors responsible for the formation of fault seals. The type of faulting and depth of burial during fault slippage are also significant. Other factors such as cementation are locally important. Post-accumulation faulting has affected the separation and readjustment of some pools; others have been partly depleted by leakage. Pressure barriers resulting from fault seals have caused abnormal reservoir pressures in some fields.

Major fault systems in the state can be related to local field patterns. This analogy has aided in the exploration of new fault-block accumulations within a proved field area as well as exploration for new fields.

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