Fault zones can control fluid flow in petroleum reservoirs by acting as seals, conduits, or combined conduit-seal systems. Evaluating their fluid flow properties, however, requires a sound understanding of the episodic mechanical and geochemical processes that control the evolution of fault zone architecture through geologic time. Integrated outcrop studies and laboratory analyses of Fault 6, east Greenland, reveal several key controls on the permeability structure of normal faults found in heterolithic reservoirs. Fault 6 is one of a system of normal faults which form an onshore analog for fault compartmentalized Upper Carboniferous through Lower Cretaceous sandstones and shales. It displays 65 m of displacement and comprises two components: a fault core and a damage zone (whose intensity decreases with distance from the fault core).

The heterogeneous lithology (clay-rich gouge and silicified breccia) of the fault core reflects the way that the protolith is assimilated into, and modified within, the fault zone to create a low-permeability seal. The damaged zone comprises a network of subsidiary structure., (e.g., small faults, fractures, veins, and folds) that yield a region of enhanced permeability surrounding the fault core. The combination of both high and low permeability rocks within the fault zone produces a complex conduit-seal system that restricts fluid flow across the fault while providing anisotropic pathways for flow along the fault. Where such faults can be identified in producing reservoirs they might be represented in reservoir simulations as distinct features with an anisotropic permeability structure that varies along the fault.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas