University of
Utah, Dept. of Geology and Geophysics
Abstract: Fault
Zone Architecture and Fluid Flow Anisotropy in
Heterolithic Reservoirs
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