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The AAPG/Datapages Combined Publications Database
Fort Worth Geological Society
Abstract
ABSTRACT: Outcrop Analogs to Subsurface Fractured Reservoirs, Arbuckle Mountains, Oklahoma
By
Russell K. Davies1
and Alton Brown2
2([email protected])
Fractures studied in four outcrops aid prediction of
fracture
characteristics in subsurface reservoirs. Outcrops are simple folds with shallow
and deep maximum burial, complex secondary structures, and fault-bounded
structural highs. The simple fold with shallow maximum burial shows dominant
fracture
sets sub-parallel and orthogonal to the fold axis. Most fractures
terminate at bedding planes. Small thrusts within beds demonstrate the
importance of layering slip. Tectonic stylolites are rare and indistinct. At
greater maximum burial,
fracture
patterns are dip and strike oriented, but
en-echelon shear fractures are locally important and tectonic stylolites are
abundant. A prominent, near vertical
fracture
set cuts bedding sub-parallel to a
regional normal fault trend. This
fracture
orientation may be related to
regional rather than local deformation.
Fracture
sets within complex structures
form a complex, heterogeneous
fracture
pattern. The heterogeneous
fracture
distribution within adjacent fault blocks makes their prediction in subsurface
reservoirs difficult. Fractures in fault-bounded highs deformed at shallow
burial depth show increasing intensity and geometric variability proximal to
faults. These form a strongly deformed damage zone. Small fractures confined to
single beds are not simply related to orientation of bounding faults or dip.
Larger through-going fractures lie along the regional trend. Fractures in chert
nodules are dilated, open and more closely-spaced than the surrounding
limestone. Together, these results indicate that general characteristics of
fracture
systems can be predicted from structural style, lithology, and burial
depth during deformation. Mineralization of fractures in this old
fracture
system is related to burial history since deformation.