Outcrop analogs to subsurface fractured reservoirs, Arbuckle Mountains, Oklahoma
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.
AAPG Search and Discovery Article #90010©2003 AAPG Southwest Section Meeting, Fort Worth, Texas, March 1-4, 2003