Abstract: Structural
and
Stratigraphic
Controls on Fracture System
Architecture: An Example from the Carmel Formation of the San
Rafael Swell, Utah
FISCHER, MARK P., Department of Geology, Northern Illinois University, DeKalb, IL 60115-2854
The architecture of fracture networks is described by a number
of parameters, including fracture spacing, aperture, length,
height, connectivity, filling, orientation, and style (i.e. joints
versus shear fractures). Accurate, early characterization of such
fracture system parameters is essential for successful exploration
and production of fractured reservoirs, but these characterizations
are often difficult to make, because the fracture system
architecture can be strongly affected by a number of structural
or
stratigraphic
variables. Ongoing work is aimed at developing
methods to predict fracture system architecture using limited
surface and subsurface data. This paper presents early results of
work on fracture systems in Laramide-style folds using mechanical
stratigraphy and four-dimensional surface analysis.
The San Rafael swell is a classic Laramide-style uplift exposing
Jurassic through Cretaceous rocks in east-central Utah. Within the
east-facing limb of the San Rafael monocline, the Carmel Formation
can be divided into 10 mechanical units based on stratigraphic
characteristics and style of deformation. In so doing, a consistent
correlation between fracture system architecture and bed thickness,
bedding style and rock type is apparent. In addition, observations
of
structural
fabrics and cross-cutting relations allow the
interpretation
of a simple kinematic history for this portion of
the monocline involving early cross-strike compression and later
strike-normal and strike-parallel extension. This sequence of
deformation is not consistent throughout a vertical section,
however, suggesting different kinematic histories for units at
initially different depths. To explain the origin of this
variability, results of simple models of the 4D evolution of
Laramide-style folds are presented.
AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah