Fracture
Characteristics of Folded Carbonates, Teton Anticline, Sawtooth Range,
Ghosh, Kajari1, Shankar Mitra1
(1)
The Teton anticline is located in the
frontal part of the Sawtooth Range, Montana, and exposes folded carbonates of
the Mississippian Castle Reef Formation. In order to characterize the
distribution and controls of fracture populations, 13 outcrops were mapped in
detail on exposed bedding planes of dolomitic limestones. Individual fracture
characteristics, such as fracture length, orientation, and density, as well as
their variation with structural position, were analyzed. The measured fracture
characteristics were used to simulate fracture map for larger areas. The
interaction of different fracture sets to form fracture networks was also
analyzed. Fracture networks were characterized by the summed lengths of
fracture traces in the largest cluster within the mapped area. Higher cluster
size corresponds to greater connectivity and thus a greater contribution of
fractures to fluid flow. Four main sets of fractures were found, with two
orthogonal sets, approximately parallel and transverse to the anticlinal axis,
being the dominant sets. Because the Teton anticline is a multi-hinge fold, it
exhibits a systematic variation of fracture density of longitudinal fractures,
with higher densities concentrated along fold hinges. The fracture density on
the hinges is typically about 2.7 times greater than that on the planar limbs.
However, transverse fractures do not show a systematic variation with position
relative to fold hinges. The fracture network size, which is primarily
controlled by fracture density and variation of fracture orientation, also
varies with structural position. The fracture analysis on Teton anticline
provides an analog for fracture characteristics and networks in subsurface
fractured carbonate reservoirs.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California