Fracture Connectivity Patterns of Folded Carbonates, Teton Anticline, Sawtooth Range, Montana

Kajari Ghosh and Shankar Mitra
University of Oklahoma, Norman, OK

Fracture network patterns were studied on Teton anticline, located in the frontal part of the Sawtooth Range, Montana. In order to characterize the distribution and controls of fracture populations, 13 outcrops were mapped in detail on exposed bedding planes of dolomitic limestones of Mississippian Castle Reef Formation. Four main sets of fractures were found, with two orthogonal sets, approximately parallel and transverse to the anticlinal axis, being the dominant ones. The connectivity of the fracture network was estimated using (1) the fractional connected area, which is defined as the proportion of the total surface area of rock connected by fracture networks, and (2) the distribution of fracture clusters of different sizes, within each sample area. Together, these two parameters quantify the probability of encountering fracture networks of different sizes in subsurface wells, and thereby provide an effective measure of the contribution of the fracture networks in draining the reservoir. The fractional connected area varies from as low as 0.16 on the limbs to 1 on the hinges of the anticline. Results show that fracture network size is sensitive to fracture density, length and orientation. The density of the longitudinal set is inversely proportional to distance from the fold hinges and the set transverse to the fold axis exhibits higher density in the vicinity of regional fractures.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas