Fracture Characteristics of Folded Carbonates, Teton Anticline, Sawtooth Range, Montana

Ghosh, Kajari¹, Shankar Mitra¹ (1) University of Oklahoma, Norman, OK

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.