ANALYSIS OF FRACTURE SYSTEMS WITHIN THE STILLWELL ANTICLINE: IMPLICATIONS FOR FLUID FLOW

Natural fractures and their geological characteristics control the hydraulic behavior of both hydrologic and petroleum reservoirs. Therefore, it is imperative to have a reliable detection and categorization model of fracture systems for the quantification of permeability. In the past twenty years, the fracture research field has experienced exponential growth, with many studies focused upon the relationship of fracture intensity, orientation, fill, and length. However, most of the research has been limited to either the microscopic or macroscopic scale. Moreover, few studies take into account fracture’s aperture in their measurements of fracture intensity. I studied the transitional scale between microscopic and macroscopic fractures at a well-exposed fold system in West Texas. The cross-sectional view of the Stillwell Anticline provided an excellent opportunity to analyze fracture systems at different structural positions such as the forelimb, forelimb hinge, middle limb, backlimb hinge, and backlimb. I maintained constant stratigraphic position and traced a Santa Elena Limestone bed along the fold system. At each locality, I measured fracture orientation, fill, morphology, length, and aperture. Each variable proved to be independent of all others. Results of fracture intensity and aperture showed significant difference at each structural position and follow a power law distribution, with fewer fractures having large apertures. Furthermore, significant fracture sets at each location appear to correlate with the macro-scale outcrop joint sets. This relationship indicates that a multivariable analysis of fractures at a transitional scale is possible, and can give a meaningful insight about fracture systems in the subsurface.