STOCHASTIC MODELS OF FRACTURE NETWORKS BASED ON MECHANICAL STRATIGRAPHY

Vertical opening-mode fractures are mapped on quarry walls in order to assess the stratigraphic controls on fracture patterns in the relatively undeformed Silurian dolomite of northeastern Wisconsin. Maps of vertical fractures are used to assess the effectiveness of various types of stratigraphic horizons (e.g. organic partings or cycle-bounding mud horizons) in terminating opening-mode fractures within two stages. First, the mechanical stratigraphy of the exposures is interpreted from the observed fracture pattern. The second stage of this study stochastically predicts mechanical stratigraphy and subsequent fracture pattern from empirical relationships between the observed sedimentary stratigraphy and the interpreted mechanical stratigraphy. For example, 63% of cycle-bounding mud horizons within the inner-middle and middle shelf facies serve as mechanical interfaces. These empirical percentages are input to a monte carlo analysis of 50 stochastic realizations of mechanical stratigraphy. Finally, comparisons of the stochastically predicted and interpreted mechanical stratigraphy yield errors ranging from 13% to 33%. This prediction yields far better results than assuming that all stratigraphic horizons act as mechanical interfaces. The methodology presented in this study demonstrates the prediction of fracture pattern within relatively undeformed strata from both complete characterization of sedimentary stratigraphy and understanding mechanical controls on fracturing.