INTEGRATED STUDIES ON WOODFORD SHALE NATURAL FRACTURE ATTRIBUTES, ORIGIN, AND THEIR RELATION TO HYDRAULIC FRACTURING

Abstract

The Woodford Shale is a prolific hydrocarbon producing formation in Oklahoma. It is a silica and TOC rich, fractured reservoir and source rock. The natural fractures present within this formation, even though vital for fluid transport, have not been rigorously studied. This dissertation presents Woodford Shale fracture related studies from several different outcrop locations in Southern Oklahoma, covering the Criner Hills and the central and eastern Arbuckle Mountains. These areas have varying degrees of tilting and folding, ranging from almost flat beds to overturned beds. Addition of fold related fracture sets with progressive folding and tilting of beds (from one outcrop to the other) were visualized and documented. These observations gave a clear picture of the fracture sets that existed before folding and that developed during folding. The presence and absence of bitumen, silica, and calcite as fracture fill also serve as clues to fracture origin timing. These outcrops present opportunities for rigorous field measurements on fracture stratigraphic intensity variation, which helps in deciding the optimum landing spots for horizontal wells. Besides, relatively large surfaces on the quarry floor and quarry walls exposing the length, aperture, and height of relatively large fractures allowed quantification of these fracture parameters. These parameters then were used as inputs into a discrete fracture network model. This model, containing the discrete fractures and log-derived rock properties provided a complete static geomechanical model. This model was then used to simulate the stimulated rock volumes using field treatment parameters. The simulated geometries were matched with field microseismic geometries for three stages. Several simulations under different subsurface and treatment conditions explain the control of natural fractures on hydraulic fracture propagation and natural fracture reactivation.