Use of anisotropy in <i>P</i> -wave and <i>S</i> -wave data for fracture characterization in a naturally fractured gas reservoir

Gas production in Bluebell-Altamont Field in northeastern Utah is from numerous sandstones and carbonates in the Tertiary upper Green River Formation at depths of approximately 6500–8500 ft. The local geologic setting is nearly flat-lying sediments with no faulting observed at target depths. The field has a very gentle anticlinal closure (less than 50 ft). Matrix porosity and permeability in the reservoir rocks are generally low, such that fracturing yields substantially higher production rates. Consequently, seismic detection of fracturing is a potentially important aid to field development.