This paper describes the use of the iso-frequency volumes resulting from the spectral decomposition of surface seismic data for the identification of subtle structural features (shear faults) that control the formation, location, and distribution of open fracture trends within the Steckman Ridge Underground Gas Storage field in south-central Pennsylvania, USA. This gas field, originally developed with five vertical boreholes, was purchased by Spectra Energy for conversion to underground gas storage. After an initial examination it was determined that this field was controlled by an open fracture system which trended approximately 70° from the dominant structural trend. Various seismic attributes were investigated in an attempt to determine the fracture controlling structures. Subtle shear faults, not observed in the full frequency volume, were located on specific iso-frequency volumes and mapped. These structural features were found to be related to major cross strike discontinuities which could be observed on other geophysical data. These features were confirmed by the subsequent drilling of eight horizontal boreholes and the formation imaging logs which were tractored through these boreholes. The resulting injection/withdrawal rates for these wells have made Steckman Ridge gas storage field one of the most successful gas storage conversion Spectra Energy has performed to date.


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