@article{epos216,
          volume = {68},
          number = {2},
           month = {April},
          author = {James T. Rutledge and Scott Phillips},
           title = {Hydraulic stimulation of natural fractures as revealed by induced microearthquakes, Carthage Cotton Valley gas field, east Texas},
       publisher = {Society of Exploration Geophysicists},
            year = {2003},
         journal = {GEOPHYSICS},
           pages = {441--452},
             url = {https://episodesplatform.eu/eprints/216/},
        abstract = {We produced a high-resolution microseismic image of
a hydraulic fracture stimulation in the Carthage Cotton
Valley gas field of east Texas.We improved the precision
of microseismic event locations four-fold over initial locations by manually repicking the traveltimes in a spatial
sequence, allowing us to visually correlate waveforms of
adjacent sources. The new locations show vertical containment within individual, targeted sands, suggesting little or no hydraulic communication between the discrete
perforation intervals simultaneously treated within an
80-m section. Treatment (i.e., fracture-zone) lengths inferred from event locations are about 200 m greater at
the shallow perforation intervals than at the deeper intervals. The highest quality locations indicate fracturezone widths as narrow as 6 m. Similarity of adjacentsource waveforms, along with systematic changes of
phase amplitude ratios and polarities, indicate fairly uniform source mechanisms (fracture plane orientation and
sense of slip) over the treatment length. Composite focal
mechanisms indicate both left- and right-lateral strikeslip
faulting along near-vertical fractures that strike subparallel to maximum horizontal stress. The focal mechanisms and event locations are consistent with activation of the reservoir?s prevalent natural fractures, fractures that are isolated within individual sands and trend subparallel to the expected hydraulic fracture orientation (maximum horizontal stress direction). Shear activation of these fractures indicates a stronger correlation of induced seismicity with low-impedance flow paths than is normally found or assumed during injection stimulation.}
}