Rutledge, James T. (1998) Analyses of the Cotton Valley Microseismic Data for AsymmetricFracture Growth. Technical Report. Gas Research Institute.
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Abstract
I have examined the entire Stage 2 microseismic data set for source location, detection range, andmagnitude distribution to determine what information regarding fracture growth asymmetry canbe obtained from the distribution of seismicity.A conservative estimate of wing lengths based on event locations of higher quality data are925 ft±20 ft east and 845±25 ft west of the treatment well at injection depth, or 12%longer to the east.Location uncertainty for a set of low-magnitude events detected near the eastern terminusof the seismicity are actually larger than the western-most locations because they occurnear the plane of the 2 monitor wells where location errors are inherently large. Based onthese low-magnitude events, a more liberal estimate of the eastern extent of seismicity is1065±100 ft, or 21% longer to the east.An examination of P- and S-wave detection ranges indicate that the larger magnitudeevents observed during the treatment could have been detected and the mapped had theyalso occurred beyond the western terminus of mapped seismicity. However, the closest200 ft of the eastern wing terminus is populated by only small magnitude events. Had asimilar set of low-magnitude events extended 200 ft beyond the western terminus ofmapped seismicity, they would have produced no detectable P-waves and only marginallydetectable S-waves on the near-treatment-zone receivers. Even if recognized, such eventswould have been unmappable with the working arrays deployed. Therefore, symmetricfracture growth, in both length and release of seismic energy, would result in the seismicobservations obtained. Although a definitive result cannot be obtained from a lack ofobservations, I conclude that it is most reasonable to assume symmetric fracture growthbased on the source locations, detection range, and magnitude distribution observed.
| Item Type: | Reports (Technical Report) |
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| Subjects: | Methodology > Other-additional study Region > USA > Texas > Cotton Valley Inducing technology > Unconventional hydrocarbon extraction |
| Project: | SERA > COTTON VALLEY: uconventional hydrocarbon extraction |