Previous practice to determine the source mechanism of microseismic events associated with hydraulic fracture typically includes only far-field terms in moment tensor inversion. The intermediate-field terms and near-field term are normally ignored because of increased complexity in the calculation. Source-receiver distances in hydraulic fracturing are usually 1000 ft and the effects of near and intermediate-field terms are still unknown. We perform a study to improve the precision of the source mechanism by including the intermediate-field term in moment tensor inversion.
We find that the intermediate-field term contributes 1/3 of the signal amplitude when the source-receiver distance is 1000 ft. The intermediate-field term contributes 1/20 of the signal amplitude when the source-receiver distance is 6700 ft. Note that "1/20" is at the noise level. Thus, when source-receiver distance is less than 6700ft, we need to consider the intermediate-field term. Especially, when the distance is 1000ft, the intermediate-field term becomes significant. Similarly, near-field terms contribute less than 1/20 of the signal amplitude when distances are larger than 300 ft. In our case, we confirm that the near-field term can be ignored in microseismic analysis.
Our results indicate that the intermediate-field terms can improve moment tensor inversion by 2% to 40% at source-receiver ranges less than 1000 ft. When distances are larger than 6700, the improvement is limited to 1%. In the presence of noise, the intermediate-field terms help to improve the moment tensor inversion (15% improvement with noise present vs 3% improvement without noise).
Our study provides a foundation for using intermediate-field terms in moment tensor inversion in the studies of hydraulic fractures.
| Identifer | oai:union.ndltd.org:LSU/oai:etd.lsu.edu:etd-01162014-150947 |
| Date | 08 May 2014 |
| Creators | Fan, Chennu |
| Contributors | Dahi Taleghani, Arash, Lorenzo, Juan, Sears, Stephen O., Smith, John Rogers |
| Publisher | LSU |
| Source Sets | Louisiana State University |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lsu.edu/docs/available/etd-01162014-150947/ |
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