Hydraulic fracture imaging from the Los Alamos hot dry rock experiment
The waveform correlation analysis and grid search method have been developed to determine the precise hypocenter locations for a cluster of 157 microearthquakes induced by hydraulic fracturing at Los Alamos Hot Dry Rock (HDR) geothermal site. Among the 157 events, 147 microearthquakes occurred in a tight cluster of dimension of 40 m, roughly defining a vertical hydraulic fracture zone. The length, height, and width of the hydraulic fracture zone are measured to be 40, 35, and 5 m, respectively. The orientation of the fracture zone is estimated about N40{degrees}W. Analysis of temporal-spatial pattern of the induced microseismicity indicates that the fracture zone grows significantly in a two-hour period and it grows toward to the northwest along the fracture zone strike with a growth rate of 0.1-0.2 m per minute. An empirical Green`s function (EGF) method has been used to retrieve relative source time functions (RSTF) and to estimate source parameters for larger induced earthquakes. The RSTFs reveal the source complexity and rupture directivity of induced seismic events. The rupture directivity indicates that the rupture propagates to the northwest, which is consistent with the growth direction of the hydraulic fracture zone determined with seismicity temporal-spatial distribution. The source duration of the induced events ranges from 2-8 ms and source radii are estimated to be 4-12 m. Values of stress drops are from 1-19 bars. Significant variation of stress drops reflects that the stress field heterogeneity within a hydraulic fracture zone extends down to a few meters.
- DOE Contract Number:
- FG02-86ER13636
- OSTI ID:
- 542846
- Report Number(s):
- CONF-951013-; TRN: 97:004463-0034
- Resource Relation:
- Conference: SEG `95: 65. annual meeting and international exposition of the Society of Exploration Geophysicists (SEG), Houston, TX (United States), 8-13 Oct 1995; Other Information: PBD: 1995; Related Information: Is Part Of SEG/Houston `95 - technical program; PB: 1623 p.
- Country of Publication:
- United States
- Language:
- English
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