Hydraulic fracture monitoring in hard rock at 410 m depth with an advanced fluid-injection protocol and extensive sensor array

Zang, Arno; Stephansson, Ove; Stenberg, Leif; Plenkers, Katrin; Specht, Sebastian von; Milkereit, Claus; Schill, Eva; Kwiatek, Grzegorz; Dresen, Georg; Zimmermann, Günter; Dahm, Torsten; Weber, M.

doi:10.1093/gji/ggw430

Cited by 115 publications

(149 citation statements)

References 52 publications

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“…Each HF experiment includes four injection cycles: a breakdown cycle (i.e., initiation of the fracture) followed by three fracture reopening cycles. In all three experiments, almost all seismic events occurred during fracture reopening, but only a few events were associated with the breakdown of the rock (similar as reported for HF experiments by Zang et al, 2017). Seismicity rates seem to depend on injection rate, even though injection rate is the same for the breakdown cycle and the first reopening cycles (i.e., 1 L min −1 ) but seismicity rates are not (Fig.…”

Section: Temporal Evolution During Hydrofracturingsupporting

confidence: 77%

“…For that purpose, we adapt the concept used by Goebel et al (2012) for laboratory event magnitudes, but we also account for the seismic attenuation of the wave as suggested by Zang et al (2017):…”

Section: Relative Magnitudesmentioning

confidence: 99%

“…We corrected the amplitude A i following the strategy of Zang et al (2017) by using the middle frequency of the band-pass filter, which is f 0 = 5 kHz, and Q P = 30 (Holliger and Bühnemann, 1996). The dominant frequencies (i.e., the maxima in the Fourier spectrum) in our case range from 1-10 kHz.…”

Section: Relative Magnitudesmentioning

confidence: 99%

“…Although the relationship between seismicity and HF growth is widely discussed in the literature, there are few field-scale observations which investigate the relationship between metre-scale hydrofractures formed during stress tests and the ambient stress conditions (e.g., Zang et al, 2017;López-Comino et al, 2017). In small-scale laboratory experiments the stress field is imposed to the samples and is precisely known (Chitrala et al, 2010;Doe and Boyce, 1989).…”

Section: Introductionmentioning

confidence: 99%

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On the link between stress field and small-scale hydraulic fracture growth in anisotropic rock derived from microseismicity

et al. 2018

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Abstract. To characterize the stress field at the Grimsel Test Site (GTS) underground rock laboratory, a series of hydrofracturing and overcoring tests were performed. Hydrofracturing was accompanied by seismic monitoring using a network of highly sensitive piezosensors and accelerometers that were able to record small seismic events associated with metre-sized fractures. Due to potential discrepancies between the hydrofracture orientation and stress field estimates from overcoring, it was essential to obtain highprecision hypocentre locations that reliably illuminate fracture growth. Absolute locations were improved using a transverse isotropic P-wave velocity model and by applying joint hypocentre determination that allowed for the computation of station corrections. We further exploited the high degree of waveform similarity of events by applying cluster analysis and relative relocation. Resulting clouds of absolute and relative located seismicity showed a consistent east-west strike and 70 • dip for all hydrofractures. The fracture growth direction from microseismicity is consistent with the principal stress orientations from the overcoring stress tests, provided that an anisotropic elastic model for the rock mass is used in the data inversions. The σ 1 stress is significantly larger than the other two principal stresses and has a reasonably welldefined orientation that is subparallel to the fracture plane; σ 2 and σ 3 are almost equal in magnitude and thus lie on a circle defined by the standard errors of the solutions. The poles of the microseismicity planes also lie on this circle towards the north. Analysis of P-wave polarizations suggested double-couple focal mechanisms with both thrust and normal faulting mechanisms present, whereas strike-slip and thrust mechanisms would be expected from the overcoring-derived stress solution. The reasons for these discrepancies can be explained by pressure leak-off, but possibly may also involve stress field rotation around the propagating hydrofracture. Our study demonstrates that microseismicity monitoring along with high-resolution event locations provides valuable information for interpreting stress characterization measurements.

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Section: Temporal Evolution During Hydrofracturingsupporting

confidence: 77%

Section: Relative Magnitudesmentioning

confidence: 99%

Section: Relative Magnitudesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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On the link between stress field and small-scale hydraulic fracture growth in anisotropic rock derived from microseismicity

et al. 2018

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“…This site is equipped with a thermal fluid loop including an electrical submersible pump and a research power plant, and is being used to investigate EGS technologies for deep sedimentary basins (e.g., Blöcher et al 2016). The Äspö Hard Rock Laboratory in Sweden has hosted a series of multi-stage hydraulic fracturing experiments in boreholes drilled in granodiorite to evaluate how differences in fluidinjection tactics (continuous, progressive, and pulse pressurization) affect the amount and intensity of induced seismicity and changes in fracture permeability (Zang et al 2016). The US Department of Energy's Geothermal Technology Office has created the Frontier Observatory for Research in Geothermal Energy (FORGE) to develop and test the next-generation technologies needed to characterize, access, create, and sustain EGS reservoirs.…”

Section: Underground Field Laboratoriesmentioning

confidence: 99%

Utilizing supercritical geothermal systems: a review of past ventures and ongoing research activities

Reinsch

Dobson

Asanuma³

et al. 2017

Geotherm Energy

157

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Transmissivity Changes and Microseismicity Induced by Small‐Scale Hydraulic Fracturing Tests in Crystalline Rock

Jalali

Gischig

Doetsch

et al. 2018

Geophysical Research Letters

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Multiple meter‐scale hydraulic fracturing (HF) experiments were executed in the crystalline rock at the Grimsel Test Site, Switzerland. The effect of the HF on the rock transmissivity has been quantified with hydraulic tests before and after each HF experiment. We observe transmissivity enhancement of 2 to 3 orders of magnitude and a change in the dominant flow regime after most of the HF tests. From microseismicity induced by the HF, we do not observe a systematic correlation between transmissivity enhancement and event numbers, frequency‐magnitude distribution, or maximum magnitude. However, the radii of hydraulic fractures inferred independently from seismicity clouds and hydraulic responses coincide, implying that slip along fractures is the common underlying mechanism for transmissivity increase and seismicity.

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Hydraulic fracture monitoring in hard rock at 410 m depth with an advanced fluid-injection protocol and extensive sensor array

Cited by 115 publications

References 52 publications

On the link between stress field and small-scale hydraulic fracture growth in anisotropic rock derived from microseismicity

On the link between stress field and small-scale hydraulic fracture growth in anisotropic rock derived from microseismicity

Utilizing supercritical geothermal systems: a review of past ventures and ongoing research activities

Transmissivity Changes and Microseismicity Induced by Small‐Scale Hydraulic Fracturing Tests in Crystalline Rock

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