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Journal Article

Insights Into Complex Subdecimeter Fracturing Processes Occurring During a Water Injection Experiment at Depth in Äspö Hard Rock Laboratory, Sweden

Authors
/persons/resource/kwiatek

Kwiatek,  G.
4.2 Geomechanics and Rheology, 4.0 Geomaterials, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;

/persons/resource/patricia

Martinez Garzon,  Patricia
4.2 Geomechanics and Rheology, 4.0 Geomaterials, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;

Plenkers,  K.
External Organizations;

/persons/resource/leonhard

Leonhardt,  Maria
4.2 Geomechanics and Rheology, 4.0 Geomaterials, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;

/persons/resource/zang

Zang,  A.
2.6 Seismic Hazard and Stress Field, 2.0 Geophysics, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;

/persons/resource/specht

Specht,  Sebastian
2.6 Seismic Hazard and Stress Field, 2.0 Geophysics, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;

/persons/resource/dre

Dresen,  G.
4.2 Geomechanics and Rheology, 4.0 Geomaterials, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;

/persons/resource/bohnhoff

Bohnhoff,  M.
4.2 Geomechanics and Rheology, 4.0 Geomaterials, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;

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3486888.pdf
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Citation

Kwiatek, G., Martinez Garzon, P., Plenkers, K., Leonhardt, M., Zang, A., Specht, S., Dresen, G., Bohnhoff, M. (2018): Insights Into Complex Subdecimeter Fracturing Processes Occurring During a Water Injection Experiment at Depth in Äspö Hard Rock Laboratory, Sweden. - Journal of Geophysical Research: Solid Earth, 123, 8, 6616-6635.
https://doi.org/10.1029/2017JB014715


Cite as: https://gfzpublic.gfz-potsdam.de/pubman/item/item_3486888
Abstract
We investigate the source characteristics of picoseismicity (Mw < −2) recorded during a hydraulic fracturing in situ experiment performed in the underground Äspö Hard Rock Laboratory, Sweden. The experiment consisted of six stimulations driven by three different water injection schemes and was performed inside a 28‐m‐long, horizontal borehole located at 410‐m depth. The fracturing processes were monitored with a variety of seismic networks including broadband seismometers, geophones, high‐frequency accelerometers, and acoustic emission sensors thereby covering a wide frequency band between 0.01 and 100,000 Hz. Here we study the high‐frequency signals with dominant frequencies exceeding 1000 Hz. The combined seismic network allowed for detection and detailed analysis of 196 small‐scale seismic events with moment magnitudes MW < −3.5 (source sizes of decimeter scale) that occurred solely during the stimulations and shortly after. The double‐difference relocated hypocenter catalog as well as source parameters were used to study the physical characteristics of the induced seismicity and then compared to the stimulation parameters. We observe a spatiotemporal migration of the picoseismic events away and toward the injection intervals in direct correlation with changes in the hydraulic energy (product of fluid injection pressure and injection rate). We find that the total radiated seismic energy is extremely low with respect to the product of injected fluid volume and pressure (hydraulic energy). The radiated seismic energy correlates well with the hydraulic energy rate. The obtained fault plane solutions for particularly well‐characterized events signify the reactivation of preexisting rock defects under influence of increased pore fluid pressure on fault plane orientations in good correspondence with the local stress field orientation.