Comprehensive data set of in situ hydraulic stimulation experiments for geothermal purposes at the Äspö Hard Rock Laboratory (Sweden)

• Published in: Earth system science data 2024-01, Vol.16 (1), p.295-310
• Main Authors: Zang, Arno, Niemz, Peter, von Specht, Sebastian, Zimmermann, Günter, Milkereit, Claus, Plenkers, Katrin, Klee, Gerd
• Format: Article
• Language: English
• Subjects: Accelerometers; Acoustic emission; Acoustic emission testing; Acoustics; Boreholes; Broadband; Crystalline rocks; Datasets; Earthquakes; Energy; Enhanced geothermal systems; Experiments; Fault lines; Field tests; Fluid injection; Geological data; Geothermal power; Hammers; Heat exchangers; Hydraulic fracturing; Injection; Inspection; Laboratories; Laboratory tests; Oil and gas field equipment; Permeability; Pressure distribution; R&D; Research & development; Rock; Rock masses; Seismometers; Sensor arrays; Sensors; Stimulation; Technical feasibility; Technology assessment; Tracking; Urban areas; Water flooding; Water injection
• ISSN: 1866-3516; 1866-3508; 1866-3516
• DOI: 10.5194/essd-16-295-2024

In this article, a high-resolution acoustic emission sensor, accelerometer, and broadband seismometer array data set is made available and described in detail from in situ experiments performed at Äspö Hard Rock Laboratory in May and June 2015. The main goal of the hydraulic stimulation tests in a horizontal borehole at 410 m depth in naturally fractured granitic rock mass is to demonstrate the technical feasibility of generating multi-stage heat exchangers in a controlled way superiorly to former massive stimulations applied in enhanced geothermal projects. A set of six, sub-parallel hydraulic fractures is propagated from an injection borehole drilled parallel to minimum horizontal in situ stress and is monitored by an extensive complementary sensor array implemented in three inclined monitoring boreholes and the nearby tunnel system. Three different fluid injection protocols are tested: constant water injection, progressive cyclic injection, and cyclic injection with a hydraulic hammer operating at 5 Hz frequency to stimulate a crystalline rock volume of size 30 m × 30 m × 30 m at depth. We collected geological data from core and borehole logs, fracture inspection data from an impression packer, and acoustic emission hypocenter tracking and tilt data, as well as quantified the permeability enhancement process. The data and interpretation provided through this publication are important steps in both upscaling laboratory tests and downscaling field tests in granitic rock in the framework of enhanced geothermal system research. Data described in this paper can be accessed at GFZ Data Services under https://doi.org/10.5880/GFZ.2.6.2023.004 (Zang et al., 2023).