Heat Propagation Through Fractures During Hydraulic Stimulation in Crystalline Rock
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2022-06-26
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Conference Paper
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Abstract
The Bedretto Underground Laboratory for Geosciences and Geoenergies (BULGG) is located in central Switzerland and serves as a test bed for geothermal energy research. Several boreholes were drilled from the laboratory section (ca. 1.1 km overburden) to serve as injection boreholes for stimulation and geophysical monitoring boreholes. During a hydraulic stimulation injection in winter 2020 into injection borehole ST2 interval ranging from 313 to 320 m, we observe a thermal perturbation using distributed fiber optic temperature sensing in a neighboring open borehole (MB1) at a depth of 275 m to 295 m. Prior to injection, there is a thermal anomaly in MB1 at about 289 m due to natural fracture fluid flow. Below this depth the temperature is approximately 1.5 °C higher than above. During injection there is a gradual upward movement of the thermal anomaly to ca. 278 m depth. After injection is stopped, the thermal signal gradually recovers to the original depth. The cause for such a temperature change is potentially due to increased warm water flow reaching the base of MB1 from deeper ST2 or poro-elastic fracture closure of the cold-water conducting fractures at 278 and 289 m depth in MB1 during stimulation.
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Proceedings of the 56th U.S. Rock Mechanics/Geomechanics Symposium
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American Rock Mechanics Association
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56th U.S. Rock Mechanics/Geomechanics Symposium
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03953 - Robertsson, Johan / Robertsson, Johan
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691728 - Demonstration of soft stimulation treatments of geothermal reservoirs (SBFI)