Hydro-Geomechanical Observations During Multistage Hydraulic Stimulation at the Bedretto Underground Laboratory, Switzerland
Abstract
A series of hydraulic stimulation experiments were performed in the Bedretto Underground Laboratory for Geosciences and Geoenergies in Switzerland to answer questions about the creation of an engineered geothermal reservoir in crystalline rocks. A 400 m long stimulation borehole was divided into 15 intervals by a multi-packer system. In this work, we present preliminary results of interval 8 in which two injection phases were performed with a 3.5 months gap in between. The two phases differ in the injected volume and injection protocol (pressure vs. flow rate controlled). Within the interval, we mapped a cluster of sub-parallel pre-existing open fractures that are reasonably well oriented for reactivation in the estimated stress field. The interval pressure and flow rate data from the injections reveal a reactivation of the pre-existing fractures, associated with a large increase in injectivity. A comparison of the expected stress field around the stimulation interval with the observed reactivation pressure indicates that the fractures were likely reactivated by hydraulic shearing. The reactivation is also supported by other data sets from the extensive monitoring network, e.g. distributed temperature and strain sensing. Show more
Publication status
publishedExternal links
Book title
Proceedings of the 57th U.S. Rock Mechanics/Geomechanics SymposiumPages / Article No.
Publisher
American Rock Mechanics AssociationEvent
Organisational unit
02334 - BULGG - Bedretto Underground Lab / BULGG - Bedretto Underground Lab
Funding
ETH-06 19-1 - Creating a hierarchy of fracture network in enhanced geothermal systems (EGS) through innovative hydraulic fracturing stimulation (ETHZ)
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