Before the EGS Collab Project, SURF underground laboratory was previously used for the kISMET (permeability (k) and Induced Seismicity Management for Energy Technologies) project also supported by the DOE. The project designed and carried out in situ hydraulic fracturing experiments in the crystalline rock at the site to characterize the stress field, understand the effects of rock fabric on fracturing, and gain experience in monitoring using geophysical methods. The project also included pre- and post-fracturing simulation and analysis, laboratory measurements and experiments, and we conducted an extended analysis of the local stress state using previously collected data (Oldenburg et al 2016). The project was conducted at the 4850ft location of SURF in phyllite of the Precambrian Poorman Formation where five nearly vertical boreholes with 10ft spacing. Hydraulic fractures were remarkably uniform suggesting corescale and larger rock fabric did not play a role in controlling fracture orientation. Electrical resistivity tomography (ERT) and continuous active source seismic monitoring (CASSM) were carried out in the four monitoring boreholes during the generation of a larger fracture. ERT was not able to detect the fracture created, nor did accelerometers placed in the West Access Drift, but microseismicity was detected for the first (deepest) hydraulic-fracturing stress measurement. Analytical solutions suggest that the fracture radius of the large fracture (stimulation test) was more than 6 m (20 ft), depending on the unknown amount of leak-off. The kISMET results for the stress state are consistent with large-scale midcontinent estimates of stress. From these tests, we have a high confidence in the characterization of the SURF geology for further projects.
The following summary is an adaption from the paper OLDENBURG 2016 Intermediate-Scale Hydraulic Fracturing in a Deep Mine kISMET Project Summary 2016 [https://www.osti.gov/biblio/1338937-intermediate-scale-hydraulic-fracturing-deep-mine-kismet-project-summary