Acoustic emission and SEM analyses of hydraulic fractures under triaxial stress conditions

Laboratory hydraulic fracturing experiments on crystalline rock for geothermal purposes

“…20 and 21 compare microscopic investigations of hydraulic fracture patterns in a tight sandstone and granite at the micrometer-or sub-grain scale. The tight sandstone has larger porosity (6%, Damani et al, 2013) compared with that of the granite (0.66%, Zhuang et al, 21). These results on fracture patterns help us to better understand the mechanism of hydraulic fracturing.…”

“…For conventional triaxial HF tests, confining stress (pressure vessel) and vertical stress (piston cylinder) are applied in most studies without any horizontal differential stress. Few triaxial tests have applied horizontal differential stresses in a triaxial cell using cylindrical specimens and transverse loading flat jacks (e.g., Smart, 1995;Damani et al, 2013;Patel et al, 2017). High temperatures are used with some testing equipment, particularly for geothermal studies.…”

“…It is necessary to differentiate between the meanings of parameters with similar names. Evolutions of AE count rate, accumulative AE hits/counts, or the seismic 𝑏-value of the Gutenberg-Richter distribution with injection time are frequently used for analyzing the initiation and propagation of hydraulic fractures (Stanchits et al, 2012;Ishida et al, 2012;Damani et al, 2013;Chitrala et al, 2013;Goodfellow et al, 2016). A higher 𝑏-value stands for more small-magnitude induced seismic events, which renders the treatment safer.…”