Abstract
A better understanding of the energy budget has important implications for enhancing the efficiency of hydraulic fracturing treatments. In particular, what percentage of the input treatment energy is released as radiated energy? What characterizes the deformation of the failure?
We use a bonded-particle modeling approach to investigate both the radiated energy release and the amount of brittle failure. To test our model, we simulate triaxial compression tests on calibrated sandstone samples. Our results show that much of the failure is marked by a tensile component, despite the development of one or two large shear planes crosscutting the samples. Additionally, only 2.5% of the input energy is radiated as seismic waves. We propose an updated empirical energy-magnitude relation: log ER = 1.9MW +8.5, where ER is the radiated energy and MW is the event moment magnitude. This relation is an alternative to the commonly used Kanamori relationship and more applicable for the small-magnitude acoustic emissions in triaxial tests and likely microseismic events in hydraulic fracturing experiments, which are both marked by strong tensile deformation. Close examination of the source mechanisms of the induced acoustic emissions reinforce the complex nature of the micromechanics behind rock fracturing in general, due to strong deviations of the local stress field from the applied external field.
