Western Australia Chapter

Micro-seismic monitoring of damage initiation and propagation in an underground gallery in the Opalinus Clay formation (Switzerland)

Joel Sarout, CSIRO Energy, Perth

Abstract

We report the results of the analysis of the micro-seismicity induced by an excavation operation in the Opalinus Clay formation in Switzerland. This formation is considered for the potential storage of radioactive waste, and the monitoring of the micro-seismicity is used to characterize the evolution of the mechanical damage of the rock surrounding the storage infrastructures. A multistep method is developed to filter and classify the recorded micro-seismic events (MSEs). The distribution and micro-mechanical processes associated with the excavation-induced damage are inferred from the spatio-temporal location and focal mechanisms of the MSEs. We observe an asymmetric geometry of the excavation-damaged zone around the gallery, without notable micro-seismic activity in the sandy facies sidewall. In contrast, the shaly sidewall exhibits a first burst of MSEs as soon as the excavation is stopped, followed by two smaller bursts. The first one is located ahead of the excavation front and is associated with a dominant double-couple component, suggesting bedding plane reworking (shear fracturing). The MSEs of the second cluster occur inside the shaly sidewall of the gallery, with a dominant compensated linear vector dipole component, suggesting extensive cracking. We identify and discuss four major factors that seem to control the micro-seismic activity: lithology, geometry of the geological features, gallery orientation and direction of the main compressive stress.

About Joel Sarout

Joel Sarout is currently a senior research scientist at CSIRO in Perth, where he leads the Rock Properties team. He holds an MSc in Geomechanics from the University of Minnesota in Minneapolis (2003) and a PhD in Rock Physics from the Ecole Normale Supérieure in Paris (2006). Since 2015, he acts as Associate Editor for Geophysical Prospecting, the ISI journal of the European Association of Geoscientists and Engineers. He authored 29 refereed articles and presented many conference papers related to rock/fluid interactions, seismic anisotropy and dispersion, thermal conductivity, rock damage, micro-seismicity, permeability. His work has been cited more than 400 times since 2007. In the past 10 years, he has been involved and managed various government- and industry-funded research projects aimed at understanding and predicting the effects of anthropogenic underground activities in the energy and resources sectors. Through a science-based approach, these projects have contributed to (i) a more accurate interpretation of 3D/4D seismic and micro-seismic data; (ii) improving reservoir depletion and borehole stability monitoring/predictions; (iii) optimising exploration for oil, gas and geothermal resources; (iv) enhancing energy resources recovery.

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