Using ground motion prediction equations to monitor variations in quality factor due to induced seismicity: a feasibility study

Vincenzo Convertito,Roberta Esposito,Raffaella De Matteis,Paolo Capuano

doi:10.1007/s11600-020-00441-0

Abstract

Sub-surface operations for energy production such as gas storage, fluid reinjection or hydraulic fracking may modify the physical properties of the rocks, in particular the seismic velocity and the anelastic attenuation. The aim of the present study is to investigate, through a synthetic test, the possibility of using empirical ground-motion prediction equations (GMPEs) to observe the variations in the reservoir. In the synthetic test, we reproduce the expected seismic activity (in terms of rate, focal mechanisms, stress drop and the b value of the Gutenberg-Richter) and the variation of medium properties in terms of the quality factor Q induced by a fluid injection experiment. In practice, peak-ground velocity data of the simulated earthquakes during the field operations are used to update the coefficients of a reference GMPE in order to test whether the coefficients are able to capture the medium properties variation. The results of the test show that the coefficients of the GMPE vary during the simulated field operations revealing their sensitivity to the variation of the anelastic attenuation. The proposed approach is suggested as a promising tool that, if confirmed by real data analysis, could be used for monitoring and interpreting induced seismicity in addition to more conventional techniques.

Highlights

The increasing demand of energy is pushing exploration of new sources involving the exploitation of sub-surface resources
It is known from the physics of the rocks that the presence of fluids, in particular when injected at high pressure, in addition to enhance the probability of earthquake occurrence, can modify rock properties and in particular seismic velocity and anelastic attenuation
Similar results have been obtained by Hutching et al (2019) by analyzing earthquakes recorded during field operations at The Geysers geothermal field and by Wcisło et al (2017) who found high attenuation values (QP ~ 48 and QP/QS < 1) analyzing seismicity induced by the injection of wastewater in the Costa Molina 2 well in southern Italy

Summary

Introduction

The increasing demand of energy is pushing exploration of new sources involving the exploitation of sub-surface resources. It is worthwhile that seismicity and medium properties variation induced by field operations have to be monitored It is known from the physics of the rocks that the presence of fluids, in particular when injected at high pressure, in addition to enhance the probability of earthquake occurrence (e.g., due to a reduction in fault strength see Guha 2000), can modify rock properties and in particular seismic velocity and anelastic attenuation. This is confirmed by both laboratory measurements and data analysis recorded during field operations. Similar results have been obtained by Hutching et al (2019) by analyzing earthquakes recorded during field operations at The Geysers geothermal field and by Wcisło et al (2017) who found high attenuation values (QP ~ 48 and QP/QS < 1) analyzing seismicity induced by the injection of wastewater in the Costa Molina 2 well in southern Italy. Wandycz et al (2019) measured the variation of the anelastic attenuation based on the microseismicity recordings in Northern Poland

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