ABSTRACT:

Efforts to quantify induced-seismicity risk and to develop mitigation strategies are hampered by a dearth of numerical schemes that can accommodate realistic Earth models while capturing the full spectrum of applicable physics. Here we present a new approach to modelling induced seismicity, whereby the three principal mechanisms for induced-seismicity triggering are accounted for, and uncertainties in input parameters are addressed stochastically to provide a probabilistic assessment of induced-seismicity hazard. The models provide probabilities for the expected maximum magnitudes of events and the sensitivities of results to the different input parameters can be analyzed. In this manner, we can estimate the probabilities of generating an event of a certain magnitude based on the modelled injection scenario and parameter distributions. This type of modelling can be used to give a site-specific assessment of the probability of generating an induced event changes, based on different treatment designs. Case studies from western Canada are used to evaluate the applicability of this approach for unconventional oil and gas development. This methodology also has potential for mitigating injection-induced seismicity in other industries, including geothermal energy and gigatonne-scale CO2 storage.

1. Introduction

Anthropogenic fluid injection into the subsurface is known to cause induced seismicity in some cases. Well-known examples include enhanced geothermal systems (Lee et al., 2019), wastewater disposal (Ellsworth, 2013) and hydraulic fracturing (Bao and Eaton, 2016). In the case of hydraulic fracturing, the stimulation process is designed to fracture the reservoir rocks and this induces microseismic events that are usually too small to be felt at surface (M < 2). Nevertheless, in rare cases, events can be large enough to exceed local regulations designed to prevent felt earthquakes. This can result in costly delays in resource extraction, moratoriums on resource development, or ultimately, infrastructure damage and human loss of life (Atkinson et al., 2020). Mitigating this issue is therefore an important goal. However, induced seismicity is a very complex problem and current mitigation strategies unfortunately have known drawbacks and therefore may not present optimal solutions to meet this objective.

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