Effective Management of Induced Seismicity for the Net-Zero Energy Transition

Progress towards a net zero carbon economy involves subsurface activities such as geothermal energy production and geological storage of carbon dioxide (long-term) and hydrogen (short-term). These activities involve injection and extraction of fluids, which actively disturb tectonic stresses in the earth’s crust. Subsurface ruptures, and associated seismicity, induced by such stress perturbations carry a risk of damage from ground motion, fluid leakage to the surface due to increased flow pathways, and potential loss of public confidence. Safe operation of these requires effective management to minimise induced seismicity.
Induced seismicity has risen significantly over the past decade due to the widespread hydraulic fracturing activities around the globe [1]. This increase has intensified the negative public perception of subsurface engineering activities. It has also led to increased research into optimal approaches for managing induced seismicity. Currently, induced seismicity is regulated using a ‘traffic light’ system based on the maximum magnitude of recorded seismic events. However, management of induced seismicity requires more advanced systems, such as that varying the injection protocol continuously instead of waiting for the thresholds when it may be too late [2,3].
To reduce the uncertainties involved in managing the risk of induced seismicity, understanding small scale processes such as the evolution of local strains and damage mechanisms in the approach to and during failure or fault reactivation is important to provide fundamental observations for informing process-based models that describe and forecast catastrophic phenomenon. In this project, rock deformation and fluid injection experiments are being conducted to understand how micro-seismicity and rock microstructure evolve during conventional rock deformation and during fault reactivation under fluid injection.
We present here preliminary results from analysis of x-ray volumes tracking the micro-mechanisms involved in conventional rock deformation. These samples were triaxially compressed using an x-ray transparent rock deformation apparatus with integrated mechanical and acoustic monitoring (Fig.1a) [4] that allowed us to capture time-resolved x-ray microtomographic volumes of shear failure by adjusting the loading rate using feedback from detected acoustic emissions (AE) to maintain a constant AE event rate. We used the open-source software spam to calculate the 3D strain fields [5]. We show the evolution of local 3D strain fields in Berea sandstone samples deformed under a constant micro-cracking rate (Fig.1b and c). In the first case the maximum principal stress is varied, while in the latter case the minimum principal stress is varied.
The results in Figure 1b and c; provide the evolution of differential stress and AE event rate during deformation of the sample. Using AE event rate feedback prolonged the failure time, providing a comprehensive view of how damage and related micro-seismic events develop. These tests and preliminary results will further inform the acquisition and analysis of planned experimental campaigns involving x-ray and seismicity acquisitions, exploring several deformation and injection scenarios.