Three-dimensional fluid-driven frictional ruptures: theory and applications to injection-induced seismicity

Alexis Saez, Brice Lecampion, & Jean-Philippe Avouac

Published September 8, 2024, SCEC Contribution #14032, 2024 SCEC Annual Meeting Poster #161

Fluid-driven frictional ruptures are important in a broad range of subsurface operations where borehole fluid injections can induce both aseismic and seismic frictional slip. Some examples of these operations are deep geothermal energy, CO2 and hydrogen geological storage, and wastewater disposal from oil and gas production. Here we present recent theoretical advances in the mechanics of injection-induced fault slip, including the nucleation, propagation, and arrest of both aseismic and seismic slips. We show how a dimensionless number containing information about the initial stress state of the fault and the intensity of the injection governs the dynamics of aseismic ruptures in all its stages. We also elucidate how the history of injection flow rate controls the spatiotemporal patterns of aseismic slip growth, with the evolution of injected fluid volume becoming a key determinant of the slip dynamics. We then examine the spatiotemporal migration of microseismicity which often accompanies fluid-injection operations. Analysis of seismicity catalogs from geothermal reservoir stimulations suggests that early-time seismicity is driven by pore pressure diffusion (following a square-root-of-time pattern), while later stages might be dominated by stress transfer from aseismic slip; following a pattern that is proportional to the square root of the injected fluid volume. The so-called back-front of seismicity which is often observed post-injection, is shown to also emerge under the presence of aseismic slip. Finally, because aseismic slip can trigger seismicity at distances far beyond those anticipated by pore pressure diffusion alone, we derive a scaling relation for the maximum extent of aseismic ruptures as it is a crucial quantity for better delineating the influence zone of injections concerning their seismic hazard. Moreover, based on mounting evidence that the moment release during these operations is often predominantly aseismic, we derive a scaling relation for the maximum magnitude of aseismic slip events. Our theoretical predictions are consistent with observations over a broad spectrum of event sizes, from laboratory to field cases, indicating that fault-zone storativity, background stress state, and injected fluid volume are key determinants of the maximum size and magnitude of injection-induced slow slip events.

Key Words
injection-induced fault slip, induced seismicity, fault mechanics, slow-slip events

Citation
Saez, A., Lecampion, B., & Avouac, J. (2024, 09). Three-dimensional fluid-driven frictional ruptures: theory and applications to injection-induced seismicity. Poster Presentation at 2024 SCEC Annual Meeting.

Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)