FLUID INDUCED EARTHQUAKES: INSIGHTS FROM HYDROGEOLOGY AND PORO-MECHANICS

Frequent seismicity has been occurring in the past decade in tectonically quiescent regions such as the central eastern United States. Studies have identified spatiotemporal associations between the seismicity and deep wastewater injection wells related to oil and gas production, but many injection sites experienced no seismicity. Although pore pressure change from deep-well injection is known to be the primary culprit for inducing earthquakes since the 60s, questions remain with regard to hydrogeological and poro-mechanical processes in causing seismicity, as well as what injection operational parameters make some sites more prone than others to induced seismicity. This presentation offers an overview and insight on fluid injection induced seismicity from hydrogeological and poro-mechanics perspectives. Case studies illustrate how pore pressures play a role in inducing observed seismicity. Modeling of pore pressure diffusion suggests that high-rate injections create an intense hydrogeological perturbation to the injection formation, which emerges as an important factor in contributing to induced seismicity. As pore pressure front propagates from the injection site, it could trigger seismicity as it encounters rock weaknesses, fractures or faults. Assuming the Earth’s crust is critically stressed, relatively small pore pressure perturbation could trigger seismicity. The spatial extent of pore pressure influence could reach tens of kilometres from high-rate injection wells in a few years. Continuing research to probe interactions among pore pressure propagation, ambient background stress, and spatial distribution of fractures and faults in heterogeneous geologic formations will further advance our understanding on hydrogeological, mechanical, and seismologic processes, which will ultimately help provide guidance for best practices and mitigate induced seismic hazard in the quest for energy resources.