De-risking carbon storage: the Oklahoma perspective

In order to mitigate the warming effects of ongoing climate change, underground long-term carbon storage is increasingly being proposed as part of a multi-pronged effort to reduce the amount of CO2 present in the atmosphere. As the US emits several gigatons per year of CO2, in the absence of substantial emissions reductions, carbon storage programs would need to scale up at a rate that would be unprecedented considering that most existing carbon storage sites have only thusfar stored on the order of megatons of CO2. Oklahoma, in the last decade, serves as the only direct analog and stark example of utilizing a reservoir as a storage or disposal target across 100s of kms and 100s of injection points. Prior to 2010, Oklahoma experienced approximately 2 M3.0 or greater earthquakes per year. That background rate of earthquakes rapidly increased so that 579 and 903 M3.0 or greater earthquakes occurred in 2014 and 2015, respectively. A broad consensus in the scientific community of the causal link between deep wastewater disposal near the Precambrian basement led to regulatory actions, combined with a market decline, that drastically reduced the seismicity. The seismicity rate is down to 38 earthquakes M3.0 or greater in calendar year 2021. The past decade demonstrates that the disposal of large volumes of fluids, such as super-critical CO2, will produce seismicity even if disposal occurs at pressures that never exceed the formation fracture gradient. An isolated and rare, though damaging, seismic event adjacent to a carbon storage site risks irreversibly damaging public perception about the risks associated with carbon storage, jeopardizing future scaling. We will show case studies that demonstrate that earthquakes can be successfully mitigated during ongoing sequences and discuss recent research efforts to better understand the limits of safe injection practices. As several midcontinent states strategize about storing carbon deep underground to realize net-zero emissions goals, seismicity risk management should be a central component in planning regional carbon storage programs.