Monitoring Seismicity near a CO2 Enhanced Oil Recovery and Sequestration Site in Kansas

The Kansas Geological Survey conducted a CO₂ Enhanced Oil Recovery Project at Wellington oil field in Sumner County Kansas, USA, in 2016. This project led to the installation of 18 seismic monitoring stations in and around the field in order to monitor seismicity before, during, and after a 22,000 ton injection of CO₂ in the Mississippian carbonate reservoir. While no earthquakes from the enhanced oil recovery project were detected, the monitoring array was used to track a marked increase in seismicity that began in 2015 in southern Kansas. The increase in seismicity has been tied to increases in waste water injections into the Arbuckle carbonate saline aquifer which sits directly above the granitic basement. From 2016 to 2018 over 3,000 local earthquakes ranging from magnitude 0.4 to 3.6 at depths of 1 to 12 km were located within Sumner County. Analysis of these earthquakes has identified previously unknown faults. Furthermore, earthquake locations show a northward progression from 2016 to 2018 that is likely caused by a change in regional pore pressure. The lessons learned in monitoring for seismicity near the EOR site will be applied to a new potential CO₂ sequestration site in western Kansas where a network of eight seismometers was installed in April of 2019. This site is expected to have very little background seismicity, although some local earthquakes have already been recorded.