EARTHQUAKES IN KANSAS: A STUDY OF BRINE DISPOSAL AND INJECTION-INDUCED SEISMICITY

Since 2013, the state of Kansas has seen a dramatic increase in earthquakes. Roughly 113 magnitude 3.0+ earthquakes were measured in the state between January of 2013 and July 5th 2016, a recurrence of 11.3 days. During the preceding three decades (1977-2012), Kansas experienced 15 such earthquakes, a recurrence of 2.4 years. Although this increase in seismicity is largely restricted to two counties (Harper and Sumner) in south-central Kansas, a statewide survey of 5 years (2010-2014) of brine disposal and oil and gas production data was conducted to holistically examine operational practices prior to and with the onset of earthquakes. The majority (~75% by volume) of brine disposal in Kansas occurs in the Arbuckle Group, a thick Cambro-Ordovician carbonate unit that rests unconformably atop the basement rock in many parts of the state. Our research indicates that concentrated high-volume disposal is a likely culprit for injection-induced seismicity. Brine disposal in the Arbuckle has occurred for decades in the state of Kansas without adverse seismic effects. Recent changes in disposal practices in one county in particular have contributed to the increase in seismicity. In Harper County, Arbuckle brine disposal volumes nearly quadrupled from 2012 to 2014 (27.8 MMbbl to 106 MMbbl), while the number of disposal wells only increased from 41 to 68. Most of this fluid comes from horizontal production wells in the Mississippian and is injected in proximal high-volume disposal wells, or shuttled via pipelines across the county to the disposal wells. In contrast, Ellis County Arbuckle brine disposal volumes were 84 MMbbl in 2014, but the county did not experience earthquakes between 2010-2014. The 84 MMbbl were disposed of via 210 wells, roughly three times the number of Arbuckle disposal wells in Harper County for the same year. One possible strategy for injection-induced seismicity mitigation in deep formations with no bottom seal is to dispose of smaller volumes across a larger geographical area. Other long-term mitigation strategies involve treating and reusing the water for petroleum and agricultural industries.