Factors influencing seismicity in south-central Kansas and northern Oklahoma

Abstract

Waste water injection and seismicity in south-central Kansas and northern Oklahoma increased dramatically from 2010 to 2016. Areas with increased well counts, elevated disposal pressures, and elevated injection volumes correlate with locations of seismic activity. The locations, history of injection, and seismic activity in three areas of interest (AOI) were examined with the aid of aeromagnetic maps to determine if seismic activity was induced by well activity in close proximity. A major northeast-southwest trend is observed in disposal well locations, earthquakes, and NewMag residual aeromagnetic maps. Moment tensors (focal mechanisms) from 180 earthquakes were obtained and detected strike-slip, normal, and reverse faulting. Eight of the strongest earthquakes (4.5-5.8 magnitude) were located along the margins of seismically active areas in Kansas and Oklahoma. A vast majority of earthquake foci are within Precambrian basement rock. The largest increases in both, seismic activity and injected volumes occurred in Harper County, Kansas as well as Grant and Alfalfa County, Oklahoma. Disposal well count increased after 2011, and by 2013 a majority of the new wells in Alfalfa, Grant, and Harper Counties disposed between 1 million barrels (MMBBL) to approximately 17MMBB per well/per year. Some of these wells also used injection pressures in excess of 300 pounds per square inch (PSI) per well/per year. By applying proper disposal practices, obtaining in-situ reservoir properties of the injection interval, and avoiding areas susceptible to seismic events, a reduction in seismic activity could occur.