INDUCED SEISMICITY ASSOCIATED WITH WASTE FLUID INJECTION WELLS

Waste disposal wells have always been an integral part of the fracking process across the country. The EPA estimates that 2 billion gallons of waste fluid are introduced to deep, porous rock layers each day from about 180,000 wells in multiple states. The highest density of wells is seen in states with the richest oil plays, such as Oklahoma, Kansas, and Texas. Some states that operate injection wells have seen a large uptick in earthquakes within a close distance to these injection wells. In 2016 alone, Oklahoma has seen over 270 earthquakes above a magnitude 3.3, with some of those events being over magnitude 5.0. About 2000 of the many injection wells that exist in Oklahoma are within 15 kilometers of an earthquake that has occurred since the year 2000. In comparison, South Dakota, which also practices waste fluid injection, has seen 7 earthquakes above magnitude 3.3 since 2000, and none of those are close enough to injection wells to establish a firm relationship with the fluid injection. This difference in numbers of possible induced earthquakes appears to be attributable to the rate of fluid injection. States with larger average rates of injection, such as Oklahoma, with an average rate of 7626 bbls/day, have heightened rates of seismicity compared to states with lower fluid injection rates, such as South Dakota, with an average rate of injection of 775 bbls/day. Factors like injection pressure and injection depth do not vary as much between states, and areas with higher pressures and deeper injection sites do not correlate strongly to higher earthquake rates. Along with the manmade component of injection practices, the presence of deep faults could also be a factor in controlling the rate of induced earthquakes. In Oklahoma, wells are placed at a safe distance from the active Meers fault, but this is not always the case in other states. Smaller, but still active faults in states such as Wyoming and Colorado appear closer to wells that have been associated with earthquakes. The distance from these faults, as well as the rate of injection, could be directly causing a higher amount of seismic activity in areas of the US.