Comment on “Accelerated Fill-Up of the Arbuckle Group Aquifer and Links to U.S. Midcontinent Seismicity” by Ansari et al. (2019)

Abstract

Spatiotemporal analysis of Arbuckle Group formation pressures and disposal volumes provides insight into contributing factors underlying the regional trends in formation pressure identified by Ansari et al. (2019, https://doi.org/10.1029/2018JB016926) using statistical analysis. Based on trends in bivariate correlation of reported values, Ansari et al. (2019) suggested that rising formation pressures were a result of fluid injection within 25 km. Our primary concern is that the correlation trends are most likely an artifact of the method used by Ansari et al. (2019), at least in part, and the conclusion that pressure diffusion is limited to within 25 km of the injection point does not necessarily follow from the analysis. We also note that estimated formation pressure depends on the depth of the pressure gauge, which, in some cases, varies from one measurement to the next and should be accounted for to accurately assess measured changes. The spatial relationship of formation pressure changes among wells provides valuable insight into the origin of those changes. For each well, we project pressure to a baseline depth to account for changes in gauge depth and reexamine trends in formation pressure. Spatiotemporal progression suggests post-2011 formation pressure changes originate from a spatially dense group of high-rate saltwater disposal wells near the Kansas-Oklahoma border well beyond 25 km (and as far as 90 km) away.