Operational Practices and Their Influence on Injection-Induced Earthquakes: Lessons Learned From a Statewide Survey of Brine Disposal in Kansas
Injection-induced seismicity has received international attention, with the State of Oklahoma becoming the poster child for the phenomenon. Since 2013, that seismicity has extended into Kansas. Between January of 2013 and August of 2016, two counties in south-central Kansas experienced more than 2000 earthquakes, with 100+ of the events recorded as M3.0 or greater. The largest of these earthquakes was a M4.8 event on 12 November 2014, centered approximately 50 km SSW of Wichita. By comparison, only 15 magnitude M3.0+ events were recorded in the state during the prior 35 years of observation, establishing a long-term recurrence rate of 1 event every 2.4 years. The spatial and temporal association between the recent spate of earthquakes and major brine disposal operations has raised concerns about safety and efficacy of underground fluid injection. Here we examine statewide brine disposal and oil and gas production data over the past 6 years (2010-2015) to determine the extent to which changes in operational practices may be influencing seismicity. Our analysis reveals that the majority (~75% by volume) of brine disposal in Kansas occurs in the Cambro-Ordovician Arbuckle Group, which consists of thick, laterally extensive, shelf carbonates that unconformably overlie Proterozoic basement or Cambrian strata. Although brine disposal into the Arbuckle has occurred for decades in the state (and across much of the midcontinent) without triggering seismicity, recent changes in disposal practices may be a contributing factor. In Harper County, where much of the recent seismicity is concentrated, Arbuckle brine disposal volumes nearly quadrupled from 2012 to 2015 (~30 MMbbl to ~110 MMbbl), while the number of disposal wells only increased 38%. Most of this fluid comes from horizontal production wells in the Mississippian and is aggregated and shuttled through pipelines across the county to the disposal wells. In contrast, Ellis County, which had no seismicity during the study period, disposed of a similarly large volume of brine (84 MMbbl in 2015). The 84 MMbbl were disposed of through more than double the number of Arbuckle disposal wells in Harper County. Our results suggest that a potential mitigation strategy is to dispose of smaller volumes across a larger geographical area. Other mitigation strategies involve treatment and reuse of co-produced brines for enhance oil recovery, industrial applications, and agriculture.
AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017