Investigating the Link Between Brine Disposal Practices and Induced Seismicity in Kansas and Oklahoma
The Cambrian-Ordovician Arbuckle Group is the primary disposal zone for Underground Injection Control (UIC) Class I and II wells across much of the U.S. midcontinent. Increases in wastewater disposal into the Arbuckle Group, linked with production from water-rich unconventional plays, is the inferred cause of a more than 40-fold increase in seismicity. Mitigating earthquakes is a challenge for oil and gas operators and the regulatory community, as a comprehensive understanding of operational factors (e.g., well spacing, injection rates, pore pressure diffusion in the Arbuckle and crystalline basement, etc.) and their relationship with seismicity is lacking. Here we investigate the influence of such operational factors in observed seismicity through time-series analysis of earthquake and injection datasets. Our study compares seismic events of magnitude 2.5+ with injection data from 3481 brine disposal wells (Class 2) and 49 industrial waste wells (Class 1), from 2010 to 2017. The analysis compares the volume injected into the Arbuckle with well density using a nodal analysis approach in R statistical software. A node lattice constructed across the data is used to measure the injected volumes and well densities within a given radius from each node. The spatial scale of the analysis is varied through adjustment of the node lattice and the radius of observation out from each node. Initial observations suggest that increasing disposal volumes without a concomitant increase in well count leads to seismicity. Thus, injection rates relative to well spatial density appears to be a predictor of induced seismicity. The analysis also reveals a linear threshold between well counts and disposal volumes, above which seismicity is likely to occur. The findings and methodology provide a simple, yet elegant relationship between well density and volumes that can be useful for siting and operation of wells in areas that may be prone to injection-induced earthquakes.
AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018