Injection induced seismicity became an issue over the past decade, and while much of the rise in seismicity is attributed to wastewater disposal, a growing number of cases have identified hydraulic fracturing as the cause. A recent study identified regions in Oklahoma where ≥75% of seismicity from 2010-2016 correlated to several hundred hydraulic fracturing (HF) wells. To identify factors associated with increased likelihood of induced seismicity, we gathered publicly available data for all HF wells that had operations in these regions. This dataset provided a means to investigate relationships to the injected volume, number of wells on a pad, injected fluid (gel vs. slickwater), vertical depth of the well, proximity of the well to basement rock, and the formation into which the injection occurred. To determine the strength of the trends, we applied logistic regression for continuous factors and odds ratios for binary data. We see no trend with total injected volume with both basins having nearly constant likelihoods across all volumes. Results from Alberta showed a much stronger trend, but we note that region has many more multiwell pads. When we examined the fluid type, we found a lower likelihood with the use of gel (15.5%) compared to slickwater (21.9%). We found a strong relationship where older formations showed higher likelihoods of induced seismicity, and then demonstrated this was primarily due to well depth. Well depth produced the strongest relationship, increasing from ~10% to ~60% likelihood from 1.5 to 5.5 km. However, no trend was seen in the depth to basement parameter, which goes against work in other basins that found this to be a controlling factor for generating seismicity. Instead, our results are consistent with work from Alberta suggesting that formation overpressure could result in increased likelihood of seismicity generation during HF operations, as modeling conducted in the Anadarko Basin has shown indications of overpressure in the deeper portions of the basin.
AAPG Datapages/Search and Discovery Article #90373 © 2019 AAPG Eastern Section Meeting, Energy from the Heartland, Columbus, Ohio, October 12-16, 2019