Coulomb Static Stress Transfer: What about the Earthquakes?
Currently, I am exploring how the induced earthquakes themselves may influence stress changes and possibly further induce seismicity in the system.
To start, I used generic models of idealized situations to test the relative importance of physical mechanisms (e.g. pore pressure change and Coulomb static stress transfer). I found that the small earthquake do matter, and earthquake interactions of small earthquakes can cause stress changes of comparable size to pore pressure change from injection. The full results are explained in Geophysical Research Letters: Brown, M. R. M., & Ge, S. (2018). Small earthquakes matter in injection-induced seismicity. Geophysical Research Letters, 45, 5445–5453. https://doi.org/10.1029/2018GL077472
Continuing this line of research, I am modeling the earthquake interactions of the small earthquake in the Raton Basin, Colorado and New Mexico that occurred between 2001 when the seismicity rate increased significantly in the area and 2011 when a M5.3 earthquake occurred in Trinidad, Colorado. Preliminary results are consistent with previous studies comparing pore pressure increase and stress changes from earthquake interactions. Early work on this project was presented at the American Geophysical Union Fall Meeting in Washington, DC in December 2018.
Evaluating the effectiveness of induced seismicity mitigation: Numerical modeling of wastewater injection near Greeley, Colorado
Following a felt earthquake located in Greeley, Colorado in June 2014, mitigation actions in the form of short cementing the bottom of the wastewater injection well closest to the earthquake and short term rate reduction occurred. However, the seismicity continues in the area. Within 30 km of the seismicity, there were 22 active wastewater injection wells as of August 2016. I modeled the wastewater injection from all 22 wastewater injection wells since the first well began injection in 1999 to end of August 2016. Model results indicate that the majority of the pore pressure increase is caused by wastewater injection from wells within 15 km of the seismicity. However, 45% of the pore pressure increase can be attributed to the wells between 15 and 30 km from the seismicity. These model results indicate that larger spacing between wastewater disposal wells may be needed to mitigate the aggregate effects of multiple wells injecting near the same area. The full study is detailed in Journal of Geophysical Research Solid Earth: Brown, M.R.M., S. Ge, A.F. Sheehan, and J.S. Nakai (2017), Evaluating the Effectiveness of Induced Seismicity Mitigation: Numerical Modeling of Wastewater Injection near Greeley, Colorado, Journal of Geophysical Research Solid Earth,122, 6569-6582, doi: 10.1002/2017JB014456
Injection-induced seismicity in Carbon and Emery Counties, central Utah
Carbon and Emery Counties in central Utah is an area of coal mining and oil and natural gas production. My master’s degree work examined seismicity rate changes in this area approximately 1-5 years following the start of wastewater injection. Estimation of b-values found a temporal evolution that coincides with the wastewater injection and is consistent with these events being injection-induced. Analytical and numerical models show that injection in the area could sufficiently increase the pore pressure to trigger seismicity within the area of increased seismicity rate. The full study is available in an article published in Geofluids. A copy is available here in Brown_and_Liu_2016-Geofluids or at this link: Brown, M.R.M. and M. Liu (2016), Injection-induced seismicity in Carbon and Emery Counties, central Utah, Geofluids, 16, 801-812, doi: 10.1111/gfl.12184