Induced seismicity refers to small earthquakes (typically between a magnitude of 1.0 and 3.5 on the Richter scale) that may occur as a result of human activity. The environmental consideration is that activities such as stimulating a geothermal reservoir or injecting fluid to replenish a geothermal reservoir may cause induced seismicity.1Aaron Levine, A., Cook, J., Beckers, K., and Young, K. (2017). Geothermal Induced Seismicity National Environmental Policy Act Review. National Renewable Energy Laboratory. https://www.nrel.gov/docs/fy18osti/70203.pdf
Learnings from the Oil & Gas Industry
Induced seismicity from fluid injection into the subsurface has become a topic of significant public concern and research since around 2010, after a significant uptick in seismicity in the southern midcontinent of the United States, especially Oklahoma. Research has shown that oilfield operations for enhancing oil and gas production from shales and other tight rocks are responsible for a significant portion of the
seismic activity. The activity primarily responsible for the induced seismicity if the injection of water that is co-produced with the oil and gas from the wells. This produced water must be disposed of by injection deep into the subsurface. If the injection rate was too rapid or injection was near pre-existing faults, some level of seismicity (often below the threshold of what humans can feel) resulted. Further research has found other cases, including hydraulic fracturing, where ‘felt’ earthquakes occur, but these are much more rare.2Beard, J.C., and Jones, B.A., eds. (2023, May 1). Chapter 10: Environmental Considerations and Impact. The Future of Geothermal in Texas. p. 268-9. https://energy.utexas.edu/research/geothermal-texas
Media attention, public meetings with hundreds of attendees, and findings from scientific research has led to responses by individual states, ranging from new regulations to deployments of state run seismic monitoring programs that can deliver near-real-time data on earthquake occurrences. For example, in Texas, the State seismicity-monitoring program (“TexNet”) is run by the Bureau of Economic Geology at The University of Texas at Austin, in which a catalog of seismic activity3https://www.beg.utexas.edu/texnet-cisr is publicly available and used by industry, regulators, researchers, and others. Several other states run seismic networks, as well as the
U.S. Geological Survey.4Beard, J.C., and Jones, B.A., eds. (2023, May 1). Chapter 10: Environmental Considerations and Impact. The Future of Geothermal in Texas. p. 268-9. https://energy.utexas.edu/research/geothermal-texas
Earthquakes can be induced when fluids are injected into the subsurface, including water for hydraulic fracturing or wastewater disposal (for example, produced water), or gasses (often CO2) for enhanced oil recovery. State agencies that regulate oil and gas exploration and production (for example, the Texas Railroad Commission) typically lead regulatory responses that can include well shut-ins, reduction of injection volumes or rates, modifications of depth of injections, requirements for enhanced reporting of injection practices (rates, volumes, downhole pressures), and/or requirements for enhanced monitoring of seismicity through deployment of seismometer stations proximal to the injection well.5Beard, J.C., and Jones, B.A., eds. (2023, May 1). Chapter 10: Environmental Considerations and Impact. The Future of Geothermal in Texas. p. 268-9. https://energy.utexas.edu/research/geothermal-texas
The most common cause of induced seismicity in the subsurface is:
Induced Seismicity and Geothermal Projects
Basel 1 Project
We have learned much about induced seismicity over the last several decades, not only with oil and gas operations, but with geothermal programs. Most infamous hydraulic stimulation event for creating an enhanced geothermal system (EGS) reservoir occurred in 2006 with the Basel 1 Project in Basel, Switzerland. Basel had known historical seismicity and the presence of nearby active geologic faults. Six days into a 21-day hydraulic stimulation project, increased seismic activity (max event of 3.4) resulted in 2,700 damage claims by local residents. Basel 1 prematurely halted injection and eventually terminated the entire project.6Aaron Levine, A., Cook, J., Beckers, K., and Young, K. (2017). Geothermal Induced Seismicity National Environmental Policy Act Review. National Renewable Energy Laboratory. https://www.nrel.gov/docs/fy18osti/70203.pdf
Induced Seismicity Concerns with Geothermal
Creating permeability in EGS reservoirs through hydraulic fracturing does lead to the onset of induced seismicity, although careful planning and knowledge of subsurface geology and attention to pressure control during injection can mitigate the magnitude of events to levels below what can be felt by humans. The general public has a heightened awareness of the potential for inducing earthquakes from energy development, particularly oil and gas, and has called upon regulators to adopt measures that will mitigate future events and reduce earthquake hazard and risk from injection.7Beard, J.C., and Jones, B.A., eds. (2023, May 1). Chapter 10: Environmental Considerations and Impact. The Future of Geothermal in Texas. p. 268-9. https://energy.utexas.edu/research/geothermal-texas
Although Conventional Hydrothermal Systems do re-inject used water, these systems have injector and producing wells, and are ideally operated in equilibrium between the two. This is in contrast to wastewater injection in oil and gas, the origin of much of the induced seismicity experienced by industry, which does not involve producing any fluids in conjunction with injection.8Beard, J.C., and Jones, B.A., eds. (2023, May 1). Chapter 10: Environmental Considerations and Impact. The Future of Geothermal in Texas. p. 268-9. https://energy.utexas.edu/research/geothermal-texas
Induced seismicity concerns are associated primarily with geothermal concepts such as conventional hydrothermal systems and EGS. Next generation geothermal concepts, particularly non-hydraulic fracture based systems and some hybrid geothermal systems, in which fluids are not injected into, or pumped from, subsurface reservoirs are being developed. These applications should carry low induced seismicity risk. This is particularly true as compared with oil and gas operations that require extensive hydraulic fracturing or significant disposal of oilfield wastewater through injection. This is an area that will require more study as next generation geothermal concepts, several in pilot phase currently, produce field data.9Beard, J.C., and Jones, B.A., eds. (2023, May 1). Chapter 10: Environmental Considerations and Impact. The Future of Geothermal in Texas. p. 268-9. https://energy.utexas.edu/research/geothermal-texas
How great are the concerns for induced seismicity with regards to conventional hydrothermal projects?
Image Credits
- Cumulative_induced_seismicity-Wiki: USGS