36. Could injecting CO2 underground cause an earthquake?

Just as with oil and gas extraction, the changes in pressure caused by CO2 injection can cause extremely small earth movements in a process called "induced seismicity." With careful control of injection pressures and extensive reservoir management techniques that are employed as standard by the oil industry, risks of damage from potential induced seismicity are reduced to insignificant levels. In fact, these very low levels of seismicity can actually be very useful, allowing monitoring by geophysicists to provide further data on the safe distribution of CO2 within the reservoir.

In the WMP, extensive monitoring of seismicity (which is more accurately termed induced micro-seismicity in this case) has shown that movement events are relatively infrequent and tiny in magnitude. Movements are not felt on the surface; in fact, some are so small they are barely measurable. Moreover, most of the monitored events have been associated with periods of water injection as opposed to CO2. In the Weyburn oilfield, most of the micro-seismic events have occurred around the location of the production wells, meaning that the increased flow of oil and water in the reservoir may be responsible for these small events, not the CO2. Depicted in Figure 25, the results obtained at the Weyburn field show that the recorded micro-seismic events are tens to thousands of times weaker than the weakest earthquakes that could be felt by humans at ground surface. Figure 26 provides context for the seismic activity at Weyburn.

Figure 25. This figure shows the approximately 100 micro-seismic events measured at the Weyburn oilfield during the period of 2003 to 2007. (Courtesy Dr. Don Gendzwill, University of Saskatchewan)

Figure 26. A comparison of the micro-seismic events recorded at Weyburn versus larger measurements. Nothing at Weyburn was above -1.0. (Courtesy Dr Don Gedzwill, University of Saskatchewan)