Passive seismic monitoring is the science of recording and analysing natural or induced seismic energy. The creaking and groaning caused by ongoing tectonic movements in the earth, or the fracturing of rocks in large (felt) and micro (unfelt) earthquakes, are just some of the signals we detect and measure. Ocean waves, wind gusts and even vehicle traffic are also sources of ambient seismic noise which we measure in continuous recordings and be can used for 3D imaging of the subsurface.
Measurement, Monitoring, and Verification (MMV), which includes passive seismic monitoring as a key component, is an important aspect of any CO2 Geo-sequestration project. UWA Geophysics is active in the MMV research of the following Australian CO2 geosequestration projects: The South West Hub Project, the CO2CRC Otway Project and the CarbonNet Project.
Passive seismic in these projects can be useful to image and monitor the injected CO2 plume, the injection pressure front and any potential CO2 migration. Furthermore, by measuring and analysing very weak (unfelt) seismicity over time, it is possible to determine whether any detected seismicity in the project area is natural, or likely to be associated with the CO2 injection. Microseismicity can reveal valuable information about in-situ stress conditions in the subsurface to constrain predictions of fault seals and fluid flow barriers. 3D imaging using ambient seismic noise fields can potentially be performed in a time-lapse way to monitor subsurface fluid movements at minimal cost and disturbance compared to repeated active 3D seismic surveys.
Seismic waves are detected with arrays of very sensitive sensors either planted near the earth’s surface, submersed on the ocean floor or buried deep underground. Part of our research is aimed at designing, optimizing and deploying sensors arrays for permanent monitoring, given site-specific noise conditions and geologic structure.
New and advanced sensors/source technologies are also trialled in these permanent monitoring arrays. In particular, we are conducting studies with Distributed Acoustic Sensing for this application, which offers substantial improvements in coverage, frequency response and size in downhole deployments.
- CGG, Paris, France
- Lawrence Berkeley National Laboratory, Berkeley, USA
- TNO, Utrecht, Netherlands
- Université Laval, Quebec City, Canada