Station #2 – Multiphysics
Electrical resistivity tomography (ERT)
The observation well #2 is instrumented with 16 electrodes between 250 m to 325 m depth. ERT is a well-established geophysical method for near-surface imaging due to its high sensitivity to the presence and composition of the pore fluids. The high resistivity contrast between injected CO2 and in-situ brine makes the use of electrical methods particularly useful for CCS applications. Daily surveys are run since September 2019, which show an increase in resistivity due to the higher resistivity of the injected CO2 compared to the brine.
Figure 6: Schematic cross-section of the FRS injection well and the FRS observation well #2.
Passive seismic monitoring
Passive seismic recording typically involves using seismic receivers such as seismometers, geophones, or accelerometers to measure ground motion created by natural earthquakes and ambient noise sources. The technique can also be applied to detecting micro-earthquakes associated with rock fracturing or fluid movement in the subsurface. Passive seismic monitoring for induced seismicity detection and characterization is widely used in CCS projects. Subsurface injection of CO2 can cause pressure increases in the reservoir, the overburden, and the underburden which might trigger micro-earthquakes. Passive seismic monitoring can help ensure that any induced seismicity, if present, is low magnitude and not indicative of containment losses. Carbon Management Canada is using different technologies at the FRS, including surface geophones, borehole geophones, surface and borehole fibre optics, and broadband seismometers, to test, compare, and optimize induced seismicity detection and characterization.
Distributed fibre optic sensing
Fibre optics is a fast-growing technology for CCS monitoring. It can be used for temperature, acoustic, or strain measurements. Distributed Temperature Sensing (DTS) is typically used for well integrity monitoring, wellbore modelling studies, and containment verification. Distributed Acoustic Sensing (DAS) uses the fibre as an alternative seismic receiver, typically in wells for time-lapse Vertical Seismic Profiling and passive seismic monitoring. Distributed Strain Sensing (DSS) is developing as well to monitor geomechanical changes for containment and conformance verification. Observation well #2 is equipped with fibre optics for temperature monitoring and data have been recorded since 2018. It is also equipped with fibre optics for acoustic and strain measurement, for active and passive seismic monitoring and passive strain surveying.
Time-lapse vertical seismic profile (VSP)
The 24-3C geophones cemented outside casing in observation well #2 are also used for time-lapse VSP. Frequent walkaway surveys (~every 6 months) are done at the FRS; the effect of the CO2 on the reservoir elastic parameters is detectable after 32 tones of injection. Time-lapse VSP shows the spatial evolution of the plume with time and helps to constrain deployment of other monitoring technologies as well as updated reservoir simulations.