Assessing Monitorability of CO₂ saturation in subsurface aquifers

We investigate the geophysical monitorability of injected supercritical CO₂ stored in subsurface saline aquifers. We use available petrophysical models to predict the effect of supercritical CO₂ on formation density, P- and S-wave velocities and attenuation, and electrical resistivity. We use Shannon’s information measure to quantify the information expected to be obtained from different Geophysical monitoring methods. Our results show that expected information is generally nonlinearly related to the level of uncertainty in the geophysical parameters, to the CO₂ saturation, and in the case of seismic measurements to the measurement frequency. We show that seismic attenuation contributes greatly to the overall information obtained, and that adding together information from different geophysical parameters and methods can significantly improve monitorability and accuracy of CO₂ saturation estimates.