Comparative Study of CO2 Mass Quantification Using Process Modelling and Geophysical Techniques

This paper presents the application and verification of a combined seismic and geoelectrical monitoring approach for CO2 storage using a virtual test side in the North German Basin. It is found, that the sensitivity of both methods to CO2 phase saturation is complementary, with the seismic reflection coefficient being most sensitive at low CO2 saturations and the resistivity being most sensitive at high saturations promising a comprehensive monitoring of the sequestration process. An integrated workflow is developed for the method assessment. Thereby, results of a numerical flow simulation (phase saturation, density, pore pressure, porosity and permeability) are used to simulate synthetic seismic and resistivity data for a realistic geophysical survey. From the synthetic data, changes of P- and S-wave velocities are calculated using 2D elastic time-lapse full waveform inversion and resistivity changes are calculated using borehole resistivity tomography. With that, the original CO2 phase distribution can be determined. The resulting CO2 mass estimation is then compared to the results of the CO2 mass distribution of the numerical flow simulation.