Time-lapse pressure-saturation discrimination for CO2 storage at the Snøhvit field

The pressure effect dominates the time-lapse seismic data, except in the near well area where a fluid effect is also estimated. The pressure increase is strong in the near well area (up to 15 MPa) and decreases rapidly with distance from the well. However, a continuous pressure buildup (4-5 MPa) is estimated terminating against the faults approximately 1-2 km away from the well. A CO2 saturation of 0.15-0.5 is estimated in the near well area, depending on the fluid distribution in the pores (uniform to patchy). There is a good correlation between predicted and conventional time-shifts. The empirical rock physics parameters indicate a CO2 saturation between 0.2 and 0.5, a patchy fluid distribution in the pore space is most likely. A pressure sensitivity corresponding to a Hertz-Mindlin exponent of 1/4 to 1/6 is estimated. This is clearly to high, and show that the uncertainties in the inverted rock physics parameters are high.