Sensitivity analysis of the petrophysical properties variations on the seismic response of a CO2 storage site

The injection of CO2 into a saline aquifer induces changes in pore pressure and fluid saturation, which in turn induce varia- tions in the petrophysical properties of the storage site. Thus, numerical modeling of CO2 sequestration combining multi- phase fluid flow and wave propagation simulators requires de- termining the time steps at which the flow parameters (porosity and absolute permeability) need to be updated during the sim- ulation of CO2 injection. For this purpose, this work presents a sensitivity analysis of the seismic response of the Utsira for- mation (where CO2 is being injected) due to variations in its petrophysical properties. A multiphase fluid flow simulator is used to determine the spatio-temporal distribution of CO2 and brine during injection. The porosity and absolute permeability are assumed to be dependent of saturation and pore pressure. InthewavepropagationsimulatortheLame ́parametersin- clude effects of mesoscopic losses due to the presence of CO2 in the pore space. The numerical experiments allow to define the time step at which the flow parameters need to be updated to obtain accurate seismic images of the spatial distribution of CO2 after injection, with a more precise definition of the zone where the pushdown effect is observed.