Modeling of seismic amplitude anomalies associated with CO2 underground storage

Abstract

Higher amounts of CO2 in the atmosphere has contributed to finding techniques to mitigate the emissions of CO2. One of those techniques is Carbon Capture and Storage (CCS). CO2 can be stored in subsurface reservoirs over time. Monitoring and modeling of reservoirs is important to avoid leakage and to predict how the CO2 could migrate. Modeling is also useful when the seismic interpreter has problems, then seismic from modeling with known parameters can be useful. The first place in the world to inject CO2 was in the Sleipner field in the Norwegian North Sea. The injection found place in 1996 in the Sleipner East field into the Utsira formation. The reservoir is estimated to have a vertical thickness about 200 m at the injection point, and the estimated caprock for the CO2 is about 100 m thick. This thesis shows modeling of the seismic response from different synthetic models associated with CO2 underground storage. The parameters is based on data from the Sleipner field to get a realistic view of the result. Incident angle, input frequency, CO2 saturation and geometry of the models are all important parameters affecting the seismic result. Modeling with various incident angles and input frequencies has been done. It showed that higher frequencies gives the best resolution as expected, and that smaller incident angle makes it easier to distinguish interfaces. A frequency of 70 Hz and an incident angle of 20°, made it possible to detect both interfaces of a layer with vertical thickness of 1 m. Several models with varying vertical and horizontal thicknesses of the plume have been made. The results shows that an incident angle of 20° with 60 Hz and realistic migration options turned on (aperture range and traveltime range) will not create any vertical reflections. Horizontal plumes with an incident angle of 20° using 30 Hz and 60 Hz, is visible with no interference for vertical thickness equal and greater than 40 m and 20 m, respectively. Tuning thickness occurred with a vertical thickness of 20 m and 10 m for respectively 30 Hz and 60 Hz. A stronger reflection in the area the plume is located is visible for vertical thicknesses equal to and greater than 3 m when using both 30 Hz and 60 Hz.