Several trapping mechanisms can be considered at play at the Utsira Formation:
The structural trapping mechanism can be exploited by injecting into locations where CO2 is expected to naturally migrate to one or several identified traps. Since this migration will be largely driven by gravity, a spill-point analysis can be used to identify such locations, as well as estimate the coresponding amounts of CO2 that will be structurally trapped.
Although structural trapping is the easiest to aim for, it is also important to benefit as much as possible from the other trapping mechanisms.
The structural trapping capacity provided by the part of the pillar that is located within a structural trap (if any)
The residual trapping capacity of the pillar, which is a property of the rock. If the rock is homogeneous, it will simply be a multiplier of the pore volume of the part of the pillar not contained within a structural trap.
The dissolution trapping capacity can be considered equal to a certain fraction of the pore water remaining in the column after the structural and residual trapping capacities have been realized.
1.13 gigatonnes of structural trapping
77 gigatonnes of residual trapping
34 gigatonnes of dissolution trapping
Structural traps of the Utsira Formation, colored by amount of pore volume (click on image for a larger version).
Structural traps of the Utsira Formation, colored by trapping capacity in mass terms (click on image for a larger version).
Map of structural traps and spil paths at the Utsira Formation caprock (click on the image for a larger version).
Diagram of aquifer cross section (click on image for a larger version).
Color plot showing the structural capacity reachable by gravity-driven migration when injecting at a specific point (click on the image for a larger version).
Diagram showing total trapping capacity of each vertical pillar of the Utsira Formation grid model. Click on image for a larger version.
Published September 15, 2014