Grid comparison

Buoyancy forces cause CO₂ to rise upwards until reaching the caprock, and will fill any structural traps present as it continues to migrate under the sloping caprock. Thus, the simulated migration of the CO₂ plume will be strongly influenced by the grid's representation of the caprock. Variants exist between the grids used previously to study the Sleipner injection project. Figure 1 shows the two Sleipner grids we considered, namely:

1. GHGT: a grid set-up by Statoil R&D group and used in Nilsen et al., 2011 [2],and
2. IEAGHG: the Sleipner 2010 Reference dataset ^[a] used in Singh et al., 2010 [1] and part of IEAGHG's publically available benchmark model.

We keep the same naming convention used in [2], which refer to these grids as GHGT and IEAGHG, respectively.

GHGT grid
IEAGHG grid	Re-centered surfaces
Figure 1: Variants of the Sleipner grid are shown in the top left and bottom left. The difference between the re-centered surfaces of the grids are evident by the figure on the right.

Comparison of the simulated match obtained using different grids and properties

Figures 2 and 3 illustrate the impact which both the grid and the input properties have on obtaining a simulated match to the observed plume outline (shown in red). Sleipner's original benchmark properties given in [1] include a porosity of 0.3571, a horizontal permeability of 1850 mD, and a CO₂ density of 760 km/m³ at reservoir conditions. Our modified properties refer to 0.6, 3, and 2/3 times the original porosity, permeability, and CO₂ density, respectively.

In Figure 2, modified properties give a slightly better match to the observed plume outline. However, a better simulated match is obtained using the GHGT grid with the original properties as shown in Figure 3, and an excellent simulated match is obtained using with modified properties.

Original properties

Modified properties

Figure 2: Simulated CO2 plume migration under the caprock represented by the IEAGHG grid. CO2's point of entry into layer 9 is shown by the red dot. The observed plume outline is shown by the red line.

Original parameter inputs

Modified parameter inputs

Figure 3: Simulated CO2 plume migration under the caprock represented by the GHGT grid.

Footnotes

^a Statoil and the Sleipner Licence are acknowledged for the provision of the Sleipner 2010 Reference dataset. Any conclusions in this webpage concerning the Sleipner field are the author's own opinions and do not necessarily represent the views of Statoil.

References

1.  V. Singh, A. Cavanagh, H. Hansen, B. Nazarian, M. Iding, and P. Ringrose. Reservoir Modeling of CO₂ Plume Behavior Calibrated Against Monitoring Data From Sleipner, Norway. In SPE Annual Technical Conference and Exhibition, Florence, Italy, 2010.
2. H. M. Nilsen, P. A. Herrera, M. Ashraf, I. Ligaarden, M. Iding, C. Hermanrud, K. A. Lie, J. M. Nordbotten, H. K. Dahle, and E. Keilegavlen. Field-case simulation of CO₂-plume migration using vertical-equilibrium models. Energy Procedia. 4: 4801-3808, 2011.