CO2 Plume Behaviour in a Cyclic, Fining Upward Clastic Sequence – Do the Claystone Intervals Seal?
F. Schaefer and G.E. Pickup
Event name: 2nd EAGE International Conference on Fault and Top Seals - From Pore to Basin Scale 2009
Session: CCS and Nuclear Waste Disposal
Publication date: 21 September 2009
Info: Abstract, PDF ( 275Kb )
We numerically modeled CO2 plume behaviour in fining upward clastic sequences, using the Middle Buntsandstein of the North German Basin as an example. The aim was to examine how vertical and lateral reservoir heterogeneities influence CO2 plume development. CO2 injection was simulated through eight wells around a closed anticlinal structure, each injecting 500,000 m3 of CO2 per year over a period of 30 years. Sensitivity studies were carried out on several parameters. Lateral facies variations with high permeability contrast seem to inhibit CO2 flow. Where siltstones with a permeability of 1 mD hardly present an obstacle in graded sequences, it forces the CO2 plume sideways, effectively forming a barrier in rocks with a bimodal permeability distribution. In laterally homogeneous, but vertically fining upward sequences, the CO2 preferrably moves laterally and updip along the high permeability layers during the injection phase, forming a two-storey plume. However, after injection stops, most of the gas soon overcomes the finer grained, low permeability intervals and migrates vertically into the uppermost part of the reservoir and from there into the structural top. The structural top then fills from top to bottom, and not from bottom to top as one might expect.