3.1 Flow and transport mechanisms

The accuracy of flow models depends mainly on the quality of the input parameters and their capability in handling the following flow and transport processes that control the spread of CO2 in the storage medium (Metz et al., 2005):

  • fluid flow (migration) in response to pressure gradients created by the injection process,
  • fluid flow in response to natural hydraulic gradients,
  • buoyancy caused by the density differences between CO2 and formation fluids,
  • diffusion,
  • dispersion and fingering caused by formation heterogeneities and mobility contrast between CO2 and formation fluid,
  • dissolution into the formation fluid,
  • mineralisation,
  • pore space (relative permeability) trapping,
  • adsorption of CO2 onto organic material.

Some of the main flow processes of CO2 are illustrated by Iding and Ringrose, 2009 in Fig. 3-1.

E. Fig . 3-1

Fig. 3-1: Main flow and CO2 transport mechanisms (Iding and Ringrose, 2009).

When modelling reservoir behaviour, it is important to consider and adequately represent the different geological formations within the storage system and their characteristics.

 

in depth

3.1.1 Structural trapping

The injected carbon dioxide tends to rise towards the top of the formation due to buoyancy forces, where it will be trap...

3.1.2 Miscible vs. immiscible flow

Carbon dioxide injected into saline aquifers in a liquid or liquid-like supercritical dense phase does not mix with the ...

3.1.3 Viscous fingering

Supercritical CO2 is much less viscous than water and oil (by an order of magnitude or more) and this induces a COnsider...

3.1.4 Buoyancy

Injection of CO2 into saline formations creates strong buoyancy forces because of the large density difference between C...

3.1.5 Dissolution

Some of the CO2 will dissolve into the formation water as it migrates through the formation. Simulation results show tha...

3.1.6 Residual trapping

Physical trapping can also occur as residual CO2 is immobilised in the storage reservoir pore spaces as disconnected dro...

3.1.7 Adsorption and Desorption

Preferential sorption occurs when CO2 molecules attach to the surfaces of coal and certain organic-rich shales, displaci...