State of the art review of CO2 Storage Site Selection and Characterisation Methods

 
1. INTRODUCTION
 
2. GEOLOGICAL CHARACTERISATION OF THE SITE
 
3. FLOW MODELLING
 
4 REACTIVE FLOW MODELLING
 
5. COUPLED GEOMECHANICAL AND FLOW MODELLING
 
6. ENVIRONMENTAL IMPACT AND RISK ASSESSMENT
 
7. ECONOMIC ANALYSIS
 
8. PUBLIC PERCEPTION AND ACCEPTANCE
 
9. CONCLUSIONS AND RECOMMENDATIONS
 
 
4.1 Reactive flow and transport modelling for CO2 storage
 
4.2 Objectives of geochemical modelling in CO2 geological storage
 
4.3 Geochemical modelling codes for CO2 storage applications
 
» 4.4 Reactive transport modelling applications
 
4.5 Reactive transport modelling in the Sleipner storage project
 
4.6 Conclusions
 
 

4.4 Reactive transport modelling applications

Xiao et al., 2009 summarised the advances in reactive transport modelling of CO2 storage and reviewed the key technical issues on; (1) the short- and long-term behaviour of CO2 injected in geological formations; (2) the role of reservoir mineral heterogeneity on injection performance and storage security; (3) the effect of gas mixtures (e.g. H2S and SO2) on CO2 storage; and (4) the physical and chemical processes acting in case of CO2 leakage from the primary storage reservoir.

Using the TOUGHREACT reactive transport modelling code, Xiao et al., 2009 investigated mixed CO2/H2S/SO2 injection and storage in both siliciclastic and carbonate reservoirs for a 1D radial reactive transport model design simulating CO2 injection 2 km depth and 70oC temperature in a siliciclastic and carbonate reservoir. CO2 and other gases were injected into the reservoir at a rate of 1 million tonnes per year over a 100 years period. The reactive transport models simulate the system from 0 to 10,000 years. Three scenarios of mixed gas injections were selected: (a) CO2 only, (b) CO2 + H2S, and (c) CO2 + SO2, in which CO2 is injected as gas phase while both H2S and SO2 (~5% each) are injected as aqueous solutes. The Reservoirs are specified to have an initial porosity of 30% and an initial permeability of 100 mD. The siliciclastic and carbonate reservoirs were defined by hypothetical mineral assemblages, representing an oligoclase feldspar-rich sandstone reservoir and a limestone-rich reservoir (Xiao et al., 2009).

Simulations provided estimates of pH evolution, mineral dissolution/precipitation and CO2 storage for sandstone reservoir Injections and pH evolution and mineral dissolution/precipitation for carbonate reservoir injection. The evolution of porosity was modelled for both Reservoirs (Fig. 4-2 and 4-3). In the siliciclastic reservoir, whatever the injected gas is (CO2 only, CO2 + H2S, and CO2 + SO2), injection induces an increase of porosity (that is much more important in case of CO2 + SO2) close to the well due to net mineral dissolution, and a decrease away from the well due to mineral trapping in all three cases (Xiao et al., 2009). In the carbonate reservoir, a significant increase of the porosity (30% to 40% after 100 years) is observed when CO2 or CO2 + H2S is injected due to calcite dissolution near the well bore. These results indicate that there is little mineral trapping in all three mixed gas injection scenarios, suggesting limited CO2 storage capacity in a limestone dominated carbonate reservoir. Xiao et al., 2009 concludes that reactive transport modelling provides valuable insights for describing, analysing, interpreting, and assessing the physical properties and dynamic behaviours of injected CO2 as well as for facilitating the screening and evaluation of CO2 storage strategy.

E. Fig . 4-2

Fig. 4-2: Porosity evolution as a function of radial distance simulated at 10, 100, 1,000, and 10,000 years for the mixed gas injection Scenarios in a siliciclastic reservoir (Xiao et al., 2009).

E. Fig . 4-3

Fig. 4-3: Porosity evolution as a function of radial distance simulated at 10, 100, 1,000, and 10,000 years for three mixed gas injection Scenarios in a carbonate reservoir (Xiao et al., 2009)