This document summarizes potential impacts of CO2 storage on groundwater resources. It discusses a study that modeled different scenarios, finding that pressure increases could extend beyond CO2 plumes but brine displacement would likely be over small distances and slow rates. While faults pose the highest risk, typical storage is unlikely to affect shallow groundwater. The document also reviews caprock properties important for storage integrity and outlines forthcoming IEAGHG studies on related topics.

1. Potential Impacts of CO2
Storage on Groundwater
Resources
Neil Wildgust
GCCSI Groundwater Workshop
Canberra, May 2011

3. Groundwater Impacts
Study
• Study commissioned by IEAGHG and
carried out by CO2GeoNet
• Led by BRGM

4. Recent IEAGHG Studies on Caprocks
• Pressurisation and Brine Displacement, Permedia,
Canada
• Literature review and modelling to assess pressure and
brine displacement effects in DSF storage
• Implications for capacity and injectivity
• Caprock Systems for Geological Storage of CO2,
CO2CRC, Australia
• Literature review to assess current state of knowledge
• Identification of knowledge gaps and R&D priorities

5. Resource Overlap - Europe
Combining GEOCAPACITY data on DSF Combining GEOCAPACITY data on DSF(pink)
both (pink) with WHYMAP thematic layers with WHYMAP thematic layers representing
representing large, uniform freshwater areas with complex hydrogeological
aquifers (blue). structure (green)

6. Resource Overlap - N America
Combining data on DSF from the Carbon Combining data on DSF from the Carbon
Sequestration Atlas (pink) with WHYMAP Sequestration Atlas (pink) with WHYMAP
thematic layer representing large, uniform thematic layer representing areas with
freshwater aquifers (blue) complex hydrogeological structures (green)

7. Typologies/Mapping Scenarios
• Areas with potential DSF storage overlain by:
• Large, uniform freshwater aquifers
• Complex hydrogeological structures where productive
potable aquifers (including karst ) may occur in close
vicinity to non-aquifers
• Localised/ very shallow aquifers
• Formations containing saline groundwater
• Over-exploited groundwater resources
• Areas with no DSF suitable for CO2 storage

8. Potential Groundwater
Impacts
• CO2GeoNet report considers:
• Chemical processes
• Natural and industrial analogues
• Review of literature/existing modelling
• Modelling undertaken
• Idealised scenarios
• Highlights difficulties in coupling processes

9. Closed versus Open Systems
• Open systems: regional
lateral brine flux,
transient pressurisation
• Closed systems: brine
flux within storage
compartment, rapid loss
of injectivity
• Semi-closed systems:
more realistic?

10. Modelling Case Studies
• Pressurisation over much larger area than associated CO2
plume
• Brine displacement over relatively small distances
• Brine displacement through the caprock at permeabilities
> 10-18 m2, though pore velocity extremely slow
• Fast flow conduits, e.g. faults have highest potential to
negatively affect shallow groundwater
• Coupled modelling of reactive transport for multiphase
flow still under active research and development.

11. Effect of Seal Permeability
Pressure build-up at 30 years of injection for different seal
permeabilities – adapted from Birkholzer et al, 2009

12. Shale Porosity-Permeability Transform
(Young and Aplin 2009)

13. Empirical Relationships affecting
Regional Shale Permeability

14. Caprocks Study
• Overall seal potential is a function of capacity,
geometry and integrity of a caprock
• Capacity refers to maximum CO2 column height
that can be retained
• Geometry refers to the thickness and lateral
extent of the caprock
• Integrity refers to geomechanical properties
• CO2CRC present a qualitative assessment
methodology for basin-level screening

15. Concluding Remarks
• More work needed on potential groundwater resource
impacts from CO2 storage
• Pressure footprint of storage will extend beyond plume
• Brine displacement may alleviate reservoir pressurisation
• Brine fluxes through caprock may be at low rates
• Faults, fractures and heterogeneity will be important in
controlling pressure evolution and brine displacement
• For many typical storage scenarios, brine displacement
unlikely to affect shallow groundwater resources
• Mitigation options include CO2/brine abstraction

16. Forthcoming IEAGHG
Storage Studies
• Brine abstraction (EERC, US DOE co-
funding)
• Implications for CCS of Shale Gas
Extraction
• Resource Interactions for CO2 Storage
• Induced Seismicity
• Phase 2 of Storage Costs (outside Europe)