Potential Impacts of CO2Storage on Groundwater

ResourcesNeil Wildgust

GCCSI Groundwater WorkshopCanberra, May 2011

Groundwater Impacts Study

• Study commissioned by IEAGHG and carried out by CO2GeoNet

• Led by BRGM

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

Resource Overlap - Europe

Combining GEOCAPACITY data on DSF both (pink) with WHYMAP thematic layers representing large, uniform freshwater aquifers (blue).

Combining GEOCAPACITY data on DSF(pink) with WHYMAP thematic layers representing areas with complex hydrogeological structure (green)

Resource Overlap - N America

Combining data on DSF from the Carbon Sequestration Atlas (pink) with WHYMAP thematic layer representing large, uniform freshwater aquifers (blue)

Combining data on DSF from the Carbon Sequestration Atlas (pink) with WHYMAP thematic layer representing areas with complex hydrogeological structures (green)

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

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

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?

Modelling Case Studies

• Pressurisation over much larger area than associated CO2plume

• 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.

Effect of Seal Permeability

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

Shale Porosity-Permeability Transform(Young and Aplin 2009)

Empirical Relationships affecting Regional Shale Permeability

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

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

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)