Remediation of Seepage from Geological Storage (GHG/07/43)

1. Remediation of Seepage from Geological Storage (GHG/07/43) • Aim of study was to: • Identify remediation approaches and techniques that are available such seepage occur from geological storage sites • Assess likely costs of remediation • Study undertaken by Advanced Resources Inc. USA • Report 2007/11, August 2007

2. Strategy • Five component plan proposed • Detailed site selection to determine most favourable sites to prevent seepage at outset • Core to strategy • Place emphasis on ensuring long term well integrity • Identify all old abandoned wells in the vicinity of the proposed CO2 storage site, • Design and install injection wells that are resistant to CO2, • Ensuring proper closure of the CO2 storage site

3. Strategy • Conduct a phased programme of simulation modeling to track and predict CO2 plume • Multiple simulations required with calibration from monitoring activities • Install and maintain a comprehensive monitoring programme • Designed to be an early warning system • Provide data for calibration of models • Response plan required to contain seepage from most likely seepage scenarios

4. Remediation Costs • Seepage prevention costs • Main cost issues are: • Rigorous site selection • Monitoring • Well integrity testing • Cost for site selection estimated to vary between $5m and $20m per site • Biggest single cost item drilling of coring/observation well • Costs vary based on data availability

5. Remediation Costs • Costs for monitoring and seepage detection Seepage • Dependent on formation • EOR/Storage • monitoring costs estimated to range from $48m to $78m • Deep saline aquifer with high residual gas saturation and low plume travel • monitoring costs estimated to range from $43m to $73m • Deep saline aquifer with low residual gas saturation • monitoring costs estimated to range from $49m to $80m • Well bore integrity monitoring costs • Dependent on depth well condition etc., • Costs estimated from $12m to $18m for 10 wells and 10 logging runs per 50 years

6. Remediation Costs • Seepage remediation costs • Costs dependent of seepage event • Examples of costs for source location: • Cost for locating a single well could be $100k per survey • Costs of running a diagnostic survey was estimated at £300k per well • 3D seismic survey to identify source of leakage estimated at $100,00 per km2 • Costs for well plugging typically $50k per well • Costs for well remediation range from $30 to 100k per well • Costs for remediation through cap rock could be $2m

7. Example Storage Case • Example storage case used to illustrate costs of remediation • Case example: 1000MWe, 50 years operation, 10 injection wells, plume extends 80 km2 • Total costs for comprehensive remediation programme was $120m per site • Equates to $0.45 to 0.5/t CO2

8. Conclusions • Costs for comprehensive remediation package for seepage is small compared to overall cost of CCS project • Only adds 0.5/t CO2 to overall costs • If costs for CCS range $35 to 50/t CO2 this equates to 1 to 1.4% of total cost