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

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 CO 2 storage site, Design and install injection wells that are resistant to CO 2, Ensuring proper closure of the CO 2 storage site

Strategy Conduct a phased programme of simulation modeling to track and predict CO 2 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

Remediation Costs 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

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

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

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 CO 2

Conclusions Costs for comprehensive remediation package for seepage is small compared to overall cost of CCS project Only adds 0.5/t CO 2 to overall costs If costs for CCS range $35 to 50/t CO 2 this equates to 1 to 1.4% of total cost