Assessment of CO2 leakage through existing wells and faults for a prospective storage site in the Southern San Joaquin Basin, California

A protocol is demonstrated for assessment of CO₂ leakage through existing wellbores and faults at CO₂ storage sites including pre-existing, plugged-and-abandoned wellbores and Quaternary faults. Total injection at the prospective saline aquifer site in the southern San Joaquin Basin, CA is planned as 12.3 Mt CO₂ with variable annual rates over 18 years followed by 100 years of monitoring. Reservoir simulation optimized CO₂ injection by minimizing the pressure build-up and the overall size of the CO₂ plume. The plume pressure and saturation history are input to one of the reduced order models in NRAP-OPEN-IAM to obtain distributions of potential leakage rates. During leakage assessment, the permeability of the plugged wellbores is assumed to be large (1 mD to 10 mD) to obtain worst-case estimates. Faults are considered to stretch from the surface to the storage zone. Leakage rates to the USDW are found to be negligible and within background expectations. The ratio of cumulative CO₂ mass leaked to injected using the optimized well scenarios is estimated to range from 0.0003% to 0.001% after 118 years. Additionally, leakage rates along Quaternary faults are predicted to be at least an order of magnitude less compared to leakage from the existing wellbores. The various injection well trajectory scenarios show different leakage rates due to the relative location of wellbores within the CO₂ and pressure plumes. In all cases, the amount of CO₂ that leaks relative to what is injected is much less than 1%.