We evaluate the potential for CO2 leakage along pre-existing wells and through the formation caprock as well as the probability of inducing slip on faults during CO2 injection and storage in a saline formation in the Southern San Joaquin Basin. Our model considers 0.6 Mt CO2/y injection for 47 years and monitoring for an additional 100 years.
The prospective CO2 storage site was selected based on previous geospatial and economic analysis of emitters and storage sites in Kern County (Kim et al., 2022). Reservoir simulation was used to calculate the pressure and CO2 saturation. Then, risk assessment tools were used to estimate potential leakage rates through the overlying formations and along vertical wells. The stress state of the storage formation was determined based on regional stress information, earthquake moment tensor inversion, and well log data. Fault slip potential software was used to calculate the probability of inducing slip on faults considering a distribution of geomechanical parameters and fault orientations. We also study the historical seismicity of the area and identify seismological metrics that may help to distinguish natural from induced events.
There was no predicted leakage for CO2 and brine into the USDW with an assumption of wellbore permeability less than 10 mD (a value greater than that of a typical wellbore cement). The worst case for leakage assessment, with less than 1 % probability, assumed that the effective permeability of the existing wellbore is extremely high (30–50 mD). Nevertheless, the ratio of leaked CO2 mass to injected mass is less than 3.8 x10−6 (0.00038%). No impacts on a drinking water aquifer are predicted. The effective wellbore permeability is the most sensitive parameter to assess the leakage rate. The probabilistic fault model indicates that the pressure buildup should be limited to 500 psi (3.45 MPa) within 1 km of the injection site in order to minimize the risk of inducing slip on large faults.
This study provides a standard procedure to evaluate the potential for CO2 leakage and induced fault slip for any candidate CO2 storage site using publicly available data. This type of probabilistic risk assessment is critical in order to encompass the uncertainties in hydrological and geomechanical parameters and any variability in operating conditions.