Application of Binary Permeability Fields for the Study of CO 2 Leakage from Geological Carbon Storage in Saline Aquifers of the Michigan Basin

The feasibility of geological carbon storage (GCS) sites depends on their capacity to retain safely CO2. While deep saline formations and depleted gas/oil reservoirs are good candidates to sequester CO2, gas/oil reservoirs typically have a limited storage capacity compared to ideal targets (∼ 1 Mt/year) considered for CO2 disposal (Celia et al. in Water Resour Res 51(9):6846–6892, 2015. doi:10.1002/2015WR017609). In this respect, deep saline aquifers are considered more appropriate formations for GCS, but present the disadvantage of having limited characterization data. In particular, information about the continuity of the overlying sealing formations (caprock) is often sparse if it exists at all. In this work, a study of CO2 leakage is conducted for a candidate GCS site located in the Michigan Basin, whose sealing properties of the caprock are practically unknown. Quantification of uncertainty on CO2 leakage from the storage formation is achieved through a Monte Carlo simulation approach, relying on the use of a computationally efficient semi-analytical leakage model based upon the solution derived by Nordbotten et al. (Environ Sci Technol 43(3):743–749, 2009), which assumes leakage occurs across “passive” wells intersecting caprock layers. A categorical indicator Kriging simulator is developed and implemented to represent the caprock sealing properties and model the permeability uncertainty. Binary fields of caprock permeability are generated and exhibit mostly low permeability, with sparsely-occurring local high permeability areas where brine and CO2 may leak out of the storage formation. In addition, the feasibility of extending the use of the semi-analytical model to large-area leakage pathways is studied. This work advances a methodology for preliminary uncertainty quantification of CO2 leakage at sites of GCS with little or no information on the sealing properties of the caprock. The implemented analysis shows that, for the considered site, CO2 leakage may not be negligible even for relatively low (∼ 1%) probabilities of finding permeable inclusions in the caprock and highlights the importance of being able to characterize caprock sealing properties over large areas.