Modeling Commercial-Scale CO2 Injection in Mt. Simon Sandstone Near Decatur, IL Storage Sites

Abstract

Advancing carbon capture and storage (CCS) to commercialization necessitates exploiting CO2 storage resources efficiently, which likely will involve multiple injection sites (or entire projects) accessing the same regional storage complex. This situation is presently occurring in central Illinois, where a series of three U.S. Department of Energy-sponsored storage projects are utilizing the Cambrian Mt. Simon Sandstone storage complex near Decatur, Illinois. From 2011 to 2014, the Illinois Basin – Decatur Project (IBDP) injected CO2 at a rate of 0.33 million tonnes per year (Mt/yr), and in 2017, the Illinois Industrial CCS Project (IL-ICCS) began injecting approximately 1 Mt/yr (planned rate) in a well 1.6 km apart. Recently, the CarbonSAFE Illinois – Macon County Project began investigating whether more than 50 Mt of CO2 can be injected into the Mt. Simon Sandstone over several decades (a target rate of 2 Mt/yr) located at a site about 5 km northwest of the other injection locations. As evaluated for this study, the Macon County well would be within the Forsyth Oil Field and drilled to access the same interval of the Mt. Simon storage complex as used by the other injection projects, namely the lower Mt Simon Sandstone. The intent of this paper is to assess the feasibility of the Forsyth site for commercial CO2 storage to further develop the storage resource by evaluating whether the target rate can be achieved, designing an injector to meet the target rate, and describing the potential contact of subsurface plumes resulting from these separate but proximal central Illinois projects. This entails modelling the behaviour of the injected CO2 and evaluating the well perforated intervals, plume sizes, pressure responses, and contact with existing CO2 plumes at the Decatur sites. To understand the interaction of three subsurface plumes, a static geologic model was generated to encompass the proposed Forsyth site (CarbonSAFE project) and the existing Decatur sites (IBDP and IL-ICCS projects), an area 22.5  22.5 km2 and a vertical section of 664 m. The static model was developed to represent the geological architecture and heterogeneity of the Mt. Simon storage complex at the Forsyth and Decatur sites through regional correlations based on geophysical data from wells at the Decatur sites. A dynamic model with integrated fluid and rock–fluid properties was constructed from the static model. The primary CO2 storage mechanisms modeled were structural and stratigraphic trapping, residual gas trapping, and solubility trapping. Mineral trapping resulting from geochemical reactions among CO2, rock, and formation water were considered negligible because the target formation is quartz sandstone.