Impact Assessment of Injection Impurities in the SPE11 Geological Carbon Sequestration Benchmark

Summary Accurate reservoir simulation of carbon dioxide (CO2) sequestration is critical for predicting the distribution of CO2 during and after injection. Therefore, the 11th SPE Comparative Solution Project (SPE11 CSP) serves as a benchmark for modeling geological carbon storage in an aquifer. In this paper, we present a convergence analysis of the SPE11 benchmark simulation using the Delft Advanced Research Terra Simulator (open-DARTS). In addition, we analyze the effect of trace amounts of impurities in the injection stream. Open-DARTS is an open-source simulation framework designed for both forward and inverse modeling, employing a unified thermal-compositional formulation and operator-based linearization (OBL). In our convergence analysis, the SPE11b (2D-reservoir conditions) starts to converge at a grid resolution of 1,340×240, after which added resolution provides diminishing returns. In addition, the 3D SPE11c benchmark is simulated with 8 million gridblocks. However, 2D results from SPE11b suggest that a greater resolution is required for a truly converged solution. Furthermore, we extend the SPE11b benchmark to include hydrogen sulfide (H2S) and/or methane (CH4) as trace impurities in the injection stream. These impurities, which are often present depending on the source of the captured CO2, are found to influence gas density and CO2 plume migration. Building upon validated thermodynamic predictions from the hybrid equation of state (hybrid-EOS) model, we simulate the SPE11b benchmark, with a total injection mass fixed at 3,024 kg/d. Impurities are introduced at varying molar fractions to assess their influence on CO2 solubility, plume migration, and trapping efficiency. While H2S can inhibit plume migration by increasing the gas density under certain conditions, CH4 increases plume buoyancy and enhances lateral spreading of the CO2 plume. Additionally, it is found that CH4 reduces solubility trapping and reduces storage efficiency of CO2, whereas H2S has a negligible impact on solubility trapping.