A parallel compositional reservoir simulator for large-scale CO2 geological storage modeling and assessment.

Storing CO₂ in deep aquifers and depleted gas reservoirs is an effective way to achieve carbon neutrality. However, the numerical simulation of CO₂ storage in these formations is challenging due to the complexity of gases-brine systems. The number of gas species included in the gases-brine fluid models of existing simulators cannot meet the rapidly evolving CO₂ sequestration scenarios. To address this intricate issue, we developed a three-dimensional fully implicit parallel CO₂ geological storage simulator (PRSI-CGCS) on distributed-memory computers based on our in-house parallel platform. This simulator uses a compositional fluid model with a diverse range of gas species, including CO₂, C₁ ~ C₃, N₂, H₂S, as well as newly added gases H₂ and O₂, which may be encountered in geological CO₂ storages. Besides, we provide more suitable scaling factors for different gases in the stability analysis bypassing (SAB) method to accelerate the gases-brine phase equilibrium calculations. PRSI-CGCS does not incorporate energy conservation equations, and salt precipitation or dissolution is also not considered. Numerical experiments show that our simulator is scalable, robust and validated to simulate large-scale CO₂ storage problems with hundreds of millions of grid blocks on a parallel supercomputer cluster. Besides, after our modification on scaling factors, the SAB method can reduce the number of stability analyses by 61.39 % to 88.71 %, thereby reducing simulation time. Furthermore, case studies indicate that injecting O₂ and H₂ along with CO₂ reduces the stability or capacity of CO₂ storage and increases the pressure required for injection. However, this impact is not significant when the impurity content is less than 10 %.