Compositional modelling of impure gas injection into saline aquifers with the MUFITS simulator

We present a recent extension of the MUFITS reservoir simulator for numerical modelling of multicomponent gas injection into saline aquifers. The extension is based on the compositional module of the simulator that implements a conventional cubic equation of state (EoS) for predicting phase equilibria of reservoir fluids [1]. Now, the module is supplemented with a new library of EoS coefficients for accurate modelling of CO₂, N₂, CH₄, H₂, O₂, H₂S, and other hydrocarbon components solubility in NaCl brine. In general, we follow the approach proposed by Søreide and Whitson [2] for modelling aqueous solutions, which involves a different and dependent on brine salinity binary interaction coefficients for aqueous and non-aqueous phases. However, we also use several published modifications to the EoS coefficients that were originally proposed in [2] to improve prediction of the mutual solubilities.

The extension is validated against 3-D benchmark studies of pure supercritical CO₂ injection into saline aquifers. Also, we consider two more complicated injection scenarios to demonstrate potential applications of the new development. First, we simulate impure CO₂ injection into a saline aquifer. We show that even a small amount of air (N₂ and O₂) in the injected gas results in a significantly more rapid spreading of the gas plume. Second, we consider a 3-D study of CO₂ injection into subsurface natural gas storage aiming at the cushion gas substitution with supercritical CO₂. The mechanical dispersion in the porous medium is accounted for an accurate modelling of CO₂ and CH₄ mixing. We simulate the propagation of CO₂ in the storage by modelling several seasons of natural gas (CH₄) injection and extraction.

The authors acknowledge funding from the Russian Science Foundation under grant # 19-71-10051.

References

1. Afanasyev A.A., Vedeneeva E.A. (2020) Investigation of the efficiency of gas and water Injection in an oil reservoir. Fluid Dyn. 55(5), 621-630.

2. Søreide I., Whitson C.H. (1992) Peng-Robinson predictions for hydrocarbons, CO₂, N₂, and H₂S with pure water and NaCl brine. Fluid Phase Equil. 77, 217-240.