Flow simulation of CO₂ storage in saline aquifers using a black oil simulator

Sequestration of carbon dioxide in geological formations has drawn increasing consideration as a potential method to reduce the level of CO₂ in the atmosphere, and therefore mitigate climate change. In particular, saline aquifers can potentially provide a large storage volume world-wide. It is essential to assess the risk involved in storing CO₂ in the subsurface, and simulations of CO₂ injection play an important role. Detailed simulations using a compositional simulator, which solves the equation of state for the fluids and calculates the partitioning of fluids between phases, is time consuming. It is therefore advantageous to use a simpler method for simulation, such as a modification of a black-oil simulator (designed for use in the oil industry), where fluid properties are input using look-up tables. In this study, we have tested the accuracy of flow simulations of CO₂ storage in saline aquifers using a black-oil simulator (BOS) compared with a compositional simulator (CS). A range of models was investigated: 2D, 3D and radial models, horizontal and tilted, and homogeneous and heterogeneous. On the whole the results compared well, although accuracy of the BOS depended on the type of grid used, being less accurate for radial models, where discretisation effects were evident. In agreement with other studies, we found that the black-oil simulations were, on average, a factor of four faster than compositional simulations.