Numerical and experimental investigation of impact of CO2 hydrates on rock permeability

Abstract

The reduction of temperature caused by Joule-Thomson effect during injection of CO₂ in low pressure reservoirs combined with presence of water can lead to formation of hydrates, which in turn reduces rock permeability and hence CO₂ injectivity. This paper introduces an empirical model to evaluate impact of hydrate formation on injectivity of CO₂ injection wells. Experiments were also conducted to validate the model. The model was then used to simulate injection of CO₂ into a multi-layered depleted gas field. The results indicate that operational parameters, particularly CO₂ injection rate and temperature, have a large influence on hydrate formation. This is because a higher CO₂ injection rate leads to a greater pressure drop within the injection well, potentially triggering conditions conducive to hydrate formation. It is also shown that the dynamics of the competition between the dry-out and temperature fronts play an important role in the final saturation of the hydrate within porous media. For large evaporation rates, the evaporation of water reduces water saturation near wellbore and hence formation of hydrates is limited.