Multiphase transient analysis for monitoring of CO₂ flooding

The potential of well test technology is discussed in this paper to estimate the miscible condition and displacement fronts position during CO₂ flooding. To interpret the multiphase well test curve of CO₂ flooding process, an accurate compositional numerical model is developed in this study. The model includes fully EoS-based compositional nonlinear formulation, unstructured gridding and multi-segmented well. A systematic well test analysis of CO₂ flooding at different regimes, including immiscible, multi-contact miscible and first-contact miscible gas injection, was performed for hydrocarbon systems with different number of components. Based on the interpretation root cause analysis, proposed in this work, the specific characteristics of the well test curve of CO₂ flooding have been identified and described. These characteristics provide the guidance for the distinction among the different regime of CO₂ displacement. It was demonstrated that the most important characteristics stay invariant from the number of components involved into numerical study. Finally, a tangent line method has been proposed to detect the key point on the pressure derivative curve corresponding to a CO₂ front. This method allows to predict the displacement front position for problems of practical interest.