Multiphase transient analysis of horizontal wells during CO2-EOR

We apply a numerical well test model that considers the transient flow in well and the complex displacement mechanisms for the multiphase transient analysis of horizontal wells during CO2-EOR. Aimed to perform a systematic and reliable analysis, we run the model on a high-resolution non-uniform grid to accurately capture the transient flow in the near wellbore region as well as the complex displacement process. In this work, we interpret the pressure response curve in two steps to find the root causes of the particular transient behaviors. First, we identify five typical flow regimes through the traditional pressure transient analysis method for horizontal wells which gives us a basic understanding of the characteristics of the pressure response curve. Second, assisted with the corresponding analysis method, we figure out the durations on the curve that correspond to different component banks. By taking the complex displacement mechanisms into consideration, we find that the component banks have a large influence on the curve and identify the root cause of each unique characteristic. Besides, we conduct a systematic sensitivity analysis with respect to multiple parameters such as miscible condition, wellbore storage coefficient, skin factor, horizontal well length, anisotropy, and amount of injected CO2. Finally, we have a better understanding of the transient pressure behavior of horizontal wells during CO2-EOR, find a way to determine the miscibility underground, and feel more confident in applying the pressure transient data for analysis and parameter estimation. •The EoS based compositional model and wellbore storage model are coupled in a fully-implicit parallel reservoir simulator.•A new interpretation method is proposed for the pressure transient analysis of horizontal wells during CO2-EOR.•The effects of flow patterns and complex displacement mechanisms on transient behavior are analyzed in detail.•The results point out a cheap and reliable way to monitor the CO2 displacement process in horizontal well patterns.