Abstract
A transient fully coupled model is proposed to investigate the two-phase flow of CO2 and water-based fluid in a wellbore, considering the complex mass and heat transfer in different flow patterns and dynamic coupling between the wellbore and reservoir. Based on mass conservation, momentum, and energy balance, the model employs a state-of-the-art equation of state and transport models to analyze the variations of multiphase flow behaviors and CO2 properties in a wellbore. Applied in the scenario of a drilled gas kick, the proposed model is used to simulate the processes of gas migration and two-phase flow in the wellbore. The results indicate that the CO2 solubility increases gradually with the increment of depth, the trend of which shows an abrupt change in 500-1000 m due to the phase transition of CO2. During kick development, the fronts of free gas and dissolved gas increase almost linearly with time. Through a comparison of CO2 and CH4 kicks, gas dissolution is found to significantly suppress the development process of CO2 kick. The error in kick prediction can reach 42% if the effect of gas dissolution is neglected. However, it can be neglected for CH4 kick.
Highlights
As an important greenhouse gas, carbon dioxide has aroused wide concern in the field of energy and environment
They developed the wellbore temperature and pressure models considering the phase transition of sour gases. These models can perform more accurate estimations of wellbore temperature and pressure fields [17,18,19]. Their simulation results indicated that the gas kicks can be “hidden” and “abrupt” successively, affected by the phase transition of the fluids in the dynamically changing temperature and pressure environment
We developed a transient fully coupled model for wellbore CO2/water flow, which considers the complicated mass and heat transfer mechanisms in different flow patterns and the dynamical coupling between wellbore and reservoir
Summary
As an important greenhouse gas, carbon dioxide has aroused wide concern in the field of energy and environment. Wang et al [14,15,16] proposed a series of calculation models of CO2 density, friction coefficient, Joule–Thomson coefficient, and so on, which can significantly improve the simulation accuracy of CO2 thermophysical parameters in the wellbore in the drilling scenario Based on that, they developed the wellbore temperature and pressure models considering the phase transition of sour gases. These models can perform more accurate estimations of wellbore temperature and pressure fields [17,18,19] Their simulation results indicated that the gas kicks can be “hidden” and “abrupt” successively, affected by the phase transition of the fluids in the dynamically changing temperature and pressure environment. The proposed model is applied to analyze the multiphase flow process during a drilled CO2 kick
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