Temperature analysis for early detection and rate estimation of CO2 wellbore leakage

Wellbore leakage of carbon dioxide (CO2) injected into storage zones can induce significant temperature anomalies. These thermal signals arise from expansion of the leaking CO2 associated with the pressure drop across the leak, known as the Joule-Thomson effect, which has the potential to reveal the nature of leakage and determine the wellbore leakage rate of CO2. We investigate the strength of the temperature signal as a function of leakage rate and develop a control volume analysis to relate these two in the complex two-phase leakage conditions. This analytical thermal model for CO2 leakage enables quick analysis with sufficient accuracy to estimate the leakage rate. The application range of this approach is identified from the results of comprehensive investigations. The nature of the thermal signal is sensitive to the balance between the Joule-Thomson effect and heat conduction. The ratio of these two effects and newly defined JT/cond Number provide general criteria for the applicability of modeling these thermal signals in the range of 40-90% and 1.6-4, respectively. Furthermore, in the case of higher leakage rate, we extend the analytical model to predict the leakage transmissibility with improved accuracy compared to the direct rate estimation from leakage thermal model in this scenario. The general procedure and flow chart to apply the proposed approach to a practical problem are provided, which is suitable for both injection and post-injection periods for a CO2 storage project. This analytical model breaks a new ground to apply recent temperature wellbore monitoring developments for CO2 leakage detection and characterization purposes. Field applications of this model can complement other leakage rate estimation techniques and be an essential part of the CO2 leakage detection tool if other approaches are not viable.