CO2 Tracer Technology for Detecting Gas Lift and Casing Leaks

Overview CO2 tracers are specialized diagnostic tools used to detect and analyze gas lift performance and identify casing leaks in oil and gas wells. In gas lift operations, CO2 tracers provide critical insights into gas flow paths, injection efficiency, and possible leakage points. In cases of suspected casing leaks, CO2 tracers allow operators to pinpoint the leak locations, assess leak severity, and take corrective actions. This article covers the philosophy behind CO2 tracer use, calculation methods, benefits, limitations, lessons learned, and best practices. CO2 Tracer Injection Philosophy and Mechanism Gas Lift Diagnostics with CO2 Tracers CO2 tracers are injected into the gas lift system to monitor gas flow paths and verify that injected gas reaches the intended zones. By analyzing tracer concentration at various production depths, operators can identify gas distribution inefficiencies or leaks along the tubing and casing. In gas lift wells with multiple injection valves, tracers can differentiate between gas entering at intended injection points and unintended leak points, ensuring effective gas management. Casing Leak Detection CO2 tracers are commonly used to identify casing leaks that can compromise well integrity and production efficiency. By injecting a small concentration of CO2 into the annulus or casing, tracer migration is monitored to detect any unintended gas flow outside the production string. Leaks are typically identified when CO2 is detected at levels inconsistent with normal flow paths, allowing for precise localization. Equations and Calculations for CO2 Tracer Analysis Tracer Transport Model for Leak Detection The transport of CO2 tracers through the wellbore can be modeled by advection-diffusion equations, which consider both gas flow velocity and molecular diffusion in the well fluid.

 This minimizes operational downtime and reduces costs associated with well workovers. Enhanced Diagnostic Accuracy Tracers can detect even small leaks and subtle flow path deviations in gas lift systems, providing accurate information on gas distribution and pinpointing leak locations with high precision. Improved Well Integrity and Safety Early detection of casing leaks improves well integrity and reduces the risk of environmental contamination or safety hazards associated with gas leaks. Optimized Gas Lift Efficiency In gas lift operations, tracers ensure that gas injection reaches intended depths without losses due to leaks. This optimization of gas utilization reduces costs and maximizes production efficiency. Constraints and Challenges Tracer Dispersal in High-Pressure Environments In high-pressure wells, CO2 tracer dispersion can be limited, complicating detection and requiring precise control over injection rates to maintain tracer detectability. Reservoir Interference In formations with high porosity or complex geology, tracer migration may be impacted by reservoir heterogeneities, leading to inaccurate readings and requiring advanced modeling to adjust for these variations. Potential CO2 Loss CO2 may dissolve into well fluids, leading to reduced detectability. In wells with high water cuts, CO2 dissolution in water may cause signal loss, affecting leak detection sensitivity. Environmental and Safety Concerns Handling and injecting CO2 requires safety protocols, as it is an asphyxiant at high concentrations. Special safety measures must be taken to mitigate risks associated with CO2 injection. Lessons Learned from Field Applications Tracer Injection and Sampling Timing is Critical In CO2 tracer tests, timing of both injection and sample collection is crucial. Poor timing can lead to diluted or missed tracer signals, impacting diagnostic accuracy. Importance of Reservoir and Flow Modeling Field experience highlights the importance of using reservoir and wellbore flow models to account for variations in gas flow paths and accurately interpret tracer data. Simulation aids in identifying leak locations and designing effective tracer injection strategies. Real-Time Monitoring Enhances Diagnostics Real-time monitoring systems, such as downhole sensors, improve the accuracy of CO2 tracer readings and enable quick adjustments to injection rates or well interventions as needed. Calibrating Tracer Injection Rates Field tests have shown that careful calibration of tracer injection rates enhances signal clarity and detection range, particularly in wells with long tubing lengths or complex flow paths. Best Practices for CO2 Tracer Implementation Reservoir Characterization and Baseline Studies Conduct thorough reservoir characterization to understand flow paths, reservoir pressure, and porosity before tracer injection. Baseline studies provide reference data for comparing tracer distribution and identifying deviations due to leaks. Optimizing Tracer Injection Rate and Duration Use calibrated injection rates to ensure effective tracer dispersal without overdilution. Maintain tracer injection for a duration sufficient to cover the entire suspected leak zone. Establish Monitoring Points at Key Intervals Position sampling or monitoring points at intervals throughout the production string, including the wellhead, to capture tracer movement and identify possible leaks at different depths. Use of Advanced Analytical Models Employ advanced advection-diffusion models to interpret tracer data accurately, especially in wells with complex flow regimes or where rapid gas breakthroughs are expected. Analytical modeling improves accuracy in detecting leaks or inefficiencies in gas lift systems. Regular Maintenance and Calibration of Monitoring Equipment Ensure that downhole sensors and surface monitoring equipment are regularly calibrated and maintained to prevent erroneous readings, particularly in high-pressure gas environments. Conclusion CO2 tracer technology is an effective and precise method for detecting casing leaks and diagnosing gas lift performance in oil and gas wells. The use of CO2 tracers allows operators to identify leaks early, optimize gas injection efficiency, and enhance well integrity. However, the effectiveness of this technology relies on careful planning, accurate calibration, and adherence to best practices. With advances in real-time monitoring and tracer modeling, CO2 tracer technology is set to become an invaluable tool for maintaining efficient and safe well operations.