The paper presented at the 17th OMC Med Energy Conference, explores risks associated with CO2 injection in legacy offshore wells for Carbon Capture and Underground Storage (CCUS). Using fluid dynamic modeling and Fault Tree Analysis (FTA), the study assesses the probability of well integrity loss due to CO2 plume migration and material degradation. The findings help determine the necessary intervention timeline to mitigate risks, offering insights into safer CCUS operations by guiding well maintenance and material selection.
Enhancing Well Integrity in Carbon Capture and Storage (CCUS) Operations
In the drive to achieve a net-zero carbon economy by 2050, Carbon Capture and Underground Storage (CCUS) operations have emerged as one of the most promising solutions. These efforts, particularly among major oil and gas operators, are essential for reducing atmospheric CO2 levels. However, the effectiveness of CCUS hinges on the integrity of storage sites, with legacy wells often presenting a significant risk to long-term containment. Understanding and managing the risks associated with these wells, particularly abandoned ones, is crucial to ensuring safe and successful CCUS operations.
The Challenge of Legacy Wells in CCUS Operations
Abandoned wells, particularly those located near CO2 injection sites, pose a unique challenge. These wells were not designed to withstand the corrosive effects of CO2, which can seep into surrounding materials over time. The migration of CO2 plumes into nearby abandoned wells can significantly increase the risk of well integrity loss. If these wells are not adequately sealed or monitored, they could serve as pathways for CO2 to escape, leading to environmental and safety hazards.
The question at the heart of managing these risks is: How much time do we have before the integrity of these wells deteriorates beyond an acceptable level? This is where advanced risk analysis models come into play.
A New Approach: Risk Analysis for Well Integrity
A recent study introduces a sophisticated methodology to assess the integrity of offshore abandoned wells in the context of CO2 injection. The approach integrates a fluid dynamic model with Fault Tree Analysis (FTA) to evaluate the evolving risks over time. This dynamic analysis helps to predict when the integrity of legacy wells is likely to fail, allowing for timely interventions before risks become unmanageable.
At the core of this model is the use of FTA, a structured, top-down method to identify and analyze potential failure modes. The FTA method breaks down complex systems into smaller components, assessing the probabilities of each individual failure event. This enables operators to identify weak points in the well’s barriers, such as safety valves, packers, or cement seals, and to calculate the likelihood of failure under various conditions.
Key Findings: Corrosion and Cement Integrity
The study revealed that the primary threat to well integrity in CCUS operations stems from the interaction between CO2 and the well materials. As the CO2 plume migrates, it alters the surrounding environment, turning it from non-aggressive to highly corrosive. Tubular materials and cement barriers, which were originally designed for different conditions, face increased corrosion rates when exposed to CO2 over extended periods. The model calculates the probability of failure for each component of the well, including the production packer, tubing, and cement seal, under various operational scenarios.
Additionally, the study incorporates sensitivity analysis, allowing for the evaluation of different materials and strategies to mitigate risk. One notable strategy is the use of “rock-to-rock” cement plugs, which have been shown to significantly reduce the probability of failure.
A Step Forward in CCUS Risk Management
This new risk assessment model represents a significant advancement in managing the integrity of legacy wells in CCUS operations. By utilizing probabilistic risk assessment and dynamic monitoring, it provides operators with a clear timeline for when intervention is required to prevent catastrophic failure. The model’s flexibility and sensitivity allow for tailored risk management strategies that account for a variety of operational conditions, including material degradation and the effects of CO2 exposure. Through proactive risk assessment, operators can reduce the likelihood of CO2 leakage, protect the integrity of storage sites, and contribute to the successful realization of the net-zero carbon strategy.