A streamlined qualitative risk assessment framework for corrective action in legacy wells: A case study from the lake Pontchartrain basin

Abstract

Legacy wells, originally drilled for oil and gas extraction, pose significant environmental risks owing to outdated construction standards and inadequate plugging or sealing. With the increasing adoption of Carbon Capture and Storage (CCS), concerns over CO₂ leakage through these wells have intensified, thereby necessitating a systematic approach to risk assessment and remediation. This study introduces a streamlined qualitative risk assessment framework designed to evaluate legacy well integrity by analyzing well construction attributes, potential leakage pathways, and associated uncertainties. The framework incorporates probabilistic modeling to quantify risk and generates a risk matrix to guide decision-making for corrective actions. To address remediation prioritization, a phased corrective action strategy is proposed, considering the proximity of legacy wells to an injection site and the projected CO₂ plume migration over time. The framework was applied to 28 legacy wells in the Lake Pontchartrain Basin, Louisiana, identifying 23 legacy wells with a significant potential for leakage, requiring remediation considerations. A phased remediation strategy was illustrated using a hypothetical injection well location and plume area modeling to optimize resource allocation. This approach provides a structured decision-making tool for regulators, operators, and policymakers, ensuring effective well integrity management in CCS projects. The streamlined framework is intended to facilitate corrective action assessment while also contributing to the ongoing development of accessible, fit-for-purpose risk assessment tools.