Challenge:
Two depleted gas fields in Australia were identified as potential CO₂ storage sites, promising a significant capacity for carbon sequestration. However, effective and safe storage required a comprehensive evaluation of well integrity for legacy wells that were P&A’d as per the historical prevailing industry standards and regulatory requirements. Integrity issues could lead to unintended CO₂ migration, risking environmental damage, public trust, and regulatory compliance. Given that the fields had decades-old wells, ensuring that all barriers would effectively contain CO₂ was crucial for both site feasibility and operational longevity.
Solution:
A structured, multi-phase well integrity assessment was employed, emphasizing both data forensics and analysis:
- Preinjection Assessment: Detailed reviews and analysis of legacy well data, including well schematics, end-of-well reports, and cement logs, were conducted to establish current integrity baselines.
- Plume modelling: Various deterministic scenarios were simulated to model the CO2 plume and assess the likelihood of the advancing flood front reaching the wells.
- Barrier Analysis: Using a Failure Mode, Effects, and Criticality Analysis (FMECA) approach, well barriers were categorized, assessed for failure probability, and evaluated for potential CO₂ leak paths. This enabled the classification of wells based on their barrier strength, integrity risks, and repurposing feasibility.
- Re-entry planning: Wells requiring corrective actions were identified and high-level P&A plans were drawn to implement rock-to-rock barrier restoration.
Value Added:
This robust well integrity assessment framework ensured a data-backed, precise evaluation of containment integrity, aligning with NORSOK-D010, OEUK, company barrier guidelines and Australian regulatory requirements. Key benefits included:
- Enhanced Risk Management: The assessment provided clear, actionable insights into the risk levels and remediation needs for each well, ensuring that only wells with acceptable containment risks were considered for CO₂ storage.
- Operational Cost-Efficiency: By identifying wells requiring corrective actions early in the project, costly plug and abandonment operations were minimized, optimizing resources and reducing unnecessary field expenses.
- Stakeholder Confidence: The transparent and structured approach to integrity and leakage risk assessment instilled confidence among regulators, investors, and the public, affirming that all storage sites meet stringent safety and environmental standards.
