Categorizing Legacy Wellbores in the Delaware Basin Based on Failure Risks Under Wastewater Injection

Abstract Driven by horizontal drilling and hydraulic fracturing, the Delaware Basin has become the world’s largest oil-producing region. This growth has led to increased fluid injection for production enhancement and wastewater disposal. Prolonged injection and zonal pressurization are linked to rising seismicity and potential leakage from legacy wells. This study quantifies these risks using a multi-criteria decision-making framework to categorize every reported legacy well per county. We first identified legacy wells that had been abandoned, orphaned, or left inactive for over multiple years as per state database. A multi-criteria decision analysis (MCDA) model was developed to categorize each well based on zonally characterized geospatial, temporal, structural, and engineering factors using supervised machine learning algorithm. The model also incorporated injected volumes per zone and pressurization, inferred from surface uplift coincident with wastewater injection in shallow strata. Risk assessment and trade-offs were guided by reservoir engineering principles and regulatory agency data. Each legacy wellbore was assigned a risk score between 0 and 1, indicating its likelihood of failure and need for attention. Results were visualized alongside Interferometric Synthetic Aperture Radar (InSAR) data for a more comprehensive analysis. Older wells with single-barrier abandonment showed the highest risk, likely due to plug failure. Few highly scored wells were near known leaking wells, suggesting subsurface conditions weakened the plug’s mechanical bond strength (MBS). Significant surface uplift was observed near these wells. However, we can infer that prolonged wastewater injections appear to degrade matrix-cement MBS, more than other similarly aged plugs, suggesting zonal pressurization leading to formation breakdown and reduced plug integrity. This study develops a scalable metric to address the leaking wells problem in West Texas. As production expands, the demand for safer wastewater disposal grows, along with the need to mitigate risks of saltwater blowouts and/or toxic fluid leakage from legacy wells. Identifying and categorizing high-risk wellbores is essential for targeted remediation efforts and serves as a foundation for future studies for innovative solutions.