Developing Practical Guidelines
Underground gas storage (UGS) facilities face increasing regulatory and operational scrutiny.
Well operators need robust tools to assess and manage safety and environmental risks—especially during periodic well entry.
In collaboration with PHMSA, this project developed practical guidelines for conducting Quantitative Risk Assessments (QRAs) for UGS wells.
Project Overview: Risk Assessment and Treatment of Wells
PHMSA Project 740, 2020 – Collaborators: PHMSA, C-FER
The guidelines support UGS well operators in developing, selecting and applying risk-based models that inform decisions around well entry activities.
While the focus is on quantitative methods, the concepts are also applicable to qualitative assessments.
What matters most in risk assessment?
Brian Wagg breaks down considerations for underground gas storage.
What the Guidelines Cover
Failure Frequency & Consequence Models:
Tools for estimating how often failures might occur and their potential impacts.
Risk Measures:
Metrics to quantify and evaluate public safety and environmental risks from UGS operations and periodic well entry.
Integrated Processes:
A process to combine failure frequency and consequence into a meaningful risk profile for well operation and entry.
Evaluation Approaches:
Guidance on evaluating safety and environmental risk estimates and applying acceptance criteria
Demonstration Analyses: Key Insights
The project applied the guidelines to representative UGS well configurations in both depleted hydrocarbon reservoirs and salt caverns, revealing:
- Risk assessments are highly dependent on the assumed failure frequencies and failure mode splits for key well components and activities.
- Cavern wells generally pose higher safety and environmental risks than reservoir wells.
- Reservoir and cavern wells pose minimal safety risk to the public unless routinely occupied locations are in proximity to the wellhead.
- Well entry is often the largest contributor to annual safety risk—especially when using coiled tubing or performing workovers.
- Setback distances can significantly reduce individual safety risk, even for higher-risk wells.
- Simpler well configurations that allow for less invasive inspection methods tend to have lower life-cycle risks.
- Well entry for integrity management is most effective when focused on components that serve as the sole barrier to gas release.
- Frequent entry for inspecting and remediation of production casing is hard to justify unless its condition is known to be poor.
Schematic and fault tree for reservoir well failure by leak scenario
Brian Wagg, MSc, PEng.
Director, Testing Services
With over 35 years with C-FER, Brian Wagg’s current focus is on applying C-FER’s analytical and full-scale testing capabilities to projects in clean energy including CCUS, hydrogen, geothermal and small modular nuclear reactors.
