A new set of guidelines has been released for conducting risk assessments of underground gas storage (UGS) wells that are subjected to periodic well entry.

These guidelines were developed by C-FER Technologies for The US Department of Transportation, Pipeline and Hazardous Materials Safety Administration (PHMSA) and are publicly available: Risk Assessment and Treatment of Wells.

Webinar Part 1: Overview of the New Guidelines

In Part 1 of this two-part webinar series, C-FER project lead Mark Stephens will provide an overview of the quantitative risk assessment (QRA) process that forms the basis for the guidelines, with a focus on the two key process elements: risk estimation and risk evaluation.

Risk Estimation

The discussion of risk estimation will include a review of analysis methods and modelling options for:

  • Failure frequency estimation,
  • Failure consequence estimation, and
  • Risk estimation.

Webinar participants will learn how to develop frequency and consequence estimates that can be combined to provide meaningful measures of public safety and environmental risk during normal well operation and during well entry. They will also learn how best to combine the operational and entry risk measures for the purpose of risk evaluation.

Risk Evaluation

The discussion of risk evaluation will focus on how to use the results of risk estimation to inform well design and integrity management using two distinct approaches:

  • Risk evaluation based on defined acceptance criteria, and
  • Risk evaluation in the absence of acceptance criteria.

Webinar participants will learn how to combine risk estimation results and acceptance criteria to make decisions when the necessary criteria do exist, and how to use the results of risk estimation to make decisions based on comparative scenario evaluation when criteria do not exist.

Part 2 of this webinar series will review the demonstration analyses that serve to Illustrate application of the QRA process. These analyses also formed the basis for the directional findings that are intended to support the development of best practices for different well completion types and well entry practices.

Download Webinar Slides

Webinar Part 2: Demonstration Analyses in the Research Report

Part 2 of this two-part webinar series will provide an overview of the demonstration analyses described in the research report. These analyses serve to illustrate application of the quantitative risk assessment (QRA) process described in the guidelines.

The six UGS well configurations considered in the demonstration analyses were selected to include a range of representative UGS well completion configurations that are applicable to typical wells serving depleted hydrocarbon reservoirs and salt caverns. Risk levels were calculated for each well configuration under both normal operating conditions and during well entry. The QRA framework described in the guidelines was then followed to develop estimates of combined well operating and well entry risk for the purpose of safety and environmental risk evaluation.

In addition, the effect on risk of a set of well entry scenarios was analyzed and assessed over a range of evaluation periods. For each well configuration and entry scenario combination analyzed, the total environmental risk over the prescribed set of evaluation periods (or entry intervals) was compared to determine which combination of entry activities demonstrated a net reduction in overall environmental risk and which was associated with the lowest risk.

With reference to the above, the webinar will cover the following:

  • Overview of the reservoir and cavern well configurations analyzed,
  • Overview of the failure frequency and failure consequence estimation models used,
  • Summary of the risk estimates obtained for each well configuration, and
  • Findings of the risk evaluation process and well entry scenario analyses carried out.

The webinar will conclude with a summary of the high-level directional findings developed based on the demonstration analyses.

Download Webinar Slides


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