Session: 07-01-02 Natural Gas Release Consequence

Paper Number: 130792

130792 - Modelling Consequence From Natural Gas Storage Wells 

Abstract: 

A fully quantitative framework for risk assessment of natural gas storage wells, including wellhead components and the connected piping, has been developed to assess SoCalGas’s underground gas storage sites in California. The approach has been developed to meet and exceed the risk assessment requirements of API RP 1171 (incorporated by reference in US regulation 49 CFR 192.12) and the recent changes to the California Code of Regulations. Further, several of the recommendations made in the recent PHMSA study, “Risk Assessment and Treatment of Wells” (2021), have been addressed and incorporated. This framework includes life‑safety and environmental consequence assessments for releases from the wells. The key steps in the consequence assessment include:

- Estimating the probability of ignition (POI) based on the rate and source of the release, using an industry model developed from historical release data.

- Adapting the Potential Impact Radius (PIR) model (Stephens, 2002) from a gas transmission pipeline context to a gas storage well context to determine the life‑safety hazard areas resulting from an ignited release.

- For life‑safety consequences:

    - Calculating the individual risk (IR) as the probability of fatality based on the distance from the well.

    - Calculating the societal risk (SR) as both an expected number of fatalities and F-N curve.

    - Differentiating the IR and SR for workers during normal operations, workers during a well workover, and the public.

- For environmental consequences:

    - Estimating the time to contain a release from both historical release data and subject matter expert (SME) experience and judgement.

    - Calculating the total mass of gas released for each potential failure event and converting to standardized measures of the Global Warming Potential (GWP), measured as the carbon dioxide equivalent over both 20- and 100-year timeframes.

- Demonstrating the impact of surface safety valves (SSVs) and downhole safety valves (DHSVs) on the life‑safety and environmental consequences.

This paper illustrates the results for field-wide assessments of these consequences, showing how the risk is differentiated by the specific well context.

Presenting Author: Shawn Smith Integral Engineering

Presenting Author Biography: Shawn has eight years of experience working in consulting roles with a focus on risk & reliability. In recent years, Shawn has worked with oil & gas operators to apply probabilistic and machine learning models to support and improve their integrity management programs across a range of assets.

Authors:

Shawn Smith Integral Engineering
Alex Fraser Integral Engineering
Pedro Petraglia Integral Engineering
Mari Shironishi Southern Californian Gas Company
Daniel Shapiro Southern Californian Gas Company