Modelling Consequence From Natural Gas Storage Wells

Abstract A comprehensive quantitative framework for the risk assessment of natural gas storage wells, inclusive of wellhead components and associated piping, has been formulated for the evaluation of SoCalGas’s underground gas storage facilities located in California. This framework has been designed to surpass the stipulated requirements set forth by API RP 1171, as referenced in the US regulation 49 CFR 192.12, and to address the recent amendments to the California Code of Regulations. Additionally, it integrates several recommendations from the 2021 PHMSA study titled “Risk Assessment and Treatment of Wells.” This framework encompasses assessments of both life safety and environmental impacts resulting from potential releases from these wells. The methodology for consequence assessment involves several critical processes, including: • Determining the probability of ignition using an empirical model based on historical release data. • Adapting the Potential Impact Radius (PIR) model, initially developed for gas transmission pipelines by Stephens et al. in 2002, to the context of gas storage wells to identify areas at risk due to ignited releases. • Computing the individual and societal life safety risk, distinguishing between normal operations, planned well interventions, and the public. • Estimating the expected quantity of methane released and the corresponding global warming potential, incorporating an empirical model for time to contain a release based on historical release data. • Combining the life safety and environmental risk using estimates for the value of a statistical life and the societal cost of carbon. • Evaluating the efficacy of surface safety valves and downhole safety valves based on the reduction in life safety and/or environmental consequences. This paper illustrates how the risk-reduction of a mitigation measure, installing a downhole safety valve, is captured by this framework, differentiating by the specific well context.