Assessing Risk and Modeling a Sudden Gas Release Due to Gas Pipeline Ruptures.

摘要

The objectives of this project were to 1) develop a computer software solution to model the behavior of wet or dry gas from a single-phase sub-sea pipeline release from sea-bed to harmless in-air concentration; 2) to utilize the software system to model the behavior of gas released from hypothetical sub-sea pipeline ruptures; and 3) to estimate the probability of occurrence of pipeline ruptures in the MMS OCS regions using relevant historical pipeline spill statistics. Minerals Management personnel in the Pacific Region provided example pipeline rupture scenarios for use in the model development, testing and impact assessment phases of the project. The pipelines selected were 12, 24 and 36-inch diameter systems with varying length, depths, operating pressures, environmental conditions and gas types. Detailed descriptions of these scenarios are provided in Table 3.1, Table 3.2 and Table 3.3. The MMS Pipeline Gas Release Computer Model (WCDgas.exe) delivered with this report provides a methodology to predict the behavior of gas discharges from sub sea pipelines. The MMS POSVCM oil pipeline discharge model was modified to accommodate gas release, the behavior of the gas bubble plume and generation of output suitable for air dispersion modeling. A summary of the WCDgas modeling results for the example scenarios developed for this project can be found in Table 7.2. Peak gas discharge rates ranging from 10,000 to 1.6 million g/s were predicted depending on the release characteristics. Release durations between 5 minutes and 3 hours were identified. The OCD/5 atmospheric dispersion model developed for MMS was used to model the behavior of the gas after exiting the water surface. Modifications were made to this software to improve its ease of use and data output reporting. A summary of the OCD/5 modeling results for the example scenarios developed for this project can be found in Table 7.3. The primary hazard surrounding natural gas dispersions in air is the explosive zone downwind of the release. The model predicts that this zone will be less than 1200 m in all of the cases studied and typically less than 500 m. Software installation instructions and a quick guide to the basic use of the software are provided in Appendix E. The potential damage to marine biota from a gas pipeline rupture will be negligible due to the non-toxic nature of the gas, the small release duration and relatively small volumes of water affected. The risk to human health and safety will be limited to the explosive zone surrounding the gas discharge location and will only be present for the short duration of the release (minutes to a few hours at most).