Abstract:

In order to evaluate the consequences of H₂S-containing associated gas leakage on the platform, ANSYS Fluent software was used to simulate the spatiotemporal changes of the gas diffusion. According to the development process of H₂S-containing gas diffusion, the toxic area of the associated gas cloud in two scenarios, namely no protective measures and emergency protective measures, were compared. A quantitative evaluation of the degree of toxic risk of H₂S-containing associated gas leakage was conducted by using the dose-response model. The results showed that compared to the scenario with no protective measures, after taking the “shutdown” measure, the volume and horizontal diffusion distance of the gas cloud with H₂S concentration ranging from 500-2 000 mg/m³ are reduced by 20%-37.5% and 15.4%-47.6%, respectively. After that, the toxic gas cloud volume and horizontal diffusion distance can be further reduced rapidly by taking the "blowdown" measures. By considering the H₂S accumulative concentration and exposure reaction, “shutdown + blowdown” measures can obviously reduce the fatality probability. The fatality of three monitoring spots near the leakage hole decreases from 0.998, 0.034 and 0.000 239 to 0.759, 0.002 9 and 0.000 000 65 respectively. The area of intolerable section and ALARP section of horizontal plane on the middle deck decrease by 63.7% and 81.7% after taking the emergency protective measures. The hazardous degree of toxic consequences caused by associated gas leakage can be significantly reduced.

Key words: offshore platform, H₂S containing gas, gas leakage, accident consequence, gas cloud, hazardous degree