The temperature profile has a decisive influence on the timing of the replacement and blending water of subsea pipeline, as well as smooth restart after shutdown. For a quantitative evaluation on the delay effect resulted from consideration heat storage and dissipation of cover layers, the energy storage capacity of each layer is analyzed theoretically, and the influence of heat storage of steel pipe and soil on the temperature drop of different types of pipelines after shutdown is simulated and calculated. Taking two practical pipelines in Bohai Sea as an example, the transportation scheme is optimized. The results show that the total stored heat by steel is about half of the heat of the crude oil in oil pipeline, 1/4 of the water in water pipeline and 4~16 times of the natural gas in gas pipeline, which depends on the system's pressure. The heat storage and heat dissipation of steel pipe and soil can delay the temperature drop of fluid shutdown. For the insulation pipeline, the stored heat by steel makes a different on temperature drop, while for the non⁃insulation pipeline, the heat by soil has a great impact on temperature profile. Within the crude oil pipeline in Bohai Bay of China, there is about a 3.5~13.5 ℃ temperature increase at the outlet of pipeline when consideration the heat storage and dissipation of cover layers. When the GOR is greater than 10, there is a particularly obvious effect on the temperature drop when shutdown, which is conducive for a safe and smooth transportation. Considering the influence of heat storage and heat dissipation of soil or steel pipe on the temperature drop of shutdown, the water mixing transportation can be delayed or cancelled.

Based on the primary production separators (CEPAV2001A/B) of an offshore center platform in domestic, models, in line with actual production, are established. Key parameters in the separators and relief characteristics are investigated when choking accident occurs. Following conclusion is drawing: Firstly, when oil or gas outlet of CEPAV2001A is blocked, separator pressure will surpass the set point of SDV and PSV, and protection devices, such as SDV or PSV, should be taken into account. However, while the water outlet is choked, the pressure will not climb too high to protection; Secondly, according to simulation and comparison, a Gtype PSV with 324.5 mmdiameter is selected for protection under blocking accident; Lastly, equipping with two separators in parallel can ease, or eliminate the pressure climbing of the system. 