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.

The research and application of supersonic separator (3S for short) have been extensively investigated and applied overseas, but is not yet adequate in China. Numerous theoretical studies have been conducted, which mainly focus on the swirl flow, the internal flow and the condensation process. However, experimental results, specially on condensation and separation mechanism of high⁃pressure natural gas are rarely reported, as well as industrial and field test. A lot of work has been carried out in structural design, mainly focusing on comparative analysis, and no feasible structural design strategies have been proposed. The basic research on droplet condensation is even rarer. At present, the process is mainly characterized by CNT and Gyamathy model. In pratical conditions, an appropriate model needs to be selected for calculation and analysis according to the characteristics of various modified models. In order to improve the efficiencies of gas condensation and gas⁃liquid separation, the next research should focus on the effect of the main factors, such as the inlet temperature & pressure, supersaturation, the converter installation position, the supersonic nozzle structure, on the condensation process, so as to the experimental researches on the high⁃pressure natural gas supersonic separation. The industrialization of domestic supersonic separators will provide an effective tools to the dehydration, deacidification, de⁃heavy hydrocarbon before pipelining for the limited offshore platform.

In order to ensure the safety production of offshore heavy oil thermal recovery platform and establish the mathematical model of thermal recovery blowoff diffusion of offshore platform, ANSYS Fluent software was used to simulate the gas diffusion in the process of steam huff and puff thermal recovery, quantify the impact of thermal recovery blowoff process on the platform, and provide guidance for platform general layout. Taking LvDa 21⁃2 oil field as an example, due to the increase of methane content in the later stage of blowout, the slow diffusion rate caused by the decrease of blowoff volume, blowoff was easy to accumulate in the steam boiler and other higher equipment, thus causing potential safety hazards. By optimizing parameters of cold vent system and equipment layout, the impact of blowout on safe operation was lowered to the utmost and platform area was cut down by 5.9%. The study could provide reference for safety design of offshore thermal discovery platform.

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. 