考虑海管各覆盖层蓄热的停输温降与输送方案

Temperature Drop and Transportation Scheme of Submarine Pipeline Considering Overburden Heat Storage

海底管道停输温降直接决定着海管置换与掺水输送时机,以及停输后能否顺利再启动。为了研究海管各覆盖层的蓄热对停输温降的延缓作用,通过理论分析各层相对流体的蓄能能力大小,模拟计算钢管和土壤蓄热对不同类型管道停输后温降的影响情况,并以渤海两条实际管道为例优化输送方案。结果表明,钢管蓄热总量约为所输原油蓄热总量的一半,所输水量的1/4,所输天然气的4~16倍(根据系统压力的不同);钢管和土壤的蓄热散热对流体停输温降均有一定的延缓作用。对于保温管道,钢管的蓄热散热具有主导作用;不保温管道,土壤的蓄热散热影响很大;对于渤海油田常见的输油海管,考虑钢管的蓄热散热能提高管线出口温度3.5~13.5℃;对于混输保温管道,当气油比(GOR)大于10时,钢管蓄热对停输温降的延缓作用尤为明显,有利于安全顺利输送;考虑土壤或钢管的蓄热散热对停输温降的影响可以延缓或取消掺水输送。

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.