The depositional sands formed inside the multiphase subsea pipeline will result in reduction of pipeline flow area as well as the inhibitor efficiency, and may lead to severe PIG block accidents. The sand deposition law in subsea pipeline has a very important influence on the distribution of corrosion inhibitor and pigging frequency, however there is little research on sand deposition law in multiphase flow at present. This paper performs numerical simulations by FLUENT to investigate the sand deposition law of horizontal and bend section of subsea pipeline associated with different parameters.
Depositional sands as well as wax and so on will be formed inside the multiphase subsea pipeline in operation for some time, which will be a serious threat to pipeline operation safety and should be cleaned regularly.
The design life of the multiphase subsea pipeline from Platform A to platform B of offshore oil and gas field is 15 years, but many leakage points appeared in less than 5 years, which seriously affected the normal production of the oil field. Leakage points are shown in Fig 1. New and old leakage points appear for more than 40 times in total. Leakage points of the inner pipe mostly occur in the middle and back of the subsea pipeline and the outlet section. The thickness of sand deposition is only a few millimeters, which has little influence on the flow area of the pipeline (less than 1%). However, it was noted (Jia,2013) that the sand covers the inner surface of the pipeline, preventing the corrosion inhibitor from covering the metal surface, making the actual concentration of the corrosion inhibitor on the metal surface less than the injected concentration, affecting the efficiency of the corrosion inhibitor (only 20%).
Therefore, the deposition law of sand particles in subsea pipeline has a very important influence on the distribution of corrosion inhibitor and pigging frequency. At present, studies (Zhang, 1997; Zhang, 2005; Fei, 1994) on pipeline transport sand deposition mainly focus on slurry transport, that is, horizontal pipeline transport with large sand content (more than 10%), while there are few studies on fluid transport with low sand content (less than 1%) and the bend part of subsea pipeline. Therefore, in this paper, FLUENT is used to numerically simulate the sand deposition law of horizontal pipe section and curved pipe under low sand content of subsea pipeline to demonstrate the feasibility of numerical simulation, so as to predict the time and location of sand deposition, guide the determination of pigging cycle and reduce the corrosion risk caused by sand deposition.
