| dc.description.abstract | Multi-phase flow-related issues in subsea pipelines and risers may cause a lot of problems in oil and gas production. One of these issues is hydrodynamic slugging. This unwanted phenomenon which is an oscillatory flow may induce large flow and pressure fluctuations, which may lead to damage to the transportation and processing facilities and unstable production. In offshore pipeline-riser systems with flexible risers, this oscillatory multiphase flow can cause Slug-Induced Vibration (SIV) which can reduce the fatigue life of the risers.
The present thesis is focused on investigating hydrodynamic slugging in two flowline-riser systems in a field on the Norwegian Continental Shelf using numerical simulation. Measures to eliminate or mitigate hydrodynamic slugging are simulated and evaluated in the simulator and observations and conclusions are issued about their effectivity.
The case studies are two pipeline-riser offshore systems of 4.5 and 19.5 [km], respectively, that are currently producing in the Bøyla field and exhibit hydrodynamic slugging. The systems were simulated using the commercial transient multiphase flow simulator OLGA version (2020.2.0). Slug mitigation methods which were believed to be helpful and feasible to tackle the problem of hydrodynamic slug were investigated, namely external gas-lifting and topside choking. After applying these two methods in the simulator and evaluating them with the three analysis methods (Manual frequency calculations, Fast Fourier Transform, and Frequency Analysis), it turned out that, only the topside choking method can be helpful for dealing with the hydrodynamic slugging problem in these case studies. However, topside choking also has the side effect of decreasing production rates considerably. | |
