Rigs-to-Reefs (R2R) is an alternative for oil and gas industry for decommissioning purpose. The program will benefit marine life as an artificial reef for a sustainable solution to promote ecosystem growth. For any oil platform considered for reefing, an extensive study on the suitability and performance of the artificial reef is essential. These studies will evaluate the stability and relevance of the structure as an artificial reef when deployed on the seabed. This paper presents the research on dynamic response and flow characteristics of a conceptual proposed R2R platform. The Computational Fluid Dynamics (CFD) simulation is intended to study the dynamic responses and flow characteristics analysis of a jacket oil platform for optimal settlement and growth of corals. Artificial reef performances were evaluated by calculating the performance indices of the upwelling and back eddy profile. It was found that the upwelling efficiency index is higher at current direction normal to the platform due to the higher frontal area exposed to the incoming flow. Meanwhile, back eddy efficiency index shows a significant low value for all directions. The CFD results presented will be discussed in terms of the possibility of better performance of an artificial reef which considering engineering and biological aspects
Drilling risers used in oil and gas operations are subjected to external loads such as wave and current. One of the phenomena that arise from the external loads is the Vortex-Induced Vibration (VIV), which affects the performance of the riser due to excessive vibration from the vortex shedding. A significant factor influencing the VIV is the design of the drilling riser and its auxiliary lines. Until now, the optimum geometrical size and gap between the auxiliary and the main riser are still very scarcely studied. In this paper, the main objective is to study the effects of the gap ratio (G/D) on the vortex shedding phenomenon on a fixed and freely vibrating riser. The riser system was modelled with a main drilling riser and six auxiliary lines with a constant diameter ratio (d/D) of 0.45 and gap ratio (G/D) = 0 to 2.0 in the laminar flow regime with Reynold Number, Re = 200. The simulations were conducted for Single Degree of Freedom (SDOF) using Computational Fluid Dynamics (CFD) software, Altair AcuSolve. It was found that the freely vibrating riser experienced higher lift and drag forces as compared to the fixed riser due to the synchronization (lock-in) of the shedding vibration and the natural frequencies. The lock-in phenomenon is normally observed on the drilling riser at different current directions. The forces are reduced when G/D is higher. The vortex shedding was significantly reduced for auxiliaries between 0.3 to 1.4. It is confirmed that by modifying the interaction of the vortices in the wake region with auxiliary lines, the hydrodynamic forces will be decreased. Finally, this fundamental study could potentially be used in the designing stage of an optimum drilling riser system by considering significant governing factors.
Platform decommissioning activities have been increasing due to unproductive fields and unstable oil prices. One of the decommissioning methods used by the oil and gas companies is by converting the platform into an artificial reef through the rigs-to-reef (R2R) programme. The programme benefits the marine life and increases the marine productions. In this study, the dynamic responses and flow characteristics of jacket platforms were investigated using computational fluid dynamics (CFD) analysis. Three jacket structures with different sizes were used to investigate the suitability of the structure as a potential artificial reef. The pressure exerted on the structure as well as the back eddies and upwelling phenomenon were also investigated. This is to ensure the settlement of the coral larvae and attract marine life to inhabit around the artificial reef. The results show that the platform size and configurations are the significant criteria to design any artificial reef. The pressure on the jacket member is in the acceptable range. Higher efficiency index of back eddy and upwelling could also be obtained by smaller jacket structures.
Vortex-Induced Vibration (VIV) has emerged as a crucial problem that may arise during a drilling operation, which could result in riser failure. Engineers focus on drilling riser's flow characteristics and controls with the intention of improving the drilling environment. Auxiliary lines or control rods are usually placed around the main drilling riser to suppress the VIV. However, the issue related to the flow past drilling riser system with auxiliaries has yet to be resolved. The flow characteristics around a riser system with auxiliaries were analysed in this research. The simulations were conducted using Computational Fluid Dynamics (CFD) software, Altair AcuSolve. This work focuses on the influence of various gap ratios (G/D) and diameter ratios (d/D) on the vortex interaction. A main cylinder with six auxiliary lines was modelled with G/D of 0 to 2.0 and d/D of 0.10 to 0.60 to simulate the riser system. The simulations were carried out at Reynold Number of 200 in the laminar flow regime. The results revealed that the hydrodynamic forces decreased when d/D and G/D increased. The vortex shedding was significantly reduced for auxiliary lines with G/D between 0.3 and 1.4. The numerical simulation results indicated that the vortex interaction in the wake region was, and the hydrodynamic forces were reduced due to the auxiliary lines configurations. The findings of this study are intended to contribute a new CFD simulation result for a better prediction of VIV on a drilling riser with auxiliary lines.
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