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Collaborating Authors
Results
Impact Damage On Pipe-in-Pipe Systems
Zheng, Jiexin (Centre for Offshore Research and Engineering, Department of Civil & Environmental Engineering, National University of Singapore) | Palmer, Andrew (Centre for Offshore Research and Engineering, Department of Civil & Environmental Engineering, National University of Singapore) | Lipski, Wacek (Subsea) | Brunning, Paul (Subsea)
ABSTRACT: Pipe-in-pipe and bundled pipeline systems are widely used in the offshore industry, because they make it possible to achieve a high level of thermal insulation and because they lend themselves to rapid and economical installation. Traditionally, mechanical design of these systems with regards to fishing gear interaction and dropped objects has used the same approach as for single pipe systems. However, this approach is likely to result in a conservative design as the outer pipe is not required to resist internal pressure and can accommodate a greater level of indentation than a single, pressure containing pipe. Eliminating conservatism in this aspect of design has the potential to eliminate the need for trenching in areas of high fishing activity and can therefore have considerable economic benefits. The paper describes experimental and numerical research directed towards a deeper understanding of this problem. The research includes indentation tests with a knife-edge indenter for both single wall pipe and a pipe-in-pipe, together with ABAQUS calculations which compare well with the experimental data. INTRODUCTION Trenching is an effective, but often high cost, method to protect a pipeline from external damage such as trawl gear impact. In the early days of offshore field development, all pipelines in the North Sea were trenched. Shell took the view that it was unnecessary to trench largediameter pipelines, and research in the period 1974 to 1980 demonstrated that this was correct. Based on the work done by Shell, the general practice accepted by the industry came to be that pipelines of 16 inch diameter and above can be left on the seabed without being trenched. The JIP recommended that the trenching decision should be based on a more comprehensive analysis process and should not be decided by diameter only. (Trevor Jee Associates, 1999).
- Europe > United Kingdom > North Sea (0.24)
- Europe > Norway > North Sea (0.24)
- Europe > North Sea (0.24)
- (2 more...)
Bulk Thermal Conductivity of Stable And Dissolved Methane Hydrate- Bearing Zones
Falser, Simon (Centre for Offshore Research and Engineering, Department of Civil & Environmental Engineering, National University of Singapore) | Loh, Matilda (Centre for Offshore Research and Engineering, Department of Civil & Environmental Engineering, National University of Singapore) | Palmer, Andrew (Centre for Offshore Research and Engineering, Department of Civil & Environmental Engineering, National University of Singapore) | Tan, Thiam Soon (Centre for Offshore Research and Engineering, Department of Civil & Environmental Engineering, National University of Singapore)
ABSTRACT The endothermic dissociation process of gas hydrate is governed by heat transfer. Bulk thermal conductivities are widely used to analyze the heat transfer in hydrate bearing sediments as a homogenous material. This study presents measurements of thermal conductivities in fully methane hydrate- and water saturated samples at steady state and no flow conditions. The results are compared with four theoretical soil conductivity models, and their agreement in the presence of free gas is then determined by experiments on partially- and fully methane saturated samples. The accuracy of the determined conductivities is finally shown by a close match between a numerical simulation and the recorded temperature histories in the transient phase. INTRODUCTION Gas hydrates are crystalline solids that are stable at high pressure- and low temperature conditions. Found worldwide in permafrost areas and continental margins, it is estimated that naturally occurring methane hydrates are estimated to contain at least twice the amount of carbon compared to all the other available hydrocarbon reservoirs on the Earth (Kvenvolden, 1988). This makes them an attractive alternative source of energy for the future. However, uncontrolled dissociation of gas hydrates, whether occurring naturally or during gas extraction for energy, can lead to seabed destabilisation, trigger sediment slides which can severely damage subsea equipments, jeopardize foundations and release methane, a potent greenhouse gas, into the atmosphere. The highly non-linear phase equilibrium of gas hydrates is sensitive to temperature changes, and small changes in temperature can result in a significant shift in equilibrium pressure, destabilising the hydrate. The hydrate dissociation itself, however, is an endothermic process, and thus strongly dependent on rate of heat energy supplied to it. An accurate knowledge of the thermal properties of hydrate bearing soil is therefore essential for their exploitation as a potential energy resource as well as to evaluate their significance as a geohazard.
- Reservoir Description and Dynamics > Non-Traditional Resources > Gas hydrates (1.00)
- Reservoir Description and Dynamics > Formation Evaluation & Management (1.00)
- Health, Safety, Environment & Sustainability > Environment (1.00)
- Facilities Design, Construction and Operation > Flow Assurance > Hydrates (1.00)