Deepwater pipelines – status, challenges and future trends

Abstract

The demand for energy is steadily increasing and, at least for the coming decades, the world has to rely on oil and gas to address this need. Most of the easiest accessible offshore petroleum reservoirs have been discovered and a great part developed over the last six decades. Thus, development of new oil and gas fields faces a lot of challenges as most of them are in remote areas, in deep waters and/or in areas with extreme environments like the Arctic region. One of the major trends in the offshore petroleum industry points towards deeper waters (e.g. outside West Africa, the Brazilian Pre-Salt developments and in the Gulf of Mexico). This trend also includes increased use of subsea installations instead of platforms, more subsea processing and increased use of pipelines to transport the hydrocarbons to shore or into a pipeline grid. This paper addresses some of the challenges pipeline design, installation and operation may face in deep and ultra-deep waters. The main design challenge is related to the high external pressure that may cause collapse of the pipeline. This potential failure mode is normally dealt with by increasing the pipe wall thickness, but at ultra-deep water depths this may require a very thick walled pipe that becomes very costly, difficult to manufacture and hard to install due to its weight. One approach to overcome this is to improve some of the parameters that determine the collapse resistance by an improved manufacturing process. Other approaches are to ensure a minimum internal pressure is maintained in the pipeline during all phases, or to install a buoyant pipeline that is anchored at a moderate water depth rather that laying on the sea bed.

Residual ultimate strength of offshore metallic pipelines with structural damage – a literature review

“…The reel-lay method is considered the most efficient installation method with a laying speed up to 3.5 km/hour (Kyriakides & Corona 2007). It is suitable for pipes with diameter smaller than 18 inches and a diameter-to-thickness ratio (D/t) between 20 and 24 (Fyrileiv et al 2013). The main advantage of the reel-lay method over the other two methods is that the entire fabrication procedure including welding, inspection and coating is conducted onshore instead of offshore, which has largely reduced installation time and costs.…”

“…A pipeline is generally considered as a thin-walled shell structure when the D/t ratio is larger than 20. The common transmission pipes in deep water have D/t ratios between 25 and 30, while much larger D/t ratios are employed in shallow water (Fyrileiv et al 2013;Guo et al 2013). The D/t ratio governs the pipe failure.…”

“…The D/t ratio governs the pipe failure. For instance, elastic-plastic collapse generally occurs on thickwalled pipes when the D/t is less than 20, while elastic buckling failure generally happens on pipes when the D/t is larger than 40 (Fyrileiv et al 2013). A combined failure mode would occur on the structures with ratios between 20 and 40.…”

A method for identifying support conditions of buried subsea gas pipelines based on forced vibration signal analysis

“…Following contents are studied for the purpose of realizing the influence of the excitation force amplitude to the free span detection. (1) Amplitude of the excitation vibration force should be high enough to excite the system, and then, information of the support condition can be involved in the response signal. (2) The contact type between the steel plate and FSDD should be designed properly to ensure that the steel plate can be excited by the excitation vibration signal stably.…”

“…Pipeline is crucial for oil and gas transportation and its safety is increasingly concerned. 1 Free spans of buried subsea pipelines may develop gradually due to current, seabed migration and so on. The free-spanning segments of subsea pipelines are more vulnerable to load change such as vortex-induced vibration.…”