| dc.description.abstract | The development of Arctic offshore hydrocarbon fields involves transportation systems for
oil and gas, which are represented either by tankers shipping or by pipeline systems. The later
have sustained behavior with respect to hydrocarbons delivery and relatively non-sophisticated
operational requirements. However, some important challenges regarding Arctic conditions have
to be carried out before the pipeline is constructed.
Attention is given to the conditions of a specific hydrocarbon field of the Sakhalin offshore
and a design of the 28 km offshore pipeline. Hydraulic assessment determines the size and
number of pipelines as also temperature and pressure profiles, while mechanical estimations
provide the wall thickness. As a result the main pipeline design aspects regarding dimensions
and stresses occur are obtained, which is required for the next stage of the thesis.
In the second part the issue of the pipeline interaction with first year ice ridges is
described. A study of probable sizes of ice ridges, their peculiarities and morphology is
performed in order to evaluate the design ridge geometry, physical properties and to understand
how a ridge interacts with the soil. Consequently, there introduced two models for estimation of
the maximum gouge depth, caused by the ice ridge scouring the seabed.
At the same time the research shows that even below the gouge the forces transmitted
through the soil could be adverse, such that the proper protection of a pipeline is required. A
beam model of a pipeline exposed to bending and tension in terms of combined transverse and
lateral loadings is proposed and analyzed. Based on the limit state design criteria the required
trench features and mainly soil conditions for the safety reasons of the pipeline are proposed.
Simultaneously the pipeline failure probability is assessed. As a result it was proven that the
pipeline might be buried just below the probable scour depth if the certain conditions of the
“sandwich” backfilling with a weak soil layer on the bottom are met.
After gaining an understanding of the physical processes related to gouging, numerical
modeling is established in the last section. A finite-element analysis in ANSYS 13.0 software is
carried out. The results obtained provide both: justification of the proposed theoretical models,
and more precise assessment of some parameters when necessary, namely the soil behavior
subscour, which is almost impossible to describe theoretically.
Conclusions summarize the acquired findings, provide reasonable recommendations for the
offshore pipelines design in the Arctic regions and give the scope for future works and studies. | no_NO |
