Download - Pipeline Stability on the Seabed
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An Innovative Approach To Increase
Pipeline Stability on The Seabed
By:
Godwin Eton
PhD Student
School of Civil Engineering
Supervisors:
Prof. Barry Clarke and Dr Terry Cousens
February 2011
School of Civil EngineeringFACULTY OF ENGINEERING
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Outline
Offshore pipelines
Behaviours of offshore pipelines
Current industry solutions and the challenges
Research in civil engineering, Leeds
Electro-kinetics principles in geotechnical engineering
Test conducted and some results
Conclusions
School of Civil EngineeringFACULTY OF ENGINEERING
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School of Civil EngineeringFACULTY OF ENGINEERING
Transportation of oil and gasUses
Diameter between 0.15m to 1.4m
Average of 0.3m for most field development
Size
Pipelines Larger diameter Flowlines Smaller diameter
Types
Offshore Pipelines
Petroleum field development using pipelines
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Flowlines are more unstable
on the seabed
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To ease the flow of oil and gas and
prevent solidification of wax components
Pipeline tries to expand but is restricted by
interface friction between the pipe and the
soft seabed
Pipe is subjected to an axial compressive
load
When this load reaches some critical
value, the pipeline becomes unstable and
is displaced in various directions- vertical
(upheaval buckling) or lateral movements
(lateral buckling) or axial ( pipe walking)
These can jeopardise the structural
integrity of the pipeline and create a
potential hazard for in-service pipelines
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Oil/gas now required
to operate at higher
temperature and
pressure
Behaviour of offshore pipelines
-The Problem
Upheaval buckling
Lateral buckling
This expansive behaviour of pipelines remains one of the major issues currently facing many
...large deep water subsea developments prompting need for research into pipe-soil interactions 4
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School of Civil EngineeringFACULTY OF ENGINEERING
Current Industry Solutions
The above are not only expensive but very difficult in deeper water
Most current and most cost effective
method is to lay the pipe in
Snake lay configuration (SLC)
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Dig a trench and bury the pipe Anchor the pipe to a fix
structureConcrete mattress/rock cover
SLC
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Schematic representation of plan view of typical lateral buckling design
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SLC design allow the pipe to buckle laterally during operation but
depends on a very large extent on the strength of the soil supporting
the pipeline
Of all the design parameters, the soil response causes the greatest
uncertainty in the design due to the extreme dependency/sensitivity
of design solutions to axial and lateral resistance imposed by the soil
Increasing the soil resistance to pipe displacement is imperative to
enhance the effectiveness of snake laying approach
School of Civil EngineeringFACULTY OF ENGINEERING
The Challenge
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None of the existing mitigation methods involved the modification of
ambient soil properties
Research is conducted here to study the deformation mechanism of
soil during pipe displacement as well as using Electrokinetic
processes to increase the strength of seabed soils which support the
offshore pipelines
School of Civil EngineeringFACULTY OF ENGINEERING
Research in Civil Engineering, Leeds
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School of Civil EngineeringFACULTY OF ENGINEERING
Electro-kinetic Principles of Soil Improvement
When a saturated fine soil
is exposed to direct electrical
current by means of
electrodes (anode (+) and
cathode (-), the cations in the
clay surface migrate to the
cathode and drag water with
them causing water flow
toward the cathode
Can result in increasing the
strength of the soil near the
anode
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School of Civil EngineeringFACULTY OF ENGINEERING
Electro-kinetic Principles in Geotechnical Engineering
L.Casagrande, 1949 - Control pore water at excavation sites
Bjerrum et al, 1967 - Increase the shear strength of slopes and walls
V. Milligan 1995 - Improve the friction/bearing capacity of piles
Micic et al , 2001 - Increase the capacity of offshore foundations
EK not yet used in pipeline stability10
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School of Civil EngineeringFACULTY OF ENGINEERING
Test conducted- small-scale and full-scale
Moisture content
Undrained shear strength
Soil pH and electrical properties of the soil
Pull-out test to investigate the resistance of the treated soil to lateral,
axial and vertical displacement of a model pipe section partially
embedded in model soil
Results were compared with control tests and the difference assumed
to be due to EK treatment
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Small-scale test
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Equipment Design and Methodology for this research
Before EK test After EK test
Test Setup for lateral, axial
and vertical pull-out tests
X-section of partially embedded
pipe section Model pipe section with electrodes in the small-scaled testing tanks
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Full-scaled test
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Equipment Design cont.
Full-scaled testing tank No EKFull-scaled testing tank during EK tests
Pipe section with electrodes used for EK testElectrodes used for full-scaled tests 13
Results from the small-scaled
tests where up-scaled to fit the
large tank to investigate effect of
EK treatment in full-scale.
Test conducted in both axial
and lateral directions
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Some results
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Some results
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Lateral Pulling Test Results from iron
and Aluminium electrodes
Vertical Pulling Test Results from iron,
copper and Aluminium electrodes 7
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Changes in Cu between FE and AL
electrodes
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Some results effects of electrode materials
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Change in CU before and after EK treatment using Al electrodes109
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EK process can be employed to increase the stability of subsea pipeline
Iron electrodes appear to be more effective for surface-laid pipes
Aluminium electrode might be better for buried pipes. Research ongoing
in this area
EK has potential applications of strengthening soft soil around subsea
pipelines and thus mitigate against axial walking and lateral buckling of
pipeline
EK Can be extended to stabilise buried pipelines, communication
cables e.g. fibre optic wires as well as other offshore foundations
This will not only reduce cost of installation but also reduce time to
commissioning of these structures
School of Civil EngineeringFACULTY OF ENGINEERING
Conclusion
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Thank You For Listening
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