Summary Introduction to Offshore Engineering Oe4606 Complete Lecture 1 16

Summary Introduction to Offshore Engineering (OE4606):complete (lecture 1-16)

Introduction to Offshore Engineering (Technische Universiteit Delft)

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Introduction to Offshore Engineering

Lecture 1: Introduction to Offshore Engineering - Kraminski Quiz

- In general, the oil temperature and pressure in an reservoir is o 200° and 100 bar

The deeper the hole, the closer to the centre of the earth higher temp and higher pressure

- What is flowing from an oil reservoir o Oil, gas, water and sand

- What are the modules on a deck for o Prepare oil for transportation

Reducing pressure Lowering temp Separating gas from oil Drying Removing sand

Biological Origin - Originally small marine animals that died and were buried under sediment on the (then) sea bed - Transformed to hydrocarbons (oil and gas) by temperature and pressure in the earth - Hydrocarbons float on water; they seep slowly upward

o Until trapped by an impervious boundary o Most have seeped all the way to the surface

Reservoirs - Oil and gas are stored in place of pore water in more or less porous and permeable (sand)stones - The tops of reservoirs are obviously capped by impervious stone layers (otherwise the oil and

gas would continue to migrate upward)

- How do we find it?


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- The reservoir is present but it must be found first in order to develop it - History: wildcat drilling (in the hope of finding something good) - Present: seismic surveys localize earth formations amenable to providing hydrocarbon storage

and prove presence of hydrocarbons with exploration drilling Exploration drilling

- Drill vertically into the top of the reservoir (usually) - Greatest chance of hitting something useful - Measure distance down; this calibrates the seismic map

o Drill hole to verify seismic profile, not to find oil Pressure constant: oil well is very big Pressure drops: bubble of water

- Measurements from hole to get reservoir quality - Drill through the bottom of the reservoir to learn as much as possible about reservoir size

Production test (of discovered well) - Short duration – a few hours - Measure flow rates and pressures - Determines

o Quality of the hydrocarbons o Estimate the ease of hydrocarbon recovery o Rough estimate of volumes

Data for reservoir engineers Reservoir Engineering

- Make a well plan which will optimally drain the reservoir - Various well types:

o Vertical or deviated or even horizontal - Various well purposes

o Oil or gas production o Gas injection o Water injection

What comes out of a well - Oil - Gas

o Dissolved in the oil in the reservoir. This comes out of solution as pressure decreases while the oil gets higher in the production well)

- Water o Sometimes even more than 95%

- Small amounts of solids Not all gas is good

- Hydrocarbons, such as methane CH4 (good) - Carbon dioxide, CO2 - CO2 mixes with water and produces carbonic acid H2CO3 – which corrodes pipelines - Hydrogen sulphide, H2S – poisonous

Heavier oil components - Asphaltines

o Produce asphalt and can make a rather stable emulsion when mixed with water. Hard to separate and to pump. Can solidify if temperature gets below its pour point temperature

- Parafines


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o A wax that can be deposited on the inside of pipelines Will seethe out of the oil and will grow on the inside of the pipe and block it so

you have to replace the pipe o Pump fluids down to mix the oil to ensure that the parafine won’t come out of the oil

and seethe into the pipe - Too much sand in oil corrosion and the pipe wears out

Processing is done on production units Top side processing

- Objectives o Separate the desired product from all the rest o Prepare the desired product for efficient export to a shore based market o Get rid of wastes in an environmentally friendly way

Embillicals: draden met info voor de apparaten op de zeebodem Offshore Platforms

- Fixed Platform (FP) - Compliant Tower (CT) - Tension Leg Platform (TLP) - Mini-Tension Leg Platform (Mini-TLP) - SPAR Platform (SP) - Floating Production Systems (FPS) - Shuttle Tanker - Subsea System (SS) - Floating Production Storage & Offloading (FPSO)

Fixed Platform (FP)

- A jacket o A tall vertical section made of tubular steel members supported by piles driven into the

seabed - With a deck placed on top, providing space for crew quarters, a drilling rig, and production

facilities - The fixed platform is economically feasible for installation in water depths up to 500 meters

Compliant Tower (CT) - Narrow flexible tower - Piled foundation - Conventional deck for drilling and production operations - Unlike the fixed platform, the compliant tower withstands large lateral deflections - Usually used in water depths between 300 and 700 meters

Tension Leg Platform (TLP)

- Floating structure held in place by vertical, tensioned tendons connected to the sea floor by pile-secured templates

- Tensioned tendons provide for the use of a TLP in a broad water depth range with limited vertical motion

- The larger TLP’s have been successfully deployed in water depths approaching 1300 meters Mini-Tension Leg Platform (Mini-TLP)


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- Floating mini-tension leg platform of relatively low cost - Developed for production of smaller deep-water reserves which would be uneconomic to

produce using more conventional deep-water production systems - It can also be used as a utility, satellite, or early production platform for larger deep-water

discoveries - The world’s first Mini-TLP was installed in the Gulf of Mexico I 1998

SPAR Platform (SP)

- Large diameter dingle vertical cylinder supporting a deck - It has a typical fixed platform topside (surface deck with drilling and production equipment)

three types risers (production, drilling and export), and a hull which is moored using a stiff mooring system of six to twenty lines anchored into the sea floor

- SPAR’s are presently used in water depths up to 1500 meters, although existing technology can extend its use to water depths as great as 2500 meters

Floating Production Systems (FPS)

- A semi-submersible unit which is equipped with drilling and production equipment - It is anchored in place with wire rope and chain, or can be dynamically positioned using rotating

thrusters - Production from subsea wells is transported to the surface deck through production risers

designed to accommodate platform motion - The FPS can be used in a range of water depths from 200 to 2500 meters

Floating Production Storage & Offloading (FPSO)

- Floating vessel used by the offshore oil and gas industry for the processing of hydrocarbons and for storage of oil

- An FPSO vessel is designed to receive hydrocarbons produced from nearby platforms or subsea template, process them and store oil unit it can be offloaded onto a tanker or, less frequently transported through a pipeline

Subsea Systems (SS)

- Subsea production units – least developed but, promising Extra

- Jack-ups - Offshore Wind Power Generators

Load on Offshore Structures

- Wind - Waves - Ice - Currents - Earthquakes

Decommissioning

-


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Lecture 2: Loads on Offshore Structures – Kaminski - Fatigue

o Repair o Failure

- Response = output, load = action - Tendons= to hang things on - LNG= liquefied natural gas - CNG= compressed natural gas - Waves create responses

o Motions o Responses

- A physical quantity, such as motion, can be either load or response depending on considered system

- Static: s*x=P(t) - Kinematic: d*(dx/dt)+ s*x=P(t) - Dynamic: m*(dx²/dt)+ d*(dx/dt)+ s*x=P(t)

o m= mass, d=damping, s=stiffness - Given loads can be classified as either static or dynamic depending on the system they act on. A

given system responds statically or dynamically depending on the loads acting on it Loads

- Dead loads o Gravity loads

Weight of structure Weight of permanent equipment Permanent ballast Weight of tendons

o Hydrostatic loads Hydrostatic pressures Buoyancy force Tendons pre-tension forces

- Live loads o Gravity loads

Weight of non-permanent equipment Oil, LNG, CNG, Fuel, Consumables Crew Furniture

o Operating loads


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Mooring and riser forces Crane forces Helicopter landing Drilling and pipe laying forces Machinery induced loads

- Environmental loads o Wind

Static (sustained) wind pressure Dynamic (gust) wind Vortex shredding

o Wave loads Pressures due to wave diffraction Flow induced pressures Impact pressures (slamming, green water)

o Current loads Static (sustained) current pressure Vortex shredding Submerged waves

o Ice loads Icing Drifting ice Icebergs

o Chemical and bio loads Corrosion Marine growth

o Temperature loads Sunshine radiation, flare radiation Air and seawater temperature Flare radiation

- Motion & deformation loads o Motion induced loads

Pressures due to wave radiation Gravity (change of direction w.r.t. structure Inertia loads Tank pressures Sloshing (coupled)

o Deformation loads Displacements and rotations of module supports (coupled) Differential settlements and uneven seabed

- Accidental loads o Fire o Earthquake o Collisions o Dropped objects o LNG spill o Explosions o Overloading

- Construction, transit & installation loads


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o Construction loads (@yard) Support (docking) forces Lifting

o Transit loads Towing forces Support forces

o Installation loads (@site) Launching Lifting

Wind loading - Important

o Wind, waves & current define jointly the direction of loads on weathervaning offshore structures

- Load combinations o Sustained wind and extreme waves o Gust wind only

Wave loading - Hydrodynamically compact e.g. ship like structures

o Loads are produced by diffracted waves - Hydrodynamically transparent e.g. jacket structures

o Flow loads – Morison’s equation

Valid for λ/D>5

D= member diameter

λ=wave length

Inertia force proportional to the particle acceleration

Drag force proportional to the square of the particle velocity

F = force per meter

u= velocity flow - Quiz:

o The wave pressures used for stress analysis of ship’s hull are Quasi-static Acceleration is too slow to be dynamic Morison’sequation: approximation

o Is this monopile hydrodynamical Depends on diameter/wave length ratio

Marine growth: close to the equator o Weight o Drag force

Punished twice o What is the temperature of LNG under 1 bar?

-160° C

Below 0°, cold, think liquid nitrogen

Where do you keep it in the ship o Calculation shrink coefficient 10^-5: steel o Steel will break isolate ship


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o Liquefy NG to minimize volume (about 600x) for easier transport

o There is a steel rode fixed between two rigid walls at 0°C. The brittle tensile strength is 200MPa. At what temperature will the rode break due to its shrinkage

-100 °C Sloshing

- Moves the liquid heats the walls of the tank high pressures can destroy the membrane - Facts about sloshing

o LNG carriers in operation since 1964 o About 350 ships built o No accident o We design, build, classify and operate o Shell is building 3 billion US$ FLNG

- How to mitigate sloshing o Prevent sloshing conditions o Increase load carrying capacity o Mitigate sloshing effects o Reduce uncertainties

Quiz - The maximum average impact pressure is with decreasing impact area? ^

o Increasing - With increasing maximum average impact pressure the average rise time is

o Decreasing Examples of hull loads

- Static (hours) o Weight o Hydrostatic pressures o Thermal loading

- Quasi-static (seconds) o Wave induced pressures o Motion induced pressures o Inertia forces due to motions

- Dynamic (milliseconds) o Slamming o Propeller induced pressures and vortices o Explosions

FPSO as a beam

-


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Quiz:

- Which waves (λ) bend an FLNG (L) mostly? o Waves with length λ=L


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Lecture 3: Fatigue of offshore structures – Kaminski Fatigue

- Fatigue is the progressive and localized structural damage of a material subjected to cyclic loading

- Cracks - FPSO – bottom – wing tank connection - Why is fatigue dangerous

o Each failure due to fatigue actually fracture o Disasters initiated by 1 failure but not caused by only 1 failure (domino effect)

- Effects o Increases risk of fracture o Changes load paths o May cause leakage o May initiate domino effect

- How to avoid Structural design – general

All possible failure mechanisms

- Yielding - Buckling - Fracture - Delamination - Fatigue - Corrosion

Fatigue lifetime

- Welding

Fatigue general

- Damage =(stress range)³ - Damage = number of stress cycles - 20 years = 100 millions of wave (stress) cycles


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- Damage is cumulative - Moderate stresses cycles are important - In general, fatigue capacity of structural details does not depend on steel grade and yield stress

Fatigue damage

- Miner’s rule - After 24 years fatigue damage of FLNG=0.5 double stresses

o How many years can she operate now? 3 years

Design tips for structured details - Avoid stress concentrations – no stiffness jumps - Place welds away of stress concentration areas - Use adequate class of details - Consider weld dressing - Protect against corrosion

Conclusion - You know how to calculate fatigue lifetime of a structural detail when fatigue loading is known

What is

- Fatigue loading - Fatigue capacity - Fatigue damage - Fatigue lifetime : design lifetime / D

o D= damage Rule of miner

D=Σni/Ni - Fatigue design criterion

Summary

- Select detail - Select appropriate SN-curve - Define fatigue loading - Calculate fatigue capacity - Apply the rule of Miner - Calculate fatigue lifetime

Exercise 1: calculate fatigue lifetime

- Follow the summary ^

- Fatigue loading

o Fatigue induced by quasi-static wave action depends mainly on moderate sea states non-linear response is less relevant


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o Method: spectral analysis - Steps of fatigue analysis

o Metocean analysis Waves

o Hydrodynamic analysis Motions & pressures

o Stress analysis Stresses

o Fatigue analysis o Lifetime

Lifetime assurance – methods

- Preliminary design o First principles, empirical methods, experience o Keep the overall stress level low

- Design/engineering o Rules and direct calculations methods o Avoid stress risers, use adequate details

- Construction o Fabrication procedures and quality assurance o Remove unacceptable defects

- Operation o Inspection, repair & maintenance procedures o Use advisory monitoring systems

Lifetime assurance – advice - Preliminary design

o Keep stresses low - Design/engineering

o Use proper details - Construction

o Allow only acceptable defects - Operation

o Monitor Sensors


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- Cabinet o Wind sensor o DGPS o LBSGs o Strain gauges o FDSs o Motion sensor o Level gauge o Wave buoy

Benefits of Octopus-Monitas

- Shows, explains and advises on fatigue integrity of FPSOs. It explains reasons for potential deviation of the actual fatigue consumption from design predictions and translates the monitoring data into operational guidance and advice in an easily understandable format.

- Prevents loss of production - Prevents unexpected damage - More time for corrective measures - Rational lifetime extension - Feedback to design

Lecture 4: Arctic Engineering Part 1 What is arctic engineering?

- Although the term Arctic engineering is often used to refer to Offshore Engineering in the Arctic, it is officially defined as:

o Everything that has to do with engineering in the Arctic - The general scope of arctic engineering may therefore consist of

o Development of natural resources in cold regions o Design and operations of constructed works in rural communities o Heat transfer and thermal engineering o Evaluation of climate change impacts o Snow control, arctic ecosystems, and much more

Polar low = low pressure area Origin of the word Arctic

- The word arctic is derived from ‘arktis’ (old Greek) or ‘arktikos’, the Greek expression used to refer to the northern sky, being the domain of the constellations of the bear

- In Greek, ‘arktos’ means ‘bear’ and ‘arktikos’ literally means ‘near the bear’ Definitions of the Arctic

- The arctic can be defined as the area north of the Arctic Circle (66° 33’N). This is the approximate limit of the midnight sun and the polar night or the region on the northern hemisphere, where at least one day/year the sun does not set.


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- Or the region north of the northern-most tree line. This definition is close to the use of the 10°C (or 50°F) isotherm.

The (high) Arctic

- Areas of interest for hydrocarbon development in the high Arctic are

o Barents Sea o Kara Sea o Laptev Sea o Chukchi Sea o Beaufort Sea o Baffin Bay

The subarctic - The subarctic consists of those regions in the

northern hemisphere that occasionally show arctic characteristics

- Ice buildups damage pipelines - 1 field in the Barents sea has enough gas to fullfill

the demand of the entire world - Examples of subarctic areas are:

o Labrador Sea o The Great Lakes o Sea of Okhotsk - Sakhalin

Historical perspective

- Oil and natural gas production began in the arctic in the 1920s. By the 1960s large reserves had been discovered on Alaska’s North Slope, in the Mackenzie Delta, Canada, and in several regions of Siberia.

- The completion of the Trans-Alaska Pipeline System (TAPS) in 1977 made production viable in the Prudhoe Bay area in the US.

- Today , oil and gas acticity is widely distributed around the states that border the arctic Oil and gas resources of the Arctic

- Among the greatest uncertainties in future energy supply and a subject of considerable environmetal concern is the amount of oil and gas yet to be found in the Arctic


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- By using a probabilistic geology based methodology, the United States Geological Survey has assessed the are north of the Arctic Circle and concluded that about 30% of the world’s undiscovered gas and 13% of the world’s undiscovered oil may be found there, mostly offshore under less than 500 m of water. Undiscovered natural gas is three times more abundant than oil in the Arctic and is largely concentrated in Russia.

Undiscovered oil Undiscovered gas

- More than 70% thought to occur in 5 provinces More than 70% in 3 provinces

Arctic offshore environment

- Harsh wind/wave environment - Polar lows – data uncertainty - Snow and ice storms - Icing - Ice fog, ice haze - Sea ice and icebergs - Polar darkness - Far from infrastructure - Pristine environment

Classification scheme for arctic structures

- This classification scheme appears to be ‘a logical means of understanding and comparing the many different types of concepts described in the literature’/ Most of the structures described pertain to oil and gas exploration or production facilities, but these structure types have also been used for


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bridge piers, lighthouses, wind turbine foundations, etc. - The three main classifincations are artificial islands, bottom mounted structures and floating

structures. Examples of artificial islands

- Earliest non-retained islands had very shallow slopes, with sandbags for erosion protection - Larger sandbags allowed steeper slope angles and smaller amounts to fill - Successive rock berms can allow for deeper water depths (although rock can be difficult to find

and transport) - The trend to deeper water eventually led to steel or concrete caissons with sand infill

Examples of bottom founded structures

- Various types of bottom-mounted structures are shown here ^ - Most popular are piled base (multi-legged) and gravity base structures - Generally platforms are designed to minimize ice loads through reducing diameter at waterline,

and introducing sloped surfaces which fail ice in bending (lower loads than vertical faces which cause failure in crushing)

- Try to minimize the amount of the structure that is exposed to the ice (mostly around the water line)

Examples of floating structures

- Moored barges, drill ships and semisubmersibles, have been used in the arctic to date - Moored caissons remain on the drawing boards - Dynamically positioned vessels have been used where ice forces are moderate, or where there

may be a need to move off quickly - Ice platforms have been used where there is a stable ice cover for much of the year - Ice itself can be used as a floating structure: heavy, stationary ice


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Not all oil and gas

- Cammaert acted as principal ice consultant to builders of 13 km bridge connecting Prince Edward Island to New Brunswick in early 1980’s

- A university team developed state-of-the art ice leading models, using probabilistic techniques - Final design loads (46 bridge piers) took 3 years of field programs, lab tests, models - 100-year ice load 15 MN, bridge instrumented to record loads each winter

Common ice features

- First year (FY) ice o Melts in 1 season and floats o Level ice o Ice floes o Rafted ice o Ice ridges o Rubble pile o Rubble fields

- Multi year (MY) ice o Ice floes o Ice ridges o Rubble fields

- Glacial ice o Ice islands o Icebergs

Comes from glaciers formed on land

Fresh water compressed snow

Layers of snow fall each year glacier grows Because of compressed snow, tiny bubbles get caught in the layers high pressures in the bubbles. So if you put it in your drink, it fuzzes

- No minerals - Absolutely pure no pollution

Sea ice pure ice


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- Salt has little pockets pockets melt away over time there is no salt pure ice - The colder the ice, the stronger it is

o At the top there is less salt and colder stronger Ice regimes, Canadian Arctic

- Ice types depend very much on region, distance from shore, and water depth - This ice regime is typical for the Canadian (and US) Beaufort Sea

Level ice - Sea ice of fairly uniform ice thickness, usually ‘land fast’ - Depending on location, level ice can grow up to 2.5 m or more

First-year ridge section -

Icebergs - Floating remnants of

glacial ice broken away from glaciers and ice shelves

- Iceberg classification o Growlers (sail < 1.5m) o Bergy bits (sail 1.5 to 5 m, mass < 5400 t) o Small bergs (sail 5 to 15 m, mass 5400 to 180,000 t) o Medium bergs (sail 15 to 45 m, mass 180,000 to 2,000,000 t) o Large bergs (mass > 2,000,000 t)

Sea ice extent

Vanishing polar ice

- This summer, the sea ice that caps the Arctic ocean melted to the lowest level since at least 1979, when satellites first began keeping track of ice over the North Pole

- That is 45% less than the average for August throughout the 1980s and 90s – and as of now the ice is still shrinking

- Some scientists believe the total volume of Arctic ice is only a quarter of what it was 30 years ago

Lecture 5: Arctic Engineering Part 2 Some definitions

- Salinity of ice : the amount of salt (measured in parts per thousand, or ppt, present in ice

o The salt in sea ice exists as brine pockets (very concentrations of salt)

o First year ice can range in salinity from 2 to 5 ppt


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o The salinity of seawater, in comparison, is about 35 ppt o Ice temperature is nearly linear over the depth of the ice feature

Factors influencing interaction scenarios Strength profile

- An ice sheet is coldest at the surface and its temperature increases up to the freezing point at its bottom. Due to the temperature profile in the ice, the ice is strong at the top and weaker at the bottom.

- The salinity and porosity profiles over the depth of an ice sheet change depending on age. In young ice, the salinity profile is almost constant, while the salinity for older ice increases with depth. Nevertheless, the porosity profile is reasonably constant and therefore hardly has an influence on the strength profile.

How do some physical properties effect strength

- Decrease of temperature yields an increase of density, causing the ice to be stronger. - Salinity, together with temperature, determines the brine volume and this largely influences the

porosity - An increase of salinity yields a larger brine volume and thus a higher porosity - An increase of porosity directly causes the ice to be weaker

Ice interaction with structures

- Crushing and bending main failure models usually considered


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Failure mechanisms

- ^ Compressive action

Ice forces vertical – sided structures

- ‘Interaction between level ice and a vertical-sided structure looks straightforward but is not.’ - Much research has been done, and there have been some serious theoretical developments,

some full-scale measurements, and some model tests. - Controversy and vigorous debate surround all of them, and it is too soon for a consensus to

emerge - In the meantime, the practical needs of design have compelled designers to adopt various

empirical and semi-empirical methodologies, and for the moment they have been incorporated in codes

Why is it so complicated?

- A complication is that the ice can deform in qualitatively different ways - Generally the ice breaks. It may break into quite small fragments, as it does in continuous

crushing against the sides of a structure, or the fragments may be larger, if the ice rides up a slope and breaks in bending, or if cracks radiate outward

- If it is moving very slowly, though, it deforms in creep, like a slow-moving Alpine glacier Creep loads on vertical structures

- If the ice is moving very slowly, it deforms in creep, like ice slowly flowing in a valley glacier. - This case is unusual and almost invariably short-lived: it happens when ice which has previously

been moving more rapidly, comes almost to a stop because the driving force has diminished. - Creep loads can also occur in land fast ice which often moves by small amounts due to thermal

strains and sometimes due to sustained winds.


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- The ice deformation is governed by the power-law creep equation where the force between the ice and the structure is proportional to the 1/n power of the relative velocity, where n is the exponent in the power law and is approximately 3.

Buckling loads

- If the ice is thin, it buckles under the edge loads applied by contact with a structure. - If the loading is rapid enough for the deformation to be essentially elastic, the relevant solid

mechanics model is a thin elastic plate on a linear Winkler foundation. - Elastic buckling is likely to be the governing mode only when the ice is rather thin, usually in the

order of 0.4 m. - “Creep buckling is generally associated with rather slow loading processes, and is unlikely ever

to constitute the design condition for offshore structures”

Evidence from measurements - This figure is a version of the famous

Sanderson pressure-area diagram. - It plots observed ice force per unit area

against contact area, in this instance both on logarithmic scales.

Pressure area data sets

- The first tests on ice-structure interaction are represented by the group of points to the left of the diagram, marked ‘lab’.

- They were on laboratory- scale systems, in which sheets of ice were pushed against rigid rectangular and circular indenters.

- A typical indenter width was 50 mm. Those tests determined a contact force per unit area, and that force per unit area could be compared with a compressive strength measured in a conventional compression test on a cube or a cylinder.

- The next tests (‘field’) were on a larger scale, in the Arctic and much more difficult and expensive to carry out.

- Square blocks of ice were cut from floating sea ice, and loaded by platens driven by hydraulic jacks. In a typical test the ice was 1 m thick, the floating block was 5 m square, and the platen was 150 mm wide.

- The force per unit area was somewhat lower than in the series 1 tests. That could be attributed to variation of ice properties through the ice thickness, variation of temperature, and eccentric loading: all those influences were indeed present.

- “The next important step forward was made possible by an ice/structure interaction that Nature generously carries out, on a much larger scale than human beings could possibly arrange.”

- Hans Island lies in the Kennedy Channel between Greenland and Canada. It is about 1700 m long and 1300 m across.

- In July the sea ice breaks up further north, and large multi-year ice floes, sometimes 5000 m across, drift down the channel.

- The force between the floe and the island decelerates the floe. A helicopter can land on the floe before it hits the island and install an accelerometer, and the accelerometer measures the deceleration.

- Simple observations and calculations then give estimates of contact area and loads. Final pressure- area curve


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Crushing loads


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Lecture 6: Introduction to Marine Pipelines (Allseas) History of pipelines

- 1st commercial well by "Colonel" Edwin Drake in Titusville (PA) in 1859. - First discoveries transported to hubs using whisky barrels and horses. - Onward transport by barges/ trains/ wagons. - First wooden pipeline (~9 miles) built in 1862. - First trunk line “Tidewater” in 1879. - First welded pipeline in 1920s. - First coastal developments in GOM by US companies in 1930s & 1940s. - Transition zone between dry land and the marshy, shallow-water flats. - Valuable know-how in a semi-protected, partially marine environment. - “Kermac Rig 16” - First offshore rig 1947, GOM, Louisiana - Lay-barge system development in early 1950s - First North Sea pipelines laid in 1970s

o Extreme low speed (2 barges, 2 years for 170 km) o Large incident rate (e.g. buckles)

- Semi submersibles from late 1970s - Positioning: mooring anchors, tug boats

o Shallow water (<300-400m) o Requires 2-3 anchor handling tugs (8-12 anchors) o Difficult near pipelines / platforms & disturbs seabed o Heavy lines, poor reference o First Dynamically Positioned (DP) vessel in 1986: Lorelay

Unlimited water depths Much smaller footprint Much higher lay-rates

Anchors vs. Dynamically Positioned (DP) vessel - Positioning by anchors

o Traditional

- Positioning by DP

o >1986, Lorelay

History of pipelines


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Considerations for offshore pipe lay

- Main oil & gas transportation method drivers: o Costs of transportation: distance of 1 ton crude for 1 USD:

Tankers 390 km Train 70 km Pipelines 320 km Air 8 km Truck 30 km

o Political strategy, stability o Available infrastructure o Technical challenges:

Water depth Environment/ metocean conditions Distance of transport Associated products

o Safety of transport: pipelines are the safest means of transport from offshore fields to onshore facilities.

On 24 March 1989, the Exxon Valdez ran aground in the Gulf of Alaska resulting in ~750,000 barrels of oil spilled.

- Russia-Ukraine (gas) disputes o 2004: 80% of Russian gas export through Ukraine. o 2005: Gas dispute leading to a 4-day cut-off in 2006. o 2008: Gas debts dispute leads to reduction of gas supply. o 2009: Supply disruptions in European markets. o 2014: Crimea & Ukraine crises; June: gas debts

- South Stream Project - Black Sea route avoiding Ukraine territory Pipelines

- Pipeline types o Infield flow lines o Feeder lines o Transmission lines o Product lines o Distribution lines


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Infield flow line

- Small size (<12-inch) - Short distances (few km)

- Multiple products Feeder line = Flow line

- Medium size (6 to 20-inch) - Longer distances (order of 100 km) - From gathering/ processing facility to transmission line

Transmission (trunk) line = export line = production line

- Linking main fields - Large size (up to 48-inch, in Russia up to 56-inch) - Large distances (1200 km from Norway to UK) -

Product lines : Carry refined products to distribution centres Distribution lines: Local distribution (to your house) Piggy back line

- Small line attached to main pipeline Pipeline materials

- Steel (X52 to X70) o Size from 2 to 48 inch (or more) o Wall thickness up to 42 mm o Non-aggressive products

- Flexible pipelines o Limited size (16 to 20 inch) o Can be used for aggressive products o More expensive then steel o Easy to install

- Duplex pipelines o Special steel type o Resistant against aggressive products o Expensive to fabricate and to weld

- 13% Cr pipelines o Less expensive to fabricate o Can withstand aggressive fluids o Welding expensive

- Cladded or lined with stainless steel o Nickel-Chromium based super alloy o Less expensive than duplex o Fabrication and welding expensive

- Plastic liner o Can withstand aggressive fluids


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o Welded section needs internal coating offshore (expensive) o Usually used by reel contractors (onshore fabrication of string)

Pipe lay principles

- Main installation methods

o S-lay: 2 to 60 inch Welded offshore, horizontal welding stations and

tensioners Currently up to 3000 m of water depth Much faster than J-lay

o J-lay: 2 to 60 inch Welded offshore, vertical welding stations and tensioners Currently up to 3000 m of water depth

o Reeled lay: 2 to 18-inch

Pipeline on a reel; produced onshore Vertical tensioners Currently up to 3000 m of water depth

Start-up methods

- Landfall or shore pull - Start-up anchor - Start-up pile - Pull-in to platform - Start-up structures - Direct hang-off on platform

Hand-over of first-end steel catenary riser


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Midline tie-in

Subsea tie-in

- Tie-in process on the seabed in an underwater welding habitat. - Welding operations are remotely controlled from a support vessel. - ROV (Remotely Operated Vehicles)s and divers assist and monitor the subsea construction work.

Suction pile installation

Mighty pipe lay vessels

- Allseas Solitaire o Largest pipe lay vessel 1996-2014 o S-lay type o Diameters up to 60-inch o Double Joint Factory o 300 m length (400 m incl. stinger) o 420 personnel on board

- Saipem CastorOne

o S-lay type o J-lay tower o Diameters up to 60-inch o Triple Joint Factory o 330 m length (450 m incl. stinger) o 720 personnel on board

- Allseas Pieter Schelte


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o World’s largest (pipe lay) vessel o S-lay type o Diameters up to 60-inch o Double joint factory o 380 m length (477 m incl. stinger) o 571 personnel on board

Lecture 7: Introduction to Subsea Engineering History

- 1943 – 1st subsea completion (Lake Erie, USA, 9.1 m water depth) - 1961 – 1st subsea well completed in Gulf of Mexico by Shell (15.2 m WD) - 1967 – 1st diver-less subsea completion. - 2004 – Shell Coulomb: 2,225 m WD, deepest subsea tieback (gas) - 2005 – BP Thunderhorse: 1859 m WD, deepest subsea tieback (oil) - 2006 – Statoil Hydro Ormen Lange: 160 km, longest subsea tie-back

Offshore & deep water supply growth

Global subsea expenditures outlook

- Step-change in subsea investments expected: o 1978 – 2005: from 140 to 2,404 operational subsea wells worldwide o 3,222 subsea wells were forecast to be installed in the period 2009-2014 o USD 106bn over next 5 years compared to USD 70bn over previous period o Largely driven by the increasing reliance on deep water developments o Installation, repair and maintenance to account for 42% of expenditures


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Considerations for subsea developments

- Safety - Solutions which improve recovery from the reservoirs - Tie-backs of small reservoirs/marginal fields into existing facilities - Technology which permits long tie-backs to land - Equipment to unlock ultra-deep water reserves - Subsea wells:

o Can be placed outside the effective drilling reach of existing platforms. o Higher flexibility with respect to well locations and future expansion. o Can usually be installed faster than the construction time for a platform. o Surface facilities may be less expensive or completely avoided.

- Financial implications o Flow assurance problems can be costly (hydrates, wax, sand, etc.). o Subsea wells cost more to drill, complete and work over. o Operating costs are higher per well. o Less reserves are recovered before reaching economic limit. o Compared to dry wellheads, the access to a subsea well is expensive.

- Time demanding - Complex planning - Visibility - Illumination - Maneuverability

Subsea structures

- Subsea wellhead o Structure placed on the seabed to provide the structural and pressure-containing

interface for drilling and production equipment. o Typically welded onto the first string of casing to form an integral structure of the well.


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- Templates

o A subsea template is a large steel structure which is used as a base for various subsea structures such as wells and subsea trees and manifolds.

- Blowout preventer

o While drilling a well, surface pressure control is provided by a blowout preventer (BOP), located directly at the wellhead and consisting of several independently operating shut-off valves, each of a different design. If the pressure is not contained by the column of drilling mud, casings, wellhead and BOP, a well blowout can occur.

- Xmas tree

o The set of (control) valves, pressure gauges, spools, fittings and chokes assembled at the top of a well to control the flow of oil and gas after the well has been drilled and completed.

o Surface (dry) Xmas tree


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o Surface (wet) Xmas tree

- Manifolds o Manifolds are used to commingle the flow from adjacent

subsea wells (“clustered” around the parent manifold) into flow line headers.

Composed of pipes, valves and control equipment Usually mounted on a template Often have a protective structure covering them Wells sometimes drilled through a common

template structure. - Subsea processing systems

o Extraction and transport of hydrocarbons o Removal of water and re-injection into drained wells o Single and multi-phase boosting of well fluids o Solid (mostly mud) and gas and liquid hydrocarbon separation o Gas treatment, compression and onward transportation

- Pipeline End Terminations and Manifolds o Connection point between pipeline and subsea structures or flow lines

PLET – Pipeline End Termination

Single hub/flange/connector & single valve PLEM – Pipeline End Manifold

Two or more hubs/flanges & two or more valves

- Jumpers

o Jumpers are used to connect subsea wells to manifolds and to connect manifolds and riser bases to flow lines.

- Umbilicals


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o Composite cable used for transferring Electric and hydraulic power Chemicals Fiber optic communication signals

Subsea assets protection

- Protection from dropped objects, anchors, trawlers & scouring.

- Additional in case of pipelines:

o Prevent lateral and upheaval buckling o Provide pipeline stability

- Template with wells, manifold and overtrawlable protective structure

- Subsea tree and manifold enclosed within protective “cocoon” structure (~9 m tall)

- Pre-cast structures - Concrete mattresses - Rock dumping


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- Pipeline burial methods

o Dredging

o Jetting

o Mechanical cutting o Ploughing

Subsea installation & repairs

- Installation support: ROVs o Remotely Operated Vehicles

Surface & subsea positioning and surveys (visual and acoustic) Installation support (valve operations, guidance, cut rigging, etc.)

o Unlimited operational water depths. o No risk to personnel. o Robotic limitations.

- Repairs o Dredge holes at cutting locations o Cut pipeline into sections using diamond wire saw o Lift pipe sections to deck o Remove coating (locally) o Connect pig insertion tool o Insert pig o Insert pipeline recovery tool o Retrieve pipeline into firing line of pipe lay vessel o Reinstall pipeline (incl. new pipe joints) o Laydown o Removal of laydown heads o Deployment of spool piece o Diver-assisted installation of pipeline lift frame


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o Matching pipeline with spool piece o Divers establishing bolted flange connection o Protection frame o As-repaired situation

Lecture 8: Dynamics of Offshore Structures - Metrikine Free hanging risers; water intake riser

- Intake risers for FLNG plants Riser: pipe that rises/conveys something Cavitation: when a flow flows really fast, it creates bubbles chance that it will blow

Water intake riser:

- Research questions o Can a uniform water flow through the intake riser destabilize it?

A very important idea.. but a wrong conclusion, as pA=-MU² the centrifugal force is zero and no instability is possible

o If the instability can occur, what would be the critical velocity of the flow through the pipe?

Water out pipe

The pipe starts shaking uncontrollably Water in pipe

The pipe starts circling in a ‘well-behaved’ manner o If the instability can occur in the range of the desirable velocities of pumping, what

would be the vibration pattern? At velocities higher than a critical pipe was observed to perform intermittent

unstable vibrations o Smaller pipe, velocity 6.9 m/s

- Early experiments

o The pipe was observed to remain stable


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- Early theories

o It was taken into account that the inflow is not just a reverse jet but an axially

symmetric inward injection that is accompanied by the depressurization at the inlet o A very important idea.. but a wrong conclusion, as pA=-MU² the centrifugal force is zero

and no instability is possible - Reason to doubt

- Model

- Experiment at TUD

o At velocities higher than a critical pipe was observed to perform intermittent unstable

vibrations o Smaller pipe, velocity 6.9 m/s

- Explanation of instability

-


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- Actual design

o Riser bundle o A shell: a bundle of risers connected to each other

Free hanging risers

- Vertical transport system for deep sea mining

o Model


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Focus on the effect of the booster stations on the VTS stability Each booster station introduces a pressure jump that leads to the change of the

effective tension

o Instability

o Effect of the booster stations

o Explanation of instability


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o Energy exchange

- More applications?

o Flow can be used to stabilize the riser during installation Deep sea mining

- Without booster stations, the distance is too far to get all the minerals up, the suction can’t get it up, pressure isn’t high enough

o So use booster stations Ice

- Bearings with special material that reduces the friction between two layers - Ice shakes deck with very small movements - Pushing ice with a constant force jerky movements : flaking of ice - Self-induced vibrations = ice induced vibrations - The ice equation is similar to the riser and windmill equation

o Damping of different motions is very different , pitch is very high because of this Ice- induced vibrations

- Motivation

- Ice loads

o Main regimes according to ISO


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- Desirable model

o A theory of ice-induced vibration based on the idea of frequency and amplitude dependent added mass and added damping

Nonexistent as yet

- Phenomenological modeling

o Empirico-Phenomenological model of ice-induced vibration

o What mechanism is the model of Karna and Turunen based upon?

It is the descending character of the force-velocity dependence

o Predictions of model of Karna and Turunen


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The predictions are reasonable but these are too sensitive to the uncertain

parameters such as the viscous damping in the undamaged ice sheet o By TUD

Frequency of vibration, mean value and variance of the waterline displacement

of the structure Floating structures in ice

- Catenary floaters

- Kulluk drilling vessel


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- Dynamics due to ice bending failure

o Modeling

First phase: bending up to the failure

Second phase: pushing the broken off piece away and reloading the buoy

Parameters tuned to the test

o Results of the modeling


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Dynamics of wind power generators

- Measurements

- Modelling


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Underwater noise from offshore pile driving

Dynamics of the rock dumping

- Rock-dumping-caused motion of a fall-pipe

Dynamics of pipelines - Vortex-induced vibration

o Von Karman’s vortex street

o Fundamentals

o Measurements


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o Physics

o Modelling

Equation of motion of the structure

Oscillator

Tuning parameters

o Model vs experiments

o TUD model


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o Power generation

Exam questions

- Offshore structures will be approximated by SDOF systems - Natural frequency, effect of damping, resonance, energy, the dynamic amplification factor - Understanding of the effect of damping, stiffness and mass on various dynamic effects - Simple degree of freedom system - What happens with the natural frequency if you reduce the wall thickness

o W= √

- Increase weight, frequency increase/decreases - Why does it decrease with 3

o Weight up more compression may lead to buckling

Natural frequency =0 - What are the damping mechanisms: which lead to reduction of frequencies?

Lecture 9: Introduction Safety – Andre van der Stap Risk

- = probability of failure x consequence o As we push technology barriers (deeper, colder, harsher, older) we become more

exposed to failures we don’t even think about (even undetected within current risk profile and/or encountering phenomena which can’t be easily extrapolated: unknown/unknowns)

o As we need large scale, capital intensive solutions and society demands ever higher standards for SD/HSE, we in parallel increase the consequence of failure cost

Platform types

- Caission Structure

o Singe well


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o Gulf of Mexico o >1500 caisson structures mostly in GoM o Not normally manned o Water depth <30 m

Monotower

Wellhead jacket -

o >4000 wellhead jackets o Not normally manned o Water depth range 10-100 m o Single pile through each leg, welded at jacket top o Wells drilled either by jack up or tender assisted drilling

- Bridge linked

o Bridge linked complex consisting of multiple jacket structures o Relatively shallow water <100m o Approximately 500 in more benign environments (far east, near shore Nigeria) o Separate platforms for functions (well heads, living quarters, compression platform,

risers, flare) - Large integrated drilling, production, accommodation platforms


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o Relatively deep water: 100-400 m o Permanently manned

In GoM they are evacuated prior to hurricanes o Several hundred, very important in terms of production & value

- Floating production systems

o Tension leg platform o Semisubmersible o Spar o FPSO

Mobile offshore drilling units

- Jack up

o 480 o Drilling over pearl wellhead jacket

- Semisubmersible drilling unit


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o 220

Hurricanes

- Katrina – august 2005 o 45 failures FP

- Rita – sept 2005 o 74 failures FP

Change in design load over time – North sea and GoM

- Old platforms in GoM fail because actual load exceeds design load (x2), not because they

deteriorate Facts & learnings from GoM failures

- No loss of life due to hurricanes because GoM installations are evacuated prior to hurricane arrival

- Majority of failures relate to old structures installed before 1980 - 17 structures installed after 2000 collapsed. This is due to inadequate deck elevation &

‘inadequate’ - 100 year wave heights - Re-evaluation of wave height criteria after Katrina/Rita led to increases of 11-25% in some

areas. Deck elevation raised to 1000 year crest level - API Bias Factor was determined to be 1.06 for Katrina & Rita and 1.09 for al recent hurricanes.

For given conditions the API design approach is ‘conservative’ by 6-9%. Confidence in wave load recipe and pushover analysis

- No failures in other regions due to extreme storms What is appropriate target safety level for L-2 wellhead platform?


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- Cost-Risk trade-off: Total jacket cost = Cost + Risk of failure = Cost + Pf(Service Life)*Loss - Target Pf=5*10^-4/year (RP=2000 years) is appropriate for new L-2 installation

What is appropriate target safety level for L-1 permanently manned installations?

- Potential for loss of lie is major consideration in addition to loss of asset and environmental release.

- Ensure that targets for extreme storm risk dovetail well with regulatory requirements for storm risk & overall risk to personnel (Pf <10^-4)

- Ensure that recourses to improve safety are used in the most effective manner considering relative difficulty of reducing each risk – ALARP principle (As Low As Reasonably Practicable)

- Based on above considerations o Extreme storm target Pf=3*10^-5/year (RP=33000 years) for L-1 installations

Design standards and safety levels for fixed platforms

- Exposure level - API RP 2A defines L-1, L-2, L-3 levels and provides performance requirements for each level - ISO also defines L-1, L-2, L-3 but provides different performance standards from those in API

o Different target reliabilities – different action factors, RSRs, deck elevation Safety levels achieved by

- API RP 2A – steel platforms

- o Suitable for manned-evacuated installations (GoM)

- ISO 19902 – steel platforms o Suitable for permanently manned installations


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o Suitable for L-2 exposure Long term load distribution in different areas

- Often referred to as hazard curve Conclusions regarding safety levels for fixed platforms

- Fixed steel platforms in GoM exhibit high failure rate (0.003/pl-year); largely legacy problem; designed to low wave heights, old wave force recipes & ‘low’ deck elevations

o No loss of life because they are evacuated - Modern GoM structures designed to latest API will achieve Pf=1 in 2000/year - Fixed steel platforms outside GoM have shown extremely good reliability (0 failures in 70,000 pl-

yrs) - New structures designed to ISO 19902 achieve

o Exposure L-1: Target Pf=3*10-5^/year (Pf=1 in 33000 years) o Exposure L-2: Target Pf=5*10-5^/year (Pf=1 in 2000 years)

Floating systems

- Hurricane damage to TLP o Drilling rig TLP overturned during hurricane Katrina, GoM (2005)

Rig tie-down inadequate - TLP capsized during hurricane rita

o Brand new Typhoon TLP capsized by hurricane RITA, GoM (2005) - FPSO, mooring line integrity

o North Sea FPSO suffered loss of 1 mooring line and damage to another 4 mooring lines during a storm, (jan 2012)

- FPSO, hull integrity & mooring line failures o West of Shetlands North Sea o Experiencing severe integrity issues o Hull cracking o Mooring line failures (out of plane bending) o Plans to replace FPSO underway

- Flexible riser performance, failures with loss of containment o Blocked annulus vent system + cracked pressure sheath o Slow leak inside end-fitting o High external pressure, no venting, smoothbore WI, collapse of internal sheath o Leaking external sheath, corrosion near waerline o Bird caging caused by external sheath damage o PVDF slipping out of end-fitting o Local bending o 3x PVDF slipping out of end-fitting o Leak in end-fitting, no annulus venting

- Flexible riser integrity o Flexible risers have seen a range of different failure mechanisms

Sand erosion Seal leak Burst sheath Bend stiffener failure Corrosion


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What are appropriate safety levels for floating systems?

- Potential for loss of life is major consideration in addition to loss of asset and environmental release.

- Ensure that targets for extreme storm risk dovetail well with regulatory requirements for storm risk & risk to personnel

- Safety critical elements (SCEs) designed to survive 10,000 yr - conditions.

o Pf(floating stability) < 1*10-4/yr (RP=10,000yrs) o Pf(stationkeeping) < 1*10-4/yr (RP=10,000yrs) o Pf(riser) < 1*10-4/yr (RP=10,000yrs)

- In GoM where installations are evacuated, survival in 1000 yr conditions is considered adequate’ Conclusions regarding floating system safety

- Experienced several integrity issues with floating systems o Capsizing of 1 TLP in GoM hurricane o Loss of P36 semisubmersible in Brazil due to fire o Severe cracking of Schiehallion FPSO plus mooring line failures resulting in early

replacement o Mooring line failures in FPSOs (Gryphon, Pierce, Anasuria, Girasol) o Flexible Riser failures o Loss of fairings and strakes in steel risers leading to VIV

Serious attention to inspection & maintenance of SCEs to maintain integrity, especially components which span water column (risers & moorings) Jack up KS ENDEAVOUR - blowout – 16-01-2012

- Fire on the rig - Built in 2010 - Offshore Nigeria - Drilling depth: 11000 ft

Jack up Kolskaya - capsize – 18-12-2011

- Fire on the rig KS ENDEAVOUR Escravos - Built in 1985 - Converted to accommodation unit: 1992 - Converted back to drilling unit: 1996 - Fatalities: 53

Jack up – punch through


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Hurricane damage – loss

Jack up – loss of legs under tow

Drilling semi sub- macondo well blow-out

Jack up – on location accidents 2000-2006


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Reasons for high failure rate of modus (jack ups & semis) - Difficulty to maintain well control in exploration wells – blow out risk - Punch through risk of jack ups difficult to manage - Every jack up move needs to be assessed like a new installation – time, data & effort - Lack of uniform industry standards on location assessments

o Return period= 5, 10, 50, 100 year o Warranty surveyor rules not uniform

- Tow risk of jack ups - Shell has spent considerable effort since 1990 to improve industry practices with MODUs

Conclusions for MODUs (jack ups & semis)

- Failure rate of MODUs continues to be too high - Accidents with MODUs are not restricted to GoM hurricane failures only - Blow-out, punch through risk and tow risk are global risks

o Tend to result in loss of life - Careful location assessment for every MODU move needed to improve safety - Location assessment should be based on 50 year return period environmental conditions as per

new ISO 19905 (jack ups) Fire & explosion risk on production platforms

- Piper Alpha accident in 1988, UK N Sea resulted in 167 fatalities - Hydrocarbon release led to fire - Gas riser rupture led to significant escalation - Key lessons learnt

o Systematic evaluation of process related risks o Mandatory use of ESD valves o Living Quarters should function as safe refuge (rated for fire, explosions, smoke) o Goal setting philosophy to reduce risks to As Low As Reasonably Practicable (ALARP)

Major industry disasters


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Process safety basic requirements

AI-PS & Offshore risks

- What is AI-PS ? o Asset Integrity/Process Safety Management (AIPSM)

Asset Integrity means the ability of an asset to perform its intended function effectively while safeguarding life and environment

Process Safety means the management of hazards that can give rise to major accidents involving the release of potentially dangerous materials, release of energy such as fire or explosion, or both. (Baker Report/UK Health & Safety Exec.)

- HEMP Process and safety case (or HSE CASE) o HEMP = Hazard & Effect Management Process

1. Identify Hazards and Potential Effects 2. Evaluate Risks 3. Record Hazards and Effects 4. Define SCE & Performance Standards 5. Establish Risk Reduction Measures. Design and construct phase

Identify risks mitigation

Design risk barriers

Formally document

Construct

Verify & handover Operate phase

Plan to operate

Schedule inspection maintenance program

Inspect & maintain risk barriers

Analyze & assure


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o What is a hazard? Something with potential to do harm (e.g. earthquake, gas release)

o What is consequence? (e.g. earthquake leading to platform loss)

o What is risk? Frequency x consequence

- Asset Integrity Process Safety Management o Design Integrity:

We design and build so that process safety risks are as low as reasonably practicable

o Technical & Operating Integrity: We prevent process safety incidents by maintaining our hardware barriers and

by working within the operational barriers o Integrity Leadership:

Leaders play an important role in avoiding process safety incidents and must demonstrate visible and felt leadership in the field

o Overall: Know your role Know your barriers and controls

- Measures of risk and risk tolerability (ALARP)

- o Risk to people

IRPA = Individual Risk Per Annum TRIF= TR Impairment Frequency (yr) PLL = Potential Loss of Life

o Risk to asset $= asset damage (risked, i.e. freq*damage)

o Risk to environment Emissions Discharges

o Risk may be tolerated if further risk reduction is impractical or if cost or effort is grossly disproportionate to the benefit gained

- Demonstration of ALARP


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Concluding remarks

- Fixed steel platforms outside GoM have shown extremely good reliability (0 failures in 70,000 pl-yrs)

o Legacy issues with old GoM platforms - New fixed steel structures designed to ISO 19902 achieve :

o Exposure L-1: Target Pf=3*10-5/yr (Pf=1 in 33,000yrs) o Exposure L-2: Target Pf=5*10-4/yr (Pf=1 in 2,000yrs)

- Some integrity issues with Floating Systems in all regions o Especially moorings, risers, hull cracking, corrosion

- Significant integrity issues with MODUs (jack ups, semis) o Focus on well integrity, tow, punch-through, location assessments o Industry harmonization

- Ensure learnings from major incidents are not forgotten o Basic requirements (mandatory)

- Carry out systematic safety assessments - HEMP o Understand risks and implement measures to reduce to ALARP

- Consistent messages that safety is top priority - A successful project is a safe project - Safety is not an after-thought – it is our responsibility as engineers

Lecture 10: Functional Profile & Structure Types FLNG (Floating Liquid Natural Gas)

- Some numbers o 488m long, 74m wide o 5 of the largest aircraft carriers would displace the same amount of water as the facility o 6,700 horsepower thrusters o 5.3 million tons per annum, enough for a city like Hong Kong o Final investment decision on the Prelude FLNG Project on 20 May, 2011 (engineers

started work before 2003)


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o Permanently moored for around 20-25 years before needing to dock for inspection and overhaul

o 50 million liters of cold water will be drawn from the ocean every hour to help cool the natural gas

- Basin test o Even the scale of FLNG models used for lab and field-scale trials have broken records:

the FLNG facility model is more than 8 meters long and weighs around 4.5 tons.

Operators and Contractors

- Offshore industrial activities may be:

o Oil and Gas recovery

o Wind Farming, (floating) tidal turbines

o Mining (manganese nodules, rare or precious metals, diamonds)

- The industrial activities more or less all follow the same path

o Government

Offshore blocks

License (placed on bid)

o Operator

Functional profile

o Field Development Scenario’s

Cost/benefits analysis

o Infrastructure & equipment definition

- Do not look at today’s market, but at the market in about 3 to 5 years from now Functional profiles – what influences the structure type selection?

- Production & Storage Capacities (gas, wind, mining) o Size & weight of topsides, deadweight/payload requirements, installation requirements

- Waterdepth o Bottom Founded, Floating, Hybrid, Station keeping aspects

- Metocean & Ice data o (Wind, waves, current, spectra, directions, persistence data) o Motion behavior, freeboard requirements, ice class etc.

- Field Life ? - Decommissioning

o Ease of removal/re-use in future, floating is easier to remove than bottom founded


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- Local Infrastructure o Supply of goods, storage on the unit, accommodation

- Rules & Regulations? Structure types

- What main structure types can be identified in the offshore? o Bottom Founded Structures (BFS) o Floating Offshore Structure (FOS) o Hybrid Offshore Structures (HOS)

Structure type selection

- Mobility, speed, DWT and motion behavior - Two options: same size hull but unequal displacement

o Slender: High speed (at same power) Low carrying capacity Motions poor (roll) Less stability More green water

o Full: Low speed (at same power) High carrying capacity Motions good Increased stability Less green water

o To have the best of both options the ship is to be increased (also increased steel and power requirements) mobility influences costs (with sufficient funding you can construct anything)

- Structures vs waterdepth

9 primary mission profiles 1. Renewable Energies (windfarms, current and wave energy) 2. Hydrocarbons Exploration & Production 3. Hydrocarbons Transport (from the field to shore and infield) 4. Hydrocarbons Production Support Services 5. Seabed Investigation & Correction 6. Infrastructure Installation & Removal


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7. Infrastructure Fixation 8. Infrastructure Support Services 9. Transport to/from Field (Structures & Goods)

1. Renewable Energies (windfarms, current and wave energy)

2. Hydrocarbons Exploration & Production

3. Hydrocarbons Transport (from the field to shore and infield)

4. Hydrocarbons Production Support Services

5. Seabed Investigation & Correction


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6. Infrastructure Installation & Removal

7. Infrastructure Fixation

8. Infrastructure Support Services

9. Transport to/from Field (Structures & Goods)

Lecture 11: Floating structures hull characteristics Hull selection criteria

- Mobility: speed, range, sailing/working ratio, transit time & costs - Carrying capacity - Motion behavior - Water depth: too deep, too shallow?, station keeping aspects - Construction costs - Versatility (upgradability)

Floaters: motion behavior The Response Amplitude Operator (RAO) Response Amplitude Operator: see response of vessel to the waves RAO for heave – example

- Why is it exactly one


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- Heuristic approach o single degree of freedom, heave (x):

o

o - How to interpret m, k and f initially?

o k =Archimedes law, hydrostatic stiffness o f = Hydrodynamic interaction: integral of the pressures over the hull o m =Mass of the floater

- But the force f is the result of incoming and diffracted waves as well as the motion of the body, how to capture that …?

- A simplified approach o Transfer to frequency domain

o We still have the problem that the force F is a result of the waves and the motion of the

body; let us split the dynamics in two cases Pressure variation by incoming and diffracted waves onto the fixed body Moving body in otherwise still water

o The theory used to calculate describes the water is using harmonic functions Incoming and diffracted waves lead to a frequency dependent Fwave(ω) Body motions in still water

o Potential theory is used to calculate A frequency dependent Fwave(ω) : forces by incoming and diffracted waves Frequency dependent added mass A (ω) and damping C (ω) leading to:

o Still one step to go, we want to relate wave forces to wave height:

o In which H is a transfer function depending on frequency and wave direction a and Z the

surface elevation o The result is the 6-dof equation of motion in the frequency domain:

o Assumptions:

Velocity field can be described potentials (no viscosity) Mathematical simplifications (linearization) based on “small” motion amplitudes

and ‘low’ waves

Vertical wave force on a vertical cylinder


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Wave spectrum

Wave diffraction

Heave motion of a vertical cylinder (RAO)


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Hull selection types

- Barge (non-self-propelled, can be HOS) - Ship - Catamaran - Semi-Submersible - Spar - Tension Leg Platform [HOS] - Jack-Up & Self-Installing Platform [HOS] - SWATH: Small Water plane Area Twin Hull

Hull types and water depth

Hull types

- Barge (non-self-propelled, can be HOS) o Transport, launch, exploration &

production Derrick barge

(=kraanschip) Pipe lay barge Accommodation barge


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Derrick lay barge o Advantages

Plentiful and cheap Simple and Strong Shallow draft Cargo capacity Versatility

o Disadvantages Unpowered Need for tugs and anchors Motion behavior Lack of mobility

- Ship

Exploration, Production, construction, pipe lay, surf, survey, servicing & supply,

support o Advantages

Construction costs Many yards / docks Speed Deadweight

o Disadvantages Stability? (Roll) Motion? Hull deflection

- Catamaran

- Crane vessels, decommissioning & installation vessel (construction vessels)


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o Advantages Twin hulls (repeat build) Large deck area Stability Shallow draft

o Disadvantages Not many yards / docks Cross loads in seas Construction costs Motion behavior (roll)

- Semi-submersible

Exploration, production, construction, pipe lay &accommodation

o Advantages Not many yards / docks Cross loads in seas Construction costs Motion behavior (roll)

o Disadvantages Construction costs Minimum operating draft Deadweight capacity Slow transit speed Small water plane area allowing for limited change in weight

- Spar


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Production platform o Advantages

Simple Shape Motion behavior (extremely limited heave) Dry production trees

o Disadvantages Complex Installation VIV’s: vortex induced vibrations Weight sensitivity / stability Restricted topsides

- TLP

Production platform

o Advantages Configurations Suppressed motions Deep water

o Disadvantages Complex Installation Expensive Weight sensitivity / Deadweight capacity No storage capacity

- Jack up & SIP

- Exploration, production, installation & accommodation

o Advantages Stable platform Adjustable elevation Relocation Easy dry-docking

o Disadvantages Limited payload Limited water depth


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Slow transfer Maintenance costs

- SWATH

- Installation vessel

o Advantages Fast: short transit time Motion behavior? Stability?

o Disadvantages Limited payload Sensitive to weight variation Wind moment aspects (sailing)

IPFS: used for heavy lifting CSD: Cutting Suction Dredges

Lecture 12: Design BFOS (Bottom Founded Structures) Classification of offshore structures based on the type of support

- Fixed platform (FP) consists of a jacket or tower (a tall vertical section made of tubular steel

members supported by piles driven into the seabed) with a deck placed on top, providing space for crew quarters, a drilling rig, and production facilities. The fixed platform is economically feasible for installation in water depths up to 450 m.

- Compliant Tower (CT) consists of a narrow, flexible tower and a piled foundation that can support a conventional deck for drilling and production operations. Unlike the fixed platform, the compliant tower withstands large lateral forces by sustaining significant lateral deflections, and is normally used in water depths between 1,000 and 2,000 feet (300 m - 600m).

- SPAR, Anchored semi-sub, FPSO, Subsea systems


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Classification of offshore structures

- Function - Degree of permanency - Material - Type of foundation - Load carrying mechanism

- Fixed bottom founded platform

- Temporary structures


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- Jack up (drilling)

o Installation

Types of fixed support structures

- In order of increasing complexity o Free standing conductor/monotower

o Guyed free standing conductor


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o Braced conductor tower

- Concrete GBS

- 3-leg steel jacket

- 4-leg steel towers: shearwater

- Self-installing jackup platform


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Classification of support structures - By load carrying mechanism

o CT: Compliant Tower o FS: fixed bottom founded platform

Focus on Bottom Founded Structures

- Fixed to seabed - Permanent or temporary - Compliant or stiff - Steel structures

Steel platform structure

- Jacket

o Jacket is fixed structure with leg piles and axial force transfer from the structure and topsides into the piles at the top of the structure. The jacket provides support for the foundation piles, conductors, risers, and other appurtenances.

- Jacket-pile foundation


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o Main pile connection above water-level

- Tower structure o A tower is a fixed structure supported by foundation

arrangements at the base. A tower foundation usually includes cluster piles which are inserted through and connected to sleeves around the legs at the base of the structure

- Tower pile sleeve

Design process – BFOS

Models and modelling

- Hence, we need o A model of the structure (topsides, substructure and foundation) to determine the

behavior under loading and estimate the resistance o Models for the loads (dead load, environmental, etc.) o A model to check the load versus resistance.

- Note : The industry uses computer programs (e.g. SACS, SESAM, Ansys, USFOS, etc.) for the design and analysis of offshore structures


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Structural interaction - Interaction: topsides substructure foundation

- Hydrodynamic loads non-linear w/ wave height - Soil-pile interaction distinctly non-linear - Substructure linear elastic

Introduction to topside design

- Design topsides o Two functions

Space and load carrying capacity for all functions and services (above water) Structural support for equipment, wells, risers, etc.

o Different configurations (e.g. integrated deck versus modular construction) o It is a multi-discipline undertaking, hence the structural engineer will interface with

many specialists: Petroleum Metocean Drilling (equipment) Process, mechanical & piping Electrical and instrumentation Pipeline Safety Materials & corrosion Drilling / production / operations

o Shallow water offshore platform complex – topsides are often separated by functionality

At deeper water locations there may be only one support structure with modular deck or integrated topsides

o Elevation above still water level


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Design of the support structure

- The support structure dimensions are determined by: o Dimensions (and lay out) of topside o Water depth o Base dimensions of structure (foundation requirements) o Elevation of top horizontal bracing / air gap

- Additional aspects are: o Number & position of the legs o Number & position of piles o Number & position of well conductors, and o Number & position of appurtenances (risers, caissons) o Fabrication & installation requirements

- Based on the above we can design a fixed steel structure: the 3D Space Frame - Brace patterns

Initial sizing of jacket members

- Diagonals : o Assume KL/R = 80 and K=0.8 for partially fixed ends. o R=SQRT (I/A). o For thin walled tubulars I=(πD3t/8) and A=πDt. o Hence, Ddiagonals =0.03L o Further assume D/t=40

- Horizontals : o Based on practical experience the horizontals may be more slender than the diagonals.


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o Assume KL/R = 100. Hence Dhorizontals =0.023L o Further assume D/t=40

- Legs : o The leg diameter is determined by the pile diameter and assume D/t = 60 in view of

lower stress levels, but with minimum of t=0.5 inch. - Note : It is normal practice to use standard API sizes for tubulars.

Loads on Bottom Founded Structures

- Internal loads: o Mass: topsides, substructure

- All external loads are environmental: o Air: wind o Sea: waves, currents o Seafloor: soil-structure interaction

- Loading types: o Static: - e.g. weights, water pressure o Dynamic and stochastic: - e.g. waves

Design loads on an offshore structure

- Permanent loads o Mass - topsides weight, support structure weight, anodes o Water pressure – buoyancy, hydrostatic pressure

- Variable loads o Mass – temporary structures/equipment, personnel, supplies o Operations – crane loads, drilling loads, ballast loads

- Environmental loads o Air - Wind o Hydrodynamic loads - Waves and Current o Marine growth

- Repetitive loads: fatigue - Accidental loads

o Collisions, fire, explosions, accidental flooding o Earthquakes (actually also an environmental load)

Loads (actions) by currents and waves

Wave loading – Morison equation


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Selection of wave theory

Wave loading (action)

- Hydrodynamic loads at a particular point - Combine Morison with wave theory (e.g. periodic airy waves & vertical circular cylinder) - Wave theory v and v. as a function of place and time

o Cylinder dimensions ‘obstacle’ o Morison local drag and inertia loads

- Question: Which of the two terms in the Morison equation is often dominant – drag term or inertia term?

- Airy (deepwater) wave

Calculation of hydrodynamic loads

- For hydrodynamic load calculation use Morison equation and the hydrodynamic model of the

structure to calculate drag and inertial loads. - Select appropriate wave theory to calculate water particle kinematics - Add current velocity profile and wave particle velocity profile for drag load calculation. - Note that drag and inertia loading are out of phase - For extreme wave load conditions for steel jackets and towers, the hydrodynamic drag loading

term is often much larger than inertial load.


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Support reactions of a tower frame

- When the external loads (actions) are known we can calculate the jacket foundation reactions and estimate the forces in the jacket members. Using some gross simplifications allows us to make an estimate as follows.

- Based on symmetry, the horizontal reactions are equal. - Consider the overturning moment around mudline support points left and

right and the vertical force equilibrium gives the vertical reactions. Sectional forces over a substructure

- Next step: o Transfer the external actions (global) to internal forces (local) in the

substructure frame - To obtain internal forces:

o Global loading is actually a distributed set of actions and is better represented by a series of point loads at the framing levels.

o Determine sectional loading in cross sections over the height of the frame/consider force and moment equilibrium at the cross section

o The internal forces follow from: Vertical: Topsides and support structure loads Horizontal: Hydrodynamic and wind loads

o Superimpose separate load cases to arrive at total internal forces in all elements Limit state design (LSD)

- ISO Standards in 19900 series have adopted the Limit State Format. - A limit state is a condition of a structure beyond which it no longer fulfils the relevant design

criteria: load versus resistance - Ultimate Limit State (ULS) safety related

o Limit state that corresponds to the maximum load-carrying capacity - Serviceability Limit State (SLS) operations related

o Limit state corresponding to the structural ability to perform daily use - Fatigue Limit State (FLS) safety or operations related

o Limit state corresponding to cumulative damage from repeated loading - Accidental Limit State (ALS) acceptable damage

o Limit state that corresponds to structural integrity due to an accident Substructure design – governing load conditions


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Design of the support structure - But, there is much more....

o So far we mainly looked at the in place conditions for extreme storm. Other in place conditions include operating, accidental loads (e.g. ship impact), fatigue limit state, or corrosion

o However we must also consider conditions during construction: Stages of fabrication Load out Transportation Launch or lift Upending Unpiled stability Piling

Cost savings - Reduction of

o Wave & current loading o Jacket steel weight o Pile weight o Jacket anode weight o Installation time o Etc.

Questions you may ask yourselves regarding design of BFOS

- What is the difference between a jacket and a tower type offshore support structure? o We looked at the loads in a steel frame and compared the leg loads.

- Are the foundation loads at seabed different when comparing a tower and a jacket? - Are the loads in the diagonal braces the same when comparing a tower and jacket? - How do we determine the deck elevation for a BFOS? - Why must the deck level be above wave crest level and what could happen to the platform if the

deck is too low? - What will be the deck elevation for given waterdepth, wave height, subsidence, etc.? - Why is a structural bracing frame of a steel jacket/tower configured of triangles? - What are the load carrying mechanisms for dynamic and static loads on a BFOS? - What are important factors for calculating the hydrodynamic loads on a steel offshore

jacket/tower? - Which limit states are considered for the design of a BFOS? - What is the difference between LRFD and WSD approach?

Fixed structure only in shallow waters

- Less materials less expensive - Less privy to currents

Jacket - The piles are driven through the legs and connection leg-pile is on top

o Load carry: legs piles Tower

- The piles go through the pile-sleeves at the bottom - Load carry


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o Legs bottom sleeves bottom piles Tower pile sleeve

- Yellow easy to find in dark water, good entrance (funnel) Reason top site never gets wet

- Forces get larger otherwise - Everybody lives and works on top site

Only formula you have to know is the Morrissey equation Tow of Malampaya

- No crane needed - Lower it between legs and set it down - Need a high carrying-thing

Learn: installation methods Shims: to connect outside diameter of the pile & inside diameter of the leg See ‘questions’ of this presentation

Lecture 13: Introduction to fabrication installation and

decommissioning Lifecycle

Fabric yard general view

- Stages of Fabrication include o Contracting o Technical preps (fabrication drawings, shop drawings, procedures) o Procurement of steel and materials o Logistics o Preparatory work in the yard o Construction of sub-assemblies and final structure o Painting and coating o Preparations for load out and tow o Handover of structure to tow master/installation contractor o HSEQ is of the utmost importance for all the activities

General view of roll-up of jacket ‘bent’

- Note the synchronized movement of cranes in the roll-up operation is essential for a smooth operation/to avoid crane overload


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Stages of roll-up operations - Bent being lifted from horizontal position

- Bent lifted towards vertical plane

Substructure ready for load out

- Load out o Load out is the operation of transferring offshore jackets, topsides and modules from

the fabrication site onto transport barge, for subsequent delivery to the installation site o Load outs may be executed by crane lift, skidding, rolling by wheeled or tracked vehicle,

or a combination of methods o Selection of load out method depends on physical structural characteristics, tow

arrangement, installation procedure at offshore site, facilities and equipment available in the fabrication yard, and tidal conditions

o The process must be thoroughly engineered for smooth (safe) operation Fabrication yard general view – load in progress

- Jacket load-out (in the fore-ground), cranes and flat-top barges

Jacket load out – reaction forces

- As jacket is progressively skidded onto the barge, different reaction forces will be imposed on the jacket due to differential elevation of the barge and other supports

- The correct sequence of ballasting and de-ballasting of the barge as the jacket is progressively transferred onto the barge is essential


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Crane lift – load out of deck

- Crane barge movement after lifting deck from yard

Module load out using wheeled trailers

Steel tower structure – tow to offshore site

Safety during tow

- Factors to be considered include the following, o A safe tow route must be selected ensuring sufficient water depth, shelter for storms

(cyclones), etc. o Primary damage or loss modes for the tow that must be addressed may including

Breakage of tow lines Stability loss (avoid capsize for anticipated wind, waves and currents) Structural strength (of seafasts, etc.) Fatigue damage

o The action of the waves on the cargo (jacket, deck) should be avoided Forces to be considered for transportation

Installation methods

- Lift (for support structures and topsides) - Launch and upend (for support structures) - Float-over (for topsides) - Self-float and lower (for support structures


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and complete platforms) - Self-floating and mooring (for floating structures)

Offshore lifting

- Crane vessels - SSCV up to 14,000mt capacity - Monohull up to 5,000mt capacity - Sheerleg up to 4,100mt capacity - Lift vessel station keeping - Traditional mooring (anchors; piles; weight,..) - Dynamic Positioning (DP)

SSCV: Semi-Submersible Cane Vessel

Lift considerations

- Everything will be engineered and prepared to ensure safe operation taking the following into account

o HSE o Balance and equilibrium (CoG underneath the hook) o Crane lift capacity at radius viz structure weight (incl. dynamic effects) o Hook height o Lifting lugs o Rigging

Rigging design (lift height, sling angle, shackles, spreader bars, etc.) o Clearances (boom clearance, vessel clearance, etc.) o Strength of all components (including, structural members, shackles, slings) o For final positioning

Hook motion envelope (especially heave) Guides, bumpers and stabbing cones (primary & secondary) Tugger/Control lines

- Weather during the lift operation Tandem lift of jacket

Launch barge

- Installation method for large jackets


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o Jacket slides off a barge (normally longitudinally) o Largest jacket is Bullwinkle jacket launched from H-851 o Note the rocker arms. These are needed to spread the load on the jacket and for

smooth final trajectory of the jacket as it “dives” into the water. - Jacket launching sequence from barge

- Upending

Pile

- Installation

o Skirt pile with free-riding underwater hammer


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- Connections o Jacket:

Welding shims Welding crown plate Grouting complete annulus

o Tower:

Grouting annulus Hydralok

What is decommissioning?

- To plan, gain approval for and implement the removal, disposal or re-use of an offshore installation.

- 6 project phases: o Develop, assess and select options o Obtain approvals and permits o Detailed planning and engineering o Stop production, plug wells and clean facilities o Removal of structure (wholly or partially) o Disposal and/or recycling of removed parts

- (Decommissioning is preferred terminology, but is sometimes also referred to as: abandonment or removal)

Questions

- What are the main stages during construction? - What are the important considerations for lifting? - What are the forces in the lifting sling, where do maximum bending moments occur? - Which installation methods are often used for offshore platforms

o i) for bottom founded support structures, o ii) for topsides?

- What are important considerations for tow transport? - Describe launch operations for a jacket structure? - What is the main purpose of the rocker arms on a launch barge

Lecture 14: Design of Drill Ships The purpose

- Exploration drilling - Production drilling - Well testing - Completions


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Main components

- Drilling

Design considerations

- General lay out o Vessel and drilling

- Payload

o Drilling Marine drilling riser Telescopic joint BOP Drill pipes, drill collars, casing, etc. Mud Brine Base oil Bulk in silos Bulk in sacks Drill water

o Vessel Marine diesel oil Fresh water People Supplies

- Stability o IMU MODU code (for damage stability no

probabilistic analysis is required)

o GME and roll motions


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The natural roll period of the vessel has to be beyond (longer) typical wave periods in operating area

The natural roll period can be estimated using the following formula

Ixx – is roll inertia and it can be calculated assuming the roll radius of

inertia equal to 0.4 ship’s breath

m44 – is added mass for roll inertia. Value of m44 depends on number of parameters including the hull geometry, natural roll period, etc. As a rough assumption it can be taken as 25% of Ixx

- DP3 o Position will be maintaining in case of any single

component failure including flooding or fire of any single compartment

o Environmental conditions Wind Current Waves Choice of

Number and power of gensets

Number and power of thrusters and their allocation

Power connectivity and switch board rooms - Here the design cycle starts

o Drilling equipment o Payload o Endurance (fuel, fresh water, etc.) o Number of persons on board o Ship speed o + ship own weight

Required buoyancy

Length – layouts

Breadth – stability

Depth/draft – freeboard

Block coefficient – ship speed Development of Huisman Drill Ship

- Vessel and drilling equipment - Integrated design

o Drilling equipment - green o Vessel design - blue o Optimized integrated design

- Typical drill ship o Engine room in aft end o Risers on main deck o BOP on main deck o Drill floor above BOP


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- Step 1 o Derrick replaced by MPT

- Step 2 o Substructure with large hatch o BOP lowered through hatch o MPT placed lower

Lower COG Easier & safer handling

o Significant increased capacity and payload with smaller displacement

- Step 3 o Engine room to front of vessel o Exhaust above accommodation

Because of low drill floor no problems with exhaust gasses

No funnel obstruction aft deck - Step 4

o Space in aft end vessel o Risers in hold below main deck

Lower CoG Large clear aft deck

- Model tests at TU Delft o Sea keeping tests o Resistance o Moonpool studies

- Model tests at Marin o Sea keeping tests o Free floating DP

- Comparison o Huisdrill

Displacement 54000 mt GM (fully loaded) = 2m GM (unloaded) = 2m VDL: 20000 mt Wind area 3250 m² Drill floor above water: 12 m Thruster power: 6 x 3.7 MW

o Typical drill ship Displacement 100000 mt GM (fully loaded) = 3.5 m GM (unloaded) = 4.5m VDL: 20000 mt Wind area: 6600 m² Drill floor above water: 26 m Thruster power: 6 x 5.5 MW

- Dual Multi-Purpose Tower o Features


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2 hoists: drilling & heavy offline activities Machinery in tower

o Top drive park system Offline indoor maintenance Tripping without top drive Safety, efficiency

o Heave compensation Active heave compensation

Measuring vessel heave and counteract with winches

Precise landing Passive heave compensation

Soft spring

Utilized for well testing

Standby during AHC o Vertical pipe handling

Main hoist: drilling Auxiliary hoist: offline stand building 135 ft stands (3 x 45 ft or 4 x 30 ft) 34000 ft drill pipe & 20000 ft casing

- The principle o

o Handling of large objects

No V-door limitation Hoistable floor

- Drill floors o Spacious drill floors, only 5m above main deck

- Tower top removal o Tower head section removable

Allowing sailing through Panama canal, Suez canal & Bosporus - Aft deck

o Transport cart o Gantry crane

Can travel up to the DMPT - Subsea winch

o Subsea installation winch SWL 75 mt at 3000 winch


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Active heave compensation - Building method – demarcation

o Huisman delivery o Yard delivery

- Smaller vessel o Lower CAPEX/OPEX

- Offline activities o Increased efficiency

- Enhanced logistics o Increased efficiency and safety

- System redundancy o Increased up-time and safety

Lecture 16: Offshore Wind Energy Two parent industries

- Onshore o Loading

+ hydrodynamic o Foundation considerations o Maintenance

- Offshore o Loading

+ (dynamic) wind + rotor harmonics

o Single structure vs serial production o Optimization gains

Most important oil&gas on on-&offshore

- Loading - Optimization

o Gain is huge

Why Offshore wind? - Onshore

o Land is increasingly occupied o Resistance against visual pollution is growing o Wind turbines are getting larger

Requires more space Visible from greater distance

- Offshore o No obstacles more & steadier wind o Space o But: remote & tougher conditions

Offshore wind farms

- Primary function o Convert wind power offshore into electric power onshore


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- Main challenge o Reducing the cost per kWh

- Main area of development: NW Europe (shallow seas & favorable wind conditions) - Fast growing industry sector - Lack of trained engineers

Political background

- Need for independent sources of sustainable energy - NL government targets 2020

o 16% sustainable energy in 2020 o 6000 MW offshore wind 2020

- EWEA European target 2020: o 40 GW from offshore wind

History

- Persian deserts - Windmills - Power from wind 1888

o Brushmill o 12 kW o Auto control

- Poul la Cour (Denmark) 1891 o Step forward

Aerodynamics o Tests in wind tunnel o Produced hydrogen

- MW size, 1941, Vermont o 1.25 MW o Largest wind turbine ever built until 1979 o Steel blades o Fatigue of blade

Only 1100 hours operational - Gedser: test turbine in Denmark

o 1957 o By J.Juul o 200 kW o 24 m rotor diameter o ‘The Danish Concept’

Domination of the market well into the 1980’s - 70’s-80’s: NASA program

o Boeing o General Electric o Purpose: develop technology and support emerging market o Largely unsuccessful o Light pretty shafts/turbines o Variables generated o After time energy prices reduced by 3

- Offshore idea’s 1970-80


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o Heerema o RSV o Boskalis o Fugro o Studying offshore wind

- Offshore: detailed plans o Copy offshore structures o Adapted to be produced in large numbers o Conclusion: bigger turbines needed

- Nogersund o Installed 1990 o Decommissioned 1996 o 1 wind world 220 kW turbine o Rotor diameter 25 m o Water depth 6 m o Distance to shore 250 m o Test facility to study influence of offshore wind turbines on:

Birds Fish and fishing Shipping Public opinion Operation & maintenance

- Vindeby o Installed 1991 o 11 bonus 450 kW turbines o Rotor diameter 35 m o Max. water depth 5 m o Distance to shore 2.5 m o Total power 5.0 MW o Gravity- based foundations

- Lely o Installed 1994 o 4 NedWind 500 kW turbines o Rotor diameter 37 m o Max. water depth 10 m o Distance to shore 750 m o Total power 2 MW o 2-bladed turbines o First driven monopiles

- Tuno Knob o Installed 1995 o 10 Vestas V39 500 kW turbines o Rotor diameter 39 m o Max. water depth 4 m o Distance to shore 6 km o Total power 5 MW o Gravity-based foundation

- Bockstigen


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o Installed 1998 o 5 WindWorld 500 kW turbines o Rotor diameter 37 m o Max.water depth 8 m o Distance to shore 3 km o Total power 2.5 MW o Monopile foundations

- Blyth o Installed 2000 o 2 Vestas V80 2.0 MW turbines o Rotor diameter 80 m o Max. water depth 6 m o Distance to shore 1 km o Total power 4 MW o Drilled monopile foundations

- Middelgrunden o Installed 2001 o 20 bonus 2.0 MW turbines o Rotor diameter 72 m o Max. water depth 10 m o Distance to shore 2 km o Total power 40 MW o Gravity-based foundations o Public involvement/investment o First windpark with public involvement

Buy shares o Also in Holland (windcentrale)

- Yttre Stengrund o Installed 2002 o 5 NEG-micon 2 MW turbines o Rotor diameter 72 m o Max. water depth 12 m o Distance to shore 4 km o Total 10 MW o Monopile foundations

- Horns Rev o Installed 2002 o 80 Vestas 2.0 MW turbines o Rotor diameter 80 m o Max.water depth 14 m o Distance to shore 14 km o Total power 160 MW o First large offshore wind farm o Driven monopile foundations o Helicopter acces o Problems with gearboxes (80)

Couldn’t handle seawater - Samso


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o Installed 2003 o 10 bonus 2.3 MW turbines o Rotor diameter 82 m o Water depth 18 m o Distance to shore 2.5 km o Total power 23 MW o Gravity- based foundations

- Nysted o Installed 2003 o 72 bonus 2.3 MW turbines o Rotor diameter 82 m o Water depth 9 m o Distance to shore 10 km o Total power 165.6 MW o Gravity based foundations

- Arklow Bank o Installed 2004 o 7 GE 3.6 MW turbines o Rotor diameter 104 m o Water depth 15 m o Distance to shore 10 km o Total Power 25.2 MW o Monopiles

- North Hoyle o Installed 2005 o 30 Vestas 3.0 MW turbine o Rotor diameter 90 m o Water depth 5 m o Distance to shore 8.5 km o Total Power 90 MW o Monopile foundations

- Scroby Sands o Installed 2005 o 30 Vestas 2.0 MW turbines o Rotor diameter 80 m o Water depth 10 m o Distance to shore 3 km o Total Power 60 MW o Monopile foundations

- Kentish Flats o Installed 2005 o 30 Vestas 3.0 MW turbines o Rotor diameter 90 m o Water depth 5 m o Distance to shore 8.5 km o Total Power 90 MW o Monopile foundations

- Egmond aan zee


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o Installed 2005 o 36 Vestas 3.0 MW turbines o Rotor diameter 90 m o Water depth 23 m o Distance to shore 10 km o Total Power 108 MW o First Dutch offshore wind farm o Monopile foundations o The heads started settling in the

2 filled all the monopoles with concrete - Beatrice

o Installed 2007 o 2 REpower 5.0 MW turbines o Rotor diameter 126 m o Water depth 45 m o Distance to shore 25 km o Total Power 10 MW o Jacket structure o Most expensive so far o Delayed by 1 year

- Princess Amalia (Q7) o Installed 2008 o 60 Vestas 2.0 MW turbines o Rotor diameter 80 m o Water depth 25 m o Distance to shore 23 km o Total Power 120 MW o Deepest monopile foundations when constructed

- Thornton bank o Installed 2008 o 6 Repower 5.0 MW turbines o Rotor diameter 126 m o Water depth 30 m o Distance to shore 30 km o Total Power 30 MW o Deepest gravity-based foundations o OWF to be built in 3 phases

- Alpha Ventus o Installed 2009/2010 o 6 Repower 5M turbines o 6 Areva Multibrid M5000 turbines o Rotor diameter 126 m o Water depth 20 m o Distance to shore 45 km o Total Power 60 MW o Demonstration project o Tripod & jacket foundations o Extensively used for research (RAVE)


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- Hywind o Installed 2009 o Floating o 2.3MW Siemens turbine o Test project o Water depth: 100m o Distance to shore: 10km

- London Array o Fully operational April 2013 o 175 3.6 MW Siemens turbines o Area: 100 km2 o Maximum water depth: 23 m o Distance to shore: 20 kW o World’s largest offshore wind farm o First with about the same size as a large coal or nuclear plant

Danish concept - Simple turbine - 3 blades - Horizontal axis

Key statistics by the end of 2013

- 2080 Offshore Wind Turbines installed and grid connected - Totaling 6562 MW - 69 Wind Farms - 11 European countries - Average offshore wind turbine size is 4 MW

o Siemens 3.6 MW cape - 2 Full-scale grid connected floating turbines

Trends in the Industry

- Installed in deeper water - Larger turbines - Larger wind farms

Offshore wind farm components

- Wind turbine - Support structure

- o Monopile o Gravity-based o Jacket


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o Tripod o Floating?

- MET mast o Placed 2-3 years before OWF o Map environmental conditions

Wind Waves Current

o Use for detailed design - Electrical infrastructure

o Infield transmission cables o Substation o Shore connection cables o Onshore substation/tie-in

Support structures and installation

- Support structure types o Monopiles o Gravity-based o Jackets o Tripods o Tripiles o Floating

Definitions

- Hub height: o Elevation of hub above sea level

- Interface level: o Elevation of bottom tower flange above sea level

- Support structure o Entire structure holding RNA in place

- Tower o Tubular structure spanning distance between

interface and RNA - Substructure

o Part of the structure spanning distance between interface level and seabed

- Foundation o Part of structure in direct contact with soil

Design objectives – support structure

- Survival - Extreme loads - Cyclic loads - Operation - Deformations - Accelerations

o Make sure the sensitive mechanisms (e.g. sensors) aren’t affected by the accelerations


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- Optimization for cost reduction - Secondary aspects - Export of energy - Access and repair

Sources of excitation : wind

- 1P = rotational frequency of rotor - 3P = blade passing frequency - Stiff – stiff: a lot of steel expensive - Soft – soft: a lot of movement - Ideal: get it in soft-stiff region

o Very difficult (only ½ Hz) o Adjust controller to not go in certain in

frequencies (because of resonance) Damping only in direction where the wind blows Sources of excitation: waves

- Generic wave spectra o Pierson-Moskowitz

Fully developed sea state o JONSWAP (JOint North Sea WAve Project)

Fetch limited situations

Other harmonic sources - Mass imbalance rotor - Tower shadow

o Region around your tower where the velocity is reduced

- Yaw misalignment o Router is not facing the wind

- Aerodynamic imbalances due to o Wind shear

Damping only in direction where the wind blows

o Blade pitch errors Transformation to loads

- Morison

o Waves o Currents o Wind BEM

Dynamic interactions

- Aerodynamic damping induced by operating rotor - Hydrodynamic forces and structural response


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- Soil and structure - Interactions between dynamics of different OWEC - Components

Monopile support structure:

- Components o Foundation pile o Transition piece o Tower

- Installation o Seabed preparation / scour protection installation o Drilling or driving of pile o Transition piece options... o Tower sections bolted

- Foundation pile o Dpile ~ 4.0 - 6.5 m o t ~ 45 – 110 mm o D/t ~ 80 – 90

- Transition piece o Grouted joints – settlements... o Conical grouted joints with shear keys o New concepts:

Hammering on flange Slip joint

o Inclination correction? o Secondary steel?

Gravity based

- Support structures o Self-weight of gravity base to resist overturning moment/slip o Extra ballast needed offshore (buoyancy forces)

- Fabrication o Constructed (hollow) on land - crane lifting

capacity - Transportation and installation


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- Ballast and scour protection

Multimember structures

- Jacket - Tripod - Tripile

Why multi-member systems

- Deeper waters, larger turbines o 𝐿 and 𝑚𝑡𝑜𝑝 increase o Natural frequency decreases

- For same environmental loading, we require:

o Increase in EI, without significantly increasing 𝜇 (mass) of support structure per unit length)

o Place material as far away from the neutral line as possible - Large diameter piles

OR - Multi-member structures

Monopiles

- Becomes more impractical and less economic - Solutions required with higher stiffness for equal mass - Multi-member structures - Monopile is the most ideal because it doesn’t have complicated joints but the needed diameter

is becoming impractical Jackets

- Definitions - Disadvantages

o Fabrication and welding of many geometrically complex joints

Expensive o Weld details susceptible to higher

stress concentrations/fatigue Extra material requirements

o Step down in width necessitates provision of substantial transition section Heavy!

o Piles needed to attach jacket to seabed - Transport - Lifting & landing

Tripod

- Definitions - Fabrication & installation - Load out - Transport of tripod


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foundations o Towed on a barge

- Lifting and landing - Pile driving - Turbine installation

o Crane - Jacket load out - Not that optimal

o Still heavy o Install foundations piles to connect it to the sea bed

Tripile

- Higher lever arms... - Developed by BARD (1st installation 2008) - 3 grouted transition pieces - Weight comparable to that of Alpha Ventus jacket (similar water

depths) - Only used once on a project

Concept selection

- Consider: o Structural design (strength and fatigue) o Fabrication (onshore) o Transportation to offshore site o Installation in-situ

- Keep operation & maintenance firmly in mind Support structure optimization

- Computer-aided (vs manual) optimization widely used in automotive and aerospace industry, but not for the design of offshore wind turbine structures

o Why? o Large number of parameters o Complexity of working with many engineering disciplines, often using different

assumptions o Uncertainty about soil conditions o Simplified models required (large number of load cases) o Etc.

CapEx

- Capital expenditure - Shows that wind turbines become more and more expensive

Piles second: postpile


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Documents

Summary Introduction to Offshore Engineering Oe4606 Complete Lecture 1 16