Structural Design Offshore_Lecture 1 Intro

SKG11: Civil, Structural, Pipelines

Structural Design Offshore Lecture 1

Overview of Offshore Structures


Lecture 1 Objective

Overview of the petroleum industry Overview of the petroleum industry

Understanding different types of offshore structuresstructures.

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Lecture Outline

1 0 Overview of the Petroleum industry1.0 Overview of the Petroleum industry

2.0 Offshore Structures

2.1 Fixed Structures

2.2 Floating Structures

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Petroleum Industry: Overview

Export pipeline or

Storage (FSO)Storage (FSO)

Off h l tf Offshore platforms are used for exploitation of oil exploitation of oil & gas.

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Petroleum Industry: Overview

Exploration

Appraisal Is there hydrocarbon?

Production Extent of reservoir, is it connected?

Storage

Platforms, production wells, produceSto age

Transportation In field storage? Storage tanks

Vroommm

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Transportation Vroommm


Oil and Gas Structures- Purposep

Structures in the Petroleum Industry Structures in the Petroleum Industry are industrial structures which must fulfil their intended purpose.fulfil their intended purpose.

The primary function for all structures is to provide support or shelteris to provide support or shelter.

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Oil and Gas Structures- Selection

Functiono Drillingo Productiono Productiono LQ (Living quarters) etc

Environmento Water depthpo Storm / hurricanes etc.o Soil / Seismicity (Earthquake)

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o Soil / Seismicity (Earthquake)


Offshore Structures

Fixed Floating

h fl

Fixed Structures

Floating Structures

Structures that extend to the seabed such as: Jacket

Structures that float near the water surface such as: Jacket

Jack-up GBS (Gravity Base)

TLP (Tension Leg) Semi-submersible G S (G a ty ase)

Compliant tower Spar FPSO

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Offshore Structures

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2 1 Offshore Structures2.1 Offshore Structures(Fixed Structures)(Fixed Structures)

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Offshore Structures- Fixed Platforms

Platform size Platform size depends on its function:

Drilling

Living quarters Living quarters

Processing

Flare or vent

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Offshore Structures- Fixed Platforms

Load TransferLoad Transfer

1.Topsides

MSL2. Jacket

Seabed / Mudline

3.3.FoundationFoundation-- PilesPiles

12-- SoilSoil


Lightweight Structures

upto 12 conductors max (limited by drilling envelope) upto 70 m waterdepth range (dynamics govern)

ll 0 d k l f h13

normally 450 Mt topsides or jacket lift weight, max


Jack-up

Topsides sits on a hull (barge) and hull (barge) and able to move from location to location

ithi th within the same operating envelope

Employ jacking Employ jacking system to move up or lower the hull

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Jack-up

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Self Installed Structures

TURKMENISTAN MOPU

HANG TUAH ACE PLATFORM

MOAB

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MOAB


GBS (Gravity Based Structure)

Shallow foundation Remains in place on

seabed because of self eight o ia s ctionweight or via suction.

Installation via ballasting the base the base

Topsides installation normally via floatover normally via floatover method

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Compliant Tower

Narrow flexible framed structure supported by piled foundation.

W t d th t 900 Water depths up to 900 m. Undergoes large lateral

deflections under wave deflections under wave loading.

Natural period is kept above Natural period is kept above wave period to reduce dynamic amplification.

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Freestanding Compliant Tower- Fundamental CharacteristicsFundamental Characteristics

Natural period longer than waves30 f G lf f M i t Fi d ~30 sec for Gulf of Mexico towers vs Fixed

platforms (3 to


Guyed Tower Platform

E "L " 1 000' 198320

Exxon "Lena", 1,000', 1983


2 2 Offshore Structures2.2 Offshore Structures(Floating Structures)(Floating Structures)

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TLP (Tension Leg Platform)

Floater that is tied down tothe seabed by vertical steelthe seabed by vertical steeltubes called tethers.

Very rigid vertically andhelps to tie in productionwells.

Flexible in the horizontal Flexible in the horizontalplane, thereby insensitiveto the primary effect ofwave forces.

Has large columns andpontoons Fairly deep draft

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pontoons. Fairly deep draft.


Semi-submersible

Held in place by anchors connected to catenary connected to catenary mooring system.

Column-pontoon junctions p jand bracings attract large loads.P i di i ti d Periodic inspection and maintenance is a prerequisite due to possibility of fatigue cracking of braces.

Limited application as dry trees due to high motion

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trees due to high motion responses.


Spar

Large diameter deep draftcylindrical floating caissoncylindrical floating caissonanchored to seafloor withmultiple taut mooring lines.supporting deck.

Heave natural period isabout 30 sabout 30 s.

Centre of buoyancy isconsiderably above centreof gravity, making it quitestable.

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Floating, Production, Storage and Offloading (FPSO) g ( )

Ship-shaped structures with several different mooring systems e.g. Single Point Mooring Single Point Mooring (SPM).

Integral oil storage capability

Suitable for deepwater where fixed platform is where fixed platform is not feasible.

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End ofEnd of

Structural Design Offshore Lecture 1

Overview of Offshore Structures

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Documents

Structural Design Offshore_Lecture 1 Intro