FPSO DESIGN- AN INTRODUCTION

Kamal K. Ravi

Engineering Projects& System Manager PTSC M&C

Introduction to Floating Production Systems

Chapter 1

Floating Production Systems

• Classified as:

Semi-submersible and tension leg platforms

- Little or no storage capacity

Spars

- Limited storage capacities

FPSO – primarily mono-hull vessel

Typical View of an FPSO

Water Depth and Sea States • Water depths

Shallow

-Less than 50m

Moderate

-Down to 300m

Deep

-Down to 1500m

Ultra Deep

-Beyond 1500m

• Sea states

Benign

-Hs 0 to 4.0m

Medium

-Hs 4.0 to 9.0m

Severe

-Hs 9.0 to 14.0m+

Hs=significant wave

height

FPS Application Chart

History of the FPSO

• 1977 First FPSO- Castellon Field

Offshore Spain

Mooring –SALM

Water dept 117m

• During 1980s

Moderate depths

Benign waters

Cost effective solution

- For marginal fields

Proven safety record

History of the FPSO

• During 1990s

- Deeper waters

- Rougher seas

- Black oil reservoirs

• Early 21st Century

-Ultra deep waters

-Large numbers of risers

-Very high throughputs

-Storage – VLCC Class

-Newly built vessels

-Handle gas liquids

The Pros and Cons

• Advantages

- Utilises existing ships

- Faster development

- Reduced upfront costs

- Early cash flow

- Re-usable

- Higher residual value

- Lower abandonment costs

• Disadvantages

- No drilling

- Subsea wells only

- Rushed design can lead to mistake

- Weather dependency

- Production

- Offtake

What is an FPSO?

• F = Floating – it looks like a ship – but is it?

• P = Production - Produces and processes a reservoir fluid

• S = Storage – Vessel’s cargo tanks store product crude

• O = offtake – Crude is offloaded to shuttle tanker

• That is the Simple Look

Mooring the FPSO

• An FPSO is essentially a ship permanently moored on the open ocean

• Stresses imposed on the hull need to be minimised

• Ship has to survive for life of project

• Weathervaning is a natural effect which minimises stressess

• Allows ship to align itself with the wind, wave and current

• Turret mooring allows weathervaning

Cargo Handling on FPSO

• An FPSO is a crude oil tanker

• Two issues are critically important

Loading and offloading the cargo

- Creates stresses on hull- have to be minimised

-Achieved by load monitoring and ballast system

Storing the product crude safely

- Cargo tank atmosphere potentially explosive

- Tanks must remain “inerted” at all times

- Achieved by use of inert gas system (IGS)

Production and Processing on FPSO

• Two issues important Sustaining and optimising reservoir productivity - Sustaining reservoir pressure - Optimising reservoir flow - Assurance of flow from reservoir to processign centre Safe, efficient and effective processing - Maximising liquids recovery - Disposal of gas safety and economically - Treatment and disposal of produced water - Efficient use of chemicals to aid both production and

processing

FPSO Design Issues

• Main Technical Questions

Selection of the mooring system

- Predominantly turret mooring, but spread mooring and yoke mooring also used

Location of the accommodation block

- Conventionally at aft end of ship

- New build vessels may have forward accommodation

Process plant layout, based on safety and operability

Turret Mooring System

• Mooring turret is unique FPSO feature

• Serves three purposes:

Anchors vessel at geo-stationary position

Allows vessel to weathervane

Provides conduit for fluid transfer

- Subsea reservoir infrastructure to

topside processing plant

Turret Designs

Turret designs based on location

- Either external to the hull of the vessel

- Or internally fitted inside the hull

Choice based on:

- Geographical location

* Sea states, strom systems, ice, etc

- Water depth

- Number of fluid transfer risers

External Turret Design

Spread Mooring

Buoy Yoke Mooring

Jacket Soft Yoke Mooring

Jacket Soft Yoke Mooring

Internal Turret Design (Tentech)

Detail of Internal Turret

Large Internal Turret

Disconnectable External Turret

Disconnectable Internal Turret

Location of Accommodation

• Largely influenced by position of turret

• Research shows that turret should be on further aft than 19% of length of vessel

• Achieves optimal operational efficiency

- Maximises weathervaning

- Minimises “pitching” effect

• May exlude choice in placement of accommodation

Accommodation in Aft Location

• Normal solution for ship conversions

• Allows for optimal positioning of turret

• Stern abandonment is safest option

• Crew downwind of fire / smoke / flame

Additional engineering may be needed

- To protect “safe refuge’

- To allow for helicopter operations

- To minimise flare radiation effects

Tantawan Explorer Aft Accommodation

FPSO Firenze – Italy Aft Accommodation

Accommodation in in Forward Location

• Most applicable for new build FPSOs

• Turret is aft of accommodation

• Crew upwind of fire / smoke / flame

• Forward abandonment may be difficult in rough weather

• Motion effects may make living conditions uncomfortable for crew

Accommodation – Forward FPSO Norne

Accommodation – Forward FPSO Asgard A

Number of FPSOs Built

Process Plant Layout

• Layout based on

-Safety

-Operability

• Most hazardous process areas

-Furthest from accommodation (TSR)

• Critical Level control

-Close to midships

Distribution of FPSOs Worldwide (2008)

Recent FPSO Developments (2000-2010)

• West Africa - Serpentina, Mystras, Sanha, Kizomba,AKPO - USAN • Brazil - Espadarte, Brasil • Australasia - Northern Endeavour, Venture 11 • South East Asia - Su Tu Den • Canada - Terra Nova

FPSO Systems

Chapter 2

FPSO Building Blocks

• Main systems for FPSO are:

- Hull type

- Oil storage

- Moorings

- Fluid transfer

- Topsides process plant

- Offtake and export

- Accommodation

Hull Types

• Classic hull type for FPSO:

- Mono-hull, crude carrier classification

- Segregated ballast

- Mono-hull meaning single steel shell

- Double- hull not standard requirement

- Exceptions – GoM, NWS Australia

• Hull can be either:

- Existing carrier- suitable for conversion

- Newly built specifically for FPSO service

Tanker Conversion

Conversion Installing Topsides Modules

New Built Hull

Northern Endeavour New-Build

Moorings

• The moorings for an FPSO can be:

- Spread moorings

- Benign conditions

- Any water depth

- Jacket or tower moorings

- Moderate conditions

- Shallow waters

- Turret moorings

- Any conditions and water depth

The External Turret System

Simple External Turret

Large External Turret

Disconnectable External Turret

Internal Turret System

Internal Turret

Fluid Transfer System

• Function of system: - To connect subsea risers to topsides process plant • Fact - Risers are stationary pipes - Topsides plant is on weathervaning ship • Problem - How to connect the two • Answer - Fluid swivel

Fluid Swivels

• Predominant fluid transfer system is the fluid swivel

• Commonly referred to as the radial swivel joint

• The term toroidal swivel is used to describe shape of fluid pathway

Radial Swivel Joint

Moorings and Fluid Transfer

• Fluid swivels only required for:

- Turret moorings

- Jacket moorings

• Spread moored FPSOs:

- Do not rotate around mooring point

- Do not require swivel joints

Topsides Process Plant

• Processing which occurs on an FPSO:

- Three phase separation of the well fluids

- Gas recompression

- Gas treatment

- Produced water treatment

- Injection water treatment

• Standard black oil processing

- Practiced worldwide

Offtake and Export

• Crude oil export from an FPSO

- Connection to a pipeline

- Direct ship transfer

- Using a surface hose either floating or reeled

- Transfer through a loading buoy

Direct Ship to Ship Offtake

CALM Loading Buoy

Accommodation • Two possible locations - Bow or Stern • Accommodation block contains temporary safe

refuge (TSR) • Layout of topsides plant must be based on: - Survivability of TSR

Greatest risks remote Gas or smoke ingression via HVAC prevented Fire and blast-proofing may need to be upgraded

- Unhindered personnel access to TSR from any point on deck

Cost Estimate Conceptual Design- Large FPSO

Turret and Mooring Systems Design

Chapter 3

Turret Mooring System

• Mooring turret is unique FPSO feature

• Serves three purposes:

- Anchors vessel at geo-stationary position

- Allows vessel to weathervane

- Provides conduit for fluid transfer

Subsea reservoir infrastructure to topside processing plant

Turret Overview

Turret Design

• Three types of turret mooring systems

- External

- Internal

- Submerged

• Each type can be sub-divided into:

- Disconnect type

- Permanent connect type

Disconnectable External Turret

External Turret Permanent Mooring

External Turret – Permanent Moored

Internal Permanently Moored Turret

Internally Permanently Moored Turret

Maersk Curlew FPSO Turret - 1996

Maersk Curlew FPSO

FPSO Anasuria Turret Manifold Decks

Large Diameter Internal Turrets

Small Diameter Turrets

Internal (Submerged) Disconnect Turret

Submerged Turret

Spread Moorings

Bow Anchoring for Spread Mooring

Jacket or Tower Mooring

Tower Mooring

Ship’s Motion

Vessel Motion across the Sea Surface

• Based on the period » Short period motion due to waves

– 6 to 20 second typically

» Longer period due to wind and waves – Can be several minutes

– This is weathervaning

• Mooring forces increase with motion » In other words in rougher the seas the greater are

the mooring forces – More or stronger anchors

Mooring Chain Table

FPSO Mooring Spreads

Process Facilities

Chapter 4

Processing Facilities on a Typical FPSO

• Functional requirements

» Oil /gas separation

» Gas compression and treatment

» Produced water treatment and disposal

» Water injection

» Gas export / re-injection

» Support utilities

» Chemical injection and distribution

Oil /Gas Separation

• First stage HP separation

• Second stage MP separation

• Third stage LP separation

• Electrostatic coalescing

• Well test separation

Oil / Gas Separator with Wave Motion Internals

Overall Topsides Module Layout

Gas Compression & Treatment

• The three compression stages and associated compressors are:

» Flash gas compression K-201

» MP gas compression K-202

» HP gas compression K-203

Water Injection

• Seawater supply

• Vacuum de-aeration

• Chemical injection

• Injection water delivery

Support Utilities

• Fuel gas

• Flare & drainage

• Compressed air system

• Heating medium system

• Cooling medium system

• MP steam

• Seawater system

• Chemical injection system

• Power generation

Utilities Integration Diagram

Chemical Injection System

• Consists of three sub-systems

» Topsides

– For oil / gas & injection water processing & protection

» Hydrate inhibition

– For production & gas processing

» Subsea

– For wellhead & flowline protection

Safety Assessment

• Need to consider

» Layout of equipment

» Consequences of fire / explosion

» Safety venting

» Design of the fire system

» Containment & drainage of process fluids

Alternative Technologies

• Multi-phase flow metering

• Subsea water separation

• Subsea raw water injection

• Multi-phase booster pumping

• Subsea power distribution

An SBM Vessel

Power Generation Module

Utilities (CM+HM) Module

Water Injection Pumps

Water Injection Module

Chemical Injection & Water Injection

Oil / Gas Separation Module

Methanol Storage & Injection

Glycol Regeneration

Flare K.O Drums

End of a Hard Day’s Work

Mess Hall

Gourmet Kitchen

Her Own Power

Marine Systems

Chapter 5

Marine Systems

• Choice of Ship

• Tank Arrangements

• Loading/Offloading System

• Cargo Pumps

• Ballast System

• Stops System

• Inert Gas System

• Vessel/Topsides Interface

Choice of Ship

• Factors affecting the choice of ship are:

» Cost of conversion vs new build

» Field life and redeployment

» Need for additional strengthening

» Cargo tank conditions

• Capacity of cargo storage and offloading

• Condition of machinery

• Propulsion type

• Free area for topsides plant

Vessel Sizes

• Tanker sizes used for FPSO conversion

» VLCC (very large crude carrier)

– 200,000 to 319,000 dwt

» Suezmax

• 120,000 to 200,000 dwt

» Aframax

• 75,000 to 120,000 dwt

FPSO Tank Arrangements

Cargo Offloading Systems

• Floating Hose

• Reeled Hose

• CALM Buoy

• Submerged Hose

Floating Hose Arrangement

FPSO Stern Offloading

Stern Offloading Hose Reel

Reeled Hose Arrangement

CALM Buoy

Submerged Hose System

Submerged Cargo Pumps

Tank Cleaning

• Crude Oil Washing – COW

» Removes wax and sediment build-up

» Carried out during offloading operations

» Uses warmed crude oil

» Following oil washing

– Water washing used prior to tank inspection

– Water washing can generate static charges

– Always done under inert gas blanket

Tank Vapour Recovery

• Today’s environment focus is on:

» Emissions!!

• Cargo tank operations – no exception

• Tank vapour recovery is modern trend

» Don’t vent tank vapour – re-use it!!

• Problem – its “inert” nature

• Answer – don’t use “inert” gas

Tank Blanketing

• Latest development is tank blanketing

» Use a gas that will:

– Exclude air, but be re-usable

» Hydrocarbon gas fills that need

• During loading tank gases

» Recovered for use as fuel

• During offloading separator gas

» Flows into tanks to exclude air