talentissimo 2012 green gas

TALENTISSIMO 2012

GREEN GAS PROJECT

Notice

The following case study is fictitious. All names and geographical descriptions are pure fiction

and all similitude with existing locations is unintentional.

The economical data included in this document and the equipment size shall not be considered

for any other purpose different than the context of this challenge. In all industrial projects, the

technical and economical data shall be evaluated in accordance with the specificities of the

studied case and the present economical conditions. Saipem declines all responsibility in case

of use of the following information in other context than the Talentissimo challenge.

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Table of contents

1. Introduction............................................................................................................................................ 4 2. Study scope of work............................................................................................................................... 5

2.1. Technology selection ..................................................................................................................... 6 2.1.1. Screening of possible solutions.............................................................................................. 6 2.1.2. Recommended solution.......................................................................................................... 6

2.2. Study of the selected solution ........................................................................................................ 7 2.2.1. Safety ..................................................................................................................................... 7 2.2.2. Design .................................................................................................................................... 7 2.2.3. Procurement, Construction, Installation, Start-up.................................................................. 8 2.2.4. Schedule................................................................................................................................. 8 2.2.5. Operations .............................................................................................................................. 8 2.2.6. Cost estimation and financial analysis................................................................................... 9

3. Design Basis........................................................................................................................................... 9 3.1. Geographical data .......................................................................................................................... 9 3.2. Meteorological data ..................................................................................................................... 10 3.3. Offshore soil data......................................................................................................................... 10 3.4. Process and fluid data .................................................................................................................. 10

4. Technical studies.................................................................................................................................. 11 4.1. General literature ......................................................................................................................... 11

4.1.1. Energy storage ..................................................................................................................... 11 4.1.2. Electrical system .................................................................................................................. 11

4.2. Subsea separation station design.................................................................................................. 12 4.3. Compressor and pumps design .................................................................................................... 12 4.4. Pipeline design ............................................................................................................................. 12 4.5. Production of energy.................................................................................................................... 12

4.5.1. Using gas turbine(s) or gas engine(s)................................................................................... 12 4.5.2. Using wind energy ............................................................................................................... 13 4.5.3. Using wave energy............................................................................................................... 14

4.6. Design of electrical system .......................................................................................................... 16 4.6.1. Context................................................................................................................................. 16 4.6.2. Hypothesis............................................................................................................................ 17 4.6.3. Requested work.................................................................................................................... 17

4.7. Energy storage design .................................................................................................................. 18 4.7.1. Energy storage technology................................................................................................... 18 4.7.2. Energy storage sizing rules .................................................................................................. 19

4.8. Design of the jackets.................................................................................................................... 22 4.9. Design of the floaters and associated mooring ............................................................................ 22

4.9.1. Design of floaters................................................................................................................. 22 4.9.2. Design of the mooring ......................................................................................................... 23

4.10. Installation................................................................................................................................ 23 4.10.1. Pipeline, cable and umbilical ............................................................................................... 23 4.10.2. Subsea equipment ................................................................................................................ 24 4.10.3. Jackets .................................................................................................................................. 24

APPENDIX A. Instruction for Performing HSE Risk Assessments ..................................................... 25 APPENDIX B. Metocean data .............................................................................................................. 28 APPENDIX C. Compressor and pumps sizing ..................................................................................... 31 APPENDIX D. Pipeline design ............................................................................................................. 35 APPENDIX E. Diesel Generators......................................................................................................... 37

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APPENDIX F. Design rules for sizing and cost of the Electrical System............................................ 38 APPENDIX G. Design of the floater and mooring lines....................................................................... 42 APPENDIX H. Economical data........................................................................................................... 47

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1. Introduction The wind was blowing harsh. Waves were regularly breaking on the jetty, throwing in the air tons

of water droplets which were splashing on Eloises face.

Eloise was standing on the harbor pier, looking at a fixed point on the horizon. Her thoughts were

about a potential gas field located very far from here, beyond the fall of the continental plateau,

where the water depth exceeds 2000m. The challenge to be solved was to exploit this gas and bring

it back to the coast, exactly where she was standing at this moment.

Not an easy task. Because of the long distance, the gas would probably need an intermediate

recompression step in order to compensate the pressure drop of the long pipeline. A compressor

needs energy, and one of the problems was to provide the required electrical power to the

compression unit located far from here. Because of the harsh sea conditions there, the safest

location for the compressor was undoubtedly on the seafloor, away from the strong waves, so

prone to batter relentlessly everything floating at the sea surface.

A first solution was to produce the electrical current here, on the coast, and transport it thanks to a

200 km submarine cable.

Eloise had the intuition that other solutions were probably possible, and without admitting it to

herself, this is why she was scrutinizing the horizon, as if the answer would show up all of a

sudden, out of the sea.

A horn disturbed her abruptly. The supply boat Nordic Sailor was leaving the harbor quay. The

large ship glided smoothly on the harbor water. She passed in all majesty before Eloises eyes and

reached the harbor mouth.

Eloise looked a long time at the Nordic Sailor as she was going away, noticing that no crew

member was staying on the deck for safety reasons. As the ship was sailing right in the direction of

this future gas field, she was rolling and pitching hard. At times, water was splashed around the

bow, soaking the deck. The waves had the power to move the large ship as if she were weighing

nothing, remembering Eloise the tremendous forces the sea is able to unleash.

Eloise was captivated. If the wind and the waves were so powerful and dangerous, couldnt it be

possible to harness a bit of this wild energy to satisfy the needs of the project?

Why not?

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2. Study scope of work In a context of growing concern about greenhouse gas effects and rarefaction of fossil resources,

methods used to develop new gas fields have to be adapted. Indeed, with the increasing pressure

associated to carbon dioxide emissions such as governmental laws and eco-taxes, and the growth

of gas demand, oil & gas producers face strong incentives to change their development schemes.

Public opinion is also growing more and more sensitive to the environmental behavior of

operators. These elements have led operators to consider powering their facilities using renewable

energies with a keen eye.

A new gas field has been discovered in a water depth of 1500 m and 200 km away from the coast.

In addition, it is located in a harsh environment preventing the installation of a conventional

floating platform. This situation led the operator to rely on subsea processing equipment. However,

small floater and platform can still be installed between the coast and the gas field.

Various schemes are being considered in order to propose a solution consistent with

environmental, governmental and economical issues. So far, three options have been identified.

A conventional solution consists in relying on a subsea processing and compression station

supplied by an electrical cable coming from the shore where gas turbines generators are installed.

This solution is mature but implies that large amounts of gas will be burnt reducing the revenue of

the gas field operator. In addition, carbon dioxide will be released and taxes shall be paid by the

operator which will decrease the profitability of the investment too.

A second possibility would consist in powering the subsea station using a wind farm to be installed

on the nearby continental shelf. This solution is attractive as it cuts down warehouse gas emissions

and benefits of a governmental incentive in the form of reduced taxes on incomes. However, this

solution implies that the power source will be intermittent and might require more maintenance.

The third identified solution is similar to the previous one, but relies on wave energy instead of

wind energy. This solution is a bit less mature than the one based on wind energy.

A scheme using renewable energy seems very attractive but presents a real drawback. As the wind

is not blowing every time and the waves have not always the same height, the production will be

intermittent. This situation have then to be managed by the use of floating diesel generator as back

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up, the use of electricity storage or the shut down of gas production during a certain time. A lot of

combinations are possible but what is the most competitive one?

Other or additional solutions are also welcome as long as they are properly presented. The various

possible solutions should be compared in accordance with the criteria given in section 2.1.

2.1. Technology selection

2.1.1. Screening of possible solutions

This screening can be mainly based on a state-of-the-art with information from general literature. Pros and cons of each production scheme shall be preliminary described assessing the following aspects: Energy production system: evaluation of the relevancy of various solutions to provide, transport and distribute energy to the system including subsea cable and connection to the shore, integration of renewable energy source, integration of storage system, and possible use of floating diesel generator. Maturity: preliminary evaluation of the maturity of the identified technologies Safety / environment: Preliminary description of the impact on safety of personnel and environment. As the environment is harsh, this point is particularly sensible. Safety should be kept in mind throughout the project, taking each of its phases into consideration including design, construction, installation and maintenance. Reliability / availability /maintenance: Comparative evaluation of the reliability of the overall system. An assessment of the need for maintenance of the various solutions should be performed. Installation: Various methods to install the required equipments should be investigated. Economics and financial analysis: preliminary cost estimation of the solutions, solution viability according to market data. Other criteria of comparison can be proposed by the candidates.

2.1.2. Recommended solution

Based on the previous comparative solution analysis, the most appropriate solution shall be selected in order to be further studied.

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2.2. Study of the selected solution

2.2.1. Safety

Considering that this project is performed facing a harsh environment, safety should be kept in mind through out the project, taking each of its phases into consideration including design, construction, installation and maintenance. A risk assessment should be performed in order to identify critical elements at every stage, with a description of the task, a list of the associated hazards and their potential effects. An attempt should be made to quantify the risks as an aid to decide what level of control / mitigation measures may be required. A Risk Assessment Worksheet shall be filled in for each macro task necessary to complete each phase. When breaking down a macro task into activities, it is suggested to remain at the level of global activities, but take into account the environment in which they will be carried out as a factor of risk. Mitigation measures should be proposed and a detailed description of the way to implement these mitigation measures shall be proposed for at least one of them. APPENDIX A should be used as a guide. Useful documents are also attached to help performing the risk analysis and risk mitigation of the proposed solution. More specifically, the risk analysis worksheet should be used in order to present a synthesis of the risk identification and remediation analyses that were conduced. Information on safety topics can be found at: www.ogp.org.uk.

2.2.2. Design

The following points shall be described if relevant: Overall production scheme Main characteristics of the process units (technology, size, energy

consumption) Jacket, vessel and mooring design (if any) Design of the power plant: location, type (gas turbine, offshore wind farm,

wave energy converter, storage unit, diesel floaters) , number and rated power of units, voltage selected,

Design of the pipeline(s): hydraulic sizing (pipeline diameter and compression need) and mechanical sizing (wall thickness)

Design of the electrical umbilicals: rated power, voltage, current The elements included in section 4 are the minimum information required to realize the study.

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The candidates are free to focus on one part of the system and to develop it with more details than required in the section 4 as long as a sufficient description of the other parts is provided.

2.2.3. Procurement, Construction, Installation, Start-up

According to the harsh environment, the safety aspects of all these operations shall be studied to prevent any human loss, through the risk assessment process outlined in section 2.2.1. Specifically, risk assessment is expected for the onshore construction, offshore installation and start-up phases. The following elements shall be provided:

Preliminary list of equipment for procurement Evaluation of the construction needs:

o Topside and hull fabrication o Subsea station fabrication o Wind/wave farm

Identification of the installation means and methods: o Offshore pipe and cable laying o Vessel mooring o Jacket and subsea structure installation o Wind/Wave farm

Start-up 2.2.4. Schedule

A first level schedule, including all the phases of the Engineering, Procurement, Construction, Installation and Start-up contract shall be proposed.

2.2.5. Operations

Inspection, maintenance and repair methods to achieve 350 days of production per year will be described. According to the harsh environment, the safety aspects of all these operations shall be studied to prevent any human injury or loss. Actions and recommendations to realize each operation in safe conditions shall be listed. One of the safety-critical operations will be maintenance, for which a risk assessment is required as per section 2.2.1.

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2.2.6. Cost estimation and financial analysis

2.2.6.1. Capital expenditure

The capital expense (CAPEX) shall be estimated according to the data provided in APPENDIX H. Each phase of the project has to be taken into account:

Engineering costs Procurement of the materials and equipment Construction costs (including transportation) Installation costs.

2.2.6.2. Operational costs

The operational expense (OPEX) shall be estimated. It includes gas (or any combustible) and lubricants consumption, maintenance, etc

2.2.6.3. Financial analysis of the project

A financial analysis of the project should be performed. This analysis should be based on the Net Present Value and the depreciation rate of the project. Information on the NPV can be found at: http://en.wikipedia.org/wiki/Net_present_value In addition the following elements should be taken into account:

Carbon dioxides emissions are subjected to a tax equal to 50/tons of CO2; Taxes on benefits are equal to:

o 40% of the benefits for solutions relying on conventional sources of energy;

o 20% for solutions relying on renewable energies; Natural gas is sold to shore at a price of 7/MMBTU; Marine diesel can be bought at the price of 1.4k/m3; Lubricants for diesel generators and gas turbines: 4/MWh; Maintenance for diesel generators and gas turbines: 10.5/MWh; An inflation rate on prices of 5% per year should be taken into account.

3. Design Basis

3.1. Geographical data

The field is located offshore at 200 km from the coast, 1500m water depth. The continental shelf extends on 175 km. Water depth of the continental shelf is 50 m. (Figure 1).

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Figure 1: Gas reservoir localization

3.2. Meteorological data

The maritime area presents harsh meteorological conditions with violent storms. Waves are significant and have an important impact on the potential solutions to develop this field. On the bright side, the local wave power resource is high and is enabling for possible powering of the process equipment using wave energy. Along with waves, wind data feature significant speed and let one think that wind energy could also provide enough energy to power the subsea station. Currents will be considered as negligible. The impact of such extreme environment should be taken into account with regard to safety. More details about the metocean data is given in APPENDIX A. Water temperature is about 12C at 50 m and 4C at 1500 m. The temperature is assumed to evolve linearly between these two water depths. Air temperature is about 20C and will be considered as constant. There is no tide in this region.

3.3. Offshore soil data

The mudline is considered good for vessel mooring and jacket installation.

3.4. Process and fluid data

Gas will be considered as a mixture of perfect gases. Compression and transport properties will be considered as equal to the methanes ones. The field is located at 4000 m under the mudline. The gas reservoir can be considered as circular with a surface of 20 km2. The proven reserve of the reservoir is 50.109 Nm3 of natural gas.

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The permeability of the reservoirs is such that the gas flow rate can be estimated at 106 Sm3/day and per well. The wellhead pressure is 70 bars and the temperature is 90C. The pressure remains constant during the whole life of the field. The chemical composition (weight %) is as follows: Methane (CH4): 100% Water: the gas is considered to be saturated in water. Therefore, for each Nm3 of produced gas, 0.001 m3 of liquid water is produced. The process unit shall be able to produce during 350 days per year. The heating value of natural gas is 950 BTU/ft3 at Normal conditions. The heating value of diesel is 955.8 kBTU/ft3 at Normal conditions. As a reminder, normal conditions to consider are 0C and 1 bar.

4. Technical studies

4.1. General literature

A general source of scientific information is: www.wolframalpha.com.

4.1.1. Energy storage

Energy storage literature is available at this web site: http://www.iea.org/papers/2009/energy_storage.pdf

4.1.2. Electrical system

Information about transformers, switchgears, VSDS, motors may be found at following Vendors Websites:

www.abb.com www.alstom.com www.converteam.com www.siemens.com

In addition, particular information about Subsea Cables / Umbilicals is available at following Vendors Websites:

www.nexans.com www.jdrcables.com www.abb.com

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Information about Electrical Subsea Structures is available at following Vendors Websites:

www.akersolutions.com www.fmctechnologie.com www.oceaneering.com

Websites of standard Electrical Manufacturers may also incorporate a Subsea Division.

4.2. Subsea separation station design

Water has to be separated from the gas. Indeed, over such distance, a phenomenon called liquid hold-up will lead to the formation of large pockets of water that would be detrimental to the pipes and other process equipment. In order to avoid such issues, a separation is performed close to the gas field The subsea separation station will be considered as a pressure loss. The pressure loss implied by the subsea gas liquid separation station is equal to 30% of the inlet pressure. Once the separation has been performed there are two options:

The water is directly injected into the gas field. In that case, the injection pressure is 200 bara. The water obtained from the separation will be considered as harmless to the environment and fit for injection (free of solid particles that may clog the well);

The water is brought to shore. 4.3. Compressor and pumps design

Compressors and pumps will be designed in accordance with APPENDIX A.

4.4. Pipeline design

Pipeline sizing criteria is given in APPENDIX D.

4.5. Production of energy

4.5.1. Using gas turbine(s) or gas engine(s)

Gas turbine(s) or gas engine(s) can be used to power the subsea processing station. Data on gas turbines and engines, such as dimensions, weight, efficiency and requirements can be found on internet site of vendors (Siemens, GE, Alstom, Solar or other) Gas turbines or engines will be powered using the gas extracted from the field. Gas turbines or engines usually require specific components so that the gas injected in

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the combustion chamber meets the requirements of the turbines or engines. Such equipments will be left aside as a first assumption. However, they can be investigated if deemed relevant. An overview of the equipment required by a gas turbine is given below.

Figure 2: Typical plant layout for single-unit gas turbine package (SIEMENS)

This solution requires electricity to be transported over a significant distance and implies that an important amount of carbon dioxide will be emitted.

4.5.2. Using wind energy

Near-shore wind turbines can be installed on the continental shelf but not directly above the gas field as floating offshore wind turbines are not very mature devices especially in these water depths. The pre-design of near shore wind turbine system for this study will however be based on typical onshore configuration:

Turbine with horizontal axis, Three-blades design, Pitch regulation for the blades.

A wind turbine is characterized by three wind velocities:

The start-up wind velocity: it is the minimal velocity required to start the rotation movement of the rotor. Typically it is 5m/s but it can be as low as 2m/s.

The maximal wind velocity: it is the velocity after which the turbine can not be operated safely (main concern is the fatigue of the blades). The blades are than put in a safety mode and the turbine production is null. Typically it is 25m/s.

The nominal wind velocity: it is the wind velocity at which the turbine reaches its nominal output power. Between the start-up and the nominal velocities, the power output increases with the cube of the velocity and

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depends on the diameter of the rotor. Between the nominal and the maximal velocity, the power output is constant and equal to the nominal rating power.

As a consequence, the normalized power output of a wind turbine depending on the wind speed has the profile given Figure 3. The pre-selected wind turbine nominal power output will be in accordance with projects requirements and with state of the art.

Figure 3: Normalized Power Output for a wind turbine

The number of devices and associated storage to install should be selected in accordance with the power needs of the subsea processing station and the associated metocean data (scatter diagram and time series). If deemed necessary a backup diesel generator can be fitted to power the subsea installation when the power generated by the wind farm is not sufficient. In that case, the characteristics and location of the backup generation plant should be detailed. Data on diesel generators is available in APPENDIX E. The preliminary design of the associated jacket or floater (if relevant) should be performed according to sections 4.8 and 4.9.

4.5.3. Using wave energy

Wave energy converters are designed to extract energy from the motions of the sea. They could be installed either on the continental shelf or close to the gas field. Wave energy converters are designed for a given range of peak period. This means that over a given range of peak period, the wave converter will produce energy, and

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outside this range, no energy is produced. An illustrative example is given on the figure below:

Figure 4: Production profile of a wave energy converter

They also feature a range of wave height over which they saturate i.e. their maximum output power has been reached and the production remains constant although more energy is available,. Considering the available metocean data, a wave converter has been selected. Its nominal power output is 300 kW. Its various components can be adjusted to modify the range on which energy is captured. However this range cannot be more than 10 s wide. Therefore the range on which the converter is efficient will be [A, A+10].

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Table 1: Power Matrix of the wave energy converter Tp A+10

0-1 0 0 0 0 0 0 0 0 0 0 0 0 0 1-2 0 38 48 53 50 44 37 30 25 20 16 15 0 2-3 0 101 118 123 116 102 89 75 62 51 42 38 0 3-4 0 174 196 200 188 169 150 130 110 92 77 69 0 4-5 0 255 277 276 258 234 212 190 165 141 120 109 0 5-6 0 300 300 300 296 284 270 251 223 194 168 155 0 6-7 0 300 300 300 300 300 290 270 250 230 210 200 0 7-8 0 300 300 300 300 300 300 290 270 250 230 220 0 8-9 0 300 300 300 300 300 300 300 290 270 250 240 0 9-10 0 300 300 300 300 300 300 300 300 290 270 260 0 10-11 0 300 300 300 300 300 300 300 300 300 290 280 0 11-12 0 300 300 300 300 300 300 300 300 300 300 300 0

Hs

12-13 0 300 300 300 300 300 300 300 300 300 300 300 0

The number of wave energy converters and associated storage to install should be selected in accordance with the power needs of the subsea processing station and the associated metocean data (scatter diagram and time series). If deemed necessary a backup diesel generator can be fitted to power the subsea installation when the power generated by the wave energy converters is not sufficient. In that case, the characteristics and location of the backup generation plant should be detailed. Data on diesel generators is available in APPENDIX E. The preliminary design of the associated jacket or floater (if relevant) should be performed according to sections 4.8 and 4.9.

4.6. Design of electrical system

4.6.1. Context

The objective of this analysis is to study the various technical inputs in order to assess the best solutions for the electrical system. Taking into account the rather harsh conditions (e.g. distances, subsea, depth), the system will have to comply with the following impositions:

Simplicity; High reliability; Security; Low consumptions & losses; Installation as simple as possible; Easy maintenance.

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4.6.2. Hypothesis

The following hypothesis will be taken into account for the design of the electrical system:

The power generation system will be considered as a black box for which internal details are not to be studied; however, sizing and main characteristics (total power needed, type & number of units, capacity of each unit, output voltage & frequency, etc) are still to be assessed.

This power generation black box does not include the possible output transformer(s) which if required shall be defined (size and main characteristics).

Should the power generation unit(s) be selected as gas turbine(s), the fuel shall be provided by the gas field itself but the gas treatment plant will be considered as part of the black box and therefore not to be studied.

Diesel generator(s) are not considered as part of the generation but can be used as back-up supply whenever needed.

Should an energy storage system be needed, its size and functioning parameters shall be defined (see section 4.7) but its management and control system is not to be studied.

4.6.3. Requested work

The study will consist in an evaluation of the relevancy of various solutions to provide, transport and distribute energy to the subsea installation according to the multiple impositions listed above. Different options and technical alternatives into each option will lead to several possible solutions, each having its advantages and drawbacks for the proposed subsea project. All possible configurations have to be assessed, and after comparison of the results a recommended solution shall be selected for in-deep study. For each solution proposed, the following documents shall be presented:

List of consumers: extensive list of all consumers (main and auxiliaries), and for each of them their electrical characteristics (power, voltage, current, power factor, efficiency);

Load balance: indicates for each consumer from which source(s) it is powered, its actual load or standby operation where required, and whether it has to be backed-up by an emergency source; This load balance summaries loads to be supplied for each switchboard and thus the sizing of switchboard

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Single line diagram: represents in a simplified manner the complete power system scheme from generation to consumers, with indication of the main electrical characteristics. The voltage levels of the generation, transport and distribution equipments shall be wisely selected in order to minimize the cost of electrical interconnection apparatuses and protection scheme;

Sizing of all main equipments: to be done according to standard formulas of Appendix F. Sizing shall lead to selection of standard rating equipment as per Vendor References.

Overall cost of the solution: includes cost of equipments and installation. Ratios are given in APPENDIX F.

4.7. Energy storage design

4.7.1. Energy storage technology

As renewable energy production is intermittent, the use of energy storage can be required to provide constant electrical power to the subsea production unit. Several technologies exist but considering the fact that the gas production unit is offshore, our experts have selected the energy bags technology. This technology is described on the following web site: http://www.theengineer.co.uk/1008374.article. In our case, the storage unit will be composed of two components: one at the surface which will be in charge of the energy conversion (electricity to high pressure air and high pressure air into electricity) and one subsea that will be in charge of high pressure air storage. The surface unit shall include the following equipments: air compressor, heat accumulator, air turbine, air pipes and electrical management system. The subsea unit is composed of big bags anchored to the seabed and storing compressed air. The following diagram shows the arrangement of the different components.

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Figure 5: Typical arrangement of a Compressed Air Energy Storage system

4.7.2. Energy storage sizing rules

4.7.2.1. Selection of principal parameters

To size the energy storage system, the following parameters shall first be selected: The storage philosophy: the two basic philosophies are either to store all the

power generated by the renewable generators and to unload the power required by the subsea station, or to store only the surplus of energy compared to the subsea station nominal duty and to unload the required power to balance the duty when the source are producing less than required. Other philosophies can be studied if deemed necessary. According to the selected philosophy, the quantity of energy E1 to be stored and E2 to be unloaded will be defined.

Location of the surface unit: there are two basic locations: on a jacket at a water depth of 50 m or on a floater at a water depth of 1500 m. Intermediate location can be considered.

Location of air storage: there are two basic locations: on the continental shelf at a water depth of 50 m or above the gas field at a water depth of 1500 m. According to this choice the storage pressure (P1) and the water temperature Twater will be defined. Intermediate location can be considered.

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4.7.2.2. Sizing of electrical equipment system

The area of electrical management system will be considered to represent 20% of the total surface of the platform or floater.

4.7.2.3. Sizing of compressors and turbine

According to the value of the energy to be stored and the energy to be unloaded, the sizing of compressor and turbine will be done according to the APPENDIX C. The outlet temperature T1 and T2 will be calculated according to APPENDIX C.

4.7.2.4. Sizing of heat accumulator

The heat accumulator will be composed of ceramic bricks installed in an insulated steel vessel. The ceramic bricks assembly will present straight channel where the gas will flow as described on the following figures.

Figure 6: Heat accumulator during storage phase

Figure 7:Heat accumulator during unloading phase

At the beginning of the storage phase, all the ceramic bricks will be at Twater temperature. The hot gas will flow into the channel and exchange its heat with the ceramic bricks during all the time of the storage phase. At the end of the storage phase most of the bricks will be at T1 temperature. During the unloading phase, the ceramic bricks will heat the cold gas coming from the air bag. The cold gas at Twater temperature will flow into the channel and will be heated during all the time of the unloading phase. At the end of the unloading phase, the entire heat accumulator will be at Twater temperature. The gas is considered to exit the heat accumulator during the unloading phase at a temperature T1-10C.

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The quantity of heat stored (in kWh) will be calculated considering the following formula:

1000)..(. 1 waterpgm TTCQHeat

Where: Heat is the stored energy (kWh) Qm is air mass flow (kg/s) Cpg is the specific heat of air (1030 J/kg/K) T1 and Twater are respectively air temperature at the outlet of the compressor

and water temperature at the storage level. (K) is the duration of the storage phase (h)

The volume of the heat accumulator will then be evaluated considering that it is feasible to store 150 KWh/m3. Knowing the volume, the size of the vessel (diameter D and height H) can be estimated considering that H = 2.D and that the diameter shall be smaller than 7 m. Several heat accumulators can be used. As an alternative, the heat can be evacuated to seawater via a heat exchanger. During unloading, the air is expanded in several steps, with intermediate reheating by the heat exchanger. Care must be given not to build up ice on the heat exchanger surface. Nota: The above design rules are very preliminary. Optimizations of the vessel size can be proposed by considering the thermal exchange between gas and bricks. The weight of the accumulator will be estimated considering the following formulas:

bricksinsulation

bricks

shell

insulationbricksshell

abs

WWVW

HDThicknessWWWWWeight

DPThickness

.2.0..7,0

...30

2.

Where:

Pabs is the absolute pressure inside the vessel (MPa);

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D is the diameter of the vessel (m); is the maximum allowable stress of the steel (80 MPa); H is the height of the vessel (m); is the density of the bricks (3 t/m3); V is the volume of bricks (m3); All the weight are in tons; Thickness is in meter.

4.7.2.5. Sizing of air storage

Air storage bags will be considered as spherical. The quantity of air to be stored will be calculated considering the volumetric air flow rate and the duration of the storage. Knowing this value the diameter and number of bags will then be obtained.

4.7.2.6. Sizing of jacket

Would a jacket be required, its sizing will be done according in accordance with section 4.8

4.7.2.7. Sizing of floater and mooring

Would a floater be required, its sizing and the sizing of related mooring will be done in accordance with section 4.9.

4.8. Design of the jackets

In the case of a development scheme considering an offshore jacket, the platform mass is proportional to the required deck surface. The ratio to consider is one ton of steel per square meter for a maximum water depth of 50 m. This information is basic and a detailed design can be proposed.

4.9. Design of the floaters and associated mooring

4.9.1. Design of floaters

A preliminary design of the required floaters should be performed. Due to the harsh environment in the area of the gas field, the floater will have to be circular. The design will consist in:

Assessing the radius and depth of the floater in accordance with the size and weight of the equipment to install on the deck;

Checking the stability of the floater according to APPENDIX G.1;

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4.9.2. Design of the mooring

A preliminary design of the mooring should be performed in accordance with APPENDIX G.2

4.10. Installation

Installation operations are usually critical from a safety point of view. This is even truer, when the surrounding environment is harsh. It implies that specific contingencies should be taken to tackle with this issue and guarantee that all operations can be performed safely. The proposed installation procedures should take safety into account. The impact of the specific contingencies to consider on the schedule and operations should be assessed and discussed. This section focuses on offshore installation needs as they are usually more critical that onshore installation needs.

4.10.1. Pipeline, cable and umbilical

Ships can lay rigid pipes using 3 methods: S-lay: ~3.0 km/day J-lay: ~1.0 km/day Reeling: ~7.2 km/day

Information on these methods in order to select the most relevant one can be found at: http://www.rigzone.com/training/insight.asp?insight_id=311&c_id=19 Though many ships are able to install small and light pipes, the number of vessels able to lay large and heavy pipes in deepwater is very limited which has an impact on the rental cost of such equipment. Indeed, as the diameter and wall thickness increase, the ship has to be equipped with better tensioning system to hold the pipe into position. The following assumptions will be made regarding the available pipe laying vessels:

Though some vessels are able to lay pipe with an outer diameter greater than 26 in, none of them is available.

Reeling cannot be performed with rigid pipes with an outer diameter greater than 18 in.

Cables and umbilicals laying is performed using reeling. Survey operations should be conducted before and after each pipe/cable/

umbilical is installed. The survey is performed at a rate of 16.8 km/day

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The S-lay method can be employed for water depth up to 1000 m. Initiation and abandonment of pipe, cable and umbilical each takes 24 hours.

As pipe, cable and umbilical laying operations are critical, they can only be performed when the environment is mild. The allowed operational window for each kind of operations is presented below.

Table 2: Allowed operational window

Max Operations Hs (m) Foundation, Modules

Lowering through water column 2 Pipelines

Initiation 2 Pipeline lay 2.5 Abandonment 2

Cable and Umbilical Lay Initiation 2 Cable or Umbilical Lay 2.5 Abandonment 2

4.10.2. Subsea equipment

The equipment required for the lifting of the subsea equipment should be selected in accordance with the requirements of the applicable standards. Once the characteristics of the required lifting equipment have been selected, components should be chosen according to APPENDIX H. The installation of one piece of equipment takes around 24 hours. A survey is performed prior and after the installation of each piece of equipment. Each survey takes 4 hours.

4.10.3. Jackets

Jacket will be installed using a jacket launching method. Each launching will take 24 hours. For schedule purposes, the barge in charge of the transit will be considered to have a speed of 8.2 knots.

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APPENDIX A. Instruction for Performing HSE Risk Assessments This appendix indicates the main steps of a risk analysis. Several documents are also attached to

ease this analysis.

A.1. Risk Rating Process

A.1.1. Activities description

Before starting the risk assessment, phases and activities of the project are defined from the overall project method statement. The project is broken down into a few macro phases, such as: construction / installation / start-up / maintenance. Each phase is then broken down further into its main operational tasks, if there is more than one. Each task is then risk assessed by considering the main activities involved to complete the task.

A.1.2. Hazard identification

The hazard identification study is carried out during meetings gathering chosen experienced personnel from the project engineering disciplines, technical specialists and operations representatives. The Risk Assessment Team identifies all hazards related to the tasks to be performed. To assist in the process, a list of typical hazards is provided in the Hazards Checklist. It is important that the list of hazards is used in a creative manner and not just as a rigid checklist. This will ensure that new or unusual hazards are recognized, and/or specific combinations of factors are identified. The hazards identified are recorded on the Risk Assessment Worksheet.

A.1.3. Hazard effect

Once all hazards associated with the task are established, the associated hazard effects shall be identified and considered. This stage of the process must consider the harm that could possibly occur to the people, environment, equipment and Companys image. The Risk Assessment worksheet is updated to include hazard effects associated with the hazards identified.

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A.1.4. Risk rating

The risk rating assesses the level of the risk associated with the task. The risk rating exercise uses the HSE Risk Matrix. The RA Team rates Likelihood of occurrence and Severity for each hazard and hazard effect identified and written on the RA form. Risk rating is defined as follows: Likelihood of occurrence x Severity of the hazard = Risk. Likelihood of occurrence and severity values are attributed based on definitions shown in the risk matrix, according to engineering judgment and operational experience (brainstorming process) from the Risk Assessment team; the Risk Assessment Scale may also be of help.

A.2. Control Measures

A.2.1. Standard control measures

Control measures are classified as follows: Administrative controls (internal / project procedures, Permit To Work,

checklist, specific measures) Technical measures (design engineering change, modification, preventive

maintenance / check, additional measures) Personnel measures (accreditation / training

Risk mitigation methods include: Termination: risk is eliminated by removing the hazard Treatment: risk is reduced by design or work method modification,

implementation of procedures and training Transfer: risk is endorsed by other more competent entities such as

Subcontractors or by compensation schemes (insurers) Control measures should be considered in the following order of preference:

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Table 3: HSE risk reduction hierarchy

1 Eliminate the HSE risk by removing the hazard - design out the problem at source. (e.g. : Replace a hazardous substance with an innocuous one)

2 Reduce the HSE risk using instead a less hazardous process, activity or substance. 3 Isolate the HSE risk (protect everyone) by effective controls such as enclosing the hazard,

removing the person from the hazard or reducing the persons exposure time to the hazard. 4 Install protective devices such as guards, emergency stops, trip switches, etc. 5 Enforce permits to work, special rules and procedures to closely control the hazard(s). 6 Provide proper supervision / monitoring, supported by training, instruction and relevant

information. 7 Provide personal protective equipment only as a last resort and in support of the above

control measures.

A.2.2. Additional control measures

When standard control measures are not sufficient, additional control measures are developed. In addition to the above, other control measures may be required in accordance with:

Legislation and approved codes of practice; Client requirements; International standards.

The purpose of mitigation actions is to reduce the level of the HSE risk.

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APPENDIX B. Metocean data

B.1. Waves

B.1.1. Definitions

B.1.1.1. Sea State:

Waves are usually described using a sea state. Sea states are usually represented by wave spectra. To each sea state is associated a type of spectrum, a significant wave height and a peak period. The significant wave height represents the wave height that would be estimated by a human observer. Statistically, it corresponds to the mean wave height (trough to crest) of the highest third of the waves. It is usually noted Hs. An illustration of the significant wave height is given on the figure below.

Figure 8: Definition of the significant wave height

The peak period, is the period that concentrates the most energy when looking at the associated spectrum. It is usually noted Tp. An illustration of the peak period (or frequency) is given on the figure below.

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Figure 9: Definition of the peak period

A sea state is considered to last 3 hours.

B.1.1.2. Scatter diagram

A scatter regroups statistics about sea state. Most commonly, it gives the number of occurrences of a given couple (Hs, Tp) over a given period of time or, more directly, the probability of occurrence of a couple (Hs, Tp). It can also provide data on the direction of waves.

B.1.1.3. Return Period

The return period defines how often is seen an event. For example, a return period of 100 years means that the associated event will occur once every 100 years.

B.1.2. Extreme wave data

Structures and platform are designed to resist extreme sea state. Structures are usually designed to the 100 years return period event.

Table 4: Extreme sea state

Return period 100 years 10 years 1 year Hs (m) 12.5 10.8 9 Tp (s) 17.2 16.1 15

B.1.3. Scatter diagram

Scatter diagrams and time series are given in the attached excel file.

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B.2. Wind

B.2.1. Definitions

Wind is usually described using the 3 seconds, 1 minute, 10 minutes, 1 hour or 3 hours average speed. The wind speed is recorded 10 m above the mean sea level. Similarly to waves, wind data is gathered into scatter diagrams giving the probability of occurrence of each wind speed.

B.2.2. Extreme wind data

Table 5: Extreme wind data

Return period 100 years 10 years 1 year V1hr (m/s) 31 28 26 V10min (m/s) 38 31 28 V1min (m/s) 44 34 32 V3s (m/s) 48 39 36

B.2.3. Scatter diagram and time series

Scatter diagrams and time series are given in the attached excel file.

B.3. Currents

B.3.1. Extreme current data

Table 6: Extreme current data

Return period 100 years 10 years 1 year Usurface (m/s) 0.88 0.76 0.64

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APPENDIX C. Compressor and pumps sizing

C.1. Compressor Sizing

C.1.1. Generalities

A compression station aims at increasing the pressure of a gas from a pressure P1 to a pressure P2 in order to ensure its export in a pipeline. A compression station mainly includes two pieces of equipment:

a centrifugal compressor, whose purpose is to increase the pressure a power source which drives the compressor

The centrifugal compressor is a device constructed at the demand depending on the needed polytropic head (i.e. a value bound to the gas composition and the inlet/outlet pressure ratio) and the required flow rate. The driving machine can be an electrical motor, a steam turbine, a gas engine or a gas turbine. Gas turbines can be really interesting for a remote or isolated development since it uses directly the process gas as an energy source.

C.1.2. Sizing

During gas compression from pressure P1 to a pressure P2 the gas temperature increases from T1 to T2. The following formula shall be used to calculate the gas outlet temperature.

1

1

1

1

2

12

PP

TT

Where: T1 and T2: Inlet gas and outlet gas temperature (K) P1 and P2: Pressure at the inlet and at the outlet of the compressor (bara) : adiabatic exponent (1.4 for natural gas and air) : compressor efficiency (~0,80)

The electrical power consumed by the compressor is calculated with the following approximated formula:

).(. 12 TTCQPower pm

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Where: T1 and T2: Inlet gas and outlet gas temperature (K) Qm: Mass flow rate of gas (kg/s) Cp: specific heat capacity (J/kg/K) and is equal to 1030 J/kg/K for air

The weight of the compressor will be calculated considering the following ratio: 7T/MW. This ratio includes the compressor and the motor. The size will be evaluated considering that a 1MW compressor has the following:

Table 7: Dimensions of compressors according to their pressure ratio

Pressure Ratio Size LxlxH (mm) 1-20 1500x1200x1200 20-50 1500x1000x1000 50-150 1500x800x800

This information shall be considered as basic. Detailed information can be obtained from vendor such as Siemens, Dresser Rand, GE, Atlas Copco.

C.1.3. Cost

The cost of a compressor is proportional to its power. For a centrifugal compressor, the following estimation formula can be used:

7.0PCCost Where:

P: power (MW) C: proportionality coefficient (see following table)

Table 8: Cost coefficient for compressors

Driving machine C (k) Compressor + Gas turbine 2300 Compressor + Electrical motor 1410

C.2. Turbine sizing

C.2.1. Generalities

A turbo-generator aims at producing power by the expansion of gas from a pressure P2 to a pressure P1. A turbo-generator mainly includes two pieces of equipment:

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a turbine, whose purpose is to transform a pressure difference into mechanical power

an alternator which converts mechanical power into electricity C.2.2. Sizing

During gas expansion from pressure P2 to a pressure P1 the gas temperature falls from T2 to T1. The following formula shall be used to calculate the gas outlet temperature.

11

1

1

221

PPTT

Where: T2 and T1: Inlet gas and outlet gas temperature (K) P2 and P1: Pressure at the inlet and at the outlet of the turbine (bara) : adiabatic exponent (1.4 for natural gas and air) : turbine efficiency (~0,85)

The electrical power generated by the turbine is calculated with the following approximated formula:

).(. 12 TTCQPower pm Where:

T2 and T1: Inlet gas and outlet gas temperature (K) Qm: Mass flow rate of gas (kg/s) Cp: specific heat capacity (J/kg/K) and is equal to 1030 J/kg/K for air

The weight of the turbine will be calculated considering the following ratio: 7 t/MW. This ratio includes the turbine and the motor. The size will be evaluated considering that a 1 MW turbine has the following dimensions:

Table 9: Dimensions of turbines

Pressure Ratio Size LxlxH (mm) 1-20 1500x1200x1200 20-50 1500x1000x1000 50-150 1500x800x800

This information shall be considered as basic. Detailed information can be obtained from vendor such as Siemens, Dresser Rand, GE, Atlas Copco.

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C.2.3. Cost

The cost of a turbo generator is proportional to its power. The following estimation formula can be used:

PCCost Where:

P: power (MW) C: proportionality coefficient (1500 k)

C.3. Pump Sizing

C.3.1. Generalities

A pump is a system which increases the pressure of a non compressible fluid. This equipment enables to provide the energy necessary to transport a fluid by converting mechanical energy provided by an electrical motor or a thermal motor. In the following chapter the inlet pressure is named P1 and the outlet pressure P2. The outlet pressure is equal to the pressure required at the end of the pipeline + the pressure loss induced by the friction in the pipeline as calculated in APPENDIX D.1.

C.3.2. Sizing

The duty of a pump is calculated with the following approximated formula:

QPPPower )( 12

Where: Q is the flowrate (m3/s) : pump efficiency (60%) P1 and P2: Pressure at the inlet and at the outlet of the compressor (Pa)

The weight of the pump will be calculated considering the following ratio: 40 tons/MW. This ratio includes the pump, the motor and the associated structure. The size will be evaluated considering that a 1MW pump and associated structure has the following size: 5 m x 3 m x 7 m (LxlxH): This information shall be considered as basic. Detailed information can be obtained from vendors.

C.3.3. Cost

The same cost ratios as for compressors should be used (C.1.3).

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APPENDIX D. Pipeline design

D.1. Pressure loss due to friction

The friction loss in a pipe can be calculated using the Fanning friction factor. This friction factor can be calculated using the formula developed by Stuart W. Churchill that covers the friction factor for both laminar and turbulent flow.

121

5.112

16

169.0

88

37530

27.07ln457.2

BAR

f

RB

De

RA

e

e

e

Where: Re: the Reynolds number; e: the absolute roughness of the pipe (typically 45 m for a steel pipe) (m); D: The inner diameter of the pipe (m); f: the Fanning friction factor.

The friction head can then be calculated according to the following formula:

gDLfvh f

22

Where: f: the Fanning friction factor; v: the speed of the fluid (m.s-1); L: the length of the pipe (m); g: the gravity; D: the inner diameter of the pipe; hf: the friction head (m).

This formula supposes that the fluid is incompressible. In order to be accurate, iterations should be performed every time the pressure varies by 10%. A good way to perform those iterations is to start with the desired outlet pressure and move backward. Hypothesis:

The gas follows the law of ideal gases.

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In addition to the pressure requirements (upstream and downstream), the gas velocity can not go beyond 20m/s in order to limit erosion and noise.

D.2. Thickness

The following formula is used to evaluate the minimum thickness of the gas pipeline.

TEFSMYSDP

tole e

21

1

)(min

Where: emin: the minimal thickness (mm) P the Maximal operating pressure (MPa) De: the external diameter (mm) SMYS: the Standard Minimum Yield Strength (MPa) F: the safety coefficient E: the welding coefficient (=1 for 100% controlled welding) T: the temperature factor

Hypothesis:

There is no negative tolerance (tol(-)=0) F=0.6 E=1 T=0.4 Maximal service pressure will be taken 20% above the maximal pressure level (i.e.

at the inlet). The minimal pressure at the inlet of plants including turbines (compression,

liquefaction, power generation) is 30barg. The same outlet pressure is required for the gas exported to shore.

For the sake of standardization in the Oil & Gas industry, the external diameter is given in typical diameter in inches (1=25.4mm).

Standard Minimum Yield Strength will be taken equal to 450 MPa which corresponds to X65 steel which is a steel grade commonly used in the offshore industry

This thickness does not include the corrosion allowance (which comes in addition to the minimal calculated thickness). For a dry gas, the corrosion allowance is generally of 3 mm.

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APPENDIX E. Diesel Generators Diesel generators are commonly used in the marine industry to power offshore facilities.

Information on diesel generators can be found at Vendors websites such as Wartsil, Caterpillar,

MAN, .

E.1. Description of a typical diesel generator set

A typical diesel generator set is composed of: A diesel engine; An alternator to generate electricity;

E.2. Diesel generator characteristics

The characteristics of the diesel generator can be found at any marine diesel generator manufacturers website. The weight and dimensions of the diesel generator should be given. The efficiency of the engine plus the alternator will be considered to be 40%.

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APPENDIX F. Design rules for sizing and cost of the Electrical System

F.1. Generation

F.1.1. Generalities

Three types of generation are proposed to the candidates: gas turbine, wind turbine and wave energy converter, but the location(s), the type(s) and the number of units are free. Although not part of the generation, any back-up supply if needed shall follow the same rules of sizing. The power generation system will be considered as a black box for which internal details are not to be sized.

F.1.2. Sizing

The generation shall be capable of powering the installation in any condition, and keep the network parameters as close as possible to the design (nominal) values. It however needs in certain circumstances to compensate some fluctuations induced by the consumers (process, maintenance, tests), so its main functioning parameters (voltage, frequency, power) have to be properly selected.

F.1.3. Costs

Information on costs can be found in APPENDIX H.

F.2. Transport and distribution

F.2.1. Generalities

Transport of energy from the generation to the consumers and control of them implies the use of various equipments (transformers, cables, switchgears, variable speed drives ), each of them having to be sized properly in order to maintain the reliability and the security of the overall electrical system.

F.2.2. Transformer

Transformers are mainly used to adapt the level of voltage to the application they are supplying. They are supposed to transfer the power between levels with a minimum of losses hence high efficiency. Their size, weight and therefore cost are linked to the technology. Functioning parameters can be remote-monitored through control cables or optical fibers.

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.

F.2.3. Cables

Standard and subsea power cables shall be sized versus nominal, ampacity while keeping the voltage drop (due to the length) below allowed limits. In addition to the conductor(s) cross section size, the insulation level has a high impact on the cost, especially for the subsea cables. Laying method(s) shall be considered from the design stage.

F.2.4. Umbilical

When different links shall be established from the shore to subsea equipment, or between two subsea systems, such as:

electrical power supply; electric or hydraulic control of actuators; control and monitoring (copper conductor or optical fiber); injection of chemicals;

Then an umbilical may be installed, carrying all of them in the same circular sheath. The sizing of the power cable within the umbilical will be assumed to be identical to a conventional or subsea cable. Although each element within the umbilical is chosen from standard series, the overall design of the umbilical is custom tailored and the cost of such equipment is high. Laying installation method(s) shall be considered from the design stage.

F.2.5. Variable speed drives (VSDS)

The speed of a squirrel cage induction motor being constant for a given frequency (generally the one of the supply system this device is powered with), then a Variable Speed Drive System (frequency converter) shall be used to vary motor speed according to the needs of the process (compressor, pump ). Subsea VSDS are usually derived from standard equipments, but re-arranged to cope with specific impositions and installed into pressure-resistant or pressure-compensated enclosure. VSDS can be manually or automatically remote-controlled and functioning parameters remote-monitored through control cables or optical fibers. Very often the supplier of a VSDS also provides the associated driven motor in order to deliver an optimized package. .

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F.2.6. Switchgear

The switchgear distributes the energy received from the generation to each consumer through circuit breakers. The circuit breakers also help to minimize the consequences of an electrical fault by isolating within milliseconds any defective equipment from the rest of the installation. Subsea switchgears are usually derived from standard equipments, but re-arranged to cope with specific impositions and installed into pressure-resistant or pressure-compensated enclosure. Switchgears can be manually or automatically remote-controlled and functioning parameters remote-monitored through control cables or optical fibers.

F.2.7. Sizing

Table 10: Electrical Equipment Sizing Equipment Sizing Value Unit Description

CompressorMotor RatedPowerRatedSpeedRatedVoltagePowerFactorEfficiency

kWrpmV%

AsperVendorReference

pf120

Where=ratedspeedf=frequencyofnetworkp=numberofmotorwindingpoles

PumpMotor RatedPowerRatedSpeedRatedVoltagePowerFactorEfficiency

kWrpmV%

AsperVendorReference

pf120

Where=ratedspeedf=frequencyofnetworkp=numberofmotorwindingpoles

Auxiliaries RatedPowerRatedVoltagePowerFactorEfficiency

kVAV%

Includesallsmallmiscellaneousconsumersandhasbeenevaluatedat3%ofthetotalofthemainconsumers

Transformer RatedPowerPrimaryVoltage

SecondaryVoltageShortcircuitImpedance

PowerFactorEfficiency

kVAVV%%

Voltagedropatsecondary sincos100 cc

n

j UPP

V where:Pj=lossesonload(kW)Pn=ratedpower(kVA)Ucc=shortcircuitvoltage(%)Cos=PowerFactorofLoadLossesP=Pj+P0WhereP0=lossesatnoload

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Equipment Sizing Value Unit DescriptionPowercable RatedVoltage

RatedCrossSection V

mmMinimumSectionSmin/In

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APPENDIX G. Design of the floater and mooring lines

G.1. Design of the floater

The ship has to be designed so that it is stable, i.e. it will not capsize. A preliminary assessment of its stability should be performed in accordance with this appendix. The stability of a floater is assessed through its meta-centric height which has to be greater than 1 m and below 2 m. The meta-centric height can be calculated according to the following formula:

GMt = GC + CMt Where:

GMt: the metacentric height (m); GC: the weight stability (m); CMt: the shape stability (m).

GC is calculated according to the following formula:

GC = ZC-ZG Where:

ZC: the distance from the keel (the lowest point of the ship) to the centre of buoyancy;

ZG: The distance from the keel (the lowest point of the ship) to the centre of gravity of the ship.

The ship will be considered as uniform, i.e. the centre of buoyancy is the centre of the hull situated underwater, and the centre of gravity is the centre of the ship. An illustration is given below.

Figure 10: Definition of ZG and ZC

The CMt corresponds to the restoring force implied by the water surface. It is calculated using the following formula:

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TD

VI

CM yt 16

2 Where:

D: the diameter of the floater (m); T: the draught of the floater (m).

G.2. Design of the mooring lines

The design of the mooring lines should be performed so that it is able to resist to environmental loads. The loads to sustain are the following: wind loads, current loads and mean drift loads. Loads should be calculated both along the longitudinal and transversal axis of the ship (which are identical for a circular floater). The steps to go through are the following:

Select a type of mooring: semi-taut, semi-taut with reduced offsets or taut; Calculate the area exposed to wind and currents (transversal and longitudinal if

relevant; Calculate the corresponding wind, current and wave induced loads; Select a cluster (set of mooring lines) configuration; Estimate the axial load on each line; Estimate the pretention in the line and impact of wave dynamics; Calculate the overall maximum tension in the line; Calculate the required minimum breaking load; Select a type of chain.

G.2.1. Selection of the type of mooring

As the ship will be of circular shape it will be spread moored. This kind of mooring is composed of several groups of mooring lines called clusters. The minimum number of cluster is 3. Additional clusters can be fitted if deemed required. Depending on requirements regarding vessel motions the mooring will be either:

Semi-taut: large vessel motions are allowed; Semi-taut with limited offset: reduced motions are required; Taut: very limited motions are required.

The mooring type is therefore chosen according to the requirements of the systems connected to the floater.

G.2.2. Estimating the area exposed to wind and currents

The area exposed to currents is the projected area of the hull that is underwater and perpendicular to the direction of currents. The area exposed to winds is the projected of the hull and topside that is above water and perpendicular to the wind direction.

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G.2.3. Calculating the corresponding wind, current and wave loads

G.2.3.1. Current induced forces

Current induced forces can be seen as a drag force. They are estimated using the following formula:

2...21

cDwaterc VACF Where:

Fc: the current induced force (N); water: the density of water (kg/m3); CD: the drag coefficient which is taken equal to 1 for a circular vessel; A: the projected area perpendicular to the current direction (m); Vc: the speed of current (m/s).

G.2.3.2. Wind induced forces

Wind induced forces can be seen as a drag force. They are estimated using the following formula:

2...21

wDairw VACF Where:

Fw: the wind induced force (N); air: the density of air (kg/m3); CD: the drag coefficient which is taken equal to 2 to take the shape of

topsides into account; A: the projected area perpendicular to the wind direction (m); Vw: the speed of wind (m/s).

G.2.3.3. Drift loads due to waves

Wave induced forces are quite difficult to calculate analytically. However they can be estimated using the following formula:

2

100...

21

sDwaterd HACF

Where: Fd: the wave drift induced force in kN; water: the density of water (kg/m3); Hs: the significant wave height (m);

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CD: the drag coefficient equal to 1 for a circular vessel (kN/(kg.m); A: the projected area perpendicular to the water direction (m).

Beware that this formula is very preliminary. Would unrealistic values be found for a round floater, provisions should be taken to rescale the results.

G.2.3.4. Overall load on the ship

The overall load on the ship is obtained by adding all the forces. cwd FFFF

G.2.4. Select a cluster configuration

The number of clusters has to be chosen. Clusters have to be uniformly distributed and the minimum allowed number of cluster is 3.

G.2.5. Calculating the axial load on each line

The horizontal load is calculated by projecting the most designing load in the most designing direction (for example for a 3 clusters spread mooring, directly opposite to one of the clusters). This horizontal load is then converted into an axial load by projecting it on the line. Lines will be considered to form an angle with reference to the horizontal equal to 45 as a first approximation.

G.2.6. Pretension and impact of wave dynamics within the lines

The pretension depends on the type of mooring. It is equal to: 30% of the axial load if the mooring is semi-taut; 50% of the axial load if the mooring is semi-taut with reduced offsets; 70% of the axial load if the mooring is taut;

Wave dynamic loads (roll, pitch and heave of the floater principally) are also estimated as a percentage of the calculated axial load. It is equal to:

5% of the axial load if the mooring is semi-taut; 10% of the axial load if the mooring is semi-taut with reduced offsets; 15% of the axial load if the mooring is taut;

G.2.7. Overall maximum tension within the lines

The overall maximum tension is equal to the maximum axial load plus the pretention load plus the wave dynamic loads.

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The required minimum breaking load on each line is obtained by dividing the overall maximum tension by the number of lines in one cluster and multiplying it by the safety coefficient (equal to 2).

G.2.8. Length and type of chain

The length of the chain is calculated with regard to the type of mooring and the water depth. It is considered that the horizontal distance between the fairlead on the ship and the anchor on the ground is equal to 4/3 of the water depth. A catenary coefficient is then applied:

1.04 if the mooring is semi-taut; 1.02 if the mooring is semi-taut with reduced offsets; 1 if the mooring is taut.

The size of the chain so that its breaking load is greater than the above calculated breaking load. The breaking load of a chain with regard to its diameter can be estimated using data provided on VICINAYs website: http://www.vicinaycadenas.net/eng/mooring_chains/mechanical_properties.html Chains will be considered to be made of R4 steel.

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APPENDIX H. Economical data Table 11: Economical data

Project Services 13% of other relevant costs

Project Management

Engineering

Procurement Services

Commissioning

Topsides - Procurement

Major rotating equipment compressors, pumps) APPENDIX C

Gas turbines, gas engines 2100 k/MW

Diesel generators 1150 k/MW

Structural steel 2 /kg

Mooring lines, anchorsEPCI 4 k/ton

Topsides - Fabrication

Fabrication, Integration 20 /kg

Topsides - Fabrication

Procurement, Installation APPENDIX F

Electrical Equipment See Table 12

Other costs

Offshore works, transportation, certification 5% of costs

Hull EPC

Engineering+ Procurement + Fabrication 8 /kg

Subsea systems

Drilling and casing 4 k/m

Pipeline, flowline procurement 2.2 k/t

Pipeline, flowline installation 1 000 k/day

Lifting Vessel 400 k/day

Renewable energy production systems

Wave energy converters 2000 /kW

Wind turbine 2000 /kW

Risks

To be determined by project team and priced

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Table 12: Electrical equipment procurement and installation costs Onshore Subsea Equipment

Cost Installation Cost Installation Transformer (oil filled)

40 /kVA 5 /kVA 400 /kVA See section

4.10.2

Power cable, Medium Voltage 30 /m 45 /m 120 /m

See section

4.10.1

Power cable, High Voltage 60 /m 75 /m 250 /m

See section

4.10.1

Umbilical --- --- 500 /m See section 4.10.1

VSDS Medium Voltage (2MW) Without transformer 200k 10 k 2000 k

See section 4.10.2

Switchgear MV (3.3kV 6kV) 30k / cell 5 k / cell Switchgear HV GIS (20kV 33kV) 50k / cell 5 k / cell

The list is not comprehensive. Other assumptions could be considered and shall be given in the

report, as well as benchmarks gathered elsewhere which should be used to cross-check the prices

obtained.

talentissimo 2012 green gas

Documents

economical data

geographical data

fluid data

meteorological data

following case study

offshore soil data

studied case

case of use