invitation to tender part c – proforma contract · pdf filedeep water tano project...

Deep Water Tano Project – Invitation to Tender – Part C – Attachment B – Scope of Work Contract No. TGHA – 02154 – Subsea FEED

INVITATION TO TENDER

PART C – PROFORMA CONTRACT

ATTACHMENT B – SCOPE OF WORK


Table of Contents

ABBREVIATIONS ............................................................................................................................. 6

1 INTRODUCTION ....................................................................................................................... 8

1.1 FIELD SUMMARY ................................................................................................................. 8 1.2 PURPOSE ........................................................................................................................... 9

2 BASE CASE DEVELOPMENT ARCHITECTURE.................................................................... 10

2.1 OVERALL DEVELOPMENT DESCRIPTION ............................................................................... 10 2.2 SUBSEA ........................................................................................................................... 10 2.3 AVAILABILITY OF DESIGN DATA ........................................................................................... 11

3 SUBSEA INTERFACES AND SYSTEMS ENGINEERING ....................................................... 17

3.1 FRAME AGREEMENTS ........................................................................................................ 17 3.2 BATTERY LIMITS ................................................................................................................ 17 3.3 PRIMARY INTERFACES........................................................................................................ 17 3.4 SYSTEMS ENGINEERING ..................................................................................................... 18 3.5 PROJECT MANAGEMENT, PLANNING AND COST ESTIMATION .................................................. 18 3.6 SAFETY STUDIES ............................................................................................................... 19 3.7 INVITATION TO TENDER PREPARATION ................................................................................. 19 3.8 IVB .................................................................................................................................. 20 3.9 ONGOING STUDIES ............................................................................................................ 20

4 SUBSEA MANIFOLDS ........................................................................................................... 21

4.1 MANIFOLD FUNCTIONALITY. ................................................................................................ 21 4.2 MANIFOLD PIPING DESIGN .................................................................................................. 21 4.3 MANIFOLD STRUCTURAL DESIGN ........................................................................................ 21 4.4 MANIFOLD FOUNDATIONS DESIGN ....................................................................................... 22 4.5 MANIFOLD SPECIFICATIONS ................................................................................................ 22

5 FLOWLINE DESIGN AND SPECIFICATIONS......................................................................... 26

5.1 INFIELD FLOWLINES ........................................................................................................... 26 5.2 FLOW ASSURANCE STUDIES ............................................................................................... 26

5.2.1 Fluids Characterisation................................................................................................ 26 5.2.2 Flow Assurance Simulation Basis ................................................................................ 26 5.2.3 Steady State Analysis of the Full Field Development ................................................... 26 5.2.4 Steady State Life of Field Analysis .............................................................................. 26 5.2.5 Provision of Data for Life of Field Corrosion Analysis ................................................... 26 5.2.6 OLGA Base Model Construction and Review............................................................... 27 5.2.7 Transient Operability and Design Assessment ............................................................. 27 5.2.8 Data to Support Slug Catcher Sizing Assessment ....................................................... 27 5.2.9 Data to Support Flowline Sizing and Design ................................................................ 27 5.2.10 Hydrate and Wax Management Studies .................................................................. 27 5.2.11 Hydrate Remediation Assessment .......................................................................... 27 5.2.12 Chemical Core and Distribution Sizing .................................................................... 28 5.2.13 System Finalisation ................................................................................................. 28

5.3 FLOWLINE DESIGN ............................................................................................................. 28 5.3.1 Route Design .............................................................................................................. 28 5.3.2 Flowline Mechanical Design ........................................................................................ 28 5.3.3 Pipeline End Termination (PLET) Design..................................................................... 29 5.3.4 Tie-In Spoolpiece Mechanical Design .......................................................................... 29 5.3.5 Flowline External Corrosion Protection Design ............................................................ 30 5.3.6 Flowline Installation, Pre-commissioning and Tie-in ..................................................... 30 5.3.7 Design for Pigging ....................................................................................................... 30

5.4 FLOWLINE SPECIFICATIONS ................................................................................................ 31

6 SUBSEA FLOWLINE RISERS TO FPSO ................................................................................ 32


6.1 SUBSEA RISER DESIGN CONCEPT ....................................................................................... 32 6.2 FEED SUBSEA RISER DESIGN ............................................................................................ 32 6.3 RISER SPECIFICATIONS ...................................................................................................... 32

7 SUBSEA CONTROL SYSTEM ................................................................................................ 34

7.1 GENERAL ......................................................................................................................... 34 7.2 SCS TOPSIDES EQUIPMENT ............................................................................................... 34 7.3 SCS SUBSEA EQUIPMENT .................................................................................................. 34 7.4 SUBSEA FEED INVOLVEMENT............................................................................................. 34

8 UMBILICALS AND UMBILICAL RISERS ................................................................................ 36

8.1 GENERAL ......................................................................................................................... 36 8.2 UMBILICAL DESIGN IN SUBSEA FEED .................................................................................. 36 8.3 UMBILICAL RISER DESIGN IN SUBSEA FEED ........................................................................ 36 8.4 UMBILICAL AND UMBILICAL RISER SPECIFICATIONS ............................................................... 37

9 SERVICES TO COMPANY ..................................................................................................... 38

10 REFERENCES .................................................................................................................... 39


Table of Figures

Figure 1.1 Deep Water Tano Location ................................................................................................ 9

Figure 2.1 Liquids Recovery Phase – Reservoir Categories ............................................................ 12

Figure 2.2 Schematic of First Oil Deep Water Tano Development.................................................... 13

Figure 2.3 Potential Full Field Development for Deep Water Tano ................................................... 14

Figure 2.4 Area Map First Oil Development Locations ...................................................................... 14

Figure 2.5 Area Map Full Field Development Locations ................................................................... 16

Figure 4.1 Subsea Manifold Functionality – Single Production Flowline ........................................... 24

Figure 4.2 Subsea Manifold Functionality – Twin Production Flowlines ............................................ 25

Table of Changes from Previous Revision

Section Change

All Client comments incorporated (HP & WH)

Sections 1 and 2 Field name changed


Table of HOLDS

Hold No. Section Description


ABBREVIATIONS

The following terms and abbreviations are used within this Scope of Work and the associated CTR pack:

AC Alternating Current

BOD Basis of Design

CAD Computer Aided Design

CAPEX Capital Expenditure

COMPANY Tullow Oil (Ghana)

CP Cathodic Protection

CRA Corrosion Resistant Alloy

CTR Cost, Time and Resource

DCS Distributed Control System

DST Drill Stem Test

DWT Deep Water Tano

ENVID Environmental (Risk) Identification

EPC Engineer, Procure, Construct

EPCIC Engineer, Procure, Construct, Install, Commission

EPIC Engineer, Procure, Install, Commission

FEED Front End Engineering and Design

FMECA Failure Mode Effect and Criticality Analysis

FPSO Floating Production Storage and Offloading (vessel)

GA General Arrangement

HAZID Hazard Identification

HAZOP Hazard and Operability

HP High Pressure

HSE Health, Safety and the Environment

ITT Invitation to Tender

IVB Independent Verification Body

km kilometre

LLI Long Lead Items

LP Low Pressure

m metre

MDR Master Document Register

mm millimetre

MTO Material Take-Off

NPS Nominal Pipe Size

OD Outside Diameter

OLGA Proprietary software for analysis of dynamic and transient multiphase fluid flow

OPEX Operating Expenditure

OREDA Offshore Reliability Data Handbook

PCT Piezo-Cone Test

PIPESIM Proprietary software for steady state analysis of multiphase flow

PLET Pipeline End Termination

PLR Pig Launcher/Receiver

P&ID Piping and Instrumentation Diagram

QA Quality Assurance

QRA Quantitative Risk Assessment

RAM Reliability, Availability and Maintainability

RAO Response Amplitude Operator

ROV Remotely Operated Vehicle

SAMS Safety Action Management System

SCM Subsea Control Module


SCMMB Subsea Control Module Mounting Base

SCR Steel Catenary Riser

SCS Subsea Control System

SAMS Safety Action Management System

SSIV Subsea Isolation Valve

TUTU Topsides Umbilical Termination Unit

UTM Universal Transverse Mercator

VIV Vortex Induced Vibration

WGS World Geodetic System

°C Degree Centigrade


1 INTRODUCTION

1.1 Field Summary

The Tweneboa and Enyenra reservoirs lie approximately 30km to the West of the Jubilee reservoir, and approximately 50km off the coast of Ghana. The reservoirs are found in water depths ranging between 1,000m and 1,800m.

Tweneboa-1, drilled by the Eirik Raude in 1,149m of water discovered a gas condensate reservoir in Turonian aged sands in March 2009. Tweneboa-2 drilled by the Atwood Hunter in 1,321m of water discovered two separate gas condensate reservoirs and an oil reservoir also in Turonian aged sands in January 2010. Tweneboa-3 drilled by the Deepwater Millennium in 1,000m of water, discovered two further condensate pools in December 2010.

The Enyenra field lies to the west of Tweneboa. The Enyenra-1 well was drilled by the Sedco 702 in July 2010. The well was drilled to a total depth of 3,890m in 1,428m of water and discovered good quality light oil in two zones of stacked Turonian aged sands. Pressure data indicates that these zones are part of the same accumulation and the oil appears to be light crude between 33 and 36 degrees API. The Enyenra-1ST was drilled to a total depth of 3,998m and discovered an extension of the same light oil reservoir and two separate gas condensate reservoirs.

Figure 1.1 below shows the location of the Enyenra and Tweneboa discoveries in the Deep Water Tano Block offshore Ghana.


Figure 1.1 Deep Water Tano Location

1.2 Purpose

The purpose of this document is to define the subsea Scope of Work associated with subsea FEED studies to be undertaken for the Deep Water Tano prospect.

The Deep Water Tano development, as described below in Section 2, is based on preliminary concept selection studies. The objective of FEED studies will be to firm up the details of the development and to engineer it to a level where FEED data and specifications would allow Contractors to tender for the detailed design, procurement, construction and installation of the development facilities, in accordance with a contracting strategy also to be developed in FEED.

It is to be noted that this FEED is considered a ‘Deep’ FEED study, where definition of subsea infrastructure such as manifolds and controls system will be developed to a very advanced stage, allowing procurement of all long lead items through COMPANY Frame Agreement contracts.


2 BASE CASE DEVELOPMENT ARCHITECTURE

2.1 Overall Development Description

The Enyenra and Tweneboa fields will be developed by the use of an FPSO spread-moored to the seabed [Ref. 1]. Subsea manifolds will be installed on the seabed, with local cluster wells tied back to them. Wells will provide facilities for oil production, gas/condensate production, gas injection and water injection. Manifolds will be tied back to the base of the FPSO using infield flowlines for the services listed above. Currently it is envisaged that flowlines will be tied back to the FPSO using SCRs.

COMPANY have developed the concept for the DWT development based on a requirement for flexibility – see following discussions regarding field/reservoir uncertainty. The concept for flexibility is to be maintained (not challenged) during FEED unless specifically requested by COMPANY.

Oil export will either be via a remote CALM buoy or via tandem tanker offloading. This will be resolved by others during the FEED period and only affects the subsea FEED in so far as the requirement for CALM buoy moorings is not yet fixed. Condensate production will be commingled with oil production in the fluid stabilisation trains on the FPSO. Gas will be utilised for power generation (fuel gas) and reinjected for voidage replacement/pressure maintenance as required.

The DWT development fields consists of oil reservoirs and gas condensate reservoirs, see Figure 2.1 below. For the oil reservoirs, it will be necessary to provide pressure support by means of water injection (a process called water flood) and/or gas injection (a process called gas flood). For rich gas reservoirs, gas will be reinjected for reservoir pressure support, but for lean gas condensate reservoirs there will be no re-injection. There are uncertainties in the reservoir structure and performance, and therefore the flooding/re-injection philosophy applicable for each section of reservoir may be subject to change. The FEED contractor shall be aware that exploration drilling is currently taking place in the field, and that results will be made available during the FEED programme. These results may change the field development plan, and the FEED contractor shall design facilities that can accept such change with the minimum of redesign.

2.2 Subsea

The fields in the DWT area will be developed as subsea tie-backs to an FPSO. Wells for oil production, gas/condensate production, gas injection and water injection will be drilled and tied back to subsea manifolds where local reservoir produced fluids will be commingled, and gas and water for injection will be distributed to wells as necessary. There will be no commingling of oil and condensate at the seabed. Uncertainty in reservoir performance will be managed by each manifold being tied back to the FPSO individually through a separate flowline, rather than manifolds being linked subsea.

The subsea wells will be located in clusters around the manifolds, so that well tie-back lengths will be limited and wells can be reached from one location of the semi- submersible drilling rig, saving costly rig moves. Deviated wells will be drilled to reach the required bottom hole locations.

As illustrated schematically in Figure 2.2 below, it is initially planned, i.e. at first oil, to develop the fields from 3 drilling centres, two located in the Enyenra field and 1 located in the Tweneboa field. The functionality of the wells drilled at each centre is also summarised in Figure 2.2 below. The manifolds located at each drill centre will be configured for the functionality as foreseen, and will be tied back to the FPSO by infield flowlines designed to transport raw produced fluids to the FPSO or to transport fluids for injection from the FPSO to the manifolds for distribution to the appropriate wells as required. Tie-back distances to the FPSO vary between approximately 2 km and 10 km.

Wells and infield flowlines will be tied in to the subsea manifolds using spools and jumpers fitted with diverless connectors. At the FPSO, it is currently envisaged that infield flowlines will be connected to the topsides via Steel Catenary Risers (SCRs). For the relatively small diameters and short distances associated with the infield flowlines, it is currently envisaged that the infield flowline and its associated SCR can be installed in a continuous section, without further requirement for significant riser base structures or connections. This premise is to be studied further and confirmed in the subsea FEED programme.


Control of the subsea systems will be managed by the FPSO and achieved via a multiplexed electro-hydraulic subsea control system.

Hydraulic fluids for control of subsea tree and manifold valves and injection chemicals will be delivered by steel tubes in umbilicals routed to each manifold from the FPSO.

The umbilicals will also supply electrical power to the control and instrumentation system, and carry fibre optic cores for communications between the FPSO and the subsea facilities.

Subsea control modules will be used to control all functions on the subsea trees and manifolds. The control modules may be located on the manifolds or on the trees, the optimum locations to be determined during subsea FEED. Subsea accumulation will be provided as required.

The potential full field development is shown schematically in Figure 2.3, utilising six or more drilling centres/manifolds. Attempts will be made during FEED to outline the facilities required for the full field development, but there will necessarily be some uncertainty regarding the nature of the facilities required post first oil. The subsea architecture is intended to allow flexibility to facilitate change as COMPANY learns more about the detail of the reservoir interconnectivity during development drilling.

The requirement for manifold design to be flexible in terms of functionality is born from uncertainty in the reservoirs. It is possible that the number of producers/injectors will be modified following data collection from the drilling of the first well at any drill centre. It is therefore imperative that the manifold design can be reconfigured from 3 producers and 1 injector to 2 producers and 2 injectors simply in the fabrication yard, within a reasonably short time frame.

Figure 2.4 below illustrates the nature of the seabed in the DWT area, and also illustrates the current plan as to the locations of the FPSO and the drilling centres/manifolds required for the first oil development. It can bee seen that the water depths vary between approximately 1,000 m and 1,700 m, giving a slope of approximately 3 degrees over the field extent, and the seabed is characterised by a series of canyons in three lines and some associated steep slopes. The FPSO location has been selected to be central to the development but to avoid steep seabed slopes. Drilling centre/manifold locations have been selected primarily on subsurface requirements, although wells will be drilled deviated by up to 3 km, providing a degree of flexibility on drill centre locations. The development layout has also been designed to minimise flowline/umbilical routes having to cross canyons or other steep seabed slopes. Figure 2.5 below illustrates the current plan as to the locations for the additional drilling centres/manifolds required for the full field development.

Whilst the above brief description is the current full field development plan for the DWT development, the subsea FEED contractor is encouraged to investigate and propose any alternative options that may add value to the project.

2.3 Availability of Design Data

It should be noted by the subsea FEED contractor that the availability of design data will change throughout the subsea FEED engineering phase, see the Project Schedule [Ref. 3]. More data will become available as a result of drilling and testing wells (Enyenra 2 and Tweneboa 3). In addition seabed survey data will also be made available, see Project Schedule [Ref 3], preliminary Geotechnical and Geophysical data being made available before the results from deep bore hole testing. The subsea FEED contractor should incorporate the timeline of this data availability into his design/offer.

COMPANY will be looking for evidence that the subsea FEED contractor has understood the implications of the phased provision of data, and planned the work in such a way as to avoid unnecessary re-work.


Figure 2.1 Liquids Recovery Phase – Reservoir Categories


Figure 2.2 Schematic of First Oil Deep Water Tano Development

Tweneboa North(488 481 E, 512 399 N)1,100msw

SeabedUmbilical

One 8 to10-inchOil ProductionFlowline

Enyenra North(485 001 E, 516 815 N)1,000msw

Enyenra Central(481 573 E, 508 269 N)1,410msw

One 10 to12 inch Gas/Condensate Production Flowline

SeabedUmbilical

FPSO(484 196 E, 507446 N)1410mswSpread Moored

One 10 to 12-inch Gas InjectionFlowline

SeabedUmbilical

ENYENRA FIELD

Well Types:OP Oil ProducerGP Gas ProducerGI Gas InjectorF Future

Oil export via remote loading buoy(HOLD)

Riser Systems,(Flowlines and Umbilicals)

Manifold

Manifold

One 10 to 12-inchGas RecycleFlowline

One 6 to 8-inchOil ProductionFlowline

GI

GI

OP

OP

Manifold

OP

OP

F

GI

GP

F

F

F

Locations:Locations a(and associated water depths) are preliminary only, and are given in metres based on WGS84 Universal Transverse Mercator Zone30N with Central Meridian 3 degrees W


Figure 2.3 Schematic of Potential Full Field Development for Deep Water Tano

Tweneboa North

(488 481 E, 512 399 N)1,100msw

SeabedUmbilical

One 8 to 10-inch

Oil ProductionFlowline

Enyenra North(485 001 E, 516 815 N)1,000msw

Enyenra Central(481 573 E, 508 269 N)1,415msw

One 10 to 12-inch

Gas/Condensate Production Flowline

Seabed

Umbilical

FPSO(484 196 E, 507 446 N)

1410mswSpread Moored

One 10 to 12-inch Gas InjectionFlowline

SeabedUmbilical

ENYENRA FIELD

Well Types:OP Oil Producer

GP Gas ProducerGI Gas InjectorF Future

Oil export via remote loading buoy(HOLD)

Steel Catenary Risers,(Flowlines and Umbilicals)Manifold

Manifold

One 10 to 12-inch Gas Recycle FlowlineOne 6 to 8-inch

Oil Production

Flowline

GI

GI

OP

OP

Manifold

OP

OP

OP

GI

GP

WI

GI

GP

Locations:Locations a(and associated water depths) are preliminary only, and are given in metres based on WGS84 Universal Transverse Mercator Zone30N with Central Meridian 3 degrees W

Manifold

OP

OPWI

Manifold

OP

GI or WI

OP

Manifold

OP

FWI

FPSO anchor

System (typ.)

OP

OP

OP

One 8 to 12-inch (HOLD)Gas or Water

Injection Flowline

One 10 to 12-inch(HOLD)Oil ProductionFlowline

SeabedUmbilical

One 8-inch (HOLD)

Water Injection FlowlineOne 6-inch (HOLD)Oil Production Flowline Seabed umbilical

One 10-inch(HOLD) Water InjectionFlowline

One 6 to 10-inch (HOLD)Oil Production

FlowlineSeabedUmbilical

Tweneboa Central

(486 836 E, 507 663 N)1,325msw

Tweneboa South(489 050 E, 501 840 N)

1,610msw

Enyenra South(479 258 E, 501 200 N)1,675msw

One 10-inch (HOLD)

Water InjectionFlowline

PossibleUpsides Manifold

Possible Future Flowline/Umbilical Corridor

PossibleUpsides

ManifoldPossible Future Flowline/Umbilical Corridor

Figure 2.4 Area Map First Oil Development Locations


Figure 2.5 Area Map Full Field Development Locations


3 SUBSEA INTERFACES AND SYSTEMS ENGINEERING

3.1 Frame Agreements

The subsea FEED contractor shall be aware that COMPANY will be establishing a number of Frame Agreement contracts from which the key subsea equipment will be drawn. These agreements include, but are not limited to; diverless connection system, subsea valves, subsea control system, subsea multiphase flow meters and ROV sampling points.

3.2 Battery Limits

The subsea FEED shall have the following battery limits:

• Subsea:

The subsea FEED battery limit shall be at the connection to the subsea trees. Selection and provision of subsea trees shall be the responsibility of others. Subsea FEED requirements as to the selection of the deep water connectors to be used shall ensure that the correct connector half is defined for the subsea trees. The umbilical and umbilical jumper system battery limits will also be at the trees, where jumpers will connect to tree stab plates.

• At the FPSO:

The subsea FEED battery limit at the FPSO shall be the flex joint and riser termination. Production and injection riser hang-offs and subsequent piping/valving shall be the responsibility of COMPANY’s FPSO contractor. Umbilical battery limits topsides will be at the TUTU. Subsea control system battery limits will be at the MCS, with an interface with COMPANY’s FPSO contractor as to integration of the subsea SCS with the FPSO DCS.

3.3 Primary Interfaces

Engineering of the subsea equipment and facilities for the development during subsea FEED will require certain primary interfaces with other aspects of the project. These shall include, but not be limited to, the following:

• Interface with COMPANY sub-surface team.

This is required to confirm number of wells, drill centre locations, well completion details, tree details, etc. In addition, the philosophies to be applied to well metering will need to be agreed.

• Interface with process engineering aspects.

Interfaces with process studies will define infield flowline sizing and thermal performance (flow assurance) and chemical injection requirements, and in concert with materials engineering, will define the materials of construction for subsea equipment. Note that Flow Assurance studies shall form part of the subsea FEED contractor’s scope of work (Section 5.2)

• Interface with FPSO engineering and design.

This will establish the FPSO layout and approaches, anchor pattern, orientation, riser sectors and layout, etc. In addition, a major interface will exist between subsea flow assurance studies and the FPSO topsides design team, in terms of slugging, chemical injection requirements, etc.

• Interface with COMPANY’s Frame Agreement contractors

Orders will be placed with COMPANY’s Frame Agreement contractors during the subsea FEED programme. These suppliers shall provide technical support to the subsea FEED contractor to guide the design of the subsea facilities. Note also that the overall design shall incorporate, as appropriate, components from the Frame agreements as defined above. The subsea FEED contractor shall support COMPANY with Frame Agreement procurement, This shall include technical specifications and data sheets for work order packages and technical evaluation of Frame Agreement technical offers.

As part of its interface management process, the subsea FEED contractor shall be required to define the information that will be required from the above primary interfaces, and to indicate a timescale for the availability of such information.


3.4 Systems Engineering

During the subsea FEED programme, subsea engineering input will be required in a number of areas considered common to the project. These shall include, but not be limited to, the following:

• Provision of subsea input to the Project Basis of Design [Ref. 2] as the subsea FEED programme progresses, including early definition of codes and standards to be applied to subsea design and equipment.

• The development of system design and operating philosophies, including, for example:

o Operating philosophy

o Inspection, maintenance and repair philosophy

o Installation philosophy

o Pre-commissioning and commissioning philosophy

o Protection philosophy

o Chemical injection philosophy

o Corrosion mitigation philosophy

o Future tie-ins philosophy

o Metering philosophy

o Pigging philosophy

• The development of system P&IDs, showing all main elements of the subsea system and its interfaces.

• The development of field layout and general arrangement drawings and schematics.

• Confirmation of materials selection for the subsea facilities.

• The definition of a corrosion management programme for the development, including confirmation of the internal corrosion allowance.

• Establishment of a subsea interface matrix for the project.

• Development of interface definition sheets for the control of all identified interfaces.

• Subsea RAM study for input to project philosophies.

• Subsea FMECA study for input to project philosophies.

• Constructability review.

• Assurance of installability. The subsea FEED contractor shall confirm that the subsea facilities designed during the subsea FEED process can be installed by a range of installation contractors. This will prevent COMPANY from having to either single source an installation contractor, or worse having to redesign as no installation contractor has the capacity to install the facilities.

3.5 Project Management, Planning and Cost Estimation

During the subsea FEED programme input will be required into subsea FEED project management, and planning and cost estimating aspects of the project. This input shall include, but not be limited to, the following:

• Subsea FEED study management, technical co-ordination, project support and services, to include/ensure:

o Attendance at project meetings at locations and times as required.

o Liaison as required with COMPANY.

o Quality Assurance.

o Study planning and progress reporting.

o Preparation of minutes, as required.

o Discipline and resource co-ordination


o Document control.

• Development of an overall project execution plan, including schedules and a procurement plan for identified long lead items. The procurement plan shall take into account the existing COMPANY Frame Agreements, and identify at the earliest possible stage the critical path long lead items. Schedules developed for the project shall compare a single installation campaign against multiple installation campaigns.

• Input into risk workshops and the development of a risks/opportunities register.

• Management, coordination, expediting and recording of all necessary interfaces for the work, and the development of required processes and procedure for such.

• Development of a project consents and approvals plan.

• Development of a comprehensive cost estimate for the management, design, engineering, procurement, fabrication and testing, installation, pre-commissioning and commissioning of the Deep Water Tano development. The subsea FEED cost estimate shall be class 3, +25%/-20%. The cost study shall also compare the CAPEX incurred by a single installation campaign and multiple installation campaigns.

• Generation of a Materials Take-Off (MTO) for the subsea facilities and equipment.

3.6 Safety Studies

Subsea input shall be required as necessary for the following:

• Subsea FEED hazard identification (HAZID) workshop.

• Hazardous Operations (HAZOP) workshop, including follow-up of actions identified during HAZOP workshop within the established SAMS.

• Chemical usage requirements.

• Studies for the requirement of SSIVs.

• Safety studies in general, for example, QRA and HSE cases.

3.7 Invitation to Tender Preparation

A primary objective of the subsea FEED is to engineer the development to a level where suitable contractors will be able to provide competitive bids for the detailed design, procurement, construction and installation of the subsea facilities required for the Deep Water Tano project. During subsea FEED a contracting strategy will be confirmed, on an EPC plus separate installation basis or on an EPCIC basis. Towards the end of the subsea FEED period, tender documentation will be developed for such a bidding process to be undertaken. Subsea FEED contractor input to the ITT process shall include, but not be limited to:

• Together with COMPANY and its other contractors, the development of an optimum contracting strategy for the project. The current plan is to issue tenders for an EPC contract for the provision of subsea facilities and equipment, and a second contract for their installation. It is to be noted that the procurement contracts will be based on a number of long lead items selected from frame agreements to be set up before and during subsea FEED. The subsea FEED contractor shall recognise that the subsea FEED will need to be tailored in some areas to fit with equipment limitations of these Frame Agreement contractors.

• Production of technical content of the ITT documentation to meet the agreed contracting strategy, including subsea Scope of Work and all specifications required. This shall be completed in line with the contracting strategy determined for the project, with appropriate specifications in appropriate ITTs.

• Assistance to the tendering process as required, which may include:

o Preparation of responses to technical queries from contractors during the bidding phase.

o Technical evaluation of the tenders received, preparation of requests for clarification and the technical normalisation of such tenders.

o Attendance at technical bid qualification meetings as required.

o Assistance with the preparation of appropriate parts of the contracts to be put in place.


3.8 IVB

An IVB will be in place throughout the subsea FEED study period. The subsea FEED contractor shall make allowance for interfacing with the IVB. The IVB shall receive all design calculations, drawings, models, reports, reviews, etc. developed by the subsea FEED contractor throughout the subsea FEED programme. All documents shall be subject to review and approval by the IVB.

The subsea FEED contractor shall be responsible for ensuring that all subsea FEED deliverables are completed to the satisfaction of the IVB.

3.9 Ongoing Studies

The subsea FEED contractor shall be aware that there are on-going studies being undertaken prior to the start of the subsea FEED programme. These include, but are not limited to, the following topics:

• Investigation of options for oil and gas export systems.

• Applicability of available deep water riser systems.

• Dynamic flow assurance studies, defining injection rates and locations, insulation requirements, etc.

• Validation of the feasibility of a spread mooring arrangement for the DWT FPSO.

Results from these studies will be made available to the subsea FEED contractor.


4 SUBSEA MANIFOLDS

4.1 Manifold Functionality.

Initially, subsea manifolds will be located at the drilling centres planned for the Deep Water Tano development. These manifolds, depending on drill centre functionality, will facilitate the commingling of produced fluids prior to transportation to the FPSO, the distribution of gas or water for injection, and distribution of chemicals for injection and control system functions to the subsea trees.

The manifolds will also provide the facility to test production wells by diverting well flow to a test header and multiphase flowmeter. This will be achieved by the use of actuated valves controlled from the FPSO host.

With the requirement for controlled actuated valves on a manifold and the multiphase meter required in the test header, it is possible that a subsea control module be provided dedicated to manifold functionality. The manifold may also support control modules for the trees, although it is possible for the control modules to be located at the trees, reducing connection requirements. FEED shall determine the optimum configuration.

Manifold functionality is currently as indicated in Figure 2.3 above.

The design of the manifolds is seen as largely common to each drill centre, but with the flexibility to interchange production and injection capability as the project progresses. The possible manifold configurations are:

3 production wells and 1 injection well, or

2 production wells and 2 injection wells

The common manifolds shall be designed such that flexible elements (shown in dotted form in Figure 4.1 below) may be selected immediately prior to (within 1 month) installation. The choice is therefore either a production branch that also allows well testing and an injection branch.

The probable functionality, where production is accommodated in a single flowline back to the FPSO, is as shown in Figure 4.1 below, taken from Reference [2].

An alternative manifold functionality is illustrated in Figure 4.2 below. This manifold layout reflects the possible requirement for twin gas production flowlines and hence the possibility of “looping” them for round-trip piggability in the event that operational pigging may be required.

It is to be noted that the injection capability is to be suitable for either gas or water injection, and the production capability should be suitable for either oil or gas/condensate production.

4.2 Manifold Piping Design

FEED studies shall develop the piping and valving required for the subsea manifolds to meet the functionality noted above. This will include, but not be limited to, the following:

• Development of P&IDs for the piping and valving and other instrumentation or facilities.

• Development of piping and valve layout design to minimise size and maximise accessibility for ROV valve operation and other ROV tasks that will be required, e.g. retrieval of multiphase flowmeter, installation and removal of temporary subsea PLR, inspection and maintenance, the collection of fluid samples, etc.

• Ease of construction, installation, pre-commissioning, commissioning and operation.

The piping design shall be fully reported, and accompanied with P&IDs, isometric drawings, piping layout drawings, and three dimensional views of the piping. The piping design shall also take full cognisance of the functional flexibility as discussed above.

4.3 Manifold Structural Design

FEED studies shall also include the initial design of the manifold structure. This shall be undertaken together with the piping design. The objective of such design is to allow reasonable estimates of structure weight and size to be generated both for cost estimation purposes and for incorporation in the ITT to be prepared for the next phase of the development.

Structural design will include, but will not be limited to:


• Structural design to suit and support the piping design. Note that protection against fishing gear interaction is not expected be a feature of such design at the given project water depths; however protection from dropped objects may be a design consideration.

• Provision of facilities for valve operation by ROV, including grab bars, etc.

• Provision of facilities for key equipment removal/replacement.

• Stress analysis of the structure under loads and load combinations to which it will be subject through life, including, but not limited to, construction, transportation, installation, environmental and operational loads.

• A design that results in ease of construction and installation.

• CP/protective coating design

The structural design shall be fully reported, and accompanied by appropriate drawings.

4.4 Manifold Foundations Design

The foundation system for the manifold shall also be designed during FEED, to derive a likely weight and cost. The foundation system in such deep water is most likely to be based on suction piles. Water depths associated with the project may be near the limits for and preclude the possibility of conventional piling.

Subsea FEED shall consider the possible methods for achieving the required foundations for the manifolds, including piling, suction piles and gravity base, demonstrating the most viable system. Design for the foundation system shall then be undertaken and analysed. The design shall address the ease of construction and installation of the foundation method.

Foundations design shall be fully reported, and accompanied with drawings of the system.

Results from a desk-top study to estimate likely soils information in the field shall be made available to the subsea FEED contractor.

4.5 Manifold Specifications

As a result of the above activities it will be possible to produce manifold related technical specifications. These shall be prepared for issue with the ITT for the next phase of the development, and shall include, but not be limited to:

• Functional Specification for Subsea Manifolds

• Specification for CS Manifold Piping

• Specification for CRA (or CRA Clad) Manifold Piping

• Specification for Piping Flanges and Fittings (CS and CRA as a required)

• Specification for Piping Bends (CS and CRA as required)

• Specification for Piping Fabrication and Testing (CS and CRA as required)

• Specification for Subsea Ball Valves (CS and CRA as required)

• Specification for Subsea Gate Valves (CS and CRA as required)

• Specification for Subsea Valve Actuators

• Specification for Subsea Double Block and Bleed Valves

• Data Sheets for all Valves (CS and CRA as required)

• Data Sheets for Valve Actuators

• Specification for Subsea Multiphase Flowmeter

• Data Sheet for Subsea Multiphase Meter

• Specification for Subsea Sampling Unit

• Datasheet for Subsea Sampling Unit

• Specification for Structural Steel


• Specification for Structural Steel Fabrication

• Specification for Structural Steel Coating

• Specification for Structure CP Design

• Specification for Structural Anodes

• Data Sheet for Structural Anodes

• Specification for Structure Installation

Note – some of the above documents may be prepared as combined documents.


Figure 4.1 Subsea Manifold Functionality – Single Production Flowline

SCM

SCMMB

To Wells (Typ.)

Xmas Tree (Typ.)

To Manifold Functions (Typ.)

To Flowmeter

Service Line (Scale Squeeze & Vent)

Hydraulically actuated valves (Typ.) (Typ.)

Multiphase Flowmeter

Sampling Unit

Umbilical

Scale Squeeze/Vent Service Line [HOLD]

Corrosion Inhibitor

Production To Host

ROV operated valves (Typ.)

Temporary Pig Launcher/Receiver OR

Future Expansion (Typ.)

SUT

SDU

Water OR Gas Injection

Test Header

Production or Injection flow path options to be determined prior to final assembly.

SCM

SCMMB

SCM

SCMMB

or

or


Figure 4.2 Subsea Manifold Functionality – Twin Production Flowlines

To Wells (Typ.)

Xmas Tree (Typ.)

To Manifold Functions

(Typ.)

To Flowmeter

Service Line (Scale Squeeze & Vent)

Hydraulically actuated valves (Typ.) (Typ.)

Multiphase Flowmeter

Sampling Unit

Umbilical

Scale Squeeze/Vent Service Line [HOLD] Corrosion Inhibitor

Production To Host

Removable Pigging Loop OR Temporary Pig Launcher/Receiver OR Future Expansion (Typ.)

or SCM

SCMMB

SCM

SCMMB

SCM

SCMMB

or

Production To Host

ROV operated valves (Typ.)

SUT SDU

Water OR Gas Injection

Production or Injection flow path options to be determined prior to final assembly.


5 FLOWLINE DESIGN AND SPECIFICATIONS

5.1 Infield Flowlines

Infield flowlines associated with the Deep Water Tano development are noted in the schematic drawing of the development (Figure 2.3).

Design activities within the FEED programme and specifications to be produced for the flowlines as defined in Figure 2.3 are discussed in the following two sections.

5.2 Flow Assurance Studies

Subsea FEED design shall include flow assurance studies to confirm flowline requirements, including the number of lines for operability, sizes and requirements for thermal insulation of the flowlines to ensure that the produced fluids arrive at the FPSO at the required temperatures. It should be noted that progression of the following work scope will first require full analysis of the results of the pre-FEED concept development flow assurance work by COMPANY and the subsequent advisement of the selected subsea architecture for FEED development. The following work shall be included in the overall Flow Assurance programme:

5.2.1 Fluids Characterisation

Further well testing and the production of clean DST fluid samples will necessitate further fluids characterisation work. Under this scope of work, the following activities will need to be performed:

• Analysis of available laboratory report data and selection of fluids for characterisation;

• Specification of characterisation procedure;

• Characterisation of fluids;

5.2.2 Flow Assurance Simulation Basis

To facilitate information transfer and confirm the basis and assumptions employed for flow assurance modelling, the subsea FEED contractor will need to develop a flow assurance simulation basis. This document will detail the relevant information provided, identify further information requirements, and where data is not available, detail the relevant assumptions. This document allows agreement to be obtained for the basis of simulation work between the subsea FEED contractor and COMPANY. Activities for this scope of work will include specification of data requirements, collation of data and production of the report.

5.2.3 Steady State Analysis of the Full Field Development

In the event that the field development is to be extended beyond the boundaries of the current full field development scope, further steady state PIPESIM analysis will be required to confirm hydraulic and thermal performance and subsequent line sizing and insulation requirements to the increased field extremities. The impact/benefit of daisy-chaining on the concept-phase defined infrastructure should also be considered. Activities for this scope of work will include construction of the appropriate PIPESIM models, conducting the simulation runs, results analysis and subsequent report generation.

5.2.4 Steady State Life of Field Analysis

PIPESIM model runs will need to be completed to assess and confirm system performance across field life. This work will need to consider specified production rates at a variety of points during field life and will also need to take into account water cut and gas leaning sensitivities. This work will require close alignment with the subsurface development in order to assess production profiles and appropriate fluids sensitivities. The output from the steady state PIPESIM models will allow confirmation of the field architecture, line sizing and insulation requirements selected under the pre-FEED concept development work and further support pipeline design activities and corrosion assessment. Activities will involve construction of PIPESIM models, development of fluid compositions, running of simulations and the analysis and presentation of results in a report.

5.2.5 Provision of Data for Life of Field Corrosion Analysis

Data will need to be extracted from the steady state life of field analysis (specified above) in order to support a life of field corrosion assessment. The data required will be dependant on the corrosion analysis methodology employed but is likely to include temperature, pressure, density and superficial velocity profiles for each tieback from the FPSO. Activities will include data extraction from the appropriate steady state simulations and presentation in report format.


5.2.6 OLGA Base Model Construction and Review

Following subsea architecture and well design development activities, it will be necessary to update/develop OLGA models to a suitable level of detail to allow accurate FEED analysis of the system. This will most likely require full modelling of the subsea tieback and wells associated with each manifold. Activities will therefore involve the construction, review and approval of base OLGA models for each system.

5.2.7 Transient Operability and Design Assessment

Dynamic analysis will be required to establish/confirm transient operation of each system. As a consequence the following operations need to be investigated:

• Unstable flow and minimum hydraulic turndown

• Artificial lift performance (if applicable)

• Shutdown

• Pipeline pressurisation (line packing)

• Settle out

• Cooldown (no touch) and minimum thermal turndown

• Ramp Up

• Ramp Down

• Sphering and benefits of operational pigging

• Depressurisation

• Well restart to depressurised, pressurised and flowing systems

• First gas start up

• Typical start up

Activities will include the specification of operating philosophies and sensitivities for investigation, definition of case matrices, setting up and running of OLGA models and the analysis of results and report generation.

5.2.8 Data to Support Slug Catcher Sizing Assessment

On the basis of transient analysis of ramp up and pigging strategies, liquid surge profiles need to be extracted from OLGA simulations in order to facilitate slug catcher design activities. Activities will include data extraction from the appropriate simulations and presentation in report format.

5.2.9 Data to Support Flowline Sizing and Design

The relevant results of the steady state and transient assessment work need to be extracted to support pipeline and manifold design activities. This data may include, but is not limited to, maximum and minimum steady state and transient wall temperatures, operating pressure ranges and full shut-in conditions for each system. Activities will include data extraction from the appropriate simulations and presentation in report format.

5.2.10 Hydrate and Wax Management Studies

On the basis of steady state and transient assessment work, hydrate and wax management strategies, particularly under transient operating conditions need to be specified and confirmed. As appropriate, this scope of work may require further detailed OLGA modelling to consider refined blowdown and liquids displacement strategies, chemical hydrate inhibitor tracking during restart and wax deposition.

5.2.11 Hydrate Remediation Assessment

In the event that a venting system is provided to allow depressurisation either side of a hydrate blockage, the sizing and operating strategy for the system needs to be investigated using transient OLGA analysis. As a consequence, this scope of work will include construction of OLGA models, identification and specification of cases for assessment, OLGA simulation runs, results analysis and subsequent case refinement and final results reporting.


5.2.12 Chemical Core and Distribution Sizing

PIPESIM modelling may be required to confirm the sizing of chemical injection cores to each system and the design of any subsea chemicals distribution network. Activities will involve construction of PIPESIM models, development of fluid compositions, running of simulations and the analysis and presentation of results in a report.

5.2.13 System Finalisation

Following the completion of design activities, a finalised set of OLGA runs is required to confirm system performance and allow integration with topsides simulation packages if required. These simulations will include finalised chemical inhibition dosing and agreed pipeline operating strategies. The following runs will be required:

• Steady state

• Ramp Up

• Ramp Down

• Pigging

• Shutdown, Settle Out and Cooldown

• Pipeline Pressurisation

• Depressurisation

• First Gas and Typical Start Up

• Well Restart

• Hydrate Remediation

5.3 Flowline Design

For flowline design, the subsea FEED scope will include, but not be limited to the following activities:

5.3.1 Route Design

A route design shall be undertaken for the infield flowlines as in Figure 2.3 and Figure 2.5 above. Initial route design shall take into account the following:

• Current selected locations for the FPSO and the drilling centres.

• Any available data from seabed surveys undertaken to date, particularly any steeply sloping areas of seabed.

• The presence of any existing infrastructure.

• Any indications from the current Admiralty Chart for the area, particularly any noted obstructions or other hindrances.

• Desktop geotechnical study.

The route design shall result in a number of alignment sheets for each flowline, with, for example, a maximum of 3.5 km flowline length captured per alignment sheet. Each infield flowline shall have a set of alignment sheets, even if routed in the same corridor as another flowline (or umbilical). A field layout shall also be produced to illustrate the presence of the drill centres, flowlines and FPSO.

It is to be noted that an engineering seabed survey will need to be undertaken prior to final detailed design of the routes. This survey will be based on the routes selected in FEED, and the locations selected for the drill centres and FPSO. In the event that such survey work is undertaken during the FEED programme, the flowline routing shall be based on these results.

5.3.2 Flowline Mechanical Design

Based on the results from FEED flow assurance work, leading to selected flowline diameters and any thermal insulation requirements to maintain fluid temperatures, together with the FEED confirmation of material selection for the flowlines, a flowline mechanical design shall be undertaken, including the following:


• Material selection

• Flowline wall thickness design.

• Flowline stability analysis (including design against pipelines “walking” down-slope).

• Flowline expansion analysis.

• Free span analysis.

• Insulation design.

• Buckling analysis (upheaval/lateral)

• Protection (if any)

• The requirement for the flowline system to be piggable (see Section 5.3.7)

The design will be based on the use of recommended materials, and shall be undertaken in accordance with recognised design codes and using verified design software. With flowlines crossing significant slopes on the seabed, the stability of the flowlines in terms of ‘walking’ across the seabed shall be analysed, and if necessary mitigation designed. Results from buckling analysis shall be fed back into flowline mechanical design as required. Buckling analysis shall take into account the on-bottom roughness, if this data is available. In the event of problems with buckling, the design shall establish means of mitigating against this, e.g. buckle arrestors.

Each of the above topics shall be reported separately, each report covering all required flowlines.

5.3.3 Pipeline End Termination (PLET) Design

PLETs will be required at the flowline ends. The design objective of the PLET is to provide a small base to host the diverless connection hub to which the diverless tie-in spool will connect and tie-in the flowline to the subsea manifold or other structure. The PLET should be small enough to allow it to be installed with the pipeline end from the pipelay vessel.

It is to be noted that PLETs have previously been adopted on the nearby Jubilee development (supplied by FMC Technologies).

In the event that it is demonstrated that it is possible to install the SCR and flowline as one continuous section, then it will not be a requirement to provide a PLET at the FPSO end of the flowlines. Instead, design of a riser holdback system shall form part of the subsea FEED study.

Design of a suitable PLET shall be included in the subsea FEED study. This design shall be generic to all flowlines. The design shall address the need to incorporate a valve in the PLET for isolation purposes during pre-commissioning. The PLET shall also be designed in light of the requirement for the flowline system to be piggable (see Section 5.3.7).

In the event that PLETs are not required at the riser ends of the flowlines, it will be necessary to include riser hold-back anchors to protect against the flowline experiencing any riser motions. Design of these anchors shall be included in the subsea FEED scope of work.

5.3.4 Tie-In Spoolpiece Mechanical Design

Subsea FEED studies shall also include for the design for the spoolpieces used to tie the subsea wells to the manifolds and from the the drill centre manifolds to the flowlines. The spoolpieces will be installed and connected remotely using appropriate diverless subsea connection systems and equipment/tooling. Spoolpiece design shall include:

• Wall thickness

• Configuration/layout of spool

• Connection system type and recommendation (vertical connections preferred from an installation viewpoint)

• Stress analysis, with expansion loads, installation tolerances and misalignment

• Cathodic protection design

• Protection (if any)

• Design for pigging (see Section 5.3.7)


Spoolpiece design shall be carried out to suit an envelope of structure to structure offsets, allowing flexibility in the location of trees/manifolds and manifolds/PLETs.

Tie-in spool design shall be fully reported.

5.3.5 Flowline External Corrosion Protection Design

FEED studies for the flowlines shall include the design of a suitable external corrosion protection system. This will involve:

• Determination of the optimum anti- corrosion coating applied to the external surface of the flowlines. Note in the case of oil and/or gas production flowlines, anti-corrosion coating systems will need to be integrated with the insulation design.

• Design of the Cathodic Protection (CP) sacrificial anode system

CP design shall be undertaken in accordance with a recognised design code and using verified design software.

External anti-corrosion coating and Cathodic Protection design shall be fully reported.

5.3.6 Flowline Installation, Pre-commissioning and Tie-in

FEED shall address the installation of the flowlines and their pre-commissioning and tie-in. In the water depths associated with the Deep Water Tano area, it is likely that the J-lay method or reel lay method will be utilised for flowline installation, but FEED shall establish the applicability and comparative costs associated with these and other pipelay techniques.

The flowline installation study shall also include operations and equipment required to pre-commission the installed flowlines, including flooding, gauging and hydrotest.

Equipment and operations required to achieve the tie-in of the flowlines by installation of tie-in spools at wells, manifolds and SCRs, and the subsequent leak testing of the completed flowlines, shall also be addressed in the FEED flowline installation study.

The installation study shall take full cognisance of the location of the Tano development and the infrastructure in place in the West African area.

5.3.7 Design for Pigging

Pigging of the DWT infield flowlines will be a requirement, and thus flowline design during subsea FEED shall be such that the flowline systems are piggable. Pigging will be required as follows:

• Installation; flooding, cleaning and gauging (for production and injection flowlines)

• Pre-commissioning; de-watering (for production and gas injection flowlines)

• Operations; cleaning (de-waxing, de-scaling) (for production flowlines only, and on an intermittent basis)

• Operations; inspection (for production and injection flowlines)

At this stage the requirement for operational pigging (either cleaning or inspection) is not foreseen as being necessary, but this will be tested in the FEED study

These requirements will have been stated in the project Pigging Philosophy developed during subsea FEED (Section 3.4 above).

Design of the flowline systems shall ensure that the identified pigging requirements can be met. As such, flowline design shall at minimum:

• Specify codes and standards used in design for pigging

• Minimise bore changes in the flowline systems

• Specify minimum radii for bends

• Specify minimum straight legs between bends, valves, branches, etc.


• Incorporate facilities and allow adequate access at the manifold headers for the installation of subsea PLR

• Provide isolation valves as required

• At minimum, space shall be allocated beyond a blind flange termination topsides to enable the installation of temporary topsides PLR for any pigging required during operations.

5.4 Flowline Specifications

As a result of the above activities it will be possible to produce flowline related technical specifications. These shall be prepared for issue with the ITT for the next phase of the development, and shall include, but not be limited to:

• Specification for Carbon Steel Linepipe

• Specification for CRA (or CRA Clad)Linepipe

• Specification for Carbon Steel Bends

• Specification for CRA (or CRA Clad) Bends

• Specification for Carbon Steel Flanges and Fittings

• Specification for CRA Flanges and Fittings

• Specification for Flowline Anti-Corrosion Coating

• Specification for Flowline Insulation Coating

• Specification for Flowline Weight Coating (if required)

• Specification for Flowline Anodes

• Data Sheet for Flowline Anodes

• Specification for Flowline Anode Installation

• Specification for Diverless Subsea Connector System

• Specification for Flowline PLET

• Specification for Flowline Valves (if required)

• Specification for Spoolpiece Design and Manufacture

• Specification for Flowline Installation, including remedial actions required post lay and post-survey.

• Specification for Carbon Steel Linepipe Welding

• Specification for CRA Linepipe Welding

• Specification for Field Joint Coating

• Specification for Subsea PLR

• Specification for Flowline Trenching (if applicable)

• Specification for Spoolpiece Installation

• Specification for Pre-Commissioning

• Survey Specification

• Positioning System Specification

• Specification for flowline ‘walking’ mitigation measures (if required)



6 SUBSEA FLOWLINE RISERS TO FPSO

6.1 Subsea Riser Design Concept

An initial study of potential deep water riser configurations has been undertaken as part of concept selection [Ref. 4]. This qualitatively recommends the Steel Catenary Riser (SCR) solution as most suitable configuration for the Deep Water Tano development, due to its simplicity, lack of requirement for a riser base and the ability to apply external installation.

The above conclusion shall be investigated in further detail in subsea FEED, comparing all potential riser configurations that might be suited to the planned FPSO development. These shall include, but not limited, to the following deep water riser types:

• Flexible Risers

• Steel Catenary Risers

• Multbore Hybrid risers

• Single Offset Hybrid Risers

• Concentric Offset Hybrid Risers

The first activity in subsea FEED shall be to confirm in more detail the riser configuration most suited to the Deep Water Tano development, bearing in mind both technical and economic viewpoints.

6.2 FEED Subsea Riser Design

On the assumption that the SCR configuration is retained as the most suitable, subsea FEED activities shall include, but not be limited to, the following, for each riser:

• SCR configuration design, interfacing with the FPSO contractor for details on FPSO size and layout and RAOs.

• Stress analysis of the risers under expected loads induced by the expected FPSO motions, metocean conditions and operational conditions.

• Anchor requirements at base of risers (to isolate the flowlines and/or to maintain configuration and limit transverse motions).

• Wall thickness definition.

• Fatigue analysis, including effects of VIV.

• Effects of insulation, if required.

• Flex-joint definition

• Top end motions.

• Installation aspects

• Interface with hang-off/support design on the FPSO

6.3 Riser Specifications

Specifications required for the ITT for the next phase of the development will, of course, be dependent on the selection of the riser system itself. For example, if the SCR solution is recommended, the following may be required:

• Specification for Riser Linepipe (if required)

• Specification for Insulation (if required)

• Specification for Riser Construction

• SCR Anchor Specification(s)

• SCR Flex-Joint Specification

• SCR installation Specification


In the event that an alternative riser configuration is recommended, a similar set of Specifications shall be generated to cover that configuration once subsea FEED design and analysis has been completed.

For example, for flexible risers, these may include:

• Specification for Flexible Riser Pipe

• Specification for Flexible Pipe End fittings

• Flexible Riser CP Specification

• Specification for Flexible Riser Buoyancy Equipment

• Specification for Anchoring Equipment

• Specification for Bend Restrictors and Bend Stiffeners

• Specification for Flexible Riser Installation

For other riser systems, if selected, the subsea FEED contractor shall develop a comprehensive set of specifications, to be approved by COMPANY, for inclusion within the ITT documentation for the next phase of the development.


7 SUBSEA CONTROL SYSTEM

7.1 General

The Deep Water Tano development will be controlled from the host FPSO using a multiplexed electrohydraulic subsea control system (SCS).

As the final SCS detailed architecture will be dependent on the ultimate system vendor, activities associated with the SCS in FEED shall be limited to defining the functionality required of the system, and liaising with COMPANY’s Frame Agreement contractor for the SCS.

The FEED study shall define the components and the functionality of the subsea control system (SCS) and define the interfaces between it and the other subsea equipment (umbilicals, manifolds, trees, etc.) and the host FPSO. Subsea equipment required for the SCS shall be designed to be diverless, i.e. accessible for ROV tie-in and intervention operations.

7.2 SCS Topsides Equipment

Items making up the topsides equipment of the SCS at the FPSO shall include, but not be limited to the following:

• Master Control Station

• Hydraulic Power Unit

• Electrical Power Unit (assuming that the uninterruptible power supply will be available from the FPSO)

• Topsides Umbilical Termination Unit

• Emergency Shutdown Link

• Interface with the FPSO Distributed Control System and ESD system

7.3 SCS Subsea Equipment

Items making up the subsea equipment of the SCS at the FPSO shall include, but not be limited to the following:

• Tree Subsea Control Modules (SCM)

• SCM Mounting Bases (SCMMB)

• Electrohydraulic jumpers

• Electrical jumpers

• Parking Plates (as required)

• Instrumentation (pressure and temperature sensors, valve position indicators, sand detectors, etc., as required)

• Subsea flowmeter(s) as applicable (at manifolds)

• Subsea sampling unit

• Manifold Subsea Control Module (SCM) and SCM Mounting Base (if required)

• Subsea Accumulation Module

• Subsea distribution unit (a separate structure or integrated with the umbilical termination unit)

• Umbilical termination unit

7.4 Subsea FEED Involvement

The FEED study shall define the components and the functionality of the subsea control system (SCS) and define the interfaces between it and the other subsea equipment (umbilicals, manifolds, trees, etc.) and the host FPSO, i.e. systems engineering.


The FEED contractor shall develop, as necessary, a comprehensive Functional Specification for the SCS, taking into account the Subsea Control System Outline Functional Requirements Ref. [5], the systems engineering completed as above and the Frame Agreement vendor’s products.

The SCS will be designed and provided by COMPANY’s selected Frame Agreement vendor, in accordance with the FEED contractors Functional Specification.


8 UMBILICALS AND UMBILICAL RISERS

8.1 General

Control of the Deep Water Tano development will require seabed umbilicals to connect the FPSO host with the subsea manifolds and hence to the subsea wells. These umbilicals will carry:

• Hydraulic fluids for HP and LP operation of well, tree and manifold valves

• Chemicals for injection into the production system, as defined by process engineering studies.

• Cables for electrical power supply to the control system and instrumentation

• Cables, or more likely optical fibres for communications between host and subsea sites.

Fluids will be transported in steel tubes. In the event that the development requires a service line for bulk injection or de-pressurisation, it is possible to construct an Integrated Services Umbilical, with the service line at its core.

8.2 Umbilical Design in Subsea FEED

Subsea FEED tasks will be to determine the optimum umbilical solution for the DWT field. The scope will include, but not be limited to, the following activities:

• Umbilical route design, taking into account:

o Selected locations for FPSO and subsea manifolds.

o Infield flowline design routes.

o Any available seabed survey results available.

o The presence of any existing infrastructure.

o Any Admiralty Chart noted obstructions or other hindrances in the area.

o Any seabed topography that should be avoided if possible.

• The definition of the requirements for the required seabed umbilicals, including:

o Umbilical components, including any bend stiffeners/restrictors.

o Umbilical make-up and construction, including any protection requirements.

o Cross-sectional design for the seabed umbilicals (from vendors).

8.3 Umbilical Riser Design in Subsea FEED

Subsea FEED tasks will be to determine the optimum umbilical riser solution for the DWT field. The scope will include, but not be limited to, the following activities:

• The definition of the requirements for the umbilical risers, including:

o Umbilical riser components.

o Hang-off support requirements on the FPSO.

o Umbilical riser make-up and construction, including any protection requirements.

o Cross-sectional design for the dynamic umbilical risers (from vendors).

o Design of transition between dynamic umbilical riser and seabed umbilical (from vendors).

• Dynamic umbilical riser analysis to establish optimum configuration for the risers, i.e. simple catenary, wave with buoyancy arch, ‘S’ with local buoyancy, location and purpose of anchor systems, etc., including:

o Stress analysis of the risers under expected loads induced by the expected FPSO motions, metocean conditions and operational conditions.

o Anchor requirements at base of risers (to isolate the flowlines and/or to maintain configuration and limit transverse motions).

o Fatigue analysis, including effects of VIV.


o Flex-joint definition

o Top end motions.

o Clashing analysis.

To achieve the above, the subsea FEED contractor shall interface with the FPSO contractor for details on FPSO size and layout and RAOs, and umbilical vendors to establish the mechanical properties of the umbilical riser construction.

8.4 Umbilical and Umbilical Riser Specifications

As a result of these activities it will be possible to produce umbilical and umbilical riser technical specifications for issue with the ITT for the next phase of the project. Such specifications shall include, but not be limited to:

• Functional Specification for Seabed Umbilicals and Dynamic Umbilical Risers, including Transition.

• Specification for Umbilical Riser Buoyancy and Anchoring Systems (if required)

• Specification for Umbilical Riser Flex-Joint

• Specification for Umbilical and Umbilical Riser Installation



9 SERVICES TO COMPANY

The subsea FEED contractor shall provide and maintain for the duration of the subsea FEED, at the

contractor’s worksite(s), serviced office accommodation with sufficient furniture and equipment suitable for

use by two (2) COMPANY representatives during all phases of the subsea FEED.

On the request of COMPANY and at the subsea FEED contractor’s cost, the subsea FEED contractor shall

provide and maintain for the duration of the subsea FEED, at the subsea FEED contractor’s location(s),

dedicated lockable serviced offices, furniture and equipment for sole use by COMPANY and shall be subject

to COMPANY written approval. The dedicated office facilities provided at each location shall be adjacent to

contractor’s FEED team offices, and shall comprise at minimum the facilities listed below:

• One office for two COMPANY representatives of minimum 15 square metres floor area, and including

heating, electric power, lighting and daily cleaning.

• Access to kitchen area with a tea, coffee and water and soft drinks machine, refrigerator, microwave

and sink.

• All consumables and all other general office supplies including stationery.

• Two direct dial telephones with international access for the sole use of COMPANY representatives,

including the cost of calls.

• Access to a facsimile machine with international access for use by COMPANY personnel including the

cost of calls.

• Access to a colour photocopying machine. The machine shall be suitable for A3 and A4 paper,

capable of automatic A3 to A4 reduction, and equipped with a collator.

• Two desktop computers (minimum specification Intel Pentium Dual Core/Core 2 Duo or equivalent, 4

Gb RAM, DVD rewriter, 22" flat screen monitor), equipped with Windows 7 operating system or later

and MS Office 2007 software or later, and dedicated colour A3/A4 laser printer and scanner complete

with associated software, consumables and cables. The computers shall have internet access and be

configured to allow e-mail communication on COMPANY network. Maintenance of the computers

shall be the responsibility of CONTRACTOR.

• Internet connections for COMPANY’ representatives’ laptop computers.

• Access to clean toilets.

• Access to canteen facilities (if available).

• Permanent parking spaces for 2 vehicles.

• COMPANY shall also require the use of a private meeting room for weekly co-ordination meetings and

for ad hoc meetings. The meeting room does not need to be dedicated, provided that it can be booked

with reasonable notice.


10 REFERENCES

1. Subsea Architecture First Oil Development, Document No. J07829B-U-TN-2007, Genesis Oil and Gas Consultants, November 2010.

2. Deep Water Tano Development Basis of Design, Document No. 00002-00-00-GEN-00-BOD-0001, Tullow Oil (Ghana), October 2010.

3. Project Schedule Doc No (HOLD)

4. Deepwater Riser Options, Document No. J07829B-U-TN-2003, Genesis Oil and Gas Consultants, November 2010.

5. Subsea Control System Outline Functional Requirements Document No. 00002-00-00-DEV-00-SPE-0003, Tullow Oil (Ghana), January 2011.

invitation to tender part c – proforma contract · pdf filedeep water tano project...

Documents