H8-SSP-00-066-N01-68585_0_006.pdf

ConocoPhillips BayuUndan Phase 3 Project Level 3, 53 Ord street West Perth PO Box 1102, West Perth WA 68721 Business 61 (0) 8 9423 6666 Facsimile 61 (0)8 6363 2042

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DOCUMENT TITLE: Flexible Flowline and Static Umbilical Installation Analysis - Campaign 2

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10.10.2014

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Supplier shall resubmit document in accordance with instructions accompanying returned document. This review and comments, if any, do not alter any of the terms and conditions of the Contract, nor does it relieve the Supplier from any responsibility or liability for the accuracy and completeness of the document, nor shall it be interpreted so as to imply approval of such document, nor shall it be interpreted as an assumption by or imposition on ConocoPhillips of any liability or responsibility as a result of such review

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ConocoPhillips Pty Ltd Bayu Undan Phase 3 Project 262163-01-BUP3

Flexible Flowline Installation Analysis – Campaign 2 AA0016-ENG-20008

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Amirhossein GHANIZADEH

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Project Engineering Manager Digitally signed by amirhossein.ghaniz [email protected] DN: cn=amirhossein.gh anizadeh@subsea7. com Date: 2014.11.27 18:19:26 +01'00'

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Prepared by

Digitally signed by Julien Capul DN: cn=Julien Capul, o=Subsea 7, ou=Engineering, email=julien.capul@ subsea7.com, c=FR Date: 2014.11.27 18:23:58 +01'00'

Julien JCA Capul

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AA0016-ENG-20008

ConocoPhillips Pty Ltd Bayu Undan Phase 3 Project

28.11.2014

Revision: 0

Flexible Flowline Installation Analysis – Campaign 2

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This document is the property of Subsea 7 and its affiliates and subsidiaries and copying and/or disclosure of the information it contains is prohibited without the permission of Subsea 7. It has been reviewed and approved in accordance with management system requirements and where applicable an audit trail is available within the relevant document management system. The most recently approved version is regarded as the controlled copy with all other copies being for information only. It is the holder’s responsibility to ensure that they hold the latest approved version. © Subsea 7

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10.10.2014

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Purpose

Description of Updated/Modified Sections (if any)

Implemented IDC comments • • • •

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28.11.2014


• • • •

Implemented IFCR comments Static umbilical scope removed Analysis for Riser EF abandonment/ recovery added (section 5.3) Analysis for Flowline-Flowline intermediate connection laydown added (section 5.4) Dynamic analysis updated throughout the document Sensitivity with max and min WD added Sensitivity with current added Crossing analysis updated with sensitivity on layback and point loading calculations (section 5.5)

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TABLE OF CONTENTS 1.

INTRODUCTION .............................................................................................. 4 1.1 OVERALL PROJECT ..................................................................................... 4 1.2 SCOPE OF DOCUMENT................................................................................ 5 1.3 ABBREVIATIONS AND DEFINITIONS ............................................................ 6 1.4 ASSUMPTIONS .......................................................................................... 6 1.5 HOLD LIST ................................................................................................ 6 1.6 REFERENCES............................................................................................. 6

2.

CONCLUSIONS ................................................................................................ 8

3.

ANALYSIS BASIS .......................................................................................... 10 3.1 PRODUCT AND ANCILLARY EQUIPMENT DESCRIPTION ................................. 10 3.2 VESSEL CHARACTERISTICS ...................................................................... 12 3.3 ENVIRONMENT INPUT DATA ...................................................................... 14 3.4 LAY ROUTE DATA..................................................................................... 14 3.5 SOIL FRICTION COEFFICIENTS .................................................................. 14 3.6 LIMITING CRITERIA FOR ANALYSIS ........................................................... 15

4.

METHODOLOGY ............................................................................................. 16 4.1 SOFTWARE ............................................................................................. 16 4.2 WAVE DATA SELECTION AND DIRECTONALITY ............................................ 16 4.3 STATIC ANALYSIS METHODOLOGY............................................................. 18 4.4 DYNAMIC ANALYSIS METHODOLOGY .......................................................... 18

5.

ANALYSES RESULTS ...................................................................................... 21 5.1 NORMAL LAY AND CURVE LAY ................................................................... 21 5.2 FLEXIBLE FLOWLINE TERMINATION ABANDONMENT / RECOVERY .................. 24 5.3 FLEXIBLE RISER TERMINATION ABANDONMENT / RECOVERY ........................ 27 5.4 FLOWLINE-FLOWLINE INTERMEDIATE CONNECTION LAY-DOWN ................... 29 5.5 CROSSING ANALYSIS ............................................................................... 34


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1.

INTRODUCTION

1.1

OVERALL PROJECT Bayu-Undan consists of two gas and condensate fields located offshore approximately 500km north-west of Darwin in the Timor Sea, and 250km south east of East Timor. The fields are located in approximately 80m water depth.

Figure 1-1: Field Location

Commercial production began in April 2004, delivering 115,000bpd of condensate and LPG through a gas recycle scheme. The next phase of development, the gas phase, began production in February 2006. This involved the extraction of lean gas from the reservoir and transportation to Darwin on Australia’s northern coast via a 500km, 26in pipeline where it is liquefied at a single-train processing plant located at Wickham Point near Darwin then shipped as LNG to customers Tokyo Electric Power Company and Tokyo Gas in Japan. The field will require approximately 26 wells over its lifetime to produce the reserves. Since production start-up, most of the necessary wells to exploit the core area have been drilled from either the Drilling Production and Processing Platform (DPP) or the existing satellite Wellhead Platform (WP1). The field remaining life is estimated to be around 13 to 15 years. However in order to sustain gas and condensate production, access to peripheral areas of the field will be necessary by 2015. For Phase 3 development, two new subsea wells, BU-DS01 and BU-DS02, have been identified and will be tied back to existing Drilling Production and Processing Platform (DPP) through individual subsea flowlines and risers. An umbilical riser shall be routed from DPP topsides to a Subsea Umbilical Distribution Unit (SUDU) near to the base of the platform, but outside of the flare radiation zone, from where two umbilicals shall route one each to BU-DS01 and BU-DS02 running roughly parallel with the flowlines.


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Figure 1-2: Field Schematic

Contractor is responsible for all project management, project services, coordination with Company and Company’s other contractors, design development, detailed engineering, procurement, construction, onshore testing, load-out, transportation, installation, offshore hook-up, pre-commissioning, commissioning support and other activities as pertinent to the Scope of Work. The Scope of Work is for subsea hardware design, flowlines, umbilical and riser system installation engineering, supply (excluding Company Provided Items), Installation and Pre-Commissioning / Commissioning for the Bayu-Undan Phase 3 Field Development: 29km of Umbilicals with a Subsea Distribution Unit and 29km of 10” Flexible Flowlines with 2 Dewatering Manifolds connected to Wellheads by flexible jumpers.

1.2

SCOPE OF DOCUMENT The purpose of this document is to present the installation analysis performed for the flexible flowline of Campaign 2 installed with the Skandi Acergy. Analyses have been done for the following operations: Normal lay and curve lay of flexible flowline Flexible flowline termination abandonment / recovery Flexible riser termination / recovery. Flexible flowline intermediate connection lay-down and sensitivity with riser/flowline intermediate connection lay-down. These analyses are based on the document Campaign 2 – Flexible Flowline Installation Procedure (ref. H8-SSP-00-066-V02-65785).


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1.3

ABBREVIATIONS AND DEFINITIONS Abbreviation A&R ART EF EL FLS Hs ID MBR OD TDP Tp WD

1.4

ASSUMPTIONS Section Ref. 3.3

1.5

Definition Abandonment & Recovery Anti-Roll Tank End fitting Elevation Flexible Lay System Significant wave height Inner Diameter Minimum Bending Radius (for installation purpose) Outside Diameter Touch Down Point Peak Period Water Depth

Assumption Detail Typical friction coefficients have been taken from previous projects

HOLD LIST Number

1.6

REFERENCES

1.6.1

Documents – Subsea 7 Reference H8-SSP-00-066-V02-65785 H8-SSP-00-066-D06-65812 H8-SSP-00-066-D06-65814 H8-SSP-00-066-N01-65766 H8-SSP-00-066-D06-65818

1.6.2

Reason for Hold

Title Campaign 2 – Flexible Flowline Installation Procedure 10" Flexible Lay Route Drawing BU-DS01 10" Flexible Lay Route Drawing BU-DS02 Flexible Risers Installation Analysis Campaign 2 – Skandi Acergy Deck Layout

Documents – Customer Reference BUP3-000-SE-R02-D-00001 H8-SSP-01-029-D45-2134 H8-SSP-01-029-D45-2138 H8-SSP-01-020-G01-64782


Title Summary of Metocean Conditions Prepared for Bayu Undan Location Bayu Undan Phase 3 DPP Tie-Back Overall Field Layout Bayu Undan Phase 3 DPP Tie-Back Field Layout Schematic Flexible Pipelay Wellstream – Pipe Data Sheets

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Reference H8-SSP-01-029-D06-64810 H8-SSP-01-029-D06-65050 1.6.3

Title Wellstream - Endfitting Configuration 10" Production Flowline Wellstream - Installation/Pull Head Configuration 55Te SWL Grayloc 12M102 10.0" Riser/Flowline

Documents – 3rd Party / Subcontractor Reference


Title

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2.

CONCLUSIONS The installation analyses of the flexible flowlines have been performed. The results demonstrate that all operations can be performed in a safe manner with the following allowable sea-states: Installation stage

Allowable Hs (m)*

Lay back range (m)

Vessel heading restriction

Governing parameter

Alternative criteria on vessel motion

No

Clearance with moon pool, MBR

Not required (high Hs)

Min WD: (16-30)

Normal lay Flowline termination abandonment or recovery Riser termination abandonment or recovery Flowline/Flowline intermediate connection laydown Flowline/Riser intermediate connection laydown

2.5

Max WD: (16-35)

2.5

(13-21)

No



2.5

(12-20)

No



2.5

(14-27)

No



No


No simple criteria available

2

Without ART: (28.5-30) With ART: (28.533.5)

*Range of Tp covered in Table 4-1

Table 2-1-Allowable sea-states for flexible flowline operations

It is noted that the alternative criteria given on vessel motion is an alternative criteria to the allowable sea-state criteria and can be used if higher sea-states are encountered or in case of doubt on the current seastate or forecast. It is not necessary to check this motion criteria if the actual sea-state is within the prescribed allowable sea-states (see section 4 and results sections for further details). Alternative criteria will be completed for next revision of this document.


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The verification of the installation criteria is provided in Table below.

Criteria

Allowable

Static Results

Dynamic Results

Max departure angle at tulip exit

14deg

6.3deg

12.9deg

Max dynamic top tension in flexible (FLS)

39mT

19.5mT

21.30mT

MBR

4.16m

5.32m

4.26m

Maximum compression

59 kN empty / 137 kN flooded @ 4.16m MBR

None

-3.85kN

MBR

4.22m

6.29m

5.71m

Maximum compression

51 kN empty @ 4.4m MBR

None

-5.29kN

Component

Vessel

Flexible flowline

Flexible riser

Table 2-2- Verification of the installation criteria


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3.

ANALYSIS BASIS

3.1

PRODUCT AND ANCILLARY EQUIPMENT DESCRIPTION

3.1.1

Flexible Flowline and Flexible Riser - Cross-section The flexible flowlines and flexible risers have the following characteristics:

Data

Unit

Reference

-

Outside Diameter Inside Diameter * Weight in air - empty Weight submerged - empty Bending stiffness @ 23°C Axial stiffness Torsional Stiffness @ 23°C MBRStorage Installation MBR

mm mm t/m t/m kN.m² kN kN.m² m m

Max compression

kN

Flexible Flowline BU-DS01 BU-DS02 H8-SSP-01-020-G0164782 (Rev 1. Issued on 18/12/13) 389.96 260.1 0.174 0.052 151.1 374875 5411 (stiff dir) 2.53 4.16 59 kN empty / 137 kN flooded @ 4.16m MBR

Flexible Riser BU-DS01 BU-DS02 H8-SSP-01-020-G0164782 (Rev 1. Issued on 18/12/13) 413.5 260.0 0.256 0.118 212.3 529147 12100 2.69 4.22 51 kN empty @ 4.4m MBR

Table 3-1 – Flexible flowline and Flexible Riser properties

Note: * For the flexibles, the internal diameter used in Orcaflex is calculated with respect to pipe internal volume (taking into account the volume “inside” the carcass). This allows to model the pipe based on its weight in air empty, and to play on fluid content density (“uniform content” option in Orcaflex) to define the filling configuration of the pipe (empty or flooded). The installation analyses presented in this report have been performed with the flexible flowline empty except for the abandonment of the last section which was done with the flowline flooded. Some analyses have been performed considering the flexible riser data (recovery of subsea end when flooded and lay-down of intermediate connection between riser and first flowline section when catenary is partially flooded).


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3.1.2

Flexible Flowline and Flexible Riser – End-fitting and pull-head The properties of the flexible flowline end-fitting and pull-head are presented in next table. Flexible Flowline

Parameter

Unit

End Fitting

Pulling Head

Reference

-

H8-SSP-01029-D06-64810 (Rev 2)

H8-SSP-01029-D06-64812 (Rev A),

Length Weight in air Weight water

m kg kg

1.051 821 668

SWL

mT

N/A

0.3 103 88 (est.) 25 (ref: H8-SSP00-066-D0670207)

Flexible Riser End Fitting

Pulling Head

H8-SSP-01029-D0664995 (Rev 1. Issued on 02/07/13) 1.20 1163 941

H8-SSP-01029-D0664811 (Rev A. Issued on 13/12/13) 0.41 430 374

N/A

55

Table 3-2 – Flowline and End-fitting and pull-head properties

Figure 3-1 – Flowline end-fitting


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3.2

VESSEL CHARACTERISTICS The Skandi Acergy is a DP Class 3 multi-purpose flexlay and offshore construction vessel. Description Length Overall Length between perpendicular Breadth Moulded Operating draft Depth Moulded (to main deck) Speed Deck Working Area (net) Deck Loading / m2 Accommodation Flag

Value 156.9m 137.7m 27m 6.5m – 7.8m 12m 15 knots (max speed 18 knots) 2,100m² 10 t/m² 140 Isle of Man

Table 3-3 – Skandi Acergy Main Properties

Figure 3-2 – Skandi Acergy

Figure 3-3 – Skandi Acergy Deck Layout


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3.2.1

Flexible Lay System The Skandi Acergy’s Flexible Lay System, comprises of a vertical lay tower on the centreline of the ship directly over the dedicated moonpool. A 3000Te underdeck carousel complete with spooling arm provides storage. There is a 125Te four track tensioner on the Skandi Acergy.

Figure 3-4 – Skandi Acergy FLS Tower and Loadout Spread

Morvin 7m TULIP There is a large tulip which had been designed to allow the maximum possible fleeting angle before contacting the bottom of the moonpool (15 Degrees): ID of top of tulip is 750mm.

Figure 3-5 – Morvin 7m Tulip

Abandonment and recovery Winch (A&R) There is a 120Te A&R winch on top of the Tower. This has a 70mm, 120Te SWL, 750m wire with a closed swivel spelter socket. It is operated from the FLS control cabin and has no Active Heave capabilities. It has a manual spooler connected via a retractable A Frame.


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3.3

ENVIRONMENT INPUT DATA Environmental data used for the analyses are extracted from the meteocean report for the Bayu Undan location (ref. BUP3-000-SE-R02-D-00001). Refer to section 4.2 for detailed explanations on how wave data have been considered. Regarding current effect, sensitivities have been performed to account for current effect in some critical cases. Unless specified otherwise, 70% of the omnidirectional 1-yr velocity profile has been used. This percentage is used to attenuate the strong conservatism in using a full 1-yr current profile (which by definition occurs only once in a year). Strong conservative assumptions have been kept though in the sensitivity calculation by considering the current profile in the same direction through the entire water column and acting in the same plane as the catenary.

3.4

LAY ROUTE DATA Water depths and lay curve radius considered in the analysis have been extracted from the alignment sheets in references and are listed in the table below for the various items: Line

76-109 71-80

Smallest curve radius (m) 100; 200 150

108

N/A

71

N/A

Water depths (m)

Flexible flowline BU-DS01 Flexible flowline BU-DS02 Last EF/EF connection BU-DS01 Last EF/EF connection BU-DS02

Table 3-4 – Water depths and curve radius considered – Flexible flowline

3.5

SOIL FRICTION COEFFICIENTS Soil friction coefficients have been considered from previous projects: Axial friction coefficient 0.51

Lateral friction coefficient 0.38

Table 3-5 – Soil Friction Coefficients


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3.6

LIMITING CRITERIA FOR ANALYSIS The limitation criteria for the analysis are presented in the table below.

Component

Vessel

Flexible flowline

Criteria

Allowable

Max departure angle at tulip exit

14deg

Max dynamic top tension in flexible (FLS)

39mT

MBR

4.16m

Maximum compression

59 kN empty / 137 kN flooded @ 4.16m MBR

MBR

4.22m

Maximum compression

51 kN empty @ 4.4m MBR

Flexible riser

Table 3-6 – Limiting Criteria


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4.

METHODOLOGY

4.1

SOFTWARE Calculations have been performed with Orcaflex (Version 9.5d)., a marine program for static and dynamic analysis of flexible pipeline and cable systems in offshore environments. It is widely used in the offshore industry for analyses of flexible risers and installation of Subsea equipment. This software is a fully 3D non-linear time domain finite element program capable of dealing with ship motions, environmental conditions, random waves, buoys, cables etc. Cable weight, structure characteristics, environmental conditions and lay vessel motions can be accurately modelled with Orcaflex.

4.2

WAVE DATA SELECTION AND DIRECTONALITY The 1yr return period wave data is considered too conservative for the installation analyses; therefore a methodology has been used to define a more appropriate seastate. The objective is to reduce the computation time while ensuring that the seastates analysed are representative of the weather conditions experienced and monitored during operations. The figures below show the sea-state scatter diagrams (Hs-Tp) extracted from H8GEN-00-095-R02-2000 for the months of January and February, period during which the Campaign 2 operations will be performed.


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Figure 4-1 – Omnidirectional Hs-Tp Scatter diagram for the months of January and February (Ref. H8-GEN-00-095-R02-2000)

The table below summarizes for each Tp bin in the scatter diagrams above the maximum Hs considered to obtain an overall operability of about 90% during the considered months.

Tp From 2 4 6 8 10 12 14 16 18 20 22

To 4 6 8 10 12 14 16 18 20 22 24 TOTAL

Hs max 2.0 2.5 2.5 2.5 2.5 2.5 2.0 -

% occurence in January 0 19.02 36.77 7.33 4.14 13.85 9.72 2.16 0 0 0 93

% occurence in February 0 16.16 31.27 9.73 8.11 13.39 8.6 2.05 0 0 0 89.3

Table 4-1 – Hs-Tp values considered in dynamic analysis

The dynamic analysis will be based on the worst Hs values in this table. This means that if an operation is proved by analysis to be safe for all sea-states listed above the operability will be at least 93% in January and 89% in February.


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Whenever possible, the installation vessel is positioned in-line with the Swell, with a typical heading tolerance of +/-15° which will be included in the dynamic cases matrix. It is noted that no operation during campaign 2 has been identified that would constrain the vessel to a particular heading. Therefore all dynamic analyses will be done with the vessel aligned with the swell and accounting for a tolerance of +/15deg. Sensitivity analyses are performed considering the 1-yr current profile.

4.3

STATIC ANALYSIS METHODOLOGY Static analysis is the first step in installation analysis and aims at establishing the static equilibrium configuration at various stages of the installation. It defines the starting point for subsequent dynamic analyses. Installation of the flexible flowline is divided into the following main stages: 1. Recovery of flexible riser subsea end-fitting on installation vessel 2. Connection of the first section of flexible flowline on riser end-fitting and laydown of intermediate end-fitting connection between riser and 3. Normal lay and curve lay of flowline 4. Lay-down of intermediate end-fitting connection between flowline sections 5. Repeat step 3 and 4 for as many flowline sections to be laid 6. 2nd end abandonment of last flowline section to be installed

4.4

DYNAMIC ANALYSIS METHODOLOGY Dynamic calculations are performed to ensure that static parameters calculated are valid and that limiting criteria are still ensured when both functional and environmental loads are applied. They also determine the maximum allowable vessel motions and sea-states with regards to limiting criteria, which includes the maximum loading of the product (tension, MBR, bending moment, etc.). For that purpose, a set of the most critical steps are selected from the static analyses to be checked with a full dynamic calculation methodology. These static steps are selected based on the limiting criteria. If the integrity of the product or its ancillary equipment or any vessel equipment is compromised with maximum wave heights, the Hs is reduced until these requirements are met. Different methodologies can be adopted to perform the full dynamic calculations in time domain. These simulations can be based on regular waves or on irregular waves. Irregular waves are generally less conservative compared to regular waves but require more calculation time. In order to optimise calculation time and to cover a large range of sea state events, a methodology involving both regular wave time domain analysis and vessel motions spectral calculations is used. This method is described hereafter:


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First, dynamic time domain simulations with regular waves are run for the parameters presented in Table 4-1 in a previous section and considering the vessel heading to be aligned with the swell with a +/-22.5deg tolerance. A typical factor of 1.86 is considered to convert the significant wave height Hs into a maximum wave height Hmax for a typical sea-state duration of 3hrs. This factor is derived from the reference [“Random Seas and Design of Maritime Structures” – Y. GODA].

with N the number of waves. To estimate the maximum wave height of a storm with 3 hour persistence and a mean period of 10 s this results in Hmax = 1.86·Hs. The objectives of this first set of dynamic calculations are: •

As a conservative approach, it can be used to estimate quickly the allowable wave Hs for the various periods and directions. If all governing parameters are fulfilled at this stage, then the allowable sea-states for the considered operation are the ones shown in Table 4-1 and the resulting operability of the operation is at least 90%. Hence, no further dynamic analysis is required.

•

It allows to understand the frequency content of the system response and determine any peak response periods due to potential resonance effect or peak vessel excitation periods

•

It can be used to determine the relationship between vessel motions and the response of the catenary. Indeed, the dynamic responses of the catenary are closely linked to the vessel motions and a direct relationship is expected to be found for most installation stages. For example, the catenary tension at hang off point is likely to be strongly correlated with the vertical acceleration at the hang-off point.

If the first set of regular wave time domain calculations has concluded on low allowable sea-states, the following methods can then be used: •

If a strong correlation between one particular vessel motion (e.g. hang-off vertical velocity) and one of the critical governing parameter (e.g. MBR) has been found, then the maximum allowable value of that specific motion (e.g. maximum hang-off vertical velocity of 1.5m/s) is determined in order to ensure that the governing parameter limiting criteria (e.g. MBR of 2m) will never be infringed. Then, by using simple spectral calculation method to calculate the vessel motions for various sea-states, it is possible to define what would be the maximum allowable sea-states that will ensure this particular vessel motion is always below the limit defined above. Furthermore, this criterion on a maximum vessel motion can be used as an alternative criterion to the traditional allowable sea-state criterion to help the decision process offshore. This method is called Vessel Motion Based Criteria (VMBC) and aims at reducing the conservatisms underlying the


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traditional approach using allowable sea-states and thus improving the operability of the vessel. •

If no satisfying correlation are found or correlation with too many different vessel motion parameters, then a time domain analysis using irregular wave can be used. Due to the time consuming aspect of irregular wave calculations, a careful selection of sea-states should be performed to minimize the computation time. Appropriate sea-states should be selected to at least capture any peak response periods (system natural periods, vessel natural periods) and capture the maximum vessel motions at hang-off points (as a minimum: vertical motion, velocity and acceleration, pitch, roll).


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5.

ANALYSES RESULTS

5.1

NORMAL LAY AND CURVE LAY Analysis was performed to calculate the layback boundaries for normal lay. Minimum and maximum water depths have been studied considering the routes of both flowlines BU-DS01 and BU-DS02, refer to Table 3-4. Curve laying stability is also checked. The acceptable layback range is established based on static and dynamic analysis. The lower layback limit is normally governed by MBR criteria and the compression limit of the product. The upper layback limit is normally governed by the maximum allowable tension at hang-off or at TDP, in some cases the departure angle.

5.1.1

Static Results Layback ranges – straight line laying The following results are presented assuming normal lay operation is performed with flowline empty.

Case

Layback (m)

Angle at tulip exit (°)

Top Tension (mT)

TDP Tension (kN)

MBR (m)

16

1.25

6.08

0.73

10.49

30

5.21

6.46

4.49

15.62

16

0.71

8.01

0.60

10.30

35

4.02

8.43

4.82

16.09

-

14

39

-

4.16

Min WD (71m) Minimum layback Min WD (71m) Maximum layback Max WD (108m) Minimum layback Max WD (108) Maximum layback Installation Criteria

Note: maximum layback given is valid for both straight and curve laying operations (see Table 5-2).

Table 5-1 – Layback range and static results for straight line laying

Layback ranges – curve laying A maximum tension must not be exceeded to ensure line stability on seabed during laying in curve. The maximum allowable TDP tension for laying in curve can be obtained from the following formula:

TCurve = Where:

𝑢.𝑊.𝑟 𝑆𝐹

;

TCurve: TDP Tension for a curve laying (kN)

𝑢: Lateral friction coefficient

W: product weight in water

𝑟: Curve radius

SF: Dynamic Factor (1.5)


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The maximum tension capacity for curve laying is presented in the table below. Parameter

Value

Lateral Friction Coefficient*

0.38

Flowline weight in Water (kN/m)

0.51

Max TDP tension (kN)

100m: 12.92

for various curve radius

200m: 25.84

*Taken from previous projects Table 5-2 – Maximum allowable TDP tension for curve laying

5.1.2

Dynamic results Conservative dynamic analysis using regular wave up to 3m Hs has been performed for normal lay operation. For this operation, the vessel has the possibility to weathervane, therefore only head sea +/-15deg has been considered. Dynamic results are presented in next table.

Case Min WD (71m) Minimum layback Min WD (71m) Maximum layback Max WD (108m) Minimum layback Max WD (108) Maximum layback Installation Criteria

Max Angle at tulip exit (°)

Max Top Tension (mT)

Max TDP Tension (kN)

MBR (m)

6.09

6.98

4.38

8.08

9.37

7.47

10.46

10.40

5.57

9.32

3.79

7.94

8.23

9.88

10.93

10.75

14

39

12.92 & 25.84

4.16

Note: maximum layback given is valid for both straight and curve laying operations (see Table 5-2).

Table 5-3 – Dynamic results for straight line laying

As all parameters are within their allowable limit, hence the normal lay operation can be performed safely up to a maximum allowable Hs of 2.5m within the specified layback range of 23m +/- 7m and 25.5 m +/- 9.5m for the minimum and maximum water depths respectively. It is also noted that the maximum layback is driven by the product top angle. Since maximum TDP tensions are below the maximum allowable TDP tension for curves


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introduced in Table 5-2, therefore the maximum laybacks for each water depth is valid for both straight and curve laying operations. Since, the resulting maximum allowable Hs is high, no alternative criteria on vessel motion is deemed required. 5.1.3

Sensitivity with current With respect to current effect on normal lay configuration, the same conclusions as for the flowline-flowline intermediate connection lay-down (see 5.4.3) can be drawn as the catenary shape is very similar and dynamic results are better. In terms of MBR, since minimum bending radius for normal lay (Table 5-3) is further away from the limit than for intermediate connection lay-down, no issue is expected on MBR. In terms of product departure angle at tulip exit, a lower maximum departure angle is observed for normal lay than for intermediate connection lay-down (10° vs. 9.4°) an furthermore the maximum angle is well below the limit (14°).


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5.2

FLEXIBLE FLOWLINE TERMINATION ABANDONMENT / RECOVERY

5.2.1

Static results Analysis is done for flowline termination abandonment this will also cover the recovery operation as this is the reverse operation of abandonment. The catenary will be flooded during this operation; the water depth is 71m. Table below summarizes the steps for abandonment of flowline termination. Figure 5-1 shows the snapshots for this operation.

Step

A&R Length (m)

Vessel Step move (m)

Layback (m)

Pull head height above seabed (m)

MBR in flowline (m)

NA, top angle 1.1° Deploying pulling head subsea

13.5

0

17.0

1 2 3 4 5 6 7 8

63.17 63.17 68.17 68.17 73.17 73.17 80.17 80.17

0 4 0 4 0 4 0 4

15.0 21.0 14.0 19.0 13.0 18.0 10.0 15.0

20.2 20.4 15.2 15.4 10.2 10.4 3.1 3.3

8.5 9.9 8.2 9.5 8.1 9.1 10.9 11.2

9

85.17

0

5.2

0.3

52.6

-

4.16

Install. Criteria

0

-

-

A&R wire angle at tulip exit (°)

-

NA

8.9

Pull Head Tension (mT)

Remarks

11.93

Release of the last endfitting off the tensioner and held above the VLS. Pull head 20m above sea bed Vessel move A&R payout Vessel move A&R payout Vessel move A&R payout Vessel move

2.0

3.0

4.3 1.6 3.8 1.2 3.5 0.6 2.6

3.2 2.4 2.6 1.8 2.0 1.2 1.2

0.4

0.0

A&R payout, Pull in head landed on sea bed

-

-

14

Table 5-4 – Static results for flowline termination abandonment, 71m WD

Figure 5-1- Flowline termination abandonment


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5.2.2

Dynamic results Conservative dynamic analysis using regular wave has been performed (as described in section 4). For this operation, the vessel has the possibility to weathervane, therefore only head sea +/-15deg has been considered. Step 2 (max layback) and Step 5 (min layback) of Table 5-4 are chosen for dynamic analysis as they are associated with max angle and lowest MBR respectively. Step 0 is also included for max dynamic top tension.

A&R Winch

Flowline

Max Angle at tulip exit(deg)

Max Hook Load (mT)


MBR (m)

Compression (kN)

Step 0 -Max top Tension

2.57

13.04

6.52

7.02

-2.06

Step 2 -max layback (21m)

11.04

3.73

8.97

7.48

-0.92

Step 5 -min layback (13m)

8.08

2.20

4.87

6.28

-3.85

Installation Criteria

14

-

-

4.16

-59

Step

Table 5-5 – Dynamic results for flowline termination abandonment, 71m WD

As all parameters are within their allowable limit, the flowline termination abandonment can be performed safely up to a maximum allowable Hs of 2.5m with layback range maintained between 13m and 21m during the operation. 5.2.3

Sensitivity at 108m WD As previous calculations were done for the smallest WD (conservative in terms of MBR and top angle), a sensitivity analysis has been performed at the maximum WD (108m) to determine the maximum load on the recovery pull-head. A&R hook load is directly correlated with crane tip heave acceleration, hence only the dynamic case leading to the maximum hook acceleration has been run for the 108m WD case. Resulting static hook load in 108m WD is 15.8mT and maximum dynamic load is 17.6mT.


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5.2.4

Sensitivity on content As laydown prior to interim mobilisation will be performed with an empty product; static analysis described in 5.2.1 is now performed with catenary empty. Table below summarizes the static results.

Step

A&R Length (m)


Layback (m)


MBR in flowline (m)



63.17 63.17 68.17 68.17 73.17 73.17 80.17 80.17

0 4 0 4 0 4 0 4

17.0 22.0 16.0 21.0 15.0 20.0 12.0 16.0

59.8 59.7 64.8 64.7 69.8 69.7 76.9 76.7

10.5 12.3 10.2 12.0 10.4 12.0 15.0 15.7

1.3

1.7

3.3 0.9 3.0 0.7 2.8 0.5 2.5

1.9 1.4 1.6 1.2 1.3 0.9 0.9

9

85.17

0

5.0

79.7

68.4

0.4

0.0

Install. Criteria

1 2 3 4 5 6 7 8

-

-

-

-

4.16

14

-

Table 5-6 – Static results for flowline termination abandonment, 71m WD, empty product

As indicated in the above table static results are improved comparing with flooded case (larger MBR for step 5 and smaller angle for step2). Therefore the layback range obtained for flooded case is also valid for empty case. FLS load transfer top tension checks Dynamic analysis has been performed for calculating max dynamic top tension of the flowline when it is suspended from A&R above the tensioner tracks (~30m above sea level); this is done with catenary empty.

WD (m) 71 108

Max Hs (m) 2.5 2.5

Static Top Tension (mT)

Max Dynamic Top Tension (mT)

10.39 12.27

11.71 13.94

Table 5-7 – Top tension of flowline suspended 30m above sea level


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5.3

FLEXIBLE RISER TERMINATION ABANDONMENT / RECOVERY

5.3.1

Static results Analysis is done for flexible riser termination abandonment this will also cover the recovery operation as this is the reverse operation of abandonment. The catenary is flooded during this operation; the water depth is 77m.

Step

A&R Length (m)

0


NA

0

Layback (m)


MBR in Riser (m)

15.0

NA

8.9



1.6

16.1

Remarks

Riser EF at worktable

Deploying pulling head subsea 63.17 63.17 68.17 68.17 73.17 73.17 80.17 80.17

0 4 0 4 0 4 0 4

15.0 20.0 13.0 18.0 12.0 17.0 10.0 14.0

20.2 20.4 15.2 15.4 10.2 10.4 3.1 3.3

8.1 9.3 7.8 8.8 7.6 8.5 10.0 10.3

9

85.17

0

4.8

0.3

82.1

-

4.4

Install. Criteria

1 2 3 4 5 6 7 8

-

-

-

2.2

4.6

4.6 1.8 4.2 1.3 3.7 0.6 2.7

5.0 3.7 4.0 2.8 3.0 1.7 1.8

0.4

0.0

6

Pull head 20m above sea bed Vessel move A&R payout Vessel move A&R payout Vessel move A&R payout Vessel move A&R payout, Pull in head landed on sea bed

-

-

Table 5-8 – Static results for riser termination abandonment, 77m WD

5.3.2

Dynamic results Conservative dynamic analysis using regular wave has been performed (as described in section 4). For this operation, the vessel has the possibility to weathervane, therefore only head sea +/-15deg has been considered. Step 2 (max layback) and Step 5 (min layback) of Table 5-8 are chosen for dynamic analysis as they are associated with max angle and lowest MBR respectively. Step 0 is also included for max dynamic top tension.


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A&R Winch

Riser

Max Angle at tulip exit(deg)

Max Hook Load (mT)


MBR (m)

Compression (kN)

Step 0 -Max top Tension

3.55

17.54

8.2

7.52

-0.02

Step 2 -max layback (20m)

12.72

5.97

15.04

7.47

-0.16

Step 5 -min layback (12m)

8.27

3.23

5.41

6.19

-5.29


14

-

-

4.4

-51

Step

Table 5-9 – Dynamic results for riser termination abandonment, 77m WD

As all parameters are within their allowable limit, the riser termination abandonment can be performed safely up to a maximum allowable Hs of 2.5m with layback range maintained between 12m and 20m during the operation.


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5.4

FLOWLINE-FLOWLINE INTERMEDIATE CONNECTION LAY-DOWN

5.4.1

Static results Static analysis is performed for laying-down the intermediate connection between two sections of flowline when the catenary is empty; this is done for the minimum water depth (71m). The table below summarizes the static results of the lay-down for maximum and minimum laybacks. The results are presented when intermediate connection is in its critical position in sagbend. Figure 5-2 shows the intermediate connection in the critical position for MBR in the sagbend. It is noted that two anodes of 25kg each have been considered on each side of the intermediate connection.

Case Min Layback Max Layback Installation Criteria

Layback (m)

Angle at tulip exit (°)

Top Tension (mT)

TDP Tension (kN)

MBR (m)

14

1.9

6.67

0.94

5.32

27

6.3

6.99

5.78

6.36

-

14°

39

-

4.16

Table 5-10 – Static results for flowline-flowline intermediate connection laydown, 71m WD

Figure 5-2- Flexible Flowline intermediate connection laydown


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For the landing of the intermediate connection on seabed, a layback value in range of 14m to 27m has to be maintained to ensure appropriate bending radius in the flexible and maintain the departure angle at the work table within an acceptable limit. 5.4.2

Dynamic results Conservative dynamic analysis using regular wave up to 3m Hs has been performed on these two steps. For this operation, the vessel has the possibility to weathervane, therefore only head sea +/-15deg has been considered. Dynamic results are presented in the next table. One case (Step 0) is also included for max dynamic top tension, this is when intermediate connection is at worktable and tensioner is engaged. Step

Step 0 –Max top Tension Min Layback Max Layback Installation Criteria

Max Hs (m)

Angle at tulip exit (deg)



MBR (m)

2.5

5.4

9.33

10.5

10.42

2.5 2.5

6.42 9.97

7.42 7.84

5.43 12.84

4.55 5.23

-

14°

39

-

4.16

Table 5-11 – Dynamic results for flowline intermediate connection lay-down

As all parameters are within their allowable limit, the intermediate connection laydown can be performed safely up to a maximum allowable Hs of 2.5m with layback range maintained between 14m and 27m during the operation. Since, the resulting maximum allowable Hs is high, no alternative criteria on vessel motion is deemed required. 5.4.3

Sensitivity with current Sensitivity with current is performed for both laybacks. Current profile described in section 3.3 is used. Current is applied in the catenary plane. Results and comparison with nominal case are presented in table below.

Layback of 27m – No current Layback of 27m – With current Layback of 14m – No current Layback of 14m – With current

Max Hs (m) 2.5 2.5 2.5 2.5

Angle at tulip exit (deg) 9.97 11.3 6.42 7.43


-

14

Connection in sagbend case

MBR (m) 5.23 5.21 4.55 4.39 4.16

Table 5-12 – Dynamic results in presence of current for flowline intermediate connection lay-down


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The results show that the MBR of the flowline and its top angle remain within their limit. 5.4.4

Sensitivity with maximum water depth The same analysis detailed in section 5.4.1 is performed for maximum water depth (108m). Following table shows the dynamic results in present of current for the same range of layback.

Step Min Layback (14m) Max Layback (27m) Installation Criteria

Max Hs (m)




MBR (m)

2.5

7.31

7.42

5.43

4.55

2.5

9.97

7.84

12.84

5.23

-

14°

39

-

4.16

Table 5-13 – Dynamic results in presence of current for flowline intermediate connection lay-down, 108m WD

As all parameters are within their allowable limit, therefore the intermediate connection lay-down can be performed safely up to a maximum allowable Hs of 2.5m with layback range maintained between 14m and 27m during the operation for both maximum and minimum water depths. Resulting static top tension in 108m WD is 10.25mT and maximum dynamic load is 11.54mT. 5.4.5

Sensitivity with flowline-riser intermediate connection lay-down Similar analysis as in section 5.4.1 is performed for laying the intermediate connection of flowline and riser. In this case riser is flooded but flowline is empty. Water depth for this operation is 77m. Figure 5-3 shows the intermediate connection in the critical position for MBR in the sagbend.

Figure 5-3- Flowline-Riser intermediate connection laydown


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To obtain a range for layback during installation conservative dynamic analysis using regular wave has been performed for intermediate connection lay-down. For this operation, the vessel has the possibility to weathervane, therefore only head sea +/-15deg has been considered. Dynamic results in presence of current are presented in the next table. One case (Step 0) is also included for max dynamic top tension, this is when intermediate connection is at worktable and tensioner is engaged. Step Step 0 –Max top Tension Min Layback (28.5m) Max Layback (30.0m) Installation Criteria

Max Hs (m)




2.5

9.54

21.30*

21.59

2

11.78

8.85

13.16

2

12.90

8.49

12.48

-

14°

39

-

MBR (m) 10.61 (riser) 4.26 (flowline) 4.34 (flowline) 4.16 (flowline)/ 4.44 (riser)

*The static top tension is 19.47mT

Table 5-14 – Dynamic results in presence of current for flowline-riser intermediate connection lay-down

As all parameters are within their allowable limit, therefore the flowline-riser intermediate connection lay-down can be performed safely up to a maximum allowable Hs of 2m with layback range maintained between 28.5m and 30m during the operation. It is noted that limiting parameters for minimum and maximum laybacks are catenary MBR and product top angle respectively. No vessel motion criteria could be obtained for this operation.


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Sensitivity with ART As mentioned before the limiting parameter for minimum layback is MBR. Lowest value for MBR happens in head see; therefore ART will not affect the minimum layback value that was given in Table 5-14. However the maximum angle at tulip exit occurs when roll motion is introduced by waves. Therefore maximum layback can be increased using ART. Following table presents the dynamic results when ART is in use in presence of current.

Step Min Layback (28.5m) Max Layback (33.5m) Installation Criteria

Max Hs (m)




MBR (m)*

2

10.38

8.85

13.29

4.26

2

11.09

8.90

16.25

4.50

-

14°

39

-

4.16

*Lowest catenary MBR happens on flowline side

Table 5-15 – Dynamic results in presence of current for flowline-riser intermediate connection lay-down

As all parameters are within their allowable limit, therefore the flowline-riser intermediate connection lay-down can be performed safely up to a maximum allowable Hs of 2m with layback range maintained between 28.5m and 33.5m provided that ART is active during the operation.


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5.5

CROSSING ANALYSIS

5.5.1

Crossing support height Point loading on the 18” WP1 production pipeline is not permitted. Therefore a minimum clearance should be maintained between the flexible flowline and the pipeline at crossing point. Analysis has been performed to determine the required height of the mattresses on either side of the pipeline to ensure that the gap between the flexible and pipeline will be sufficient. The mattresses are located 4m from centreline of the pipeline and installed at the edge of this tolerance with consideration to the potential lateral movement of the pipeline (Figure 5-4). Max deflection of flowline over the free span happens assuming flow line is fixed at one end and free (no tension) at the second end. When the line is flooded max deflection is 25 cm.

Figure 5-4 – Crossing support arrangement

Therefore the total height (h) of the mattresses required can be calculated as below: hmax = ODWP1 + Required clearance + max deflection of flooded line Parameter

Value

Remarks

OD of production pipeline

66cm

Required clearance

30cm

Including 10cm contingency

Max deflection

25cm

Under no back tension

hmax

121cm

-

Including concrete coating and marine growth; also no pipeline burial is assumed

Table 5-16 - Maximum required mattress height


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Sensitivity has been performed with different residual tensions and contents for a mattress height of 1.5m above mudline. The residual tension is obtained by simulating the laying over the mattress with various laybacks. It is noted that the layback range simulated here will cover the layback range specified for the offshore operations. Results are shown in table below and the configuration modelled is shown in snapshot after.

Layback (m)

Fluid content (kg/m3)

40 40 30 30 20 20 15 15

1025 0 1025 0 1025 0 1025 0

TDP Max tension deflection (kN) (m) 15.5 7.1 9.3 4.5 4.7 1.8 1.9 0.64

0.131 -0.045 0.134 -0.064 0.126 -0.100 0.170 -0.122

Max point loading (kN) 17.1 9.22 16.45 9.09 16.1 8.47 14.6 8.48 Allowable MBR:

Min bending radius (m) 10.0 15.2 9.4 14.5 8.9 14.7 9.4 14.1 4.16

Table 5-17: Sensitivity on residual tension and content

Figure 5-5: Flowline configuration for sensitivity check

From these results the conclusions are: •

No MBR issue is encountered, the safety factor on MBR is always greater than 2.0 so above any operating, storage, accidental requirements

•

Point loading is mainly depend on fluid content,

•

Point load is less dependent on residual tension (hence layback)


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5.5.2

Current stability Stability of the flexible flowline against 100-year return period omni-directional current when resting over the mattresses is investigated here. The analysis is done assuming the flowline is empty. The flowline is considered stable if friction force between the mattress and flowline is greater than drag force produced by current (Ffric > Fdrag). Drag and friction forces can be calculated using the following formulas respectively. Fdrag = 0.5×ρ×Cd×L×OD×U² (drag force term in Morison's equation) Ffric = 9.81×L×w×f (lateral friction force before sliding)

Parameter

Value

Remarks

L

40m

length of flexible over which the current is applied

OD

0.39m

OD of flexible

Cd

1.2

Drag coefficient

rho

1.025 t/m3

Seawater density

U

0.4 m/s

Current velocity

Fdrag

1.54 kN

-

Table 5-18 – Drag force calculation

Parameter

Value

Remarks

L

4m

length of contact between flexible and mattress

w

0.175 t/m

Mass per unit length of flexible empty

f

0.3

Friction coefficient flexible/mattress

Ffric

2.06 kN

-

Table 5-19 – Friction force calculation

To conclude as shown the two above tables; Ffric > Fdrag and therefore the flowline is stable.


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